Reactor designs for photocatalytic o2 evolution from water with integrated green h2 compression

Abstract

A safe and scalable solar particle-based PEC water splitting system that has a photoreactor that drives half-Z-Scheme photosynthetic O2 evolution from water coupled with reduction of the oxidized form of a redox mediator. This now-reduced redox mediator is then transported to an integrated second unit operation, a dark galvano-catalytic compressor that spontaneously evolves H2 at increased pressure, driven by oxidation of the reduced form of the redox mediator. By coupling an H2 compressor technology with intrinsically safe particle-based PEC approaches, and the ability to spatially control deposition of semipermeable ultrathin oxide coatings, a new reactor was developed with significant decrease in both complexity and materials requirements that is projected to generate green H2 at unprecedented low costs, in a form factor that is easily deployed, thus increasing U.S. energy and chemical resiliency.

Description

UCI 24.19 PCT, 2025-788-2 Inventor’s last name: Ardo et al. Document Date: December 15, 2025REACTOR DESIGNS FOR PHOTOCATALYTIC O2EVOLUTION FROM WATER WITH INTEGRATED GREEN H2COMPRESSIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. Provisional Application No. 63 / 733,857 filed December 13, 2024, the specification(s) of which is / are incorporated herein in their entirety by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under Grant No. DE- SC0021266 and Grant No. DE-SC0023431 awarded by the Department of Energy. The government has certain rights in the invention.FIELD OF THE INVENTION

[0003] The present invention relates to solar energy conversion and storage, namely, to reactors for solar water splitting and green H2production.BACKGROUND OF THE INVENTION

[0004] To power our planet using renewable energy, energy must be stored cleanly for long periods of time, e.g. seasons. H2is the simplest molecule that can meet this need, when it is formed via water electrolysis / splitting. Moreover, H2is also a necessary reagent for many chemical reactions of widespread industrial use, e.g. ammonia production, desulfurization, cracking of heavy crude oil, among others, and is responsible for a significant amount of their energy consumption. Additionally, H2can be used as a transportation fuel. Yet, no technology exists that can generate green H2that is cost- competitive with state-of-the-art means of generating H2, e.g. CO2-emitting steam methane reforming. This is because system designs rely on expensive photovoltaic-grade materials, use large amounts of costly glass, stainless steel, or other balance of plant components, require additional H2compression, and / or present explosive hazards due to the existence of an oxyhydrogen gas mixture, which is unsafe.

[0005] The most cost-effective means of generating widespread clean renewable electricity uses photovoltaic solar cells, which could be used to drive water electrolysis. But even assuming ambitious future grid-scale electricity prices of $0.02 - 0.03 / kWh,UCI 24.19 PCT, 2025-788-2Inventor’s last name: Ardo et al.Document Date: December 15, 2025 using this electricity to drive ambient-temperature water electrolysis at its thermoneutral voltage has a projected cost that is comparable to the cost, on an energy basis, of H2 generated by steam methane reforming in the U.S. In practice, such a device will be even more costly, because this projection does not include the cost of all other aspects of the reactor, including a device to convert electricity into H2 and O2, e.g. an electrolyzer, and any associated inefficiencies.

[0006] An alternative approach combines light absorption with water splitting into what are generally termed photosynthetic, photocatalytic, photoelectrosynthetic, or photoelectrochemical processes, depending on whether they are driving inherently nonspontaneous “synthetic” reactions or spontaneous “catalytic” reactions, and whether or not interfacial charging to formally generate “electricVelectro” photovoltages occurs. Because the present invention is in general agnostic to this classification, we term these all PEC processes. A state-of-the-art demonstration of a particle-based PEC water splitting system was reported in 2021 by Domen and coworkers. This demonstration defined the technology readiness level (TRL) of particle-based PEC at ~7, which is important because this is the largest TRL ever reported for any PEC system, irrespective of Type, i.e. I, II, III, or IV using designations defined by the U.S. Department of Energy. While important, this reported technical baseline will not be cost-competitive with H2 generated by steam methane reforming in the U.S. due to its use of large amounts of glass and associated stainless steel support structures, which resemble those necessary for photovoltaics and electrolyzers, and it was a Type I design, meaning that it coevolved H2 and O2 in the same compartment, forming an explosive oxyhydrogen gas mixture that requires dangerous and costly separation and compression.

[0007] Type II designs, which utilize soluble redox mediators, have been reported to evolve H2 and O2 in separate compartments, thus requiring tandem light absorbers that operate in what has been termed a Z-Scheme configuration. While these systems are envisioned to use plastic baggies in place of glass and stainless steel structures, the complexity of this design calls into question its scalability, and the use of plastic means that H2 cannot be generated at a significant pressure, e.g. 30 bar, thus requiring a separate mechanical compressor.BRIEF SUMMARY OF THE INVENTION

[0008] A new design for a particle-based PEC reactor for solar water splitting isUCI 24.19 PCT, 2025-788-2 Inventor’s last name: Ardo et al. Document Date: December 15, 2025 presented with advances that are projected to result in a drastic cost reduction for green H2 that, at large scales, can be cost-competitive with H2 generated by steam methane reforming in the U.S., as specified in the independent claims. Embodiments of the invention are given in the dependent claims. Embodiments of the present invention can be freely combined with each other if they are not mutually exclusive.

[0009] In some aspects, the present invention features a safe and scalable design for a solar particle-based PEC water splitting system that is quasi-Type II, comprising 2 modular unit operations of a photoreactor that drives the half-Z-Scheme photosynthetic O2 evolution reaction from water (OER), tightly integrated with a dark galvano-catalytic compressor that spontaneously undergoes the H2 evolution reaction from water (HER) to produce H2 at 30 bar.

[0010] In some embodiments, the present invention features reactor designs to convert sunlight into chemical fuel as H2 via water splitting. This process is clean and green as it produces no CO2 byproducts during H2 fuel production. Without wishing to limit the invention to any theory or mechanism, the new reactor design results in a significant decrease in capital costs from prior designs due to the use of less plastic baggie materials and integrated galvano-catalytic H2 compression. Moreover, it presents a single compartment photocatalytic design that does not coevolve H2 and O2, thus simplifying operation while not introducing an explosive hazard that is present in alternative singlecompartment designs, i.e. Type I, which do coevolve H2 and O2. The present design overcomes the cost and safety bottleneck of prior designs and is projected to provide green H2 that, at large scales, is cost-competitive with H2 generated by steam methane reforming in the U.S. None of the presently known prior references or works have all of the combined unique inventive technical features of the present invention.

[0011] In some embodiments, the present invention features the synthesis of metal- oxide, metal-nitride, metal-sulfide, or mixed-metal-oxide / nitride / sulfide PEC photoabsorbers using solution-phase or solid-state protocols with sufficient sunlight absorption for >0.5% solar-to-hydrogen energy-conversion (STH) efficiency. Fabrication of photocatalytic particles can include photodeposition, atomic-layer deposition, solution chemistry, and / or impregnation to deposit metallic, metal oxide, or molecular cocatalysts and / or ultrathin oxide "membrane" coatings with sufficient redox selectivity and inherentUCI 24.19 PCT, 2025-788-2 Inventor’s last name: Ardo et al. Document Date: December 15, 2025 stability for long-term, safe operation at a high energy-conversion efficiency in the presence of a suitable redox mediator molecule or particle.

[0012] In other embodiments, the present invention features modular integration of reactor components of a heat-sealed plastic baggie compartment and a small-footprint stainless steel compartment connected for electrolyte flow, resulting in leak-tolerance, long-term durability, and safety.

[0013] In some other embodiments, the reactor design of the present invention may also be used in conjunction with other reagents to reduce N2 to ammonia, or other products, or CO2 to a variety of products.

[0014] Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0015] The features and advantages of the present invention will become apparent from a consideration of the following detailed description presented in connection with the accompanying drawings in which:

[0016] FIG. 1 shows a non-limiting embodiment of a water splitting reactor design of the present invention.

[0017] FIG. 2 shows a water splitting reactor design of the prior art.

[0018] FIG. 3 shows linear sweep voltammograms at 30 mV / s of Pt electrodes coated in ultrathin SiOx(5 nm) and immersed in aqueous 25 mM V(ll) at pH ~0, demonstrating selective OER over V(ll) oxidation, and supporting use of ultrathin oxide coatings to achieve redox selectivity. Also shown is a linear sweep voltammogram for bare Pt in aqueous 0.5 M H2SO4 without and with vanadium. The SiOxcoating has limited effect on the OER while nearly eliminating the vanadium oxidation signal.

[0019] FIG. 4A shows how to engineer particles for desired selective reactivity. Particles must reduce a redox mediator and drive the OER, which can be achieved by depositing cocatalysts that are known to be redox-selective for the redox mediator, e.g. V(lll)UCI 24.19 PCT, 2025-788-2 Inventor’s last name: Ardo et al. Document Date: December 15, 2025 reduction, and an ultrathin oxide coating that is known to be permeation-selective for the OER. These can be deposited (i) in one order, or (ii) the other.

[0020] FIG. 4B shows deposition of the cocatalysts onto the particles, followed by the coating.

[0021] FIG. 4G shows deposition of the coating onto the particles, followed by the cocatalysts.

[0022] FIG. 5 shows an experimental setup to assess photocatalytic performance from small-scale reactors (~1 mL) with inline quantification of gaseous reaction products of H2 and / or O2 via mass spectrometry and in situ quantification of redox mediator speciation using spectroscopy with two laser lines as probes, one of which is also the excitation line, i.e. 405 nm (color-coded dashed lines and highlights are guides for the eye).

[0023] FIG. 6A shows the chemical storage of H2, as an embodiment where the particle is also the redox mediator.

[0024] FIG. 6B shows a graph of the thermal release of H2, which is the process that would occur in the galvano-catalytic reactor, and illustrates that heat can also catalyze H2 evolution.

[0025] FIG. 7 shows graphs of the photochemical storage of H2 (1) and thermal release of H2 (2), demonstrating that these processes can be driven by light.DETAILED DESCRIPTION OF THE INVENTION

[0026] According to some embodiments, the present invention features a reactor for an evolution reaction. In some embodiments, the reactor comprises a reactor pool containing a fluid, a transparent plastic film barrier disposed on top of the water in the reactor pool, and a galvano-catalytic compressor fluidly coupled to the reactor pool. The compressor can contain a catalyst for producing a gas product of the evolution reaction.

[0027] In some embodiments, the gas product of the evolution reaction is H2 or a product of hydrogenated N2 or CO2. In some embodiments, the gas product is generated in the dark or without sunlight.

[0028] In an non-limiting embodiment, the present invention features a water splitting reactor comprising a galvano-catalytic compressor for producing H2, coupled to a reactor for half-Z-Scheme photosynthetic O2 evolution from water.

[0029] According to some embodiments, the present invention features a water splittingUCI 24.19 PCT, 2025-788-2Inventor’s last name: Ardo et al.Document Date: December 15, 2025 reactor comprising an O2 reactor pool containing water, a transparent plastic film barrier disposed on top of the water in the O2 reactor pool, and a galvano-catalytic H2 compressor fluidly coupled to the O2 reactor pool, wherein the compressor contains a catalyst for producing H2.

[0030] In some embodiments, the compressor operates at a pressure of at least 15 bar or at least 20 bar. In other embodiments, the compressor operates at a pressure of at least 30 bar. In accordance with the embodiments described herein, the compressor may be coupled to the reactor pool by pipes, valves, and / or pumps. In some embodiments, the compressor may comprise a tank or vessel. The tank or vessel may be sealed so as to allow the gas product to be collected.

[0031] In some embodiments, the H2 can be generated in the dark or without sunlight. In other embodiments, O2 is generated by photoevolution.

[0032] In some embodiments, the water has a pH that is greater than 7. In other embodiments, the water has a pH that is less than 7. In some embodiments, the water has a pH of about 7. In some embodiments, the water contains a salt or other material. In some embodiments, the water is pure water.

[0033] In some embodiments, a photocatalyst layer may be deposited on an underside of the plastic film barrier such that the photocatalyst layer is contacting the water.

[0034] In some embodiments, the photocatalyst layer comprises a photoabsorber. The photoabsorber may be particles that are nanometers-to-microns in size. In some embodiments, the photoabsorber is undoped, unintentionally doped, or intentionally doped with alkali metals, alkaline earth metals, transition metals, etc. Examples of the photoabsorber include, but are not limited to, Fe2O3, TiOa, SrTiOa, ZnO, SnO2, WO3, BiVO4, NaTaOs, Ga2Os, TaON, SrTaC N, BaTaO2N, LaMgi / 3Ta2 / 3O2N, (GaN)x(ZnO)i-x, TasNs, C3N4, C, Y2Ti20sS2, (CuGa)o.8Zno.4S2, CuGazS2, Cu3Nbo.9Vo.1S4, etc., or any ll-VI, lll-V, or IV semiconductor, or a combination thereof.

[0035] In some embodiments, the catalyst for galvanic H2 evolution is MoCx, C, etc. In other embodiments, the catalyst reacts with a redox mediator to generate H2. Non-limiting examples of the redox mediator include the photocatalyst particle itself or based on vanadium, chromium, zinc, [Fe(CN)6]3’ / 4’, metallocenes, 2,2,6,6-tetramethyl-1-UCI 24.19 PCT, 2025-788-2 Inventor’s last name: Ardo et al. Document Date: December 15, 2025 piperidinyloxy, quinones, phenazines, viologens, etc., and their derivatives.

[0036] In some embodiments, a cocatalyst for the O2 evolution reaction is FeNi(O)OH, NiOx, CoOx, RuOx, IrOx, etc., and other ion-permeable electrocatalytic oxides, nitrides, sulfides, or a combination thereof. In other embodiments, a cocatalyst for redox mediator reduction is C, Au, a molecular catalyst, etc. In some embodiments, an ultrathin oxide coats the cocatalyst, wherein the coating is SiOx, TiOx, AI2O3, HfO2, etc.

[0037] In some embodiments, the depth of the O2 reactor pool ranges from about 1-10 cm. In other embodiments, the depth of the O2 reactor pool ranges from about 1 -5 cm. In some other embodiments, the depth of the O2 reactor pool ranges from about 5-10 cm. In yet other embodiments, the depth of the O2 reactor pool ranges is at least 10 cm.

[0038] Referring now to FIG. 1 , the present invention features a water splitting reactor. In some embodiments, the reactor comprises an O2 reactor pool containing water and photocatalytic nanoreactor particles that are nanometers-to-microns in size and including a transparent plastic film barrier disposed on top of the water in the O2 reactor pool, and a galvano-catalytic H2 compressor fluidly coupled to the O2 reactor pool, wherein the compressor contains a catalyst for producing H2 from a reduced redox mediator.

[0039] The present invention replaces the traditional compressor with a new galvano- catalytic H2 compressor that the inventors invented and converts a redox mediator directly into H2 at pressure with proven compression up to 700 bar, which also translates to a significant reduction in baggie cost as compared to FIG. 2 because only a single photoreactor compartment is needed, with little-to-no nanoporous filter membrane and conceivably thinner plastic material, such as HDPE, since the only photo-evolved gas, i.e. O2, can be vented at the site of production.

[0040] Photoabsorbers with sufficient sunlight absorption for >0.5% STH efficiency are desired. They can be synthesized in various ways and consist of various semiconductor materials, and be disposed on the underside of the top plastic film barrier by, for example, spray coating or doctor blading, such that they are in contact with the water and mitigate competitive light absorption by the redox mediator, if necessary.

[0041] Fabrication of photocatalytic particles includes deposition of cocatalysts and ultrathin species-selective coatings on photoabsorbers, if necessary, by, for example,UCI 24.19 PCT, 2025-788-2 Inventor’s last name: Ardo et al. Document Date: December 15, 2025 photodeposition, atomic-layer deposition, solution chemistry, or impregnation, with sufficient redox selectivity and inherent stability for long-term high STH efficiency and safe operation. Cocatalysts should be effective at redox mediator reduction, i.e. e- + D+-> D, but ineffective at H2 evolution, e.g. C, Au, and can be deposited by, for example, impregnation, photodeposition, or calcining chemical precursors. These cocatalysts must also be inert to conformal coating by a species-selective coating by, for example, atomic- layer deposition, so that photogenerated electrons can drive desired redox mediator reduction selectively over H2 evolution. For example, metal cocatalysts can be photodeposited from aqueous precursors in the presence of a sacrificial electron donor, such as aqueous methanol, followed by gas-phase atomic-layer deposition to nucleate and grow, on metal-oxide surfaces first, electrically insulating ultrathin oxides permeable to reactants and products of the OER.

[0042] Ultrathin species-selective nanoporous oxide coatings of, for example, SiO% can be deposited using, for example, selective-area gas-phase atomic-layer deposition, solution-phase growth, or photodeposition via pH-swing-induced formation. Area- selective atomic-layer deposition can be used to coat photoabsorber particle surfaces with ultrathin species-selective nanoporous oxides, leaving cocatalyst regions uncoated. This ensures that photogenerated holes perform the OER selectively over redox mediator oxidation, i.e. h++ D D+. When coupled with photogenerated electrons driving redox mediator reduction at cocatalyst sites, or directly on the photoabsorber surface, i.e. e~ + D+- D, this constitutes overall photosynthetic OER (FIG. 1).

[0043] Modular integration is possible using reactor components of a sealed plastic photosynthetic OER compartment and a small-footprint galvano-catalytic H2 compressor compartment to provide sufficient leak tolerance, long-term durability, and safety. Device area can be decreased and coupled to optical concentration using an inexpensive Fresnel lens, if desired. Unique from solar photovoltaic designs and prior PEC demonstrations, a 1-10 m2photosynthetic OER unit can effectively be the module. Ports to the plastic baggie reactor can be chemically or thermally sealed for interfacing with the galvano-catalytic H2 compressor. A nanoporous dialysis separator may be used to exclude particles that may break loose from the baggie substrate, with flow reversal to dislodge them, or small concentrations of particles could flow directly to the galvano-catalytic H2 compressor, either unintentionally or intentionally when not affixed onto the baggie and serving directlyUCI 24.19 PCT, 2025-788-2 Inventor’s last name: Ardo et al. Document Date: December 15, 2025 as the redox mediator (FIGs. 6A-6B and 7).

[0044] An important new aspect of the particle-based PEC design is the tradeoff in replacing a second photo-compartment with a dark galvano-catalytic H2 compressor driven by energy stored in the redox mediator, i.e. D. The initial intended application for the galvano-catalytic H2 compressor was coupling to electrochemical OER in an electrolyzer design, which showed >99% selectivity for D+= V(lll) reduction at carbon cloth in aqueous acidic electrolyte and stability of product D = V(l I), reacting little with O2 orwaterto evolve H2. Notably, 0.1 or 1.0 M aqueous V(lll) / V(ll) in a 1” tall reactor provides ample supply of redox capacity to support charging at a 1% or 10% STH efficiency, respectively, over an 8-hour day of sunlight. This supports the option for only daily discharge in the galvano-catalytic H2 compressor, which at a flow rate of about 100-1000 Liters-per-minute can discharge an acre of device in about 16 hours of non-full sunlight or darkness. This flow rate through a galvano-catalytic H2 compressor with a volume of 100- 1000 L results in a residence time of 1 min, which suffices to galvanically discharge V(ll) at MoCx into pressurized H2.

[0045] Vanadium ions are darkly colored. Affixing particles onto the plastic that forms the top inside of the baggie is possible because at average ~1 pm diameters, a single layer of particles, or tandem particles for higher STH efficiency, can absorb most sunlight, as shown for state-of-the-art photocatalyst sheets, and the remaining sunlight can heat the solution, increasing PEC rates and mixing by natural convection. Careful consideration of operating pH is important as high charge-separation-quantum-yield Al-doped SrTiCk may have alumina deposits that will dissolve at acidic pH < 2, yet oxidized vanadium is insoluble as neutral V2O3 at pH > 3, which is undesired unless solids prove useful as a redox mediator.

[0046] Vanadium is expensive and its supply is limited. While redox mediators based on vanadium and bromine represent the state-of-the-art used commercially in redox flow batteries, their use stems from near-perfect stability and therefore sufficient amortization of capital expenditures and no negative long-term impact from species crossover, because the same molecules are used in both the anolyte / posolyte and catholyte / negalyte. This crossover benefit is irrelevant for the present invention because it uses a single redox mediator supporting consideration of other redox mediators with greater optical transparency and / or that can be made more readily available, while notUCI 24.19 PCT, 2025-788-2 Inventor’s last name: Ardo et al. Document Date: December 15, 2025 negatively affecting projected cost or performance characteristics.

[0047] EXAMPLE

[0048] The following is a non-limiting example of the present invention. It is to be understood that said example is not intended to limit the present invention in any way. Equivalents or substitutes are within the scope of the present invention.

[0049] To advance the state-of-the-art particle-based Type I and Type II reactor designs, the present invention demonstrates an intrinsically-safe quasi-Type II design, meaning that it does not coevolve H2 and O2 (which is a benefit of Type II designs), but only has one baggie compartment (which is a benefit of Type I designs). Thin plastic baggies, which transmit sunlight well and attenuate H2 permeation as a replacement for glass, can afford green H2 that, at large scales, is cost-competitive with H2 generated by steam methane reforming in the U.S. Use of a single semiconductor simplifies materials synthesis and device fabrication, and ~$2 / kg-H2 would be cost competitive in many H2 markets in comparison to low-carbon alternatives, such as hard-to-abate sectors like heavy-duty transportation (e.g. shipping and aviation), steel, and cement, as well as uses in the chemical industry that require H2 (e.g. ammonia for fertilizer and petrochemical refining).

[0050] In order to overcome prior cost pinch points, the present invention replaces the traditional compressor with a new galvano-catalytic H2 compressor, which converts a soluble redox mediator directly into H2 at pressure, with proven compression up to 700 bar using an aqueous V(l l) / V(l 11) redox mediator. This is expected to translate into a ~50% reduction in cost and mass of plastic required for a traditional Type II design since only a single photoreactor compartment is needed, with little-to-no nanoporous filter membrane and thinner HDPE since the only photogenerated gas, i.e. O2, can be vented at the site of production.

[0051] The overall work scope and approach of the present invention includes, as needed, synthesis of metal-oxide semiconductor particles as photoabsorbers, their functionalization with cocatalysts and semipermeable ultrathin oxide coatings for selective redox reactivity, their deposition onto the top underside of a plastic baggie photoreactor, and flow coupling of redox mediators to a dark galvano-catalytic H2 compressor. Without wishing to be bound to a particular theory or mechanism, the present invention has the following technical advantages: photosynthetic energy storage using an ensemble ofUCI 24.19 PCT, 2025-788-2Inventor’s last name: Ardo et al.Document Date: December 15, 2025 particles that can use sunlight to drive the OER; photochemical reactions that selectively oxidize water, or OH-, over a redox mediator and selectively reduce a redox mediator over water, or H+; deposition of a thin layer of particles on a plastic substrate; and galvanic discharge of redox mediators into high-pressure H2 at catalysts in the dark in a stainless steel reactor.

[0052] In some embodiments, the present invention synthesizes high-quality nanomaterials, e.g. Al-doped SrTiOs, BiVO4, WO3, and identifies surface treatments, like coating in an ultrathin metal oxide, that result in high-efficiency operation. The highly stable and active metal-oxide semiconductor particles for solar water splitting can be synthesized using solid-state synthesis, hydrothermal synthesis, a polymerizable complex method, microwave synthesis, etc. For example, in a previous work, Al-doped SrTiOs particles were synthesized using flux growth and then coated with Rh / Cr2O3 and CoOOH cocatalysts to achieve near-unity external quantum yield for overall water splitting when illuminated with ~360 nm light.

[0053] To achieve desired reactivity for the particle-based PEC design, two general strategies can be used toward device fabrication. Referring to FIG. 4B, in one approach, cocatalysts that are inefficient for the HER and are inert to subsequent atomic layer deposition are deposited so that photogenerated electrons (e~) can drive desired redox mediator reduction, i.e. e~ + D+D, e.g. D+= V(lll). Semipermeable ultrathin oxide coatings are then deposited using area-selective atomic layer deposition, which selectively coats SrTiCh particles conformally but not metal cocatalysts. Moreover, coatings of SiOxand TiOxdeposited by atomic layer deposition allow holes (h+) to perform the OER selectively over redox mediator oxidation, i.e. h++D+.

[0054] In one embodiment, ultrathin SiOxfrom PDMS precursors was deposited by a wet chemical method onto a Pt electrode and showed that it does not affect OER catalysis but attenuates oxidation of V(ll) (FIG. 3). These data unequivocally demonstrate that the coatings significantly attenuate permeation and / or redox reactivity of vanadium species so that the OER is driven selectively.

[0055] A second approach (FIG. 4C) is to first coat the entire particle in an electron- selective contact, like TiO2, that is also made permselective to H2O and O2 by tuning the extent of oxidation and densification. This would provide electronic selectivity forUCI 24.19 PCT, 2025-788-2Inventor’s last name: Ardo et al.Document Date: December 15, 2025 photogenerated e~, while ensuring that reactants and products of the OER can access photogenerated h+. Desired functionality is achieved via reductive photodeposition of cocatalysts selective for redox mediator reduction over the HER. In either case, OER activity and redox mediator reduction from particle-based PEC can be assessed using an inline detection system for gaseous reaction products, e.g. O2, and in situ spectroscopy for soluble products, e.g. V(ll), as shown in FIG. 5.

[0056] Particles can be deposited onto the underside of the top plastic sheet to mitigate competitive light absorption by the redox mediator, e.g. V(l I l) / V(l I). Other redox mediators that absorb far less visible light and have optimal reduction potentials may be used for the application in near-neutral pH conditions, e.g. Cr(lll) / Cr(ll) chelated with congeners of ethylenediaminetetraacetic acid. Nevertheless, affixing particles onto the plastic that forms the top inside of the baggie compartment is a suitable strategy because they are typically ~1 pm in diameter, meaning that a single layer of particles can absorb sunlight nearly as well as a thicker layer and the remaining sunlight can heat the solution, increasing the rate of H2 evolution and introducing mixing by natural convection. Moreover, a nanoporous dialysis separator that is common to Type II designs could be implemented in the present invention to exclude particles that may break loose from the baggie substrate, with flow reversal to dislodge them. It may also be suitable for particles to flow directly into the galvano-catalytic H2 compressor, either unintentionally or intentionally when not affixed onto the baggie and serving directly as the redox mediator (FIGs. 6A-6B and 7).

[0057] An important new aspect of the present invention is the tradeoff in replacing a second light-driven compartment with a dark galvano-catalytic H2 compressor driven by free energy stored in the reduced version of the redox mediator, i.e. D. Utilization of V(l I l)AZ(ll) is plausible for this application because its thermodynamic pH phase stability is very similar to that of Fe(lll) / Fe(ll), which is used in state-of-the-art Type II particlebased PEC designs. This indicates that, from a stability standpoint, the same suite of particles and conditions used for Fe redox are likely also suitable for V redox. Moreover, energetically it is spontaneous for electrons in the conduction band of doped SrTiCh to reduce V(lll) to V(l I) under standard-state conditions, even though the standard reduction potential, E°, of V(lll / ll) differs from that of Fe(lll / ll) by >1 V (E°(Fe(lll / ll)) = +0.77 V vs SHE and E°(V(III / II)) = -0.27 V vs SHE). This is further enabled by the fact that E(V(III / II)) isUCI 24.19 PCT, 2025-788-2 Inventor’s last name: Ardo et al. Document Date: December 15, 2025 independent of pH yet E for the HER and metal-oxide band edges generally do depend on pH, supporting that pH can be used to tune the driving force for V(lll) reduction from doped SrTiOs, and in general all metal oxides.

[0058] In some embodiments, to achieve larger STH efficiencies in the long term, single particles proposed herein to drive both redox reactions, each requiring a photogenerated free energy that is consistent with >1.23 V, can be replaced with tandem particles that exhibit similar internal quantum yields for the OER as Al-doped SrTiOs but where electronic charge is mediated between them by either a solid contact or a solution soluble redox mediator.

[0059] As used herein, the term “about” refers to plus or minus 10% of the referenced number.

[0060] Although there has been shown and described the preferred embodiment of the present invention, it will be readily apparent to those skilled in the art that modifications may be made thereto which do not exceed the scope of the appended claims. Therefore, the scope of the invention is only to be limited by the following claims. In some embodiments, the figures presented in this patent application are drawn to scale, including the angles, ratios of dimensions, etc. In some embodiments, the figures are representative only and the claims are not limited by the dimensions of the figures. In some embodiments, descriptions of the inventions described herein using the phrase “comprising” includes embodiments that could be described as “consisting essentially of or “consisting of’, and as such the written description requirement for claiming one or more embodiments of the present invention using the phrase “consisting essentially of or “consisting of is met.

Claims

UCI 24.19 PCT, 2025-788-2 Inventor’s last name: Ardo et al. Document Date: December 15, 2025WHAT IS CLAIMED IS:1) A reactor for an evolution reaction, comprising: a) a reactor pool containing a fluid, b) a transparent plastic film barrier disposed on top of the water in the reactor pool; and c) a galvano-catalytic compressor fluidly coupled to the reactor pool, wherein the compressor contains a catalyst for producing a gas product of the evolution reaction.2) The reactor of claim 2, wherein the gas product is H2 or a product of hydrogenated N2 or CO2.3) The reactor of claim 1 or 2, wherein the gas product is generated in the dark or without sunlight4) A water splitting reactor comprising a galvano-catalytic compressor for producing H2, coupled to a reactor for half-Z-Scheme photosynthetic O2 evolution from water.5) A water splitting reactor comprising: a) an O2 reactor pool containing water, b) a transparent plastic film barrier disposed on top of the water in the O2 reactor pool; and c) a galvano-catalytic H2 compressor fluidly coupled to the O2 reactor pool, wherein the compressor contains a catalyst for producing H2.6) The reactor of any one of claims 1-5, wherein the compressor operates at a pressure of at least 15 bar or at least 30 bar.7) The reactor of claim 4 or 5, wherein H2 is generated in the dark or without sunlight.8) The reactor of claim 4 or 5, wherein O2 is generated by photoevolution.9) The reactor of claim 5, wherein the water has a pH greater than 7 or less than 7.10)The reactor of claim 5, wherein the water contains a salt.11)The reactor of any one of claims 1-10, wherein a photocatalyst layer is deposited on an underside of the plastic film barrier such that the photocatalyst layer is contacting the water.12)The reactor of claim 11 , wherein the photocatalyst layer comprises a photoabsorber.13)The reactor of claim 12, wherein the photoabsorber are particles that areUCI 24.19 PCT, 2025-788-2 Inventor’s last name: Ardo et al. Document Date: December 15, 2025 nanometers-to-microns in size.14)The reactor of claim 12, wherein the photoabsorber comprises Fe2O3, TiO2, SrTiOs, ZnO, SnO2, WO3, BiVC , NaTaOs, Ga2O3, TaON, SrTaO2N, BaTaO2N, LaMgi / 3Ta2 / 3O2N, (GaN)x(ZnO)i-x, TasNs, C3N4, C, Y2Ti20sS2, (CuGa)o.8Zno.4S2, CuGazS2, Cu3Nbo.9Vo.1S4, etc., or any ll-VI, lll-V, or IV semiconductor, or a combination thereof.15)The reactor of claim 12, wherein the photoabsorber is undoped, unintentionally doped, or intentionally doped with alkali metals, alkaline earth metals, transition metals, etc.16)The reactor of claim 5, wherein the catalyst for galvanic H2 evolution is MoCx, C, etc.17)The reactor of claim 5, wherein the catalyst reacts with a redox mediator to generate H2.18)The reactor of claim 17, wherein the redox mediator is the photocatalyst particle itself or based on vanadium, chromium, zinc, [Fe(CN)6]3 / 4; metallocenes, 2, 2,6,6- tetramethyl-1-piperidinyloxy, quinones, phenazines, viologens, etc., and their derivatives.19)The reactor of claim 5, wherein a cocatalyst for the O2 evolution reaction is FeNi(O)OH, NiOx, CoOx, RuOx, lrO , etc., and other ion-permeable electrocatalytic oxides, nitrides, sulfides, or a combination thereof.20)The reactor of claim 5, wherein a cocatalyst for redox mediator reduction is C, Au, a molecular catalyst, etc.21)The reactor of claim 20, wherein an ultrathin oxide coats the cocatalyst, wherein the coating is SiOx, TiOx, AI2O3, HfO2, etc.22)The reactor of claim 5, wherein a depth of the O2 reactor pool ranges from about 1-10 cm.

Images