A method for controlling the microenvironment of an acidic system to produce methanol directly from CO₂ via electrocatalysis.

Abstract

This invention discloses a method for direct methanol production from CO₂ via electrocatalysis in an acidic system, belonging to the field of CO₂ resource utilization electrocatalysis technology. Addressing the problems of carbonate accumulation in traditional alkaline / neutral systems and severe hydrogen evolution in acidic systems, this invention constructs a positively charged hydrophobic interface microenvironment on the surface of a gas diffusion electrode in an acidic electrolyte with a pH of 0.5-2. By controlling the local proton and CO₂ concentrations, hydrogen evolution side reactions are effectively suppressed without the need for external hydrogen gas, stabilizing the methanol reaction intermediate conversion pathway. This process generates no carbonate, significantly improves the methanol Faradaic efficiency, and greatly enhances continuous operation stability. This invention simplifies the process flow and can directly utilize industrial CO₂ tail gas and deionized water as raw materials to prepare green methanol, showing promising prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, and more specifically, to a method for the direct production of methanol from water by electrocatalytic reduction of CO2 in an acidic electrolyte through interfacial microenvironment regulation, and particularly to an electrochemical method for preparing green methanol from industrial CO2 tail gas and deionized water as raw materials. Background Technology

[0002] With the acceleration of global industrialization, carbon dioxide (CO2) emissions continue to rise, and the greenhouse effect and climate change problems are becoming increasingly serious. The electrocatalytic reduction of CO2 to methanol (CH3OH) is considered one of the most promising CO2 resource utilization routes due to methanol's high energy density (22.7 MJ / kg), ease of storage and transportation, and direct use as fuel or chemical feedstock (upstream feedstocks such as formaldehyde and olefins). The shortcomings of existing technology:

[0003] (1) Problems with alkaline systems. Most current research focuses on alkaline or neutral electrolyte systems. In alkaline systems (such as 1 M KOH), CO2 reacts rapidly with OH⁻ to form carbonates (CO3²⁻ / HCO3⁻), leading to: ① electrolyte composition drift and a continuous decrease in conductivity; ② carbonate deposition on the electrode surface and in the pores of the gas diffusion layer, blocking gas mass transfer channels; ③ low single-pass CO2 utilization, requiring a large amount of excess purge gas to maintain the reaction. These problems make it difficult for the electrode's operational stability to exceed the tens of hours range.

[0004] (2) Problems with neutral systems. Although neutral systems (such as 0.5 M KHCO3) alleviate carbonate deposition, CO2 has extremely low solubility in the aqueous phase (about 0.033 M, 25 °C), making mass transfer the rate-controlling step. Furthermore, methanol selectivity is generally below 30%, and product distribution is diffuse (multiple products such as CO, HCOOH, and CH4 compete for dominance).

[0005] (3) Bottleneck of acidic systems. Acidic systems (pH<2) thermodynamically completely avoid the problem of carbonate formation, and the high bulk proton concentration is conducive to the kinetics of multi-electron transfer reactions. However, the thermodynamic driving force of the hydrogen evolution reaction (HER: 2H⁺ + 2e⁻ → H₂) under acidic conditions is extremely large and the overpotential is extremely low, causing it to exhibit explosive competition at the electrode surface. The Faraday efficiency of CO₂ reduction (CO₂RR) is suppressed to an extremely low level, and the methanol selectivity is almost negligible. Existing attempts and their limitations:

[0006] Chinese patent application CN112817963A discloses a method for the electrocatalytic reduction of CO2 to formic acid in an acidic medium, but the product remains at the C1 oxide formic acid stage, rather than the deeper reduction product methanol. Chinese patent application CN115113115A reports using ionic liquid-modified electrodes to improve CO2 reduction efficiency, but ionic liquids are expensive, have poor stability, and are difficult to scale up industrially. US patent US20220183045A1 discloses CO2 reduction in an acidic flow cell via high overpotential, but the methanol selectivity is less than 20% and energy consumption is extremely high.

[0007] In summary, how to simultaneously achieve (i) effectively shielding the impact of bulk protons on active sites to suppress HER, (ii) maintaining or even enhancing the local concentration of CO2 at the interface to drive multi-electron C-O activation and deep reduction of C1, and (iii) stabilizing the continuous hydrogenation pathway of *CO→*CHO→*CH2OH→*CH3OH in an acidic system remains an unsolved technical problem in this field. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for direct methanol production from water via CO2 electrocatalysis under the microenvironmental regulation of an acidic system. This method fundamentally avoids the problem of carbonate formation. At the same time, through interface engineering design, a local weakly acidic / near-neutral, CO2-rich, and H⁺-poor three-phase microenvironment is "created" in the strongly acidic bulk phase, making highly selective methanol production possible. Technical concept of the invention:

[0009] In acidic electrolytes with pH 0.5–2, although the concentration of H⁺ in the bulk phase far from the electrode is high (≈0.03–0.3 M), this invention performs "microenvironment surgery" by constructing a positively charged hydrophobic polymer network (i.e., a positively charged hydrophobic functional layer) on the surface of the catalyst layer, utilizing two parallel mechanisms: 1) Electrostatic repulsion (Donnan-type repulsion) proton depletion: Positively charged polymers protonate under acidic conditions and carry a high density of positive charge, creating an electrostatic repulsion barrier against the cation H⁺ in the solution. This causes the local [H⁺]_local ≪ [H⁺]_bulk near the catalytic active site, effectively raising the local pH to about 3-5—which falls within the "selective window" where the HER overpotential increases significantly, but the proton supply required for CO2 reduction with multiple electrons is still sufficient. 2) Hydrophobic network enrichment of CO2: Hydrophobic additives (PTFE, etc.) reduce the wettability of the interface water, forcing the liquid phase to retreat and leaving a stable gas-liquid-solid three-phase contact line. CO2 gas molecules in dissolved state pass through the extremely thin liquid film directly to the vicinity of the active site. The local CO2 concentration can be increased by more than an order of magnitude compared with the bulk solution, which removes the mass transfer bottleneck and enhances the generation and residence of CO intermediates.

[0010] The synergy of these two effects "locks" the reaction pathway onto the C1 methanol channel (CO → CHO → CH2OH → CH3OH), suppressing the competing pathways of premature desorption to CO and excessive hydrogenation to CH4. The technical solution of the present invention is as follows:

[0011] A method for direct methanol production via CO2 electrocatalysis using an acidic microenvironment control system includes the following steps: S1. Fabrication of the gas diffusion electrode

[0012] The catalytic active material, conductive agent and binder are dispersed in an organic solvent (such as isopropanol, ethanol or a mixture thereof with deionized water), and ultrasonically mixed to obtain a uniform catalyst slurry; the slurry is coated (sprayed / scraped / dropped) onto a gas diffusion layer substrate (such as PTFE-treated carbon paper, model TGP-H-060, etc.) and dried at room temperature or low temperature to form a catalyst layer.

[0013] The catalytically active material is at least one of copper-based composite materials—Cu, Cu2O, CuO, Cu-M alloy (M = at least one of Sn, In, Zn, Ag, Au) or Cu-M oxide composite catalysts, with a copper content of 50%–95% by mass. Copper is the core active center for CO2→*CO activation and deep reduction with C—O retention; the second metal M acts as an electronic facilitator to regulate the Cu d-band center and *CO adsorption intensity.

[0014] The conductive agent is selected from at least one of carbon black, acetylene black, carbon nanotubes (CNTs), graphene, or Ketjen Black; the binder is selected from at least one of Nafion solution (5 wt%, etc.), PVDF, or PTFE emulsion. The mass ratio of the three is preferably (7–8.5):(1–2):(0.5–1.5), and the catalyst loading is generally 0.5–2.0 mg / cm². S2. Interface Microenvironment Regulation – Construction of a Positively Electrohydrophobic Functional Layer

[0015] A positively charged polymer electrolyte (at least one of PEI, PDDA, chitosan quaternary ammonium salt, and polylysine hydrochloride) and a hydrophobic additive (at least one of PTFE microparticles, fluorinated graphene, hydrophobic SiO2, and long-chain alkylsilane) are dispersed in water or an alcohol solvent to prepare a 1–20 mg / mL modification solution. This solution is then applied to the surface of the catalyst layer by spraying / dipping / dropping at a rate of 0.05–1.0 mg / cm². After drying at room temperature, a positively charged hydrophobic functional layer with a thickness of 0.5–5 μm is formed. The mass ratio of the polymer electrolyte to the hydrophobic additive is controlled at (2–8):(1–5).

[0016] The core physicochemical function of this layer is: 1) Positively charged groups (such as —NH2 / —NH3⁺ of PEI and quaternary ammonium groups of PDDA) are fully protonated under pH conditions of 0.5 to 2 to form a cationic polymer network, exerting Donnan repulsion on H⁺ and suppressing interfacial proton activity; 2) The hydrophobic components create a hydrophobic gas-channeling network on the surface of the catalyst layer, allowing CO2 gas mass transfer to pass directly to the interface below, forming a stable thin liquid film / three-phase boundary region, and realizing local enrichment of CO2. 3) This layer also provides a certain degree of "encapsulation protection" for the catalyst layer, slowing down the direct corrosion and dissolution of the Cu-based active phase by the acidic medium. S3. Electrocatalytic reaction

[0017] Using the aforementioned gas diffusion electrode as the cathode (with the counter electrode as the anode, such as an IrO2 / Ti mesh or stainless steel, and the reference electrode being Ag / AgCl or an internal RHE), the experiment is conducted in an H-type cell or a flow cell. The electrolyte is an acidic aqueous solution with a pH of 0.5–2 (H2SO4, HCl, H3PO4, or HClO4, concentration 0.1–2.0 mol / L, which may contain 0.1–1.0 mol / L of supporting electrolyte KCl / NaCl / K2SO4).

[0018] A continuous flow of CO2 gas (high-purity gas or pretreated industrial waste gas, flow rate 10–100 mL / min) is maintained at a temperature of 15–45°C and a cathode potential of -0.5–-1.2 V vs. RHE, operating under constant potential or constant current. Water itself serves as the proton donor / solvent, eliminating the need for external H2 gas supply throughout the process. S4 (Optional). Product Collection and Analysis

[0019] Gas phase products (H2, CO, CH4, C2H4, etc.) are quantified online or offline by gas chromatography (GC, with TCD / FID detector); the liquid phase product, methanol, is quantified by high-performance liquid chromatography (HPLC, such as Aminex HPX-87H column) or ¹H NMR. The methanol Faraday efficiency is generally ≥50%, typically reaching 62%–71%. The beneficial effects of this invention are: carbonate accumulation Severe, lifespan <20 hours Mild, still present Carbonate-free, lifespan >100 hours Hydrogen evolution competition medium Strong <![CDATA[Microenvironment electrostatic repulsion inhibits HER, FE_H2 can be reduced to < 30%]]> Methanol FE (typical) Initially ≈45% → Rapid Decline ≈15%～25% ≥50%, maximum ≈71%, still >58% after 120 hours <![CDATA[Raw material CO2 requirements]]> High purity is required (to prevent electrode poisoning). High purity required 92%–99.9% of industrial exhaust gas can be used directly. process complexity Alkali cycle + carbonate regeneration medium No alkali circuit, no carbonate regeneration, greatly simplifying the process. <![CDATA[External supply of H2]]> Not needed but the system is complex unnecessary No, water is not needed as a proton source. 1) Elimination of carbonate problem: CO2 does not combine with OH⁻ in the acidic bulk phase, the electrolyte composition is stable in the long term, the electrode channels are not blocked, and there is no attenuation after continuous operation for hundreds of hours. 2) Microenvironment "selective window": The positively charged hydrophobic layer rewrites the local interfacial conditions from "strong acid / full wet" to "weak acid / near neutral + CO2-rich gas phase", which reverses the HER / CO2RR competition balance and pushes methanol FE to 50%~80%. 3) No external hydrogen supply required, and feedstock tolerance: It only consumes CO2 + H2O → CH3OH + ½O2 (theoretical), and industrial flue gas can be fed in with only conventional dehydration / desulfurization / denitrification. 4) Engineering scale-up is feasible: The scale-up effect is small in the 10 cm² flow cell verification (methanol FE≈59.6%), which is suitable for the fluctuating load of renewable green electricity (photovoltaic / wind power). Attached Figure Description

[0020] Figure 1 A schematic diagram of the process of the present invention (CO2 → pretreatment → acidic electrolytic cell cathode chamber GDE / positive electrohydrophobic layer → CH3OH separation and purification).

[0021] Figure 2 Schematic diagram of electrode cross sections before and after the construction of the positively charged hydrophobic functional layer: (a) bare catalyst layer; (b) GDE with PEI+PTFE functional layer.

[0022] Figure 3 Schematic diagram of microenvironment regulation mechanism: High acidity zone with pH≈0.6 in the bulk phase → positively charged H⁺ repulsion in the functional layer → local pH≈3~5 at the interface + CO2 enrichment in the hydrophobic channels of PTFE.

[0023] Figure 4 Comparison of the potential-product FE distribution curves of Example 1 and Comparative Example 1.

[0024] Figure 5 Example 2: Trend of methanol FE variation at different pH values ​​(pH 0.5-2 is the optimal window).

[0025] Figure 6 Example 3: PEI:PTFE ratio optimization curve.

[0026] Figure 7 Example 1: Stability curves after 120 hours of continuous operation (methanol FE vs. time).

[0027] Figure 8 Example 4: Comparison of the effects of industrial flue gas feed and pure CO2 feed.

[0028] The diagram is labeled as follows: 101-Industrial CO2 tail gas feed end; 102-Gas pretreatment unit (dehydration, desulfurization, denitrification); 103-Acidic electrolytic cell; 104-Gas diffusion electrode (GDE); 105-Positively electrohydrophobic functional layer; 106-Cathode chamber; 107-Anode chamber; 108-Methanol product collection and separation unit; 109-Unreacted gas circulation pipeline; 201-Gas diffusion layer substrate (e.g., PTFE-treated carbon paper); 202-Catalyst layer (containing copper-based catalyst, conductive agent, binder); 203-Positively electrohydrophobic functional layer; 204-Transition layer; 301-Acidic electrolytic liquid phase (pH... 0.5~2, high H⁺ concentration); 302- Positively charged hydrophobic functional layer (positively charged polymer electrolyte and hydrophobic additive); 303- Electrostatic repulsion barrier (Donnan repulsion effect, blocking H⁺); 304- Hydrophobic gas channel (enriching CO2); 305- Catalytic active site; 306- Local microenvironment; 401- Example 1 Methanol FE; 402- Example 1 Hydrogen evolution FE; 403- Comparative Example 1 Methanol FE; 404- Comparative Example 1 Hydrogen evolution FE; 501- Methanol FE corresponding to different H2SO4 concentrations; 502 - Optimal pH window (0.5~2) defined by this invention; 601 - Methanol FE under different ratios; 602 - Optimal ratio range (2.5:1~4:1); 701 - Change in methanol Faraday efficiency over time; 702 - Change in current density over time; 703 - 120h continuous operation node; 801 - High-purity CO2 feedstock; 802 - Industrial flue gas feedstock; 803 - Performance degradation rate (approximately 6.5%). Detailed Implementation

[0029] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention. Example 1: Baseline Example (PEI+PTFE positive electrohydrophobic layer, pure CO2, H-type tank) S1. Fabrication of the gas diffusion electrode

[0030] Take 80 mg of Cu2O nanoparticles (particle size 50-200 nm) as the catalytic active material, 15 mg of acetylene black (conductive agent), and mix with 50 μL of 5 wt% Nafion solution (binder, dry weight about 5 mg), add 1 mL of isopropanol + 0.5 mL of deionized water, and sonicate in an ice bath for 30 min to obtain a uniform catalyst slurry.

[0031] The slurry was evenly sprayed onto PTFE hydrophobic treated carbon paper (model TGP-H-060, size 2 cm × 2 cm, effective area 1 cm²) using a spray gun and dried at room temperature for 12 h to form a catalyst layer (catalyst loading ≈ 1.0 mg / cm²). S2. Modification of the positively charged hydrophobic functional layer

[0032] 50 mg of polyethyleneimine (PEI) (Mw≈600, branched type, positively charged —NH2 / —NH3⁺ under acidic conditions) and 20 mg of PTFE microparticles (particle size≈200 nm) were dispersed in 10 mL of anhydrous ethanol and sonicated for 20 min to obtain a 5 mg / mL modified solution (PEI:PTFE mass ratio = 2.5:1).

[0033] The modification solution was drop-coated onto the surface of the catalyst layer using a microsyringe at a concentration of 0.2 mg / cm². After drying at room temperature for 6 h, a positively charged hydrophobic functional layer was formed, with an estimated total thickness of ≈1.5 μm. S3. Electrocatalytic reaction

[0034] The modified GDE was used as the cathode, the IrO2 / Ti mesh as the anode, and the Ag / AgCl as the reference electrode (positioned via a salt bridge / Luggin capillary). The Nafion 117 membrane separated the cathode and anode chambers.

[0035] 0.5 M H2SO4 (pH≈0.6) was injected into the cathode chamber, and 1.0 M H2SO4 was injected into the anode chamber. High-purity CO2 (99.99%, 50 mL / min) was continuously bubbled into the cathode chamber for 30 min to saturate the electrolyte with CO2 before electrolysis began. The operation was carried out at a constant temperature of 25℃ and a constant potential of -0.8V vs. RHE.

[0036] Product analysis: Gas phase was sampled every 30 min using GC-FID / TCD (H2 was quantified by TCD, CO / CH4 was quantified by methanator + FID); 500 μL of catholy solution was diluted and methanol concentration was determined by HPLC (Aminex HPX-87H column, RI detector), supplemented by ¹H NMR cross-validation.

[0037] Results (data from 2 hours of operation): <![CDATA[CH3OH]]> 62.3 <![CDATA[H2]]> 28.5 CO 6.2 <![CDATA[CH4]]> 3.0

[0038] Methanol production rate = 15.6 μmol / (cm²·h), operating current density ≈ 120 mA / cm².

[0039] After 120 hours of continuous operation, the methanol FE remained above 58%, with no carbonate deposition observed and the electrode morphology intact.

[0040] Potential scan tests (-0.6 to -1.2 V vs. RHE) confirmed the methanol selectivity peak at -0.8 V; when the potential is too negative, HER rises and the CH4 branch is activated (CH4 FE rises to >10% at -1.1 to -1.2 V), so locking the operating window at -0.7 to -0.9 V is optimal. Comparative Example 1: No positively charged hydrophobic functional layer (bare catalyst layer, under the same acidic conditions)

[0041] Completely repeat Example 1, but skip S2 (do not modify the PEI+PTFE layer), otherwise the same. <![CDATA[CH3OH]]> 3.2 <![CDATA[H2]]> 91.5 CO 4.1 <![CDATA[CH4]]> 1.2

[0042] Note: In the absence of a positively charged hydrophobic layer, the acidic bulk phase H⁺ penetrates directly into the catalytic site surface, and HER completely dominates. Trace amounts of methanol may originate from a very small number of locally hydrophobic microregions that spontaneously form "quasi-triple points," but these are uncontrollable and extremely low—confirming that interfacial microenvironment engineering is a necessary means to reverse the HER / CO2RR competition. Comparative Example 2: Same electrode (with positively electrophobic layer) but with a different alkaline electrolyte (1 M KOH).

[0043] The electrodes are the same as those in Example 1, but the electrolyte is changed to 1.0 M KOH, and the cathode potential is adjusted to -0.6 V vs. RHE (due to thermodynamic correction of CO2RR under alkaline conditions).

[0044] Initially, after 2 hours, the FE content of methanol was approximately 45.8%. However, after 4 hours, it suddenly dropped to 12.3%, white K2CO3 / KHCO3 deposits were observed on the electrode surface, the pores of the carbon paper were partially blocked, and the electrolyte conductivity dropped from 0.52 S / cm to 0.18 S / cm.

[0045] Note: Even with a good electrode coating, once back to an alkaline system, carbonate chemistry is inevitable → the lifespan bottleneck is unsolvable. This highlights that an acidic approach combined with microenvironmental inhibition of HER is the fundamental solution. Comparative Example 3: Same electrode, neutral electrolyte (0.5 M KHCO3)

[0046] When the electrolyte was changed to 0.5 M KHCO3 (pH≈7.2), the potential was -0.9 V vs. RHE.

[0047] 2-hour data: Methanol FE = 18.6%, and CO FE = 28.4%, HCOOH = 14.8%, resulting in a significant loss of electrons and a yield of only 4.2 μmol / (cm²·h). Limited mass transfer and product branching are significantly inferior to those of this invention. Example 2: pH Window Validation (Changing H2SO4 Concentration)

[0048] Same electrode and operating conditions as in Example 1, only the H2SO4 concentration was varied to control pH: 0.01 1.7 51.4 0.05 1.1 57.8 0.1 0.8 61.0 0.5 0.6 62.3 1.0 0.3 48.7 2.0 0.2 36.5

[0049] ⇒ pH 0.5~2 (corresponding to ≈0.01~0.5 M H2SO4) is the optimal window; if the pH is too low (>1 M strong acid), the bulk [H⁺] overwhelms the Donnan repulsion buffering capacity, and HER rebounds; if pH>2, CO2 solubility drops and trace amounts of OH⁻ are sufficient to trigger local carbonate nucleation. Example 3: Optimization of Positively Electrohydrophobic Layer Ratio

[0050] With a fixed total coating amount of 0.2 mg / cm², the PEI:PTFE mass ratio was: 8:1 52.1 <![CDATA[Partial hydrophilicity, insufficient CO2 enrichment]]> 4:1 63.8 Collaborative Advantage 2.5:1 62.3 Example 1 Conditions 2:1 58.6 Still possible 1:1 47.2 As positive charge density decreases, H⁺ shielding weakens. 1:2 38.4 Although it is hydrophobic, proton mass transfer is also hindered, and multi-electron dynamics decelerates. 1:4 29.7 The interface is close to pure PTFE, with dual interruption of electron / proton pathways.

[0051] The PEI:PTFE ratio of (2-8):(1-5) (i.e., polymer electrolyte: hydrophobic additive within the same range) as defined in the claims covers the optimal plateau region. Example 4: Direct Feeding of Industrial Flue Gas

[0052] Same electrode and electrolyte conditions as in Example 1, except the CO2 gas source is changed to flue gas from a coal-fired power plant:

[0053] Dehydration (silica gel / molecular sieve drying tower) → Desulfurization (activated carbon adsorption, outlet SO2 < 1 ppm) → Denitrification (SCR or pre-oxidation washing of residual NO) x ).

[0054] The pretreated gas is approximately 92% CO2 (the remainder is mainly N2 / O2, with trace amounts of inert gas), and is directly introduced into the cathode chamber at a rate of 50 mL / min.

[0055] Results: Methanol FE = 55.8% (a decrease of approximately 6.5 percentage points compared to 62.3% for pure CO2), and remained >50% for 100 consecutive hours. This indicates that inert components such as N2 / O2 do not inherently interfere with CO2RR within the three-phase microenvironment, demonstrating the practicality of this invention for directly digesting low-grade industrial waste gas. Example 5: Adding a transition layer (catalytic layer ↔ functional interlayer buffer)

[0056] A transition layer slurry was added between the S1 catalytic layer and the S2 electrohydrophobic layer in Example 1: 1) Disperse 10 mg CNT + 20 μL 5 wt% Nafion in 1 mL isopropanol and sonicate for 20 min; 2) The coating was applied to the surface of the catalyst layer at a rate of 0.1 mg / cm² and dried at room temperature for 2 h to obtain a transition layer with a thickness of ≈0.5 μm.

[0057] Then perform S2 (PEI+PTFE) on it. Test under the same reaction conditions: 1) Methanol FE = 68.5% (↑ + 6.2 pts vs. no transition layer) 2) Current density = 145 mA / cm² (↑ + 20.8%)

[0058] The CNT transition layer provides a high-speed channel for interlayer electrons, while Nafion provides cross-layer proton conduction, reducing interfacial contact resistance and mass transfer polarization—demonstrating that multi-level interface engineering can further extract performance margins (corresponding to claim 9). Example 6: Cu-Sn alloy catalyst variant

[0059] The catalytic active material in Example 1 was replaced by Cu-Sn alloy nanoparticles (Cu:Sn atomic ratio 3:1, particle size 30-100 nm, which can be prepared by coprecipitation-H2 reduction method), and the rest were the same. <![CDATA[CH3OH]]> 71.2 <![CDATA[H2]]> 20.5 CO 5.8 <![CDATA[CH4]]> 2.5

[0060] Methanol rate = 22.4 μmol / (cm²·h). Sn provides an electronic modification effect to the Cu d band, moderately weakening the CO adsorption energy (preventing premature desorption → reducing CO bypass), while also hindering deep C + O cracking → inhibiting deep CH4 reduction, allowing more electrons to flow into the methanol-specific channel CHO→CH2OH→CH3OH. Example 7: Scale-up verification of a flow electrolyzer (effective area 10 cm²)

[0061] The electrode of Example 1 was enlarged to 5 cm × 2 cm (effective area 10 cm²), and a flow cell was assembled (0.5 M H2SO4 cathode electrolyte flows through the flow field from the back of the GDE, and CO2 gas is supplied in parallel to the back side).

[0062] Conditions: Electrolyte flow rate 10 mL / min, CO2 200 mL / min, -0.8 V vs. RHE, 25℃. 1) Methanol FE = 59.6% (similar to 62.3% in a 1 cm² H cell, scale-up deviation < 5%) 2) j ≈ 115 mA / cm² 3) Methanol rate ≈ 14.8 μmol / (cm²·h) 4) FE remains >55% after 72 hours.

[0063] The proposed solution is not subject to the mass transfer artifact of small H-cells and has the potential for real-world scaling and engineering application. Overview

[0064] The above examples and comparative examples demonstrate that in acidic systems with pH 0.5–2, the intrinsic activity of the catalyst alone cannot resolve the overwhelming competition in the HER process. Only by superimposing a dual microenvironment of positive charge (proton repulsion) and hydrophobicity (CO2 enrichment) on the catalyst surface can the local reaction field be forcibly shifted into the "selective window" for methanol generation. This approach simultaneously eliminates the carbonate deadlock of the alkaline route, the mass transfer bottleneck of the neutral route, and the safety / cost burden of external hydrogen supply. Furthermore, it is directly compatible with industrial low-purity CO2 exhaust gas, and its overall techno-economic profile is well-suited for green electricity-driven distributed green methanol scenarios.

Claims

1. A method for direct methanol production from water via CO2 electrocatalysis under acidic microenvironment regulation, characterized by: Includes the following steps: S1. Preparation of gas diffusion electrode: A catalyst slurry is prepared by dispersing catalytic active material, conductive agent and binder in an organic solvent; the catalyst slurry is uniformly coated on a gas diffusion layer substrate and dried to form a catalyst layer; The catalytically active material is a copper-based composite material, including at least one of Cu, Cu2O, CuO, Cu-M alloy or Cu-M oxide composite catalyst, wherein M is selected from at least one of Sn, In, Zn, Ag, Au; S2. Interface Microenvironment Regulation: A positively charged hydrophobic functional layer is modified on the surface of the catalyst layer. The positively charged hydrophobic functional layer is composed of a positively charged polymer electrolyte and a hydrophobic additive. The polymer electrolyte is selected from at least one of polyethyleneimine (PEI), polydiallyldimethylammonium chloride (PDDA), chitosan quaternary ammonium salt, or polylysine hydrochloride. The hydrophobic additive is selected from at least one of polytetrafluoroethylene (PTFE), fluorinated graphene, hydrophobic silica, or long-chain alkylsilanes. S3. Electrocatalytic reaction: Using the gas diffusion electrode as the cathode and an acidic electrolyte as the reaction medium, the pH of the electrolyte is controlled at 0.5–2. CO2 gas is introduced into the cathode chamber, and the electrocatalytic reduction reaction is carried out in constant current or constant potential mode. The reaction temperature is controlled at 15–45℃, the CO2 gas flow rate is 10–100 mL / min, and the cathode potential is controlled at -0.5–-1.2 V vs. RHE. Water is used as the proton source during the reaction, and no external hydrogen is required.

2. The method according to claim 1, characterized in that, In step S1, the mass content of copper in the catalytic active material is 50% to 95%; the conductive agent is selected from at least one of carbon black, acetylene black, carbon nanotubes, graphene or Ketjen Black; the binder is selected from at least one of Nafion solution, polyvinylidene fluoride (PVDF) or PTFE emulsion; the mass ratio of the catalytic active material, conductive agent and binder is (7 to 8.5):(1 to 2):(0.5 to 1.5).

3. The method according to claim 1, characterized in that, In step S2, the modification method of the positively charged hydrophobic functional layer includes: dispersing the polymer electrolyte and the hydrophobic additive in water or an alcohol solvent to prepare a modification solution with a concentration of 1 to 20 mg / mL, coating it onto the surface of the catalyst layer by spraying, dipping or dripping, with a coating amount of 0.05 to 1.0 mg / cm², and drying it at room temperature to form the positively charged hydrophobic interface microenvironment regulation layer.

4. The method according to claim 1 or 3, characterized in that, In step S2, the mass ratio of polymer electrolyte to hydrophobic additive in the positive electrohydrophobic functional layer is (2-8):(1-5), and the total thickness of the positive electrohydrophobic functional layer is 0.5-5 μm.

5. The method according to claim 1, characterized in that, In step S3, the acidic electrolyte is at least one of sulfuric acid solution, hydrochloric acid solution, phosphoric acid solution or perchloric acid solution, with a concentration of 0.1 to 2.0 mol / L; the acidic electrolyte may also contain supporting electrolytes KCl, NaCl or K2SO4, with a supporting electrolyte concentration of 0.1 to 1.0 mol / L.

6. The method according to claim 1, characterized in that, In step S3, the electrocatalytic reduction reaction is carried out in an H-type electrolytic cell or a flow electrolytic cell; when carried out in a flow electrolytic cell, the electrolyte flow rate is 1 to 50 mL / min, and the effective area of ​​the gas diffusion electrode is 1 to 25 cm².

7. The method according to claim 1, characterized in that, In step S3, the CO2 gas originates from industrial exhaust gas, which includes flue gas from coal-fired power plants, cement plants, steel plants, or chemical plants. The CO2 gas undergoes dehydration, desulfurization, and denitrification pretreatment before use, and the CO2 purity is 90% to 99.9%.

8. The method according to claim 1, characterized in that, It also includes step S4. Product collection and analysis: During the reaction, the amount of gaseous products H2, CO, CH4 and C2H4 generated is monitored in real time by gas chromatography, and the concentration of methanol in the liquid product is detected by liquid chromatography or nuclear magnetic resonance hydrogen spectroscopy. The methanol selectivity is calculated according to the Faraday efficiency formula, and the methanol Faraday efficiency is ≥50%.

9. The method according to claim 1, characterized in that, In step S1, a transition layer is provided between the catalytic layer and the positively charged hydrophobic functional layer; the transition layer is composed of conductive carbon material and proton-conducting polymer, with a thickness of 0.2 to 2 μm, and is used to improve the efficiency of interfacial charge transfer and mass transport.

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