Systems and methods for water splitting and / or carbon dioxide reduction

Abstract

Systems and methods for water splitting and / or carbon dioxide production, and related materials, are generally described.

Description

[0001]SYSTEMS AND METHODS FOR WATER SPLITTING AND / OR CARBON DIOXIDE REDUCTION AND RELATED MATERIALS This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 63 / 679,973, filed August 6, 2024, and entitled “Systems and Methods for Water Splitting and / or Carbon Dioxide Reduction and Related Materials” and to U.S. Provisional Patent Application No. 63 / 683,821, filed August 16, 2024, and entitled “Systems and Methods for Water Splitting and / or Carbon Dioxide Reduction and Related Materials,” each of which is incorporated herein by reference in its entirety for all purposes. TECHNICAL FIELD Systems and methods for water splitting and / or carbon dioxide reduction, and related materials, are generally described. SUMMARY Systems and methods for water splitting and / or carbon dioxide reduction, and related materials, are generally described. The subject matter of the present disclosure involves, in some cases, interrelated products, alternative solutions to a particular problem, and / or a plurality of different uses of one or more systems and / or articles. In certain embodiments, a system is provided. The system comprises, in some embodiments, a vessel comprising water and / or carbon dioxide (CO2); and a pyroelectric material; wherein the system is configured such that, when the pyroelectric material and the water and / or CO2 are thermally cycled, hydrogen gas is produced and / or CO2 is reduced. In some embodiments, the system comprises: a first heat exchanger comprising: a first inlet configured to receive an input comprising pyroelectric material at a first temperature and water and / or carbon dioxide; and a first outlet configured to output at least a portion of the pyroelectric material at a second temperature that is higher than the first temperature, and to output hydrogen gas (H2(g)), oxygen gas (O2(g)) and / or carbon monoxide, and a second heat exchanger comprising: a second inlet fluidically connected to the first outlet, the second inlet configured to receive at least a portion of the output from the first heat exchanger; and a second outlet fluidically connected to the first inlet, the second outlet configured to output at least a portion of the pyroelectric material that is output from the first outlet of the first heat exchanger at a third temperature that is lower than the second temperature. 12734848.1 Some aspects are related to methods. In some embodiments, the method comprises thermally cycling a mixture of a catalyst comprising pyroelectric material and water and / or carbon dioxide (CO2) such that hydrogen gas is produced and / or CO2 is reduced. In some embodiments, the pyroelectric material comprises a planar molecule. In certain embodiments, the pyroelectric material comprises cobalt phthalocyanine (CoPc): . In certain embodiments, the pyroelectric material comprises graphene. In certain embodiments, at least 0.01, at least 0.05, at least 0.1, at least 0.108, at least 0.117, at least 0.122, at least 0.165, at least 0.2, at least 0.215, at least 0.25, or at least 0.28 mmol of CO is produced per gram of catalyst. In some embodiments, at least 0.01, at least 0.05, at least 0.1, at least 0.5, at least 1, at least 2, at least 2.19, at least 2.26, at least 2.33, at least 2.37, at least 2.4, at least 2.52, at least 3, at least 4, or at least 5 mmol of H2 is produced per gram of catalyst. In certain embodiments, at least 50%, at least 75%, at least 90%, at least 95%, at least 99%, or at least 99.9% of the water is converted to H2. In some embodiments, at least 50%, at least 75%, at least 90%, at least 95%, at least 99%, or at least 99.9% of the CO2is converted to reduced CO2(e.g., CO). In certain embodiments, the thermal cycling involves a change in temperature of less than or equal to 200°C, less than or equal to 150°C, less than or equal to 100°C, less than or equal to 75°C, less than or equal to 60°C, or less than or equal to 50°C. In certain embodiments, during at least a portion of the thermal cycling, the temperature of the catalyst is 25°C. Other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments of the disclosure when considered in conjunction with the accompanying figures. In cases where the present 12734848.1 specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control. BRIEF DESCRIPTION OF THE DRAWINGS Non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale unless otherwise indicated. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure. FIG. 1 is a schematic depicting a system comprising a vessel, pyroelectric material, carbon dioxide, and water, according to some embodiments. FIGS. 2A-2E show (FIG. 2A) High-Resolution Electron Microscopy (HRTEM) of CoP / G, (FIG. 2B) HRTEM of crystalline CoPc (insert image: SEM of CoPc); X-ray photoelectron spectra (XPS) narrows of (FIG. 2C) Co 2p (FIG. 2D) N 1s in CoPc / G, and (FIG. 2E) XPS survey scans of CoPc, CoPc / G and G samples (insets show the magnified view of the Co 2p, O 1s, N 1s, and C 1s regions), according to some embodiments. FIGS. 3A-3G show a schematic depicting pyroelectricity in CoPc (FIG. 3A), pyrocurrent density versus time (mA cm-2) (FIG. 3B), thermal dependence of lattice parameters in CoPc: lattice volume (FIG. 3C), and lengths and their response to thermal cycling (FIGS. 3D- 3G), according to some embodiments. FIGS. 4A-4E show the pyrocatalytic CO2 conversion products under CO2 including (FIG. 4A) H2; (FIG. 4B) O2, and (FIG. 4C) CO, the pyrocatalytic conversion products under N2including (FIG. 4D) H2, and (FIG. 4E) O2using CoPc / G, according to some embodiments. The concentration of products reported is based on the mol of products per gram of the CoPc catalyst. FIGS. 5A-5C show the pyrocatalytic CO2conversion products including H2(FIG. 5A), O2 (FIG. 5B), and CO (FIG. 5C) using CoPc / G hybrid with different ratios between CoPc and graphene, according to some embodiments. FIGS. 6A-6F show pyrocatalysis products monitored over heating and cooling half- cycles (FIG. 6A) under N2 (FIG. 6C and FIG. 6E), and CO2 (FIG. 6B, FIG. 6D, and FIG. 6F), according to some embodiments. 12734848.1 FIG. 7 shows the proposed mechanism behind the pyrocatalytic behavior exhibited by the CoPc / G throughout the half-cycles applicable to the CO2RR and water splitting, according to some embodiments. FIGS. 8A-8C show (FIG. 8A) Experimentally measured OCP (solid and dash dot lines) in presence of pyrocatalysts under CO2, compared with the predicted values (dashed lines) based on the mixed electrode theory and Nernst relation, using concentration values tabulated in Example 1, (FIG. 8B) Experimental LSV curves in presence of pyrocatalysts, under CO2 atmosphere, at 60 °C, and (FIG. 8C) at 10 °C, according to some embodiments. FIG. 9 shows a schematic of a system for continuous pyroelectric processing, according to some embodiments. FIG. 10 shows a scheme of CoPc molecule and its carbon and nitrogen atomic positions, according to some embodiments. FIGS. 11A-11B show (FIG. 11A) a schematic presentation of making a CoPc pellet, and (FIG. 11B) a sandwich three-electrode fabrication for pyrocurrent measurements, according to some embodiments. FIGS. 12A-12B show Pyrocurrent density versus time (mA cm-2) (FIG. 12A) under a constant temperature, and (FIG. 12B) for CoPc and CoPc / G, according to some embodiments. FIGS. 13A-13C show the pyroelectric catalytic CO2conversion products including (FIG. 13A) H2; (FIG. 13B) O2, and (FIG. 13C) CO, using CoPc / G hybrid in the absence of Na2SO3, according to some embodiments. FIGS. 14A-14C show the pyroelectric catalytic CO2conversion products including (FIG. 14A) H2; (FIG. 14B) O2, and (FIG. 14C) CO, using CoPc pyrocatalyst, according to some embodiments. FIGS. 15A-15B show a comparison of the OCP predicted by the model (dashed lines) with the experimentally measured OCP (solid and dash dot lines) in presence of CoPc / G under (FIG. 15A) CO2 and (FIG. 15B) N2 atmospheres, according to some embodiments. As a guide to the eye, additional to the initial and final points of modeled OCPs, a central point was added in the mid-time of these plots, calculated as the weighted average of the initial and final points (2 / 3 weight from the final and 1 / 3 from the initial point). FIGS. 16A-16B show a comparison of the OCP predicted by the model (dashed lines) with the experimentally measured OCP (solid and dash dot lines) in the absence of pyrocatalysts under (FIG. 16A) CO2 and (FIG. 16B) N2 atmospheres, according to some embodiments. As a guide to the eye, additional to the initial and final points of modeled OCPs, a central point was 12734848.1 added in the mid-time of these plots, calculated as the weighted average of the initial and final points (2 / 3 weight from the final and 1 / 3 from the initial point). FIGS. 17A-17B show experimental LSV curves (right-side) in presence of CoPc / G, (FIG. 17A) and (FIG. 17B) under CO2at 10 °C and 60 °C, according to some embodiments. FIGS. 18A-18B show experimental LSV curves (right-side) in presence of CoPc / G under N2 atmospheres, at (FIG. 18A) 10 °C and (FIG. 18B) 60 °C, according to some embodiments. Evans diagrams of the corresponding half-reactions are shown on the left-side diagram. FIGS. 19A-19B show experimental LSV curves (right-side) in absence of the pyrocatalysts, at (FIG. 19A) 10 °C and (FIG. 19B) 60 °C under CO2, according to some embodiments. Evans diagrams of the corresponding half-reactions are shown on the left-side diagram. FIGS. 20A-20B show experimental LSV curves (right-side) in absence of the pyrocatalysts, at (FIG. 20A) 10 °C and (FIG. 20B) 60 °C under N2, according to some embodiments. Evans diagrams of the corresponding half-reactions are shown on the left-side diagram. DETAILED DESCRIPTION Systems and methods for water splitting and / or carbon dioxide reduction, and related materials, are generally described. In some embodiments, the system comprises a catalyst comprising a pyroelectric material. In some embodiments, the system comprises a vessel comprising water and / or carbon dioxide and the pyroelectric material. When the contents of the vessel are thermally cycled (e.g., from a first temperature to a second temperature that is higher than the first temperature, then to a third temperature that is lower than the second temperature) the pyroelectrical material may produce an electrical potential that may catalyze chemical and / or electrochemical reactions (e.g., hydrolysis reactions and / or carbon dioxide reduction reactions). In some embodiments, the system is configured to produce hydrogen gas and / or reduce carbon dioxide when the catalyst and the water and / or carbon dioxide is thermally cycled. In some embodiments, the system is operated in a continuous manner. For instance, the system may receive an input comprising the catalyst and water and / or carbon dioxide and continuously thermally cycle at least a portion of the input such that value-added chemicals are produced (e.g., hydrogen gas and / or carbon dioxide). In some embodiments, the system comprises one or more heat exchangers configured to thermally cycle the input comprising the catalyst and water and / or carbon dioxide. The conversion of CO2 into value-added chemicals presents a promising avenue for addressing escalating energy demands and environmental challenges. However, the mitigation of 12734848.1 atmospheric pollution and global warming caused by the uncontrolled emission of greenhouse gases is a multifaceted challenge that may involve a diverse array of solutions. Conventional photochemical and electrochemical approaches for converting CO2 to valuable products generally encounter limitations such as low selectivity, low efficiency, and high energy consumption. Given these challenges, there is a pressing need for the identification of innovative CO2 reduction reaction (CO2RR) approaches with advantageous efficiency and reduced energy consumption. Such a need may be fulfilled via the strategic design of more sophisticated systems, and developing systems capable of autonomously generating electrochemical energy from low-grade heat sources would be desirable. Pyroelectric materials, exemplified by perovskite oxides exhibiting non-centrosymmetric structures, convert energy from the variation of electric dipoles through spontaneous changes in polarization during dynamic heating and cooling operations. This electricity induces electrons and holes for redox reactions within the pyroelectric material functioning as a closed-circuit electrochemical cell with an actual flow of charges. Consequently, pyroelectric polarization emerges as a viable power source for diverse electrocatalytic processes, including but not limited dye degradation, hydrogen evolution reaction (HER), and CO2RR. In certain embodiments, pyroelectric properties attributed to certain ceramic and polymeric phases, such as perovskites or highly polar polymers like polyvinylidene fluoride, can be leveraged to channel the electric energy to promote a targeted electrochemical reaction. Exploitation of the pyroelectric driving force in other structures tailored to promote a desired electrochemical reaction (e.g. CO2RR) can be enhanced, in some embodiments, via the identification or synthesis of materials advantageously having both pyroelectric and electrocatalytic properties. Moreover, molecular transition metal catalysts offer numerous advantages over alternative heterostructures, allowing for precise control of steric and electronic properties near the metal active site through rational design of ligand-metal interactions to achieve asymmetrical changes in polarity. Certain metalated macrocyclic molecules, such as metallo-phthalocyanines (MPcs), including FePc, CuPc, and SnPC exhibit pyroelectric behavior, particularly at temperatures exceeding 100 °C. Variations in their dielectric properties may stem from both the inherent characteristics of the metal center and intermolecular ^-^ interactions. Cobalt phthalocyanine (CoPc) immobilized onto conductive carbon supports may reduce CO2 into valuable products under external electric currents. One potential solution may involve exploiting the pyroelectric and electrocatalytic properties of planar molecules such as cobalt phthalocyanine (CoPc), with synergistic enhancement in electron dynamics and transfer provided by graphene (G), a two-dimensional 12734848.1 carbon support with advantageous electrical and thermal conductivity. In some embodiments, the hybrid CoPc / G pyrocatalyst, benefiting not only from the intrinsic merits of the two constituents but also from their fluent and mutual electronic communication (e.g., connection), may allow for the simultaneous CO2reduction reaction (CO2RR) and water splitting, driven by a thermal cycling process at near-room temperature. Such cycling may not need an external electrical power source. As described elsewhere in this disclosure (e.g., Example 1), CoPc has a desirable CO2RR capacity with a CO production yield of ^ 0.25 ^^^^^^^^^^^^^^^^^^obtained over twelve thermal cycles between 10 and 60 °C. Additionally, the yields of water splitting products, namely H2 and O2, reached ^ 2.5 ^^^^^^^^^^^^^^^^^^^. By hindering or controlling the intricate dynamics of the half-reactions, a further multifold increase in continuous operation yield of products is described, and possible through technical modifications such as frequent flushing of the product gases, or theoretical improvements regarding the choice of electrolyte, sacrificial agent, and galvanic coupling inhibitors. The systems, articles, and methods proposed herein may, in accordance with certain embodiments, allow for efficient, cost-effective, and green CO2conversion to value-added chemicals. The systems, articles, and methods proposed herein may also allow, according to some embodiments, for the production of carbon-free fuels like H2 by harnessing natural and industrial thermal fluctuations, which has positive implications for the fields of energy and environmental science. Generally, pyroelectric materials are capable of outputting a voltage (e.g., an electrical potential) in response to a change in temperature. In some embodiments, the pyroelectric material is capable of outputting a voltage when the pyroelectric material is heated and / or cooled, such as when exposed to a thermal cycle. As described above, changes in temperature may alter the atomic structure of the pyroelectric material such that dipole moments within the atomic structure of the pyroelectric material change, and an asymmetric charge distribution across the material may be created. Such changes may result in increased and / or decreased polarization of the pyroelectric material and a net change in electrical potential across the material. The voltage outputted from the pyroelectric material may facilitate (e.g., catalyze) electrochemical reactions including but not limited to hydrolysis reactions and / or carbon dioxide reduction reactions. In some embodiments, the pyroelectric material is a planar molecule. For instance, the pyroelectric material may have a stereochemistry wherein atoms of the pyroelectric material are predominantly arranged on a single geometric plane. In some embodiments, the planar molecule is a two-dimensional material. Planar molecules, when exposed to thermal cycling, may 12734848.1 advantageously experience a greater change in net polarization compared to changes in net polarization experienced by nonplanar molecules. A relatively large change in net polarization may advantageously result in relatively large output voltages which are desirable in catalytic applications. The pyroelectric material may comprise any of a variety of planar molecules. In some embodiments, the pyroelectric material comprises cobalt phthalocyanine (CoPc), copper phthalocyanine (CuPc), tin phthalocyanine (SnPc), iron phthalocyanine (FePc), graphene, and / or combinations thereof. In some embodiments, the pyroelectric material comprises cobalt phthalocyanine having the following structure: . In some embodiments, CoPc generally involves a cobalt atom that is coordinated to a phthalocyanine ligand, forming a relatively stable, often planar structure. In some embodiments, the catalyst may have any of a variety of compositions. In some embodiments, the catalyst comprises the pyroelectric material. In some embodiments, the catalyst comprises the pyroelectric material and carbon-based conductive materials (e.g., graphene, carbon nanotubes, graphite, graphitic carbon nitride (g-C^N^), conductive polymers (e.g., polyaniline and / or polypyrrole), and / or other two-dimensional materials (e.g., transition metal dichalcogenides and MXenes). In some embodiments, the catalyst comprises the pyroelectric material and graphene. In some embodiments, the catalyst comprises the pyroelectric material and carbon nanotubes. Phthalocyanine may form ^-^ interactions with highly conjugated materials, such as carbon nanotubes and graphene. These interactions may arise from the alignment of the conjugated ^-electron systems, which facilitate relatively strong ^-^ stacking. However, due to the differing planarity of these materials, the nature and strength of the interactions can vary. For instance, while carbon nanotubes provide a stable platform for ^-^ interactions with phthalocyanine, graphene, due to its unique two-dimensional structure and enhanced planarity, may have a greater influence on the pyroelectric properties of the CoPc complex. In some embodiments, the catalyst comprises a plurality of sheets, such as a plurality of graphene sheets. In some embodiments, the catalyst consists essentially of cobalt phthalocyanine (CoPc) and graphene. For instance, in some cases, the pyroelectric material and 12734848.1 graphene, when used together, exhibit advantageous catalytic properties under thermal cycling, but other components, such as a solvent, may also be present along with and / or within the catalyst to allow for the practical implementation of the catalyst. In some embodiments, the catalyst can be used along with an electrolyte (e.g., an aqueous electrolyte) to facilitate one or more electrochemical reactions. The electrolyte may comprise any of a variety of metal carbonates and / or bicarbonates. In some embodiments, the electrolyte is an aqueous solution comprising potassium bicarbonate (KHCO^), lithium bicarbonate (LiHCO^), sodium carbonate (Na^CO^), potassium carbonate (K^CO^), sodium sulfate (Na2SO3), and / or sodium bicarbonate (NaHCO3). In some embodiments, the catalyst may have any of a variety of forms. In some embodiments, the catalysts comprises a plurality of particles having a relatively small size. For instance, in some embodiments, the catalyst comprises a plurality of particles, such as microparticles and / or nanoparticles (e.g., a plurality of CoPc nanoparticles). In some cases, the plurality of particles comprise aggregates of CoPc particles. In some embodiments, the plurality of particles comprise CoPc and / or graphene. In some embodiments, the plurality of particles have a diameter (e.g., a number average diameter) of at least 200 nm, at least 250 nm, at least 300 nm, at least 350 nm, at least 400 nm, at least 500 nm, at least 600 nm, at least 700 nm, at least 800 nm, or at least 900 nm, and / or up to 5 micrometers, up to 10 micrometers, up to 100 micrometers, or more. In some embodiments, at least 50 vol%, at least 75 vol%, at least 90 vol%, at least 95 vol%, at least 98 vol%, at least 99 vol%, or 100 vol% of the total volume of the plurality of particles is made up of particles having a diameter of at least 200 nm, at least 250 nm, at least 300 nm, at least 350 nm, at least 400 nm, at least 500 nm, at least 600 nm, at least 700 nm, at least 800 nm, or at least 900 nm, and / or up to 5 micrometers, up to 10 micrometers, up to 100 micrometers, or more. In some embodiments, a plurality of CoPc particles are disposed on a plurality of graphene sheets. For instance, in some cases, graphene sheets may be immobilized and / or otherwise attached to CoPc particles. In some embodiments, the catalyst comprising CoPc particles disposed on graphene sheets may advantageously increase the asymmetry of charge distribution across the pyroelectric material and increase the voltage output of the pyroelectric material under thermal cycling. In some embodiments, the pyroelectric material may have a relatively high pyroelectric coefficient. In some embodiments, the pyroelectric material has a pyroelectric coefficient of greater than or equal to 2 C / m2K, greater than or equal to 3 C / m2K, greater than or equal to 4 C / m2K, greater than or equal to 5 C / m2K, greater than or equal to 10 C / m2K, greater than or equal to 20 C / m2K, and / or less than or equal to 100 C / m2K, less than or equal to 500 C / m2K, or 12734848.1 less than or equal to 1000 C / m2K. Combinations of these ranges are possible (e.g., greater than or equal to 2 C / m2K, and / or less than or equal to 1000 C / m2K). Other ranges are also possible. The pyroelectric coefficient can be calculated according to Equation 5 using the methods described in Example 1 below. In some embodiments, the catalyst comprising the pyroelectric material is thermally cycled. For instance, in some embodiments, the temperature of the pyroelectric material may be increased from a first temperature to a second temperature that is higher than the first temperature. In some embodiments, the temperature of the pyroelectric material may be decreased from the second temperature to a third temperature that is lower than the second temperature. Such thermal cycling of the catalyst may allow the pyroelectric material to exhibit catalytic properties such that a hydrolysis reaction, a carbon dioxide reduction reaction, and / or other reactions may take place at advantageous reaction rates. In some cases, the temperature of the pyroelectric material can be held at the second and / or third temperature for a duration of time such that the pyroelectric material catalyzes an electrochemical reaction that produces one or more products. In some embodiments, the catalyst comprising the pyroelectric material is thermally cycled such that the pyroelectric material is capable of catalyzing an electrochemical reaction. For example, when thermally cycled, the pyroelectric material may produce (e.g., generate) a voltage that is capable of catalyzing a hydrolysis reaction and / or a carbon dioxide reduction reaction. In some embodiments, the voltage may be capable of initiating and / or facilitating electrochemical reactions. In some embodiments, when the pyroelectric material is thermally cycled in the presence of carbon dioxide, the pyroelectric material generates a voltage that catalyzes a carbon dioxide reduction reaction. In some embodiments, when the pyroelectric material is thermally cycled in the presence of water, the pyroelectric material generates a voltage that catalyzes a hydrolysis reaction. It should be appreciated that, while the above examples thermally cycle the pyroelectric material in the presence of water and / or carbon dioxide, in some embodiments, the water and / or carbon dioxide may also be thermally cycled along with the pyroelectric material. In some embodiments in which water is present, the system is configured such that, when the pyroelectric material and the water are thermally cycled, hydrogen gas is produced. For instance, when thermally cycling the pyroelectric material in the presence of water, the water may undergo a hydrolysis reaction (e.g., a water-splitting reaction), catalyzed by the catalyst, to produce oxygen gas (e.g., diatomic oxygen gas) and / or hydrogen gas (e.g., diatomic hydrogen gas). For example, as shown in FIG. 1, system 100 comprises vessel 102 comprising pyroelectric 12734848.1 material 104 and water 108. In accordance with certain embodiments, when pyroelectric material 104 and water 108 are thermally cycled, a hydrolysis reaction takes place producing hydrogen gas 110. In certain embodiments, hydrogen gas 110 exits vessel 102 to be collected and / or repurposed. In some embodiments, the system is configured such that, when the pyroelectric material and the water are thermally cycled, at least 0.01 mmol of H2, at least 0.05 mmol of H2, at least 0.1 mmol of H2, at least 0.5 mmol of H2, at least 1 mmol of H2, at least 2 mmol of H2, at least 2.19 mmol of H2, at least 2.26 mmol of H2, at least 2.33 mmol of H2, at least 2.37 mmol of H2, at least 2.4 mmol of H2, at least 2.52 mmol of H2, at least 3 mmol of H2, at least 4 mmol of H2, or at least 5 mmol of H2, and / or up to 100 mmol of H2, up to 500 mmol of H2, up to 1000 mmol of H2, or more is produced per gram of catalyst. In some embodiments, the system is configured such that, when the pyroelectric material and the water are thermally cycled, at least some of the water is converted to H2. In some embodiments, the system is configured such that, when the pyroelectric material and the water are thermally cycled, at least 50%, at least 75%, at least 90%, at least 95%, at least 99%, at least 99.9%, and / or up to 99.95%, up to 99.99%, or up to 99.999%, of the water is converted to H2. In some embodiments in which CO2 is present, the system is configured such that, when the pyroelectric material and CO2 are thermally cycled, CO2 is reduced. When carbon dioxide, or another chemical compound, is reduced, the chemical compound gains electrons via a process known as reduction. For instance, when thermally cycling the pyroelectric material in the presence of carbon dioxide, the carbon dioxide may be reduced (e.g., gain electrons) to form carbon monoxide (e.g., carbon monoxide gas). For example, as shown in FIG. 1, system 100 comprises vessel 102 comprising pyroelectric material 104 and carbon dioxide 106. In accordance with certain embodiments, when pyroelectric material 104 and carbon dioxide 106 are thermally cycled, carbon dioxide 106 is reduced via a carbon dioxide reduction reaction to produce carbon monoxide 112. In some embodiments, carbon monoxide 112 exits vessel 102 to be collected and / or repurposed. In some embodiments, the system is configured such that, whenthe pyroelectric material and CO2are thermally cycled, at least 0.01 mmol of CO, at least 0.05mmol of CO, at least 0.1 mmol of CO, at least 0.108 mmol of CO, at least 0.117 mmol of CO, at least 0.122 mmol of CO, at least 0.165 mmol of CO, at least 0.2 mmol of CO, at least 0.215 mmol of CO, at least 0.25 mmol of CO, at least 0.28 mmol of CO and / or up to 10 mmol of CO, up to 50 mmol of CO, and / or up to 100 mmol of CO is produced per gram of catalyst. In some embodiments, the system is configured such that, when the pyroelectric material and CO2 are thermally cycled, at least 50%, at least 75%, at least 90%, at least 95%, at least 99%, at least 12734848.1 99.9%, and / or up to 99.95%, up to 99.99%, or up to 99.999% of the CO2is converted to reduced CO2 (e.g., CO). In some embodiments, the reduced CO2 comprises carbon monoxide (CO). In some embodiments, as described above, thermally cycling the catalyst involves a change in temperature from a first temperature to a second temperature, and a change in temperature from a second temperature to a third temperature. In accordance with some embodiments, the change in temperature is the absolute value of the difference between the second temperature and the first temperature. In some embodiments, the change in temperature is the absolute value of the difference between the second temperature and the third temperature. In some embodiments, thermal cycling involves a change in temperature of less than or equal to 200 °C, less than or equal to 150 °C, less than or equal to 100 °C, less than or equal to 75 °C, less than or equal to 60 °C, or less than or equal to 50 °C. In some embodiments, thermal cycling involves a change in temperature of greater than or equal to 50 °C, greater than or equal to 60 °C, greater than or equal to 75 °C, greater than or equal to 100 °C, greater than or equal to 150 °C, or greater than or equal to 200 °C. Combinations of these ranges are possible (e.g., less than or equal to 200 °C and greater than or equal to 50 °C). Other ranges are also possible. In some embodiments, during at least a portion of the thermal cycling, the temperature of the catalyst may be at any of a variety of temperatures. In some embodiments, during at least a portion of the thermal cycling, the temperature of the catalyst is 25 °C. For example, as described above, the catalyst comprising the pyroelectric material may be thermally cycled from a first temperature (e.g., 10 °C) to a second temperature that is greater than the first temperature (e.g., 30 °C). The pyroelectric material may then be thermally cycled to a third temperature that is less than the second temperature (e.g., back to 10 °C). During such thermal cycling, the temperature of the catalyst would be at 25 °C at at least one point in time while the catalyst is being heated from the first temperature to the second temperature and would also be at 25 °C at at least one point in time while the catalyst is being cooled from the second temperature to the third temperature. Such embodiments may be advantageous as the thermal energy needed to heat the pyroelectric material from the first temperature to the second temperature and / or the thermal cooling needed to cool the pyroelectric material from the second temperature to the third temperature may be relatively low when such temperatures are close to 25 °C. In some embodiments, during at least a portion of the thermal cycling, the temperature of the catalyst is 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, and / or 50 °C. Thermal energy needed to thermally cycle the pyroelectric material and water and / or carbon dioxide may originate from any of a variety of sources. In some cases, heat from industrial processes (e.g., energy generation, waste disposal, material processing, among others) 12734848.1 can be used to thermally cycle the pyroelectric material and water and / or carbon dioxide. By repurposing thermal energy released from such processes, the systems described herein may be environmentally advantageous as it does not require a dedicated, external energy source to catalyze reactions of interest (e.g., carbon dioxide reduction reactions and / or hydrolysis reactions). The embodiments described herein are, however, do not necessarily require the use of repurposed thermal energy, and other sources of thermal energy (e.g., sunlight, electrically- generated heat, combustion-generated heat, etc.) could also be used. In some embodiments, the system is configured such that the catalyst is thermally cycled in a continuous manner. In such embodiments, the system operates under steady state conditions. For example, the system can be operated, in some embodiments, at steady state conditions that are desirable at commercial scales. In some embodiments, the temperature of the catalyst comprising the pyroelectric material may be increased from a first temperature to a second temperature that is greater than the first temperature. The temperature of the catalyst may then be decreased from a second temperature to a third temperature that is less than the second temperature and substantially the same as the first temperature (e.g., within 0.5 °C, within 1 °C, within 2 °C, and / or within 5 °C). In some such embodiments, this process (cycling from the first temperature to the second temperature and to the third temperature) may be repeated (e.g., at least 1, at least 2, at least 5, at least 10, at least 50, or at least 100 additional times, and / or, up to 15, up to 25, up to 50, up to 100 additional times, or more). In some such embodiments, for each repetition of the thermal cycling, the higher temperature is within 0.5 °C, within 1 °C, within 2 °C, and / or within 5 °C of the numerical average of the higher temperatures. In some such embodiments, for each repetition of the thermal cycling, the lower temperature is within 0.5 °C, within 1 °C, within 2 °C, and / or within 5 °C of the numerical average of the lower temperatures. In accordance with some embodiments, by continuously thermally cycling the catalyst, carbon dioxide reduction reactions and / or hydrolysis reactions may advantageously produce chemical products (e.g., hydrogen gas, oxygen gas, and / or carbon monoxide) in acontinuous manner. In certain embodiments, the products described herein (e.g., CO, O2, and / orH2) can be produced in the amounts and / or at the rates described herein during each cycle of the repeated cycles. In certain embodiments, the reactants described herein (e.g., CO2 and / or H2O) can be consumed in the amounts and / or at the rates described herein during each cycle of the repeated cycles. In some embodiments, systems comprising one or more heat exchangers can be used to, for example, perform continuous cycling of the catalyst and water and / or carbon dioxide. In some embodiments, the system comprises a first heat exchanger and a second heat exchanger. 12734848.1 For example, as shown in FIG. 9, system 900 comprises first heat exchanger 902 and second heat exchanger 904. Any of a variety of suitable heat exchangers may be used. In some embodiments, the first and / or the second heat exchanger are shell-and-tube heat exchangers, shell-and-coil heat exchangers, flat plate heat exchangers, finned-tube heat exchangers, spiral heat exchangers, air-cooled heat exchangers, double-pipe heat exchangers, and / or regenerative heat exchangers. Other types of heat exchangers could also be used. The type of heat exchanger may be chosen based on any of variety of factors including but not limited to heat transfer efficiency, pressure drop, fluid compatibility, and / or space constraints. In some embodiments, one or more heating streams and / or one or more cooling streams enter the first and / or second heat exchanger. For example, as shown in FIG. 9, heating stream 920 enters first heat exchanger 902 via heating stream inlet 922 and cooling stream 924 enters second heat exchanger 904 via cooling stream inlet 926. In some embodiments, the heating stream entering the first heat exchanger exits the first heat exchanger via a heating stream outlet. For example, as shown in FIG. 9, heating stream 920 exits first heat exchanger 902 via heating stream outlet 928. In some embodiments, the temperature of the heating stream at the heating stream inlet is greater than the temperature of the heating stream at the heating stream outlet. In some embodiments, the cooling stream entering the second heat exchanger exits the second heat exchanger via a cooling stream outlet. For example, as shown in FIG. 9, cooling stream 924 exits second heat exchanger 904 via cooling stream outlet 930. In some embodiments, the temperature of the cooling stream at the cooling stream inlet is greater than the temperature of the cooling stream at the cooling stream outlet. In some embodiments, the first heat exchanger comprises a first inlet. For example, as shown in FIG. 9, first exchanger 902 comprises first inlet 906. In some embodiments, the first inlet is configured to receive an input. For example, as show in FIG. 9, first heat exchanger 902 comprises first inlet 906 configured to receive first input 908. The first input may flow through the first heat exchanger such that the temperature of the pyroelectric materials increases to the second temperature. At the second temperature, the pyroelectric material may generate a voltage that catalyzes a hydrolysis reaction and / or a carbon dioxide reduction reaction. In some embodiments, the first heat exchanger comprises a first outlet. For example, as shown in FIG. 9, first heat exchanger 902 comprises first outlet 910. In some embodiments, the first outlet is configured to output at least a portion (e.g., at least 0.01 wt%, at least 0.1 wt%, at least 0.5 wt%, at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt%, at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, and / or at least 99 wt%, or more) of the pyroelectric material of the first input. For example, as 12734848.1 shown in FIG. 9, first heat exchanger 902 comprises first outlet 910 configured to output all of the pyroelectric material of first input 908 via first output 912A. In some embodiments, the first outlet is configured to output the pyroelectric material at a second temperature that is greater than the first temperature. For example, as shown in FIG. 9, first output 912A exiting first outlet 910 has a temperature that is greater than the temperature of first input 908 entering first inlet 906 of first heat exchanger 902. In some embodiments, the first outlet of the first heat exchanger is configured to output products comprising hydrogen gas (H2(g)), oxygen gas (O2(g)), and / or carbon monoxide. For example, as shown in FIG. 9, first outlet 910 is configured to output first product output 912B comprising hydrogen gas (H2(g)), oxygen gas (O2(g)), and / or carbon monoxide. In some embodiments, the second heat exchanger comprises a second inlet. In some embodiments, the second inlet is fluidically connected to the first outlet. For example, as shown in FIG. 9, second heat exchanger 904 comprises second inlet 914 that is fluidically connected to first outlet 910 of first heat exchanger 902. In some embodiments, the second inlet is configured such that at least a portion (e.g., at least 0.01 wt%, at least 0.1 wt%, at least 0.5 wt%, at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt%, at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, and / or at least 99 wt%, or more) of the output exiting the first outlet of the first heat exchanger enters the second inlet of the second heat exchanger. For example, as shown in FIG. 9, second inlet 914 is configured to receive all of first output 912A exiting first outlet 910 of first heat exchanger 902. As the second input is transported through the second heat exchanger, the temperature of the second input may decrease from the second temperature to the third temperature that is less than the second temperature. In some embodiments, the second heat exchanger comprises a second outlet. In some embodiments, the second outlet is fluidically connected to the first inlet. For example, as shown in FIG. 9, second heat exchanger 904 comprises second outlet 916 fluidically connected to first inlet 906 of first heat exchanger 902. In some embodiments, the second outlet is configured to output at least a portion (e.g., at least 0.01 wt%, at least 0.1 wt%, at least 0.5 wt%, at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt%, at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, and / or at least 99 wt%, or more) of the pyroelectric material that is input to the second inlet of the second heat exchanger. For example, as shown in FIG. 9, second outlet 916 is configured to output all the pyroelectric material that is input into second inlet 914. 12734848.1 In some embodiments, the second outlet is configured to output at least a portion (e.g., at least 0.01 wt%, at least 0.1 wt%, at least 0.5 wt%, at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt%, at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, and / or at least 99 wt%, or more) of the pyroelectric material that is output from the first outlet of the first heat exchanger. For example, as shown in FIG. 9, second outlet 916 is configured to output all the pyroelectric material that is output from first outlet 910. In some embodiments, the second outlet is configured to output pyroelectric material at the third temperature that is less than the second temperature. For example, as shown in FIG. 9, second output 918A exiting second outlet 916 of second heat exchanger 904 has a temperature that is less than the temperature of first output 912A exiting first outlet 910 of first heat exchanger 902. In some embodiments, the first temperature is less than the second temperature. In some embodiments, the first temperature and the second temperature are different by less than or equal to 200 degrees Celsius, less than or equal to 150 degrees Celsius, less than or equal to 100 degrees Celsius, less than or equal to 75 degrees Celsius, less than or equal to 60 degrees Celsius, or less than or equal to 50 degrees Celsius, and / or greater than or equal to 0.1 degrees Celsius, greater than or equal to 1 degree Celsius, greater than or equal to 5 degrees Celsius, greater than or equal to 10 degrees Celsius, greater than or equal to 20 degrees Celsius, greater than or equal to 35 degrees Celsius, or greater than or equal to 50 degrees Celsius. In some embodiments, the first temperature is room temperature (e.g., 25 degrees Celsius). In some embodiments, the second temperature is greater than the third temperature. In some embodiments, the second temperature and the third temperature are different by less than or equal to 200 degrees Celsius, less than or equal to 150 degrees Celsius, less than or equal to 100 degrees Celsius, less than or equal to 75 degrees Celsius, less than or equal to 60 degrees Celsius, or less than or equal to 50 degrees Celsius, and / or greater than or equal to 0.1 degrees Celsius, greater than or equal to 1 degree Celsius, greater than or equal to 5 degrees Celsius, greater than or equal to 10 degrees Celsius, greater than or equal to 20 degrees Celsius, greater than or equal to 35 degrees Celsius, or greater than or equal to 50 degrees Celsius. In some embodiments, the third temperature is room temperature (e.g., 25 degrees Celsius). In some embodiments, the first temperature and / or the third temperature is relatively low. In some embodiments, the first temperature and / or the third temperature is less than or equal to 55 degrees Celsius, less than or equal to 40 degrees Celsius, less than or equal to 30 degrees Celsius, less than or equal to 25 degrees Celsius, less than or equal to 20 degrees Celsius, and / or 12734848.1 greater than or equal to 5 degrees Celsius, greater than or equal to 7.5 degrees Celsius, greater than or equal to 10 degrees Celsius. Combinations of these ranges are possible (e.g., greater than or equal to 5 degrees Celsius and less than or equal to 55 degrees Celsius). Other ranges are also possible. In some embodiments, the second temperature is relatively high. In some embodiments, the second temperature is greater than or equal to 55 degrees Celsius, greater than or equal to 57.5 degrees Celsius, greater than or equal to 60 degrees Celsius, greater than or equal to 65 degrees Celsius, greater than or equal to 75 degrees Celsius, and / or less than or equal to 210 degrees Celsius, less than or equal to 200 degrees Celsius, or less than or equal to 190 degrees Celsius. Combinations of these ranges are possible (e.g., greater than or equal to 55 degrees Celsius and less than or equal to 210 degrees Celsius). Other ranges are also possible. In some embodiments, the input comprises the pyroelectric material and water and / or carbon dioxide. In some embodiments, the input comprises the pyroelectric material and water. In some embodiments, the input comprises the pyroelectric material and carbon dioxide. In some embodiments, the input comprises the pyroelectric material, carbon dioxide, and water. In some embodiments, the input comprises a suspension comprising a plurality of pyroelectric material particles and water and / or carbon dioxide. In some embodiments, the input received by the first heat exchanger comprises the pyroelectric material. In some embodiments, the input comprises the pyroelectric material in an amount of at least 0.0005 wt%, at least 0.001 wt %, at least 0.005 wt %, at least 0.010 wt%, at least 0.015 wt%, at least 0.020 wt%, at least 0.050 wt%, at least 0.10 wt%, at least 0.15 wt%, at least 0.50 wt%, at least 1 wt%, and / or up to 5 wt%, up to 7.5 wt%, or up to 10 wt%. Combinations of these ranges are possible (e.g., at least 0.15 wt% and up to 10 wt%). Other ranges are also possible. In some embodiments, the first inlet of the first heat exchanger receives a first input comprising the pyroelectric material and water. For example, as shown in FIG. 9, first heat exchanger 902 receives first input 908 comprising the pyroelectric material and water via inlet 906. In such embodiments, water, the pyroelectric material, hydrogen gas and / or oxygen gas may exit the first outlet of the first heat exchanger. For example, as shown in FIG. 9, first output 912A comprising pyroelectric material and water and first product output 912B comprising hydrogen gas and / or oxygen gas exit first heat exchanger 902 via first outlet 910. In some embodiments, water and / or the pyroelectric material exiting the first heat exchanger via the first outlet can be transported into the second heat exchanger via the second inlet. For example, as shown in FIG. 9, first output 912A comprising water and the pyroelectric material exiting first heat exchanger 902 via first outlet 910 is transported to second heat exchanger 904 via second 12734848.1 inlet 914. In such embodiments, water, the pyroelectric material, hydrogen gas and / or oxygen gas may exit the second outlet of the second heat exchanger. For example, as shown in FIG. 9, second product output 918B comprising hydrogen gas and / or oxygen gas exits second heat exchanger 904 via second outlet 916. In some embodiments, the input comprises at least a portion (e.g., at least 0.01 wt%, at least 0.1 wt%, at least 0.5 wt%, at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt%, at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, and / or at least 99 wt%, or more) of the second output exiting the second heat exchanger. For example, as shown in FIG. 9, first input 908 comprises all of second output 918A exiting second heat exchanger 904. In some embodiments, the concentration of hydrogen gas is greater (e.g., by at least 0.1 wt%, at least 2 wt%, at least 5 wt%, at least 10 wt%, or more) at the first outlet than a concentration of hydrogen gas at the second outlet. In some embodiments, the concentration of oxygen gas is greater (e.g., by at least 0.1 wt%, at least 2 wt%, at least 5 wt%, at least 10 wt%, or more) at the first outlet than a concentration of oxygen gas at the second outlet. In some embodiments, the first inlet of the first heat exchanger receives a first input comprising the pyroelectric material and carbon dioxide. For example, as shown in FIG. 9, first heat exchanger 902 receives first input 908 comprising the pyroelectric material and carbon dioxide via inlet 906. In such embodiments, the pyroelectric material, carbon dioxide, and / or carbon monoxide may exit the first outlet of the first heat exchanger. For example, as shown in FIG. 9, first product output 912B comprising carbon monoxide exits first heat exchanger 902 via first outlet 910. In some embodiments, carbon dioxide and / or the pyroelectric material exiting the first heat exchanger via the first outlet can be transported into the second heat exchanger via the second inlet. For example, as shown in FIG. 9, first output 912A comprising carbon dioxide and the pyroelectric material exiting first heat exchanger 902 via first outlet 910 is transported to second heat exchanger 904 via second inlet 914. In such embodiments, carbon dioxide, carbon monoxide, and / or the pyroelectric material exit the second outlet of the second heat exchanger. For example, as shown in FIG. 9, second output 918A comprising pyroelectric material and / or carbon dioxide and second product output 918B comprising carbon monoxide exit second heat exchanger 904 via second outlet 916. In some embodiments, the first input comprises at least a portion (e.g., at least 0.01 wt%, at least 0.1 wt%, at least 0.5 wt%, at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt%, at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, and / or at least 99 wt%, or more) of the second output exiting the second heat exchanger. For example, as shown in FIG. 9, first input 908 comprises all of second output 918A exiting second heat exchanger 904. In some 12734848.1 embodiments, a concentration of carbon monoxide is greater (e.g., by at least 0.1 wt%, at least 2 wt%, at least 5 wt%, at least 10 wt%, or more) at the first outlet than a concentration of carbon monoxide at the second outlet. As described above, in some embodiments, the system comprises a vessel. The vessel may be capable of being at least partially filled with catalyst, water, and / or carbon dioxide. In some embodiments, the vessel is partially or completely filled with catalyst, water, and / or carbon dioxide. For example, in the embodiment shown in FIG. 1, vessel 102 of system 100 is capable of being at least partially filled with pyroelectric material 104, water 108, and carbon dioxide 106. The vessel may include at least one or more openings to introduce, remove, and / or replace the catalyst, water, and / or carbon dioxide. In some cases, the vessel comprises a mechanism configured to convect and / or mix the components therein (e.g., via agitation). For example, the mechanism may include one or more of a stirrer, an impeller, and / or a propeller. Convection of the contents of the vessel during operation of the system may improve the rate and / or yield of the one or more reactions catalyzed by the catalyst. In some embodiments, the vessel may be in the form of a heat exchanger (e.g., any of the heat exchangers shown in FIG. 9. EXAMPLE 1 In this example, the potential pyroelectric effect of CoPc / G whereby CoPc is immobilized onto graphene (G) is described. This example also describes a pyrocatalytic effect under a near-room temperature fluctuation (below 60 °C). This effect is harnessed to promote CO2RR and water splitting in an externally unbiased system, leveraging the inherent self-driving force of CoPc / G. This force facilitates the conversion of CO2 to CO alongside H2 and O2 evolution reactions (HER and OER), providing an interesting perspective on pyroelectric- catalytic (pyrocatalytic) properties and their capabilities in fostering sustainable and eco-friendly processes. X-ray photoelectron spectroscopy (XPS, FIGS. 2C-2E, Tables 1-2) was employed to analyze the surface composition of the hybrid and the support and to compare the chemical states of the elements. FIG. 2E illustrates the XPS survey spectra of the CoPc, CoPc / G, and G samples, with Table 1 summarizing the spectral features. Evident Co 2p and N 1s transitions in CoPc are discernible at lower intensities in CoPc / G and absent in the G sample, whereas the C 1s transition is strong in both CoPc / G and G and weaker in CoPc (a scheme of CoPc molecule and its carbon and nitrogen atomic positions can be seen in FIG. 10). Quantification from XPS survey data (Table 1 and Table 2) reveals a 6.48-fold lower cobalt concentration and a 6.11-fold lower nitrogen concentration in the CoPc / G sample 12734848.1 compared to pure CoPc, suggesting a mean dilution factor of approximately 6.25-fold for the CoPc in the hybrid. The corresponding apparent surface concentration of CoPc in the hybrid, indicates nearly complete utilization or negligible loss of CoPc during hybrid synthesis. The XPS narrow scans of both pure and carbon-hybridized CoPc overlap with the theoretical spectra (see FIGS. 2C-2D for Co 2p and N 1s transitions of CoPc / G, and the corresponding discussion for the deconvolution interpretation and comparison of Co 2p, N 1s, C 1s, and O 1s transitions of all samples), confirming the target structure. Asymmetric polarity in cobalt phthalocyanine molecule A schematic representation of the pyroelectric phenomenon is illustrated in FIG. 3A. Below its Curie point (TC), a pyroelectric material exhibits temperature-dependent self- polarization with the internal charge separation balanced by the external accumulation of charges upon the surfaces of the material. Upon a temperature rise, the extent of internal charge separation within the material changes, and the need for a compensating change in the external pyroelectric charges leads to a potential difference across the material, and hence to a pyrocurrent flow within the electrically closed circuit with a load (e.g., a pair of redox reactions). Conversely, upon cooling, the redistribution of pyroelectric charges results in a pyrocurrent in the opposite direction. The output current attenuates when there is no temperature change. Although a direct experimental determination of the TCfor the pyroelectric behavior of CoPc has not been reported, based on the temperature-dependent dielectric constant studies on this material, a TC of about ~150 °C, corresponding to the pyro / ferro- to para-electric state transition, is expected. FIG. 3B displays the pyroelectric behavior of CoPc pellet with 1cm diameter, manifested as an electrical current resulting from self-polarization induced by temperature fluctuations (fabrication details for the sandwich three-electrode pellet for pyrocurrent measurements can be found in FIGS. 11A-11B and the Methods section). In CoPc, temperature-induced changes in charge separation, i.e. a pyroelectric behavior, can be linked to the interaction between 3d orbitals and the electrons of phthalocyanine, and / or in addition, to molecular distortions. Notably, the presence of Co metal within the phthalocyanine macrocycle, which interacts with the extensive ^-electron cloud of the macrocycle system as phthalocyanine, contributes to the pyroelectricity. This fluctuation in self-polarization could potentially be contingent upon intermolecular distances, as evidenced by a more pronounced intermolecular ^-orbital overlap within CoPc. The deposition of CoPc onto graphene sheets magnifies the asymmetry in charge distribution, leading to an amplification of the pyroelectric charges and, consequently, of the electric field generated as the charge distribution relaxes during the dynamic heating and cooling 12734848.1 (e.g., thermally cycling) (see FIG. 12B). This voltage, arising from the pyroelectric effect, can serve as a potential driving force to initiate electrochemical reactions. For an in-depth analysis of the crystal structure of CoPc, phase purity, possible polymorphism, and temperature-related crystallographic changes with potential pyroelectric implications, X-ray diffraction (XRD) studies were conducted in operando conditions over a heating–cooling cycle from room temperature to 125°C. The structural analysis at each temperature point, shows that cell volume changes (FIG. 3C) follow a quasi-linear and reversible pattern, primarily along the c-axis, while the a and b parameters and the beta angle remain relatively constant (FIGS. 3D-3G). This behavior indicates a preferential expansion of the crystal along the c-direction. Additionally, although the central Co atom maintains its position, the phthalocyanine rings exhibit slight adjustments and rotations. Reversible macromolecular changes in response to temperature variations are therefore possible. It is experimentally demonstrated that PC, despite not having a permanent dipole moment, exhibits a high electronic polarizability—as evidenced by CuPc polarizability of 1.2 × 10–22cm3. This significant polarizability might facilitate the alignment of induced dipoles under certain conditions. While the observed modifications do not provide a definitive explanation for the pyroelectric properties, they suggest a potential mechanism: if induced dipoles can be generated within the CoPc molecule, their effects might be desirably altered by the pronounced repositioning and reorientation of the CoPc molecules and lattice parameters during thermal cycling. Thus, the pyroelectric behavior could stem from the collective realignment of these induced dipoles. Similar pyroelectric properties have been reported in FePc and CuPc, yet the underlying mechanisms have remained elusive. Simultaneous CO2 Reduction and Water Splitting To explore the pyrocatalytic properties of CoPc / G on catalytic activity in the CO2 reduction and water splitting reactions, thermal cycling experiments were carried out on aqueous suspensions of CoPc / G particles in the temperature window between 10 and 60 °C and under two different saturating gas atmospheres, namely, CO2 and N2, over twelve consecutive cycles in a sealed 50 mL cell (see Methods for experimental details). FIGS. 4A-4E illustrate the pyrocatalytically produced gaseous species under thermal cycles of CoPc / G with a 2:1 wt% ratio between 10 and 60^°C under CO2(FIGS. 4A-4C) and N2(FIGS. 4D-4E); gas chromatography (GC) samples were collected from the headspace after each complete heating–cooling cycle. The processing time during thermal cycles is shown in FIG. 4A to be about 50 s per full cycle. The CO2atmosphere graphs (FIGS. 4A-4C) illustrate the production of CO, H2and O2, 12734848.1 corresponding respectively, to CO2RR, HER, and OER. Remarkably, over the twelve thermal cycles (each lasting about 50 seconds), the CoPc / G pyrocatalyst demonstrated an unprecedented CO2 to CO conversion yield of ~0.25 ^^^^^^^^^^^^^^^^^^(FIG. 4C). Additionally, CoPc / G has shown to have a high activity for the pyrocatalytic water splitting reaction as demonstrated by the yields of H2and O2under both CO2and N2atmosphere. Under N2, CO is expectedly not produced, since the precursor content provided by the bicarbonate salt is not sufficient to drive the CO2RR under the rather alkaline pH conditions therein (pH range: 9 to 9.5). The overall importance of the graphene in the materials on the pyroelectric conversion effectiveness for the CO2RR is evident from the results presented in FIGS. 5A-5C, where the yields are seen to decrease as the proportion of CoPc in the CoPc / G particles increases. The significant role played by the graphene relates to the various pathways it opens for electron transfer during the operations, as discussed below. Approximation of the apparent equivalent moles of electrons exchanged for the production of these gases (see Tables 3-8), reveals that under N2atmosphere, electrons exchanged for the reduction products (CO, H2) outweigh those for the oxidation products (O2), whereas under CO2, the equivalent reduction electrons fall behind those of oxidation. Since OER is the only GC detectable oxidation half-reaction, any contribution of the SO32–(provided by the Na2SO3sacrificial agent) to the oxidation half-reactions (i.e., SO32–^ SO42–) would appear in the form of an equivalent oxidation electrons deficit, and this explains the results under N2. Under CO2, there is in principle even more driving force for the SO32–participation in the reactions, namely, O2scavenging and CO shielding role in the post-catalysis stage, in addition to the role of an individual oxidation half-reaction in the pyrocatalysis stage (as a demonstration, see the CO yield in the control experiment without Na2SO3, FIGS. 13A-13C, and compare it FIG. 4C). Therefore, the reduction electrons deficit under CO2, can only be explained by the formation of the reduction products or intermediates hidden to the experimental probe. Incomplete CO2RR leading to the absorbed CO formation, is for instance, a well-documented example which can explain the charge imbalance under CO2. Overall, GC measurements after thermal cycling, demonstrated clearly the promising capacity of CoPc / G for the pyrocatalytic propulsion of several electrochemical reactions. A control experiment using unsupported CoPc (FIGS. 14A-14C), revealed a decreased yield of all gaseous species (e.g. by more than 60% for CO), highlighting the synergistic role of the graphene support. The outstanding thermal conductivity and charge mobility of graphene, render it a promising substrate for pyroelectric structures. Beyond the intrinsic merits of graphene in 12734848.1 terms of thermal and electrical behavior, its interactions with the catalyst play a key role in the successful formation of a robust hybrid structure. Several pathways have been explored for the electronic interactions between MPcs (e.g., CoPc) and carbon materials (e.g., graphene), including: 1- ^-^ stacking (van der Waals) interactions, 2-coordination (covalent bond) interactions, 3-electronic donor-acceptor (covalent or non-covalent bond) interactions, and 4- a combination of electrostatic (hydrogen bonds or van der Waals forces) and covalent interactions. Based on microscopic and spectroscopic evidence, it is observed that most of these interaction pathways are active in the hybrid pyrocatalyst system. ^-^ interactions, involving the alignment of ^-electron systems of MPc with those of carbon, have implications for the anchoring and dispersion of MPc on the carbon, such as molecular level homogeneity in the distribution, which is as confirmed by the microscopic evaluations (SEM-EDS and TEM). Additionally, ^-^ interactions facilitate electronic communication between CoPc and the carbon substrate through an electron exchange process between the graphitic domains of carbon and CoPc. This process is evidenced in the present work by a BE downshift of the Co core holes (e.g., Co 2p3 / 2 and Co 2p1 / 2), suggesting that the overall direction of the electron transfer is from G (donor) towards the metal center of CoPc (acceptor), leading to a relative increase in the electron density of Co in the hybrid compared to in pure CoPc. The slight BE downshift of the N–H component of the N 1s transition in the hybrid and its relative enlargement compared to pure CoPc, suggests the activation of electrostatic interactions (hydrogen bonding) between the nitrogen sites of the Pc ring (presumably pyridinic N, acting as hydrogen bond acceptor) and the hydrogen-containing functional group traces of G. Finally, the observed increase in oxygenation extent of cobalt in the hybrid compared to pure CoPc (relative enlargement of satellites by ^ 5%) along with the slight BE downshift of the C–OH and C=O components (C 1s transition) in the hybrid compared to pure G, suggests coordination-like bond formation between the cobalt center of CoPc and the oxygen functional groups of carbon (the latter being the electron acceptor, while the electron donor is not necessarily CoPc). The counterintuitive electron density gains of several components (MPc center, MPc ring, oxygen functional groups of the carbon support), can be explained by a complex mutual electronic interaction between CoPc and carbon. Without wishing to be bound by any particular theory, in the two-way communication process, the graphitic sp2domains of the carbon support serve as the global source of electrons, donated firstly to the center (via ^-^ interactions) and the ring (via hydrogen bonds) of the adsorbed CoPc (the forward communication), and subsequently, to the ligand-like oxygen functional groups of carbon attached to the cobalt centers (the backward communication). 12734848.1 The multifaceted interaction scheme outlined above has implications for both the pyroelectric and electrocatalytic properties of the CoPc / G hybrid. The pyroelectric properties are primarily influenced by the ^-^ interactions, where the attachment of the dimensionally vast electron delocalization domains of G to those of CoPc, significantly increases the charge motion distances and, consequently, polarizability of CoPc, even beyond the already colossal “nomadic polarization” figures recognized for such polymers. Regarding the electrocatalytic properties, the mentioned interactions enhance the performance of the CoPc / G hybrid in more than one way. First, ^-^ stacking interactions between CoPc and carbon, stabilize the anchoring of CoPc on the support, preventing its aggregation and increasing the electron conjugation across its interface. This facilitates the charge transfer to / from the catalytic active sites for any redox reaction. Second, the increased electron density of the cobalt center in CoPc makes it an appropriate electron source site for reduction reactions in need of electrons, such as CO2RR. Third, the electron donation from G to Co, places the latter in a partially reduced state and enhances its nucleophilicity via particular modifications in its molecular orbitals, planar structure symmetry, and spin states, thereby increasing its affinity for CO2chemisorption and subsequent reduction. Fourth, other interactions pathways, such as hydrogen bonds or coordination-like linkages, provide additional channels for communication between the catalytic active sites and the electron reservoir of the ^ systems of both CoPc and the carbon support. All these pathways have contributed to the unparalleled pyrocatalytic yields for CO2RR and water splitting products observed in the present work. The pyrocatalytic performance of CoPc / G was additionally examined over individual heating or cooling half-cycles (FIGS. 5A-5C) for two reasons. Firstly, the yield in the complete heating-cooling cycles reveals a relatively linear trend of increase with the number of cycles, but it has a non-zero y-intercept, suggesting an evolution of gas products already in the first cycle (intercept > slope). Secondly, designing different temperature windows or thermal fluxes for the heating and cooling half-cycles, provides another way to observe the pyrocatalytic nature of CoPc / G, relying on the dT / dt sensitivity of the pyrocurrent response of the pyroelectric materials. The oxidation-reduction half-reactions are listed as Eq. 1 to Eq. 4. 12734848.1 Results in FIGS. 5A-5C show both of the above postulates. Note that the results are not cumulative, and the cell atmosphere has been reset after each thermal half-cycle. It is seen that the average yield at the first cycle, is always larger than the slope of the yield increase in subsequent cycles in FIGS. 4A-4E, irrespective of the product gas and the purging atmosphere. For instance, the CO production rate based on the aforementioned cumulative yield of ^ 0.25 ^^^^^^^^^^^^^^^^^^over twelve cycles, is ^ 0.02 ^^^^^^^^^^^^^^^^^^^^^^^^^by simple averaging, or ^ 0.017 ^^^^^^^^^^^^^^^^^^^^^^^^^by assessing the slope of the rise between cycles 2 to 12. Whereas, results in FIGS. 5A-5C give on average a yield value of 0.197 ± 0.067 ^^^^^^^^^^^^^^^^^^for the first heating half-cycle, and 0.152 ± 0.055 ^^^^^^^^^^^^^^^^^^for the first cooling half-cycle. The decreased rate in successive operation, supposedly caused by the reduced thermodynamic driving force for the reactions due to increased concentration of the product gases, as well as the internal coupling of half-reactions leading to partial consumption of some gases, implies that in practical applications, technical maneuvers such as frequent flushing of the product gases, could increase the yield and the rate by almost an order of magnitude. Regarding the second aspect, reasonable reproducibility can be observed for the trend of yield as a function of dT / dt, irrespective of the product gas and the purging atmosphere. Higher dT / dt of the heating half-cycles (T window of 25 to 60 °C vs. 25 to 10 °C in cooling half-cycles) has clearly produced higher amounts of gaseous products. This dT / dt sensitivity, as pointed out earlier, is a confirmation of the pyrocatalytic behavior of CoPc / G. Additionally, similar to the thermal full-cycles (FIGS. 4A-4E), no CO is produced under the N2 (FIG. 5C), confirming that the observed CO production under CO2is solely due to pyrocatalytic CO2RR. The higher H2yield under N2(vs. CO2) in thermal half-cycles (similar to full-cycles) can be justified by the competition between CO2RR and HER under CO2. The higher O2 yield under CO2 (vs. N2) in thermal half-cycles (which is not adequately confirmed in full-cycles due to same thermodynamic and half-reactions coupling reasons mentioned before for prolonged continuous operation), can be explained by the facilitation of the OER in the presence of two cathodic half- reactions under CO2 (i.e., CO2RR and HER) instead of only one under N2 (i.e., HER). FIGS. 6A-6F show the CoPc / G pyrocatalytic yield of the gaseous species after individual heating or cooling half-cycles. The observed results are not cumulative, and the cell atmosphere has been reset after each thermal half-cycle (FIG. 6A). Reasonable reproducibility can be observed for the trend of yield as a function of dT / dt, irrespective of the product gas and the purging atmosphere. Higher dT / dt of the heating half-cycles has clearly produced higher amounts of gaseous products. This dT / dt sensitivity, as pointed out earlier, is a confirmation of 12734848.1 the pyrocatalytic behavior of CoPc / G. Additionally, similar to the thermal full-cycles (FIGS. 4A- 4E), no CO is produced under the N2 (FIGS. 6A-6F), confirming that the observed CO production under CO2 is solely due to pyrocatalytic CO2RR. Other similarities with the thermal full-cycles include higher O2production under CO2(vs. N2) and higher H2production under N2(vs. CO2). While the latter can be justified by the competition of CO2RR and HER under CO2, the former is explained by the facilitation of the OER in presence of two cathodic half-reactions under CO2 (i.e., CO2RR and HER) instead of only one under N2 (i.e., HER). FIG. 7 illustrates schematically how the pyroelectric properties of CoPc / G and its corresponding self-polarization under thermal fluctuations can be coupled to redox reactions in an environment containing species prone to such reactions. The schematic depicts two snapshots of the CoPc / G stabilized at low and high temperatures (labeled as 1 and 3, respectively), and two snapshots during temperature rise and fall (labeled as 2 and 4, respectively). At any stabilized temperature (dT / dt = 0) below its TC, the pyroelectric material has a certain degree of internal polarization (represented by a thought “polarization charge layer”) which is counteracted and compensated for by a “compensation charge layer” from the surrounding environment. Thus, the internal charge separation and pyroelectric field is shielded at any steady state temperature. Upon any temperature perturbation, the internal pyroelectric field varies instantaneously, but there is a lag time for the compensation charges to follow and counteract the internal polarization, the so-called “relaxation time, ^”. The physical compensation processes and ^, are dictated by the available environmental pathways for supply or removal of these charges and their corresponding kinetics (e.g., conduction, diffusion, adsorption, reaction, and so forth). Given that the pyroelectric material possesses sufficient internal polarization and adequate electrocatalytic activity, and depending on the environmental circumstances (parameters such as the concentration of the available reactants, temperature, pH, mobility of the species and their interactions with the surrounding medium), redox reactions can play a major or minor part in the global compensation process. When the CoPc / G is heated (dT / dt > 0, FIG. 7, snapshot 2), itundergoes a depolarization as it approaches its TC, and thus, a relative attenuation of thepyroelectric field occurs. Accordingly, the relaxation period and compensation process involve the down-tuning of the magnitude of the shielding field. This could be done via either the consumption of some uncompensated charges on the surface of the pyroelectric, or provision of some new charges thereon opposing the uncompensated charges and thus neutralizing them. Considering the electron-transfer nature of the redox reactions, the contribution of such reactions to the overall readjustment of the compensation charge layer would be in the form of: (a) electron consuming reactions (reduction half-reactions) on the surface sites with negative 12734848.1 uncompensated charges and (b) electron releasing reactions (oxidation half-reactions) on the surface sites with positive uncompensated charges. In this example, the former includes HER and CO2RR, and the latter includes OER and oxidation of a sacrificial agent, whenever present. Conversely, when the CoPc / G is cooled down (dT / dt < 0, FIG. 7, snapshot 4), it undergoes an enlargement in its internal polarization as it departs from its TC, and thus, a relative amplification of the pyroelectric field occurs. Accordingly, the relaxation period and compensation process involve the up-tuning of the magnitude of the shielding field. Although the contribution paradigm of the redox reactions to the compensation process would remain limited to the same two forms mentioned for the heating period, the reaction sites would be reversed due to the inverse trend of the pyroelectric polarization. That is, the surface sites that initially experience an uncompensated charge of the negative character thus promoting the reduction half-reactions during heating, would experience a positive uncompensated charge during cooling and thus would promote the oxidation half-reactions, and vice versa. Exploring Pyrocatalytic Behavior during the Reactions and Polarization Window in CoPc / G Particles To further assess the potential role of the cell internal dynamics, specifically the coupling of half-reactions, on the pyrocatalytic yield under prolonged service conditions, and to develop a more comprehensive understanding of the redox species involved in the overall process, electrochemical characterizations were conducted under customized conditions such as no temperature ramping. These experiments provided additional confirmation of the pyrocatalytic behavior of CoPc / G and allowed for the approximation of their self-polarization potential window. Briefly, cells similar in content and conditions to those used in previous experiments, but additionally equipped with Pt working and counter electrodes and an Ag / AgCl reference electrode, were initially heated or cooled from room temperature to either 60°C or 10°C (as in the thermal half-cycle experiments of FIGS. 5A-5C). Subsequently, these cells underwent static and dynamic electrochemical measurements at fixed temperatures, namely, open circuit potential (OCP) and linear sweep voltammetry (LSV) in anodic and cathodic directions (FIGS. 8A-8C). The anodic sweep starts from OCP and extends 1.5 V towards more positive potentials, while the cathodic sweep starts from OCP and extends 1.5 V towards more negative potentials. Solid horizontal lines represent the potential at which current waves related to different half-reactions emerge in agreement with the predicted electrode potentials based on the mixed electrode theory. For the sake of brevity, letters O, H, C, and S, highlight the position of H2O / O2, H2 / H+, CO / CO2, and SO32– / SO42–electrodes. The central, low current, plateau-like zone of LSVs, represents the current inversion region, the approximate span of which is indicated by an arrow 12734848.1 (left side of graph). The separation of O and S lines is indicated by an arrow (right side of graph) to give a minimalistic approximation of the required self-polarization of pyrocatalysts, to steadily trigger the pyrocatalytic gas production. The OCP results could only be justified and simulated under conditions where no further pyrocatalytic production of gases (CO, O2, H2) could occur (FIG. 8A for CO2atmosphere). This confirms, as expected from pyroelectrics, that self-polarization has diminished at the fixed temperature (dT / dt = 0). Additionally, the concentrations of previously produced gases during the initial temperature ramping, could not have remained constant over the 30 min OCP period, as suggested by the OCP trend. Gas products associated with the half-reactions possessing the highest and lowest electrode potentials, O2 and CO respectively, experienced decreased concentrations (reconsumption) over time despite the presence of the sacrificial agent. Whereas, H2, with an intermediate electrode potential, served as a balancing moderator and could play a dual role depending on the concentrations of other species. The internal galvanic coupling of the half-reactions was thus realized to be inevitable over prolonged service conditions. Conclusion This example presents an unexplored aspect of the catalytic properties of metal- phthalocyanines (MPcs) for electrochemical reactions such as CO2RR, HER, and OER, driven by pyroelectric self-polarization induced by thermal fluctuations. Specifically, the use of CoPc in this study demonstrated pyrocatalytic capabilities for simultaneous CO2RR and water splitting, with significantly enhanced performance when supported on graphene. The pyrocatalytic production yields of CO, H2and O2reached unprecedented values of 0.25 ^^^^^^^^^^^^^^^^^^, 2.4 ^^^^!^^^^^^^^^^^^and 2.4 ^^^^^!^^^^^^^^^^^, respectively, over twelve successive thermal cycles between 10 and 60 °C. It was further observed that the yield during the first thermal cycle was extraordinarily higher than in subsequent cycles. The decline in yield with successive operations was attributed to the reduced thermodynamic driving force for the reactions due to increased concentration of the product gases, as well as the internal coupling of half-reactions leading to partial consumption of some gases. This suggests that practices such as frequent flushing of the product gases could further increase the yield and rate by up to an order of magnitude. Beyond the intrinsic merits of each constituent –namely, the pyroelectric and electrocatalytic properties of CoPc and the electrical and thermal conductivity of graphene– the synergistic enhancement in the pyrocatalytic performance of the hybrid structure is attributed to strong and mutual electronic connection between the two. This interaction comprises a complex network of ^-^ interactions, electrostatic forces, and chemical bonds, contributing to both 12734848.1 pyroelectric self-polarization and electrocatalytic activity. The strategy proposed and demonstrated in this work opens a new avenue in the range of solutions aimed at providing sustainable and economically viable approaches for environmental decontamination, remediation and recovery of resources. This can be achieved through the removal of atmospheric pollutants (such as CO2via CO2RR) and their conversion into value-added products, or through the production of fuels like H2 and O2 essential for a low carbon footprints in developing energy technologies, such as fuel cells, all while utilizing waste thermal energy from the environment. Methods Materials All reagents and materials were analytic grade and used as received without further purification. Cobalt phthalocyanine (CoPc) crystalline powder (> 95.0%) was purchased from ThermoFisher SCIENTIFIC. Dispersible single-layer graphene with a flake diameter of 0.4- 5 µm and BET surface area of 400-1000 m2 / g was acquired from ACS MATERIAL. N, N- Dimethylformamide (DMF), anhydrous 99.8%, and deionized water were purchased from Sigma-Aldrich. CO2and N2were purchased from Airgas with purity of 99.99% and 99.999%, respectively. Synthesis of CoPc / G The immobilization of CoPc onto graphene sheets was prepared by mixing separate solutions of 4.5 mg CoPc and 30 mg graphene prepared in 5 ml and 30 ml DMF solutions, respectively. This mixture underwent 30 min of sonication followed by 20 hours of stirring to ensure the uniform deposition of CoPc within the graphene layers, facilitated by non-covalent ^- ^ stacking interactions. The outcome was the formation of the CoPc / G composite. SEM and TEM Characterization The morphology was characterized by a Zeiss Merlin High-resolution SEM with an accelerated voltage of 200 kV at MIT. nano. TEM was carried out with a ThermoFisher Scientific (TFS) Themis Z G3 aberration-corrected scanning transmission electron microscope (STEM) with a < 0.6 Å resolution. The instrument was equipped with an optimized monochromator for < 30 meV energy resolution in EELS at 60 kV and a super X-4 quadrant EDS detector with separable signals from each detector (atomic resolution elemental mapping with energy-dispersive X-ray spectroscopy (EDS)). XPS Calibrations and Considerations To investigate the bonding energies and surface electronic states between CoPc and graphene, XPS was carried out using an ESCA SSX-100 system with a 1486.6 eV monochromatic Al K^ X-ray source. Survey scans were obtained with a pass energy of 200 eV 12734848.1 with an energy step size of 1.0 eV and narrow scans were collected with a pass energy of 50 eV with an energy step size of 0.1 eV. The binding energy (BE) scale of the G and CoPc / G spectra was calibrated based on the C 1s (284.6 eV) signal. For the CoPc, a combination of C 1s (284.8 eV, slightly higher than the standard 284.6 eV for sp2carbon, due to the different nature of the carbon in CoPc and ubiquitous C–H bonds therein) and N 1s (399 eV for CoPc) was used for the energy calibration. Survey scans and narrow scans were calibrated separately in all cases since the charging drifts were different based on the pass energy used. For the background subtraction, a Shirley-type line shape was employed in all cases. Table 2 compares the surface elemental composition of CoPc obtained by XPS with the theoretical values ideally expected from the molecular formula of CoPc (C32 H16 Co N8). For a better comparison, the theoretical values are presented both with and without consideration of H (which is out of the XPS probe) and experimental values are presented both with and without consideration of O (which should be considered an impurity). Pyrocurrent Measurement and the Sandwiched Pyroelectric Fabrication A solid pellet of the CoPc was prepared by mixing 260 mg of this powder with 13 mg poly (acrylic acid) (PAA) as a polymer binder. To ensure a homogenous blending, a modest amount of ethanol was added to the mixture powder which was subjected to grinding for 30 min to ensure uniform mixing of the CoPc within the polymer matrix. Following this step, the mixture was pelletized using a hydraulic press to compact the mixing powder into a pellet with 1cm2diameter. The pellet was annealed under N2 at 350 °C for 3h to remove the binder. The pyroelectric measurements were done on a three-electrode configuration of the prepared CoPc pellet (D= 1cm) sandwiched between two electrodes with the same materials (silver) to avoid a thermoelectric effect (FIGS. 11A-11B). The pyroelectric coefficient can be expressed by Equation 5, where Ipyro and Cp are the pyroelectric current and the pyroelectric coefficient, respectively. A is the contact area, and dT / dt is the rate of temperature change (°C / s). Temperature-dependence XRD The in-situ temperature-dependent XRD was carried out on PANalytical Empyrean instrument equipped with a PIXcel1D 1D position-sensitive detector. In addition, the system was outfitted with a molybdenum X-ray source (K^1= 0.7093187 Å, K^2= 0.7136090 Å) which enables measurements on cobalt-rich samples. The instrument was equipped with an Anton Paar CHC and heating stage. The CoPc powder was heated up from room temperature to 125 °C and 12734848.1 cooled down from this temperature to the initial state at a rate of 5 °C / s. The sample was held at each temperature for around 1 min and data were collected before going toward the next step. Theoretical Analysis of Lattice Structure Characteristics The Rietveld refinement of the XRD pattern of CoPc was carried out to confirm the obtained phases and the lattice parameters during the pyroelectrical process. The sample was heated to 125°C with a step size of 25°C and then cooled down to room temperature. The peaks were indexed using a Pawley / Le Bail fitting method, and the space group P21 / c is proposed for the crystal structure. The Z matrix for CoPc was not constrained as for a completely rigid body. To enhance the refinement process, allowances were made for bond lengths to deviate within a range of ±0.1Å from their original values, while bond angles remained fixed. Furthermore, the entire molecule was permitted to rotate freely. Two distinct approaches were employed for structure determination: Global Optimization (Monte-Carlo, Simulated Annealing), and Charge Flipping. These methods were executed within the TOPAS v6 software, and subsequent refinement was carried out using the Rietveld algorithm. Mitigation of possible preferred orientation effects was partially achieved through the utilization of the spherical harmonic preferred orientation algorithm in TOPAS. Pyroelectrical CO2 Reduction and Water Splitting The catalytic reaction tests were done with 30 mg of CoPc / G suspended in 30 of an aqueous solution of 0.1M NaHCO3, 0.1 M Na2SO3, and 30 mg of CoPc / G. The reaction solution was initially purged with CO2 for 15 min, to ensure saturation with CO2, and then sealed for the ensuing thermal cycles. The produced gases from the reaction were collected from the cell headspace (20 ml volume) after each cycle using a gas-tight syringe and subsequently analyzed via gas chromatography (GC) to quantify the produced gases. Electrochemical Characterization Electrochemical Measurements In the three-electrode set-up, a Pt plate (2 cm2) was used as the working electrode (WE),a long (20 cm) spiral Pt wire as the counter electrode (CE), and an Ag / AgCl (3 M, 0 VAg / AgCl=+0.210 VSHE) electrode as the reference electrode (RE). The aqueous electrolyte (30 mL overall) was prepared by mixing 25 mL of 0.2 M Na2SO3, and 5 mL of 0.2 M NaHCO3. The three- electrode set-up was contained in a 50 mL flask. The experimental matrix consisted of three types of variables and three types of measurements. Variables included 1- presence vs. absence of pyrocatalysts in the electrolytic medium (accounting for 2 conditions), 2- high vs. low temperature (2 conditions), and 3- N2 vs. CO2 purging atmosphere (2 conditions). 12734848.1 Electrochemical measurements included 1- open circuit potential (OCP) measurement for 30 min, 2- anodic linear sweep voltammetry (LSV) starting from OCP and extending to 1.5 V above the OCP at a scan rate of 10 mV / s, and 3- cathodic LSV starting from OCP and extending to 1.5 V below the OCP at a scan rate of 10 mV / s. For experiments intending to assess the effect activity of pyrocatalysts, 35 mg CoPc / G (4.5 mg of which was CoPc) was dispersed in the base electrolyte. Purging of different gaseous atmospheres and temperature ramping, were according to the same procedure used in the CO2RR experiments. OCP and LSV measurements were always conducted after completion of the temperature ramping, i.e., at a constant temperature, either below the room temperature (cold condition, 10°C) or above the room temperature (hot condition, 60 °C). Modelling To interpret and translate the measured OCPs to the concentration of species, or otherwise, to translate the expected / measured concentration of species into an OCP value to be compared with the experimentally measured OCPs, an electrochemical model is needed. Such a model can additionally be used for interpretation of the LSV results. Development of a rigorous model for addressing both purposes would require consideration of many thermodynamic and kinetic aspects, which is out of the scope of this work. Nevertheless, as far as “electrode potentials” are concerned –a concept closely matching the OCP readings as well as the inversion potentials in LSV, careful consideration of the thermodynamic aspects may adequately fulfill the requirements. In the following, a simplified semi-theoretical (regarding the thermodynamic aspects) semi-graphical (regarding the kinetics aspects) model is employed to firstly, gain some global insight into the electrochemical map of half-reactions involved in the pyrocatalytic behavior of CoPc / G observed in this work, and secondly, to develop a schematic framework for interpretation and OCP and LSV, and validation of the assumptions drawn and approximations made. Assumptions used for developing this framework included: 1. CoPc / G particles are pyrocatalysts. Implications of this assumption include: a. Any pyrocatalytic consumption of reactants and generation of products, can occur only during temperature ramping before the initiation of OCP and LSV experiments, b. The pyrocatalytic activity of CoPc / G particles during temperature ramping before the initiation of OCP and LSV, generates a perturbation in the concentration of the reactants (decrease) and products (increase). The magnitude of this 12734848.1 concentration perturbation, does not depend on the direction of temperature (heating or cooling), but does depend on the magnitude of dT / dt, c. During the OCP and LSV measurements at fixed temperature, CoPc / G particles should by definition be non-active since dT / dt = 0 and there is no driving force for pyrocatalytic activity, d. Despite the lack of pyrocatalytic activity of CoPc / G particles during OCP and LSV measurements, concentration changes of both reactants and products, do continue in this period, driven either by diffusion (aiming to eliminate the initially formed concentration gradients, by minimizing the chemical potential difference of species across the electrolyte, as well as the headspace), or a redox coupling of the species in the cell, 2. The electrochemical cell is a thermodynamically closed system, 3. An ideal behavior is considered for the ionic and gaseous species, i.e., activities of different species are not different from their concentrations or partial pressures, 4. Electron transfer between the CoPc / G particles and WE is negligible, thus the potential and current characteristics of the Pt WE probe are just indirectly influenced by the pyrocatalysts through modifications they cause in the concentration of species, 5. Half-reactions considered in this assessment include: CO / CO2, H2 / H+, SO32– / SO42–, H2O / O2 (see Eq. 1–4), 6. OCP can be treated as the equilibrium potential of a mixed electrode (a full redox cell, formed on the WE), i.e., the potential at which anodic and cathodic half-reactions are kinetically equilibrated, 7. Equilibrium potentials of individual half-reactions can be approximated by the Nernst equation at non-standard conditions, 8. Exchange current densities of individual half-reactions on the WE can be approximated based on literature reports, 9. Overportials of individual half-reactions on the Pt WE can be neglected, 10. For an approximation of the kinetics of individual half-reactions on the WE (current as a function of potential), in both electron-transfer and mass-transfer controlled regions, instead of deployment of known theoretical models (e.g., Butler-Volmer and else), a simple graphical mimicking of the general shape of Evans diagrams can be used, 11. The intersection point of the anodic branch of the half-reaction with the highest anodic current density, and the cathodic branch of the half-reaction with the highest cathodic current density, would represent both the equilibrium potential of the given mixed 12734848.1 electrode in static potentiometry (OCP), and its inversion potential in potentiodynamic amperometry (LSV), and 12. The intersection point sought in line 11, under experimental conditions of the present work, is mainly dictated by the equilibrium potentials of individual half-reactions (line 7, Nernst equation) and their corresponding exchange current densities (line 8). Accordingly, the graphical simplification described in line 10, shall not thoroughly invalidate the global trend in search. Continuous Pyroelectric Processing All experimental reduction results were obtained using temporally cycled temperatures to drive the pyroelectric reactions. These cycles were obtained via external heating and cooling of pyroelectric particle suspensions in a flask using oil and ice baths. Other implementations have been considered with pyroelectric materials immobilized on substrate surfaces, but these still generally require that the entire system be heated and cooled in a cyclic swing operation. Here, a continuous process is proposed that can be operated under steady state conditions that would be very amenable to processing at large scale. The concept is shown in FIG. 9. The cold nanoparticle suspension can be fed to the tube side of a shell-and-tube heat exchanger, where it is contacted counter-currently with a hot waste stream on the shell side. The temperature of the suspension increases as it flows through the exchanger- i.e., the temperature ramp is with respect to position and not time. In a Langrangian sense, however, i.e., following a particle as it flows through the exchanger, the particles are experiencing a temporal temperature ramp, as in the stirred flask experiments. The time dependent increase in temperature of any flowing particle is dT / dt = V(dT / dx) where T is the temperature of the particle when it is at a given position x within the tube, and V is its linear flow velocity. Here, t = x / V is the time since the particle entered the tube. So, in essence the axial position within the exchanger is equivalent to the time during the flask experiments. The actual temperature distributions within the exchanger are constant, even though the particle temperatures are not, because they are flowing. The reaction products can be removed from the suspension in a flash tank external to the exchanger. A second heat exchanger can then be used to cool down the nanoparticle suspension in a like manner, and the particles can be circulated in a closed loop between the two heat exchangers. The rate of temperature change, and hence reaction rate, can be controlled by changing the flow rates of the waste stream and the nanoparticle suspension. 12734848.1 Make up water, CO2and other reagents can be introduced to the circulating suspension before it is fed to the exchangers. Supporting Information S1. XPS Spectral features of the XPS survey scans (FIG. 2E) and the surface elemental composition of CoPc, CoPc / G, and G samples obtained by surveys' quantification, are summarized in Table 1. Regarding the purity and quality of the CoPc precursor, for a better comparison of the elemental composition obtained by XPS with the theoretical values ideally expected from the molecular formula of CoPc (C32 H16 Co N8), Table 2 compares the two sets of values. For the sake of clarity, theoretical values are presented both with and without consideration of H (which is out of the XPS probe) and experimental values are presented both with and without consideration of O (which should be considered an impurity). There is in general a good agreement between the experimental and theoretical values, except for a slight positive deviation of C and O content in experimental data (C: 83%(exp.) vs 78%(theor.) and O: 8.4%(exp) vs. 0% (theor.)), suggesting the CoPc surface might be contaminated with atmospheric gases such as carbon dioxide, oxygen, and humidity. The graphene precursor is fairly pure and only a slight amount of surface oxygen is observed, stemming either from the synthesis process, or the adsorption. The hybrid CoPc / G sample shows a 6.48-fold lower cobalt concentration and a 6.11-fold lower nitrogen concentration compared to pure CoPc, suggesting a mean dilution factor of approximately 6.25-fold for the CoPc during hybrid synthesis. The corresponding apparent surface concentration of CoPc in the hybrid (^ 1 / 6.25 = 16 %), along with the designed concentration of CoPc in the hybrid (^ 13 wt% and ^ 0.31 mol%, refer to the method section for details), indicates nearly complete utilization or negligible loss of CoPc during hybrid synthesis. Table 1. Summary of the features of the survey spectra of CoPc, CoPc / G, and graphene samples. Regarding the cobalt, the mentioned position and FWHM refer to the Co 2p 3 / 2, while the atomic concentration is calculated based on the entire Co 2p region (area of both Co 2p 3 / 2 and Co 2p ½).^ 12734848.1 Table 2. Theoretical and experimental composition of CoPc. ^ Characteristics such as the position of Co 2p 3 / 2 (781.19 eV for CoPC and 780.57 eV for CoPc / G), Co 2p 1 / 2 (796.27 eV for CoPC and 796.01 eV for CoPc / G), and the energy separation of the spin-orbit splitting in the Co 2p doublet (^E 2p [3 / 2–1 / 2]: 15.08 eV for CoPc and 15.44 eV for CoPc / G) match optimally with the standard characteristics of pure, namely, Co 2p 3 / 2: 781.09 eV, Co 2p 1 / 2: 796.36 eV, ^E 2p [3 / 2–1 / 2]: 15.27 eV. Nevertheless, some features typically observed in oxygen containing cobalt compounds are also present. The two satellite peaks –labeled as sat1 and sat2– observed for both Co2p 3 / 2 and Co2p 1 / 2 transitions of CoPc (at 785.50, 790.85, 803.05, 806.99 eV), as well as CoPc / G (784.50, 789.94, 801.00, 805.42 eV), despite commonly seen in CoPc literature, should not be present in the spectrum of ideally pure paramagnetic CoPc molecules with Co2+in the low-spin state (S = 1 / 2). Such satellites are typically observed in oxygen containing cobalt compounds with Co2+ions at the high-spin state S =3 / 2. The energy separation of the satellite and the principal peak is determined by the Co2+crystallographic site (^ 5 eV for octahedral vs ^ 10 eV for tetrahedral sites). Although the presence of both type of satellites in our CoPc and CoPc / G samples suggest some degree of oxygen contamination, our deconvolution practice over the Co 2p principal line has confirmed almost negligible contribution from the “oxides”. Even for the CoPc / G with slightly broader Co 2p allowing for deconvolution, The second component (labeled as Co 2p 3 / 2 (2) or Co 2p 1 / 2 (2) 12734848.1 in FIG. 2C, is due to the well-known multiplet splitting of the Co 2p caused by the exchange interactions between the 2p and 3d orbitals. Taking all the above aspects into account, and noting the modifications of the Co 2p transition of CoPc / G with respect to CoPc (down-shift of the principal line by approximately 0.5 eV, down-shift of the satellites by at least 1 eV, relative enlargement of satellites by ^ 5%), it is concluded that oxygenation extent of cobalt has increased in CoPc / G with respect to CoPc. A possible pathway for this, could be the bonding of the cobalt in the center of the CoPc, to the oxygen functional groups of carbon, as discussed in. Regarding the origin and character of oxygen, another insightful approach would be the assessment of O 1s transition in CoPc and CoPc / G. Atmospherically adsorbed non- stoichiometric oxygen generates an O 1s signal at about 531.2 eV, atmospherically adsorbed CO2,and CO, appear at about 531.7 eV, and atmospherically adsorbed H2O create an O 1s component at 533.5 eV. The weak oxide peak at 529.55 eV and the clear adsorbed H2O peak at 533.5 eV are therefore unambiguous in the CoPc sample. However, the component at 531.55 eV remains open to interpretations as either atmospherically adsorbed non-stoichiometric oxygen, CO2and CO, or hydroxides. The main contribution to the 531.55 eV component may be from atmospherically adsorbed CO2 and CO, since firstly, it has the closest BE to 531.55 eV, and secondly, based on the excess carbon observed in the survey quantification of CoPc, as presented in Tables 1 and 2. Nevertheless, the likelihood of formation of surface layers of adsorbed oxygen and hydroxide cannot be ignored, even at short periods of atmospheric exposure. Likewise, the G sample shows a remarkable contribution from H2O to the O 1s transition, which is also inherited by the hybrid CoPc / G sample. The N 1s transition of CoPc is characterized by two components, a major one centered at 398.97 eV and a minor one at 400.53 eV. Both pyridinic and pyrrolic nitrogen (N^ and N^, respectively, in FIG. 10) are represented by the major peak at 398.97 eV. The G sample lacks any nitrogen, while the CoPc / G hybrid sample retains both N 1s features of CoPc, namely, a major N^+ N^ component at 398.94 eV, and a small N–H component at 400.12 eV. The N–H component is larger in CoPc / G with respect to CoPc (^ 30% of the N 1s transition in the former vs.5% in the latter). This difference could be attributed to possible interactions of the CoPc with the hydrogen-containing functional group traces of G through the pyridinic nitrogen sites. The C 1s region of the CoPc sample is characterized by a main component at 284.81 eV representing the carbon at C^position in FIGS. 11A-11B, two components at 285.41 and 286.20 eV representing respectively carbon at C^ and C^ positions (FIGS. 11A-11B), a component at 287.59 representing the adsorbed CO2, either in its original or in the hydrogenated form such as formate, being specified by a BE in the range of carbonyl groups, and the ^-^* satellite at 291.58 12734848.1 eV. The graphene C1s region is characterized by a main component at 284.54 eV representing the sp2carbon, a hydroxyl component at 286.39 eV, a carbonyl component at 287.48 eV, and the satellite at 290.38 eV. The minor oxygenated carbon components, accounting for 4.47% of all carbon, are unwanted residues originating from the synthesis and preparation history of the G sample. The hybrid sample reveals characteristics like G, with slight enlargement of the two middle components representing the non-sp2characters of carbon. The component at 286.23 eV represents, in addition to intrinsic hydroxyl groups of the as-received G, the carbon bound to nitrogen in CoPc, and this justifies both, the minor enlargement of the peak, and its negative shift. The component at 287.32 eV representing the carbonyl groups, has similarly enlarged in CoPc / G with respect to G, since the carbonyl type carbon content of CoPc, which is caused by CO2adsorption –and in the meanwhile, is more concentrated relative to carbonyl content of graphene, has added up to the overall carbonyl concentration of the hybrid. S2. Pyrocatalysis Tables 3-8 show the calculated “apparent” equivalent moles of electrons exchanged for the production of gases observed in the GC results. Although the approximation given here are simplistic since they rely on the following assumptions, they are insightful regarding some general aspect of the process. 1- Pyrocatalytic reactions are limited to those traceable by GC, i.e., OER, HER, and gaseous CO forming CO2RR, 2- The charge number “z” is 2 for HER and CO2RR, and 4 for OER, 3- Pyrocatalytic products are “frozen” after generation. That is, the products contents cannot alter by any means other than pyrocatalysis, 4- hidden products (e.g., sulfate, adsorbed CO, etc.) are ignored. Since OER is the only GC detectable oxidation half-reaction, any contribution of the SO32–(provided by the Na2SO3 sacrificial agent) to the oxidation half-reactions (i.e., SO32– would appear in the form an equivalent oxidation electrons deficit, and this explains the results under N2. Under CO2, there is in principle even more driving force for the SO32–participation in the reactions, namely, O2 scavenging role in the post-catalysis stage, additional to role of an individual oxidation half-reaction in the pyrocatalysis stage. Therefore, the reduction electrons deficit under CO2, can only be explained by the formation of the reduction products hidden in our experimental probe. Incomplete CO2RR leading to the adsorbed CO formation, is for instance, a well-documented example which can explain our charge imbalance under CO2. 12734848.1 Table 3: Calculated equivalent moles of electrons in the full thermal cycle under CO2atmosphere. Table 4: Calculated equivalent moles of electrons in the full thermal cycle under N2atmosphere. Table 5: Calculated equivalent moles of electrons in the heating half-cycle at 60oC under CO2atmosphere. Table 6: Calculated equivalent moles of electrons in the cooling half-cycle at 10oC under CO2 atmosphere. 12734848.1 Table 7: Calculated equivalent moles of electrons in the heating half-cycle at 60oC under N2atmosphere. Table 8: Calculated equivalent moles of electrons in the cooling half-cycle at 10oC under N2 atmosphere. Table 9: Average concentration of different gaseous products after individual heating or cooling half-cycles. S3. Electrochemical characterization The general rationale behind why and how these experiments could be used for demonstration of the pyrocatalytic behavior of CoPc / G particles, is as in the following. 12734848.1 1- The self-polarization of a pyrocatalyst, is driven by a temporal gradient of temperature (dT / dt ^ 0). Therefore, during the constant temperature OCP and LSV measurements, no further generation of pyrocatalysis products should occur. This could be monitored and verified via a passive potentiometry method (OCP) which is sensitive to the concentration of the species in the cell. It should be noted that the progress of pyrocatalysis, is characterized by simultaneous generation (concentration increase) of O2 and SO42–(oxidation direction of half-reactions shown in Eq. 9 and Eq. 6 respectively) as well as H2 and CO (reduction direction of half-reactions shown in Eq. 8 and Eq. 7, respectively). In contrast, the cessation of pyrocatalysis, in the absence of any possible redox pair coupling, would lead to a slight concentration decrease of gaseous species in the electrolyte (driven by diffusion to homogenized and equilibrate the species across the electrolyte and the headspace), and in the presence of some possible redox pair couplings, would lead –apart the diffusional effects– to remarkable and non-similar trends of concentration change of the species – both ionic and gaseous– involved in the redox pair coupling. In the latter case, while some species may undergo a concentration drop (e.g., O2– if present due for instance to pyrocatalytic formation in the temperature ramping stage preceding the OCP– can be consumed through participation in a reduction half-reaction, i.e., oxygen reduction reaction, ORR), some other may undergo a concentration rise (e.g., SO42–, whether or not formed previously, can be further formed through SO32–participation in the sulfite oxidation reaction (SOR), SO32–^ SO42–). 2- The extent of self-polarization of a pyrocatalyst and the emerged pyrocurrent, is proportional to the magnitude of the temporal gradient of temperature (dT / dt). Therefore, stimulating the pyrocatalyst with different magnitudes of dT / dt, must result in different concentrations of pyrocatalysis products. Accordingly, if any direct or indirect concentration sensitive experimental method (direct: GC, indirect: OCP) could show tangible difference between the concentration of species generated under remarkably different dT / dt, it would demonstrate, from another viewpoint, the pyrocatalytic behavior of CoPc-G. In the heating / cooling experiments before OCP / LSV, temperature up-ramping was from ^25 °C to ^60 °C within ^25 s, while down-ramping was from ^25 °C to ^10 °C within ^35 s. Therefore, dT / dtheating has been 2-3 times as large as dT / dtcooling. Table 10: Nernst Equation for half-cell (oxidative representation). 12734848.1*5 , 678 ^7^^^ ^^ *+^^<^^^ , *^- . / 3^^^=3^4^<^^^^ ^012 3^^=3^, 678 ^7^ ^ 787^^>? 123^^^=3^4, 678 ^7^ ^^^3^^=3^^^ Eq.9 787^9?>^ 1@A3^^^^ ^=3^43^^=3^^^ OCP evaluation To proceed with the development of the aforementioned simplified model for the prediction of OCP trends, estimates of species concentrations are necessary. Regarding the starting instant of OCPs, and for gaseous species, averaged values for the concentrations observed in the thermal half-cycle experiments in presence of the pyrocatalyst (Table 9) were used, after due conversion to partial pressure, for feeding into the model. Regarding the CO2and CO concentrations under N2 atmosphere, it should be noted that due to dissolution of some NaHCO3 in the electrolyte, the CO2 concentration is not zero. However, due to long N2 purging, major part of carbonate species has left the cell (in the form of CO2) before its sealing. The corresponding CO signal in the GC results after thermal cycling has been below the 12734848.1 quantification limit, though observable. For feeding to the model, concentrations of these gases in such experiments were set to a small value, i.e., 1E–7. The thermal half-cycle experiments in absence of the pyrocatalyst did not lead to the formation of O2, H2,and CO, and therefore, the starting concentrations of these gases in such experiments were set to a very small value close to zero, i.e., 1E–10(note that setting absolute zero values would return mathematically meaningless results in the Nernst equation whenever activities of such gases occur to appear in the denominators of equations 6-9, Table 10). The starting concentration of [H+] (or [OH–]) was estimated based on our pH readings after thermal half-cycles. The starting concentration of [SO42–] was estimated based on the difference between the apparent anodic electrons exchanged (twice as much the moles of produced O2, each mole of which requires the exchange of 4 mole electrons according to Eq. 9) and the cathodic electrons exchanged (sum of the moles of produced CO and H2, each mole of each of which requires the exchange of 2 mole electrons according to Eq. 7 and Eq. 8). The starting concentration of [SO32–] was estimated based on the difference between the total initial supply of Na2SO3salt (i.e., ^ 0.15 M) and the portion oxidized to SO42–as estimated earlier. Table 11. Average concentration of different gaseous products after individual heating or cooling half-cycles. Regarding the termination points of the OCPs, concentrations of species were estimated based on the general assumption of formation of internal galvanic cells (coupling of the redox pairs within the cell), forcing the concentrations of species –by consumption of some and generation of some other– towards an equilibrium where the net exchanged current between the oxidation and reduction half-reactions approach zero. This is manifested through, for instance, consumption of the major part of O2 produced in the thermal cycles prior to OCP, in the course of ORR coupled to oxidation half-reactions such as SO32–^ SO42–, CO ^ CO2, and H2^ H+. The same example can also reveal how concentrations of species such as SO32–, CO, and H2can decrease. Differently, whenever O2 is absent or remarkably depleted, H+^ H2 can act as the main reduction half-reaction in coupling with oxidation half-reactions such as SO32–12734848.1 CO ^ CO2, leading to regeneration of H2. Decoupling of the galvanic and pyrocatalytic contributions to the H2 generation is not possible in the present experimental set-up and even part of the H2 measured right after the thermal cycles may potentially be due to formation of internal galvanic cells, which is presently neglected. In any event, given on the one hand, the dynamic nature of the electrode's potential for both oxidation and reduction half-reactions due to simultaneous variation of all concentrations, and on the other hand, the dual role that electrodes with an intermediate potential –such as H2 / H+– can play in such a complex multi-component system, any approximation of the final concentrations cannot be considered “rigorous”. Yet, adopting logical reasoning frameworks can allow plausible and defendable approximations. The principal assumptions towards this goal include: 1- The final O2 concentration will inevitably be very low (set to 1E–9for cells containing pyrocatalyst and 1E–10for cells lacking pyrocatalyst) since all other half-reactions serve its reduction, 2- The final SO32–concentration will inevitably be very low (set to 1E–9) since all other half-reactions serve its oxidation to SO42–, and for the same reason, the final SO42–concentration will be close to total initial supply of Na2SO3salt (^0.15 M), 3- The electrode with intermediate potential (H2 / H+) will never move towards significant H2 depletion, rather, it would finally gain an H2 concentration higher than it had right after the thermal cycles. Since in the presence of O2, SO32–plays a scavenging role thus shielding the H2(as well as CO) oxidation, and in the absence of O2, it serves as the reducing agent for HER, the H2 concentration would inevitably rise during OCP, 4- The final CO concentration will inevitably be very low (set to 1E–9for cells containing pyrocatalyst and 1E–10for cells lacking pyrocatalyst) due to lost protection of SO32–as explained in assumption 3, and thus, its oxidation to CO2 driven by HER. Accordingly, the final H2 concentration was approximated in all experiments as the sum of initial concentrations of SO32–(minus the fraction consumed on O2scavenging), CO, and H2. Approximated activities of the species involved in the determination of the OCP of the mixed electrode at the initial and final instants of the electrochemical measurements are listed inTable 12 (in presence of CoPc / G and under CO2atmosphere), Table 13 (in presence of CoPc / Gand under N2atmosphere), Table 14 (in absence of the pyrocatalysts and under CO2atmosphere), and Table 15 (in absence of the pyrocatalysts and under N2 atmosphere). Table 12. Concentration (activities) of the species involved in the determination of the OCP of the mixed electrode at the initial and final instants of the electrochemical measurements in the presence of CoPc / G and under CO2 atmosphere. 12734848.1 Table 13. Concentration (activities) of the species involved in the determination of the OCP of the mixed electrode at the initial and final instants of the electrochemical measurements in the presence of CoPc / G and under N2 atmosphere. Table 14. Concentration (activities) of the species involved in the determination of the OCP of the mixed electrode at the initial and final instants of the electrochemical measurements in the absence of the pyrocatalysts and under CO2atmosphere. 12734848.1 Table 15. Concentration (activities) of the species involved in the determination of the OCP of the mixed electrode at the initial and final instants of the electrochemical measurements in the absence of the pyrocatalysts and under N2 atmosphere. FIGS. 15A-15B compare the OCPs predicted by the simplified semi-theoretical semi- graphical model, with the experimentally measured OCPs in presence of CoPc / G. Reasonable agreement is observed between the modeled and experimental data, in terms of 1- the trend (over time) and magnitude of OCP in each individual experiment, 2- relative position of OCPs related to different thermal conditions under the same atmosphere. These results verify the assumptions drawn regarding the pyrocatalysts, including their inactivity at constant temperature, and their dT / dt sensitivity. FIGS. 16A-16B compare the OCPs predicted by the model, with the experimentally measured OCPs. The agreement between the modeled and experimental data in absence of the pyrocatalysts is as good as that in the presence of pyrocatalysts in terms of the trend (over time, which are almost steady without remarkable rise or drop) and relative position of OCPs. Nevertheless, the predicted magnitude of OCPs seems more accurate in presence of CoPc / G. Uncertainties in the absolute values of OCPs predicted by the model stem from, 1- the graphical and approximate nature of most kinetic aspects involved in this practice, 2- approximate concentration values at the end of OCP period, 3- negligence of the speciation effects related sulfur and carbon species, 4- assumption of the ideal behavior for all ionic and gaseous species. Overall, the level of consistency observed, allows the acknowledgment of correctness of principal aspects of the model and its assumptions. These results verify the assumptions drawn regarding the pyrocatalytic nature of CoPc / G, including their inactivity at constant temperature, and their pyrocatalytic yield sensitivity to dT / dt. 12734848.1 LSV evaluation Experimental LSV results could help assessing the dynamism of electrochemical redox reactions in the medium used for pyrocatalytic CO2RR. Of prime importance, for instance, has been searching for clues to the potential extent of self-polarization of pyrocatalysts for simultaneous activation of OER, HER, and CO2RR. Additionally, investigation of the relative coordinates of different half-reactions on the polarization window at different thermal and atmospheric conditions, could provide insight to the mechanistic aspects of catalysis, possible interconnections of the half-reactions, and the role of environmental conditions. Nevertheless, it should be noted that the use of Platinum WE in LSV experiments, which is a robust electrocatalyst with relatively low overpotential for most electrochemical reactions, implies that should similar experiments were conducted on CoPc / G, most redox features would emerge with a potential delay with respect to on Pt. Therefore, approximation of the pyrocatalysts' self-polarization level based on these experiments, possesses underestimations. FIGS. 17A-17B and FIGS. 18A-18B show the experimental LSV results (on the right- side) in presence of CoPc / G and FIGS. 19A-19B and FIGS. 20A-20B in their absence. Each LSV plot consists of two superimposed sweeps: an anodic sweep starting from OCP towards more positive potentials and a cathodic sweep starting from OCP towards more negative potentials. In all FIGS. 17A-20B, electrode potentials predicted by the model at the initial instants after the thermal ramp and before LSV initiation, and their schematic Evans diagrams, appear on the left-side for comparison. The anodic sweep starts from OCP and extends 1.5 V towards more positive potentials, while the cathodic sweep starts from OCP and extends 1.5 V towards more negative potentials. Evans diagrams of the half-reactions involved in the process are shown on the left-side diagram. Predicted electrode potentials for H2O / O2, H2 / H+, CO / CO2, and SO32– / SO42–are linked to the experimental results by horizontal dashed lines labeled on the left side of the figure. On the experimental curves, solid lines with same colors, are representing the potential at which current waves related to those electrodes occur in practice. For the sake ofclarity, letters O, H, C, and S, further highlight the position of H2O / O2, H2 / H+, CO / CO2, andSO32– / SO42–electrodes, respectively. Additional to the above four lines, a dashed line (long dash – dot, unlabeled) is used to indicate the intersection point of the cathodic branch of H2O / O2 electrode (ORR) with the anodic branch of any of the other three electrodes with lowest current density (usually, CO ^ CO2). Overall, assignment of the features on the experimental LSV curves based on the suggestions of the model seems reasonable, since in most cases, variation of the experimental conditions (atmosphere, temperature, pyrocatalysts), has led to agreeing trends of change of features in the left- and right-side plots. Regarding the mismatches between dashed 12734848.1 and solid lines (potential separations), wherever applicable, several possibilities could be considered, including, the overpotential for each reaction at the given condition, dynamic nature of LSV causing a scan rate dependent lag between the theoretical and practical voltametric features, and, uncertainties caused by the model assumptions and concentration approximations. LSV plots typically consist of 1- a central, low current, plateau-like zone around OCP with a potential width of ^ 0.4–0.8 V and current density level of ^ 1E–2 mA cm–2, 2- a smooth anodic wave above (more positive than) the central plateau, continuously rising without particular features before reaching the maximum current density level, 3- a shouldered cathodic wave below (more negative than) the central plateau, featuring an intermediate hump before reaching the maximum current density level. The central plateau, is in fact, the current inversion region, which instead of appearing as a single sharp valley (as is expected in mixed electrodes with only two half-reactions), has occurred over a widened potential window due to both, multiplicity of half-reactions with changing current sign at that region, and anodic–cathodic branch intersections. Even symptoms of cathodic loops can be observed at this region in some experiments (particularly, under N2at low temperature, i.e., FIG. 18A and FIG. 20A). An arrow is used to indicate the approximate span of the plateau. It appears that the lower limit of this central zone, particularly in presence of CoPc / G, shows proximity to the dashed line indicating the expected equilibrium potential of the H2 / H+electrode, and its upper limit, to the dashed line (long dash – dot, unlabeled) indicating the intersection of O2 ^ H2O and CO ^ CO2. It is only above / below these indicative potentials that currents with dominant anodic / cathodic character can emerge. The fact that in absence of pyrocatalysts, the dashed line indicating the expected equilibrium potential of the H2 / H+electrode shows a positive deviation from the lower limit of this central zone, suggests that either the local pH near the WE is in practice higher than in bulk (leading to inadvertent feeding of the model with a higher H+concentration), or the estimate H2partial pressure fed to the model is underestimated. In fact, the plausible assumption of HER galvanic coupling to SO32–^ SO42–,can simultaneously satisfy both conditions. CO2purging shows a clear shrinking impact on theplateau width (FIGS. 17A-17B and FIGS. 19A-19B, compared to FIGS. 18A-18B and FIGS. 20A-20B, respectively), confirming the assumption of CO ^ CO2 contribution to the anodic wave onset. The fact that the plateau width under CO2 purging, shows a larger shrinkage in presence of CoPc / G (FIGS. 17A-17B) compared to in the pyrocatalysts absence (FIGS. 19A- 19B), verifies that the CO produced in the course of pyrocatalytic CO2RR at the thermal ramping stage prior to LSV (former figures), is tangibly larger than that produced just by redox 12734848.1 coupling of CO2^ CO to SO32–^ SO42–in the same period of time (latter figures), in particular, at 60 °C. The interpretation of the anodic zone (denoted by region 2 earlier), as mentioned before, is relatively straightforward; the potential at which all the three bottom half-reactions find an anodic harmony, determines the onset of the global anodic wave, and beyond the H2O / O2potential, OER activation sets off. There are no intermediate half-reactions or branch cross- sections between the line indicating the expected equilibrium potential of the H2 / H+electrode, and line indicating the intersection of O2^ H2O and CO ^ CO2. In contrast, the cathodic zone (denoted by region 3 earlier), is associated with equilibrium potentials of three half-reactions, and in many cases, reveals a shoulder right after the cathodic wave onset and before reaching the sulfate reduction reaction (SRR). Based on several reasons as comes in the following, the shoulder is a doublet peak and may be initiated by HER and followed by CO2RR. First, the onsets of the cathodic wave and the shoulder, basically coincide, and show close proximity to the H2 / H+line (particularly in presence of pyrocatalysts as discussed earlier). Second, the shoulder's center, shows close proximity to the CO / CO2line (particularly in presence of CoPc / G, due to the same reasons mentioned for H2 / H+line). Third, the shoulder is most intense under CO2, and by switching to conditions strongly promoting CO2 depletion (N2 atmosphere at 60°C), the shoulder almost vanishes (FIGS. 18B and 20B). Fourth, in all modeled conditions, the predicted CO / CO2 electrode's potential is more negative than that of H2 / H+electrode. Despite these reasons, finding experimental evidence for this argument (HER–CO2RR mixed character of the shoulder) is not easy, since conditions encouraging / discouraging one, would as well encourage / discourage the other. Purging with CO2 promotes CO2RR for clear reasons, and as well the HER due to concomitant acidification (vice versa holds during N2 purging). Nonetheless, there exists an experimental condition wherein the CO2concentration is neither so high to lead to the merging of HER and CO2RR, nor is so low to cause CO2RR diminution, namely, N2 purging at 10°C. The only CO2 source there, is the speciation products of the initiallysupplied NaHCO3, which in the meantime, experiences a remarkable dilution during N2purging,but does not quite approach zero at 10°C (Tables 13 and 15). The LSV at this condition, particularly in presence of pyrocatalysts (FIG. 18A), demonstrates reasonably well the doublet character of the shoulder. This argument has mechanistic implications about the CO2RR in such a system. HER and CO2RR are contestant cathodic reactions not only because they compete on consuming the cathodic current, but also because of their common reliance on protons. HER has thermodynamic and kinetic merits (higher exchange current density and generally more positive electrode potential, respectively) in this competition and therefore, it is not surprising to find it 12734848.1 securing a larger contribution to the cathodic reactions and products. Nevertheless, CO2RR seems to be a serious challenger as can be inferred from the shoulder's shape. The fact that cathodic wave triggered by HER undergoes an attenuation after CO2RR steps in, thus taking the shape of shoulder –rather than a continuously rising wave, suggests that the latter, in one way or another, makes a decelerative interference with the kinetics of the former, causing its suppression. Several possible mechanisms have been proposed in explanation of the inhibiting role of CO2RR against HER, including among others, (a) competitive consumption of protons in acidic media, (b) CO2RR use of H2O as the proton source (in non-acidic media) and thus, generating OH−, which along its escape from the cathode, could act as an interceptor of HER feed protons counterflowing towards the cathode, (c) CO2RR intermediates (particularly, adsorbed CO) blocking the surface active sites for HER, thus avoiding any of the Volmer, Heyrovsky, or Tafel steps. Accordingly, given that a certain catalyst can further boost the kinetics of CO2RR, as CoPc / G is doing, even comparable products of CO2RR and HER can be achieved at experimental conditions favorable for CO2RR (see Table 12 at 60 °C). Finally, in search of clues to the potential extent of self-polarization of pyrocatalysts, the separation of O and S lines in FIGS. 17A-17B and FIGS. 18A-18B (right-side), is indicated by a arrow to give a minimal approximation of the polarization window. The current densities of H2O / O2and SO32– / SO42–electrodes at those points are ^10 mA cm–1in most cases, thus the onset potentials of OER and SRR can reasonably be considered to be reached. Relying on these data, a self-polarization window of ^ 1.5 V could be estimated for the CoPc / G pyrocatalysts. It may be worth noting again that the practice conducted here, neither tries to generalize the voltametric features observed on the Pt WE to CoPc / G pyrocatalysts, nor suggests that the self- polarization window of the latter is identical to the potential separation of OER and SRR on the former. Rather, in the lacking opportunity of conducting physically meaningful three-electrode set-up experiments with CoPc / G particles as the WE, this work takes advantage of the global perspective provided by such experiments using Pt WE, to more reliably consider and interpret the behavior of different half-reactions involved and their possible interconnections, and to give a minimal approximation for the self-polarization of CoPc / G particles complying with their experimentally observed pyrocatalytic yields. While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily 12734848.1 appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the teachings of the present invention is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and / or methods, if such features, systems, articles, materials, and / or methods are not mutually inconsistent, is included within the scope of the present invention. The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and / or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting 12734848.1 essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law. As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. As used herein, “wt%” is an abbreviation of weight percentage. As used herein, “at%” is an abbreviation of atomic percentage. Some embodiments may be embodied as a method, of which various examples have been described. The acts performed as part of the methods may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include different (e.g., more or less) acts than those that are described, and / or that may involve performing some acts simultaneously, even though the acts are shown as being performed sequentially in the embodiments specifically described above. Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed 12734848.1 transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03. 12734848.1

Claims

CLAIMS What is claimed is:

1. A system, comprising: a vessel comprising water and / or carbon dioxide (CO2); and a pyroelectric material; wherein the system is configured such that, when the pyroelectric material and the water and / or CO2are thermally cycled, hydrogen gas is produced and / or CO2is reduced.

2. The system of claim 1, wherein the pyroelectric material comprises a planar molecule.

3. The system of any one of claims 1-2, wherein the pyroelectric material comprises cobalt phthalocyanine (CoPc):.

4. The system of any one of claims 1-3, wherein the pyroelectric material comprises graphene.

5. The system of any one of claims 1-4, wherein the vessel comprises water, and the system is configured such that, when the pyroelectric material and the water are thermally cycled, hydrogen gas is produced. 12734848.

16. The system of any one of claims 1-5, wherein the vessel comprises CO2, and the system is configured such that, when the pyroelectric material and the CO2 are thermally cycled, CO2is reduced.

7. A method, comprising: thermally cycling a catalyst comprising pyroelectric material and water and / or carbon dioxide (CO2) such that hydrogen gas is produced and / or CO2is reduced.

8. The method of claim 7, wherein the thermally cycling comprises thermally cycling the catalyst and water such that hydrogen gas is produced.

9. The method of any one of claims 7-8, wherein the thermally cycling comprises thermally cycling the catalyst and carbon dioxide (CO2) such that CO2is reduced.

10. The method of any one of claims 7-9, wherein the pyroelectric material comprises a planar molecule.

11. The method of any one of claims 7-10, wherein the pyroelectric material comprises cobalt phthalocyanine (CoPc):. 12734848.

112. The method of any one of claims 7-11, wherein the pyroelectric material comprises graphene.

13. The method of any one of claims 7-12, wherein at least 0.01 mmol of CO is produced per gram of catalyst.

14. The method of any one of claims 7-13, wherein at least 0.1 mmol of H2 is produced per gram of catalyst.

15. The method of any one of claims 7-14, wherein at least 50% of the water is converted to H2.

16. The method of any one of claims 7-15, wherein at least 50% of the CO2 is converted to reduced CO2.

17. The method of claim 16, wherein the reduced CO2 comprises CO.

18. The method of any one of claims 7-17, wherein the thermal cycling involves a change in temperature of less than or equal to 200°C.

19. The method of any one of claims 7-18, wherein, during at least a portion of the thermal cycling, the temperature of the catalyst is 25°C.

20. A system, comprising: a first heat exchanger comprising: a first inlet configured to receive an input comprising pyroelectric material at a first temperature and water and / or carbon dioxide; and a first outlet configured to output at least a portion of the pyroelectric material at a second temperature that is higher than the first temperature, and to output hydrogen gas (H2(g)), oxygen gas (O2(g)), and / or carbon monoxide, and a second heat exchanger comprising: 12734848.1a second inlet fluidically connected to the first outlet, the second inlet configured to receive at least a portion of the output from the first heat exchanger; and a second outlet fluidically connected to the first inlet, the second outlet configured to output at least a portion of the pyroelectric material that is output from the first outlet of the first heat exchanger at a third temperature that is lower than the second temperature.

21. The system of claim 20, wherein the first temperature and the second temperature are different by at least 50 degrees Celsius.

22. The system of any one of claims 20-21, wherein the input received by the first heat exchanger contains the pyroelectric material in an amount of at least 0.15 wt%.

23. The system of any one of claims 20-22, wherein: a concentration of hydrogen gas is greater at the first outlet than a concentration of hydrogen gas at the second outlet; and / or a concentration of oxygen gas is greater at the first outlet than a concentration of oxygen gas at the second outlet, and / or a concentration of carbon monoxide is greater at the first outlet than a concentration of carbon monoxide at the second outlet.

24. The system or method of any one of claims 1-23, wherein the pyroelectric material has a pyroelectric coefficient of greater than or equal to 2 C / m2K.

25. The system or method of any one of claims 1-24, wherein the pyroelectric material comprises cobalt phthalocyanine (CoPc), copper phthalocyanine (CuPc), tin phthalocyanine (SnPc), and / or iron phthalocyanine (FePc). 12734848.1

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