Green electrosynthesis method of ammonium formate under non-noble metal catalytic system

Abstract

A green electrosynthesis method of ammonium formate under a non-noble metal catalytic system comprises the following steps: cleaning copper foam with isopropanol and a hydrochloric acid solution in sequence, then placing the cleaned copper foam in a three-electrode electrolytic tank as a working electrode to obtain copper foam with the surface covered with a light blue precursor film, washing the precursor film with deionized water, and drying the washed precursor film for a long time to obtain the green electrosynthesis method of ammonium formate under a non-noble metal catalytic system. And carrying out heat preservation in a flowing argon atmosphere to obtain the nanowire structure anode electrode consisting of metal copper, copper oxide and cuprous oxide. According to the invention, the anode adopts an in-situ constructed gradient heterojunction nanowire structure, metal Cu provides an excellent electron conduction channel, rapid charge transmission under high current density is ensured, optimal balance is realized in a nitrate eight-electron reduction path through the cathode, and NOI initial adsorption and activation are facilitated.

Description

Technical Field

[0001] This invention belongs to the field of ammonium formate synthesis technology, specifically a green electrosynthesis method for ammonium formate under a non-precious metal catalytic system. Background Technology

[0002] Ammonium formate (NH4HCO2), as an important chemical raw material and intermediate, has significant applications in pharmaceuticals, agriculture, and analytical chemistry. In pharmaceuticals, it is a key intermediate in the synthesis of various anti-infective drugs and vitamins. In agriculture, it can be used as a nitrogen source soil conditioner and a component of high-efficiency nitrogen fertilizers. In analytical chemistry, it is an important additive in the mobile phase of high-performance liquid chromatography (HPLC). The efficiency, product purity, economics, and environmental friendliness of its synthesis process directly determine the production costs and sustainable development capabilities of downstream industries. Currently, existing ammonium formate synthesis technologies face the following technical challenges: First, the exothermic reaction is difficult to control, leading to a decrease in yield. During the reaction, if the ammonia gas is introduced too quickly, the local temperature of the system will rise sharply. Ammonium formate is prone to decompose into formic acid, ammonium, and carbon dioxide when the temperature exceeds 60°C, affecting the final yield.

[0003] Secondly, ammonia gas is highly corrosive to equipment and poses a significant safety risk. Ammonia, the core reactant, is a highly toxic and corrosive gas. Once introduced into the reaction apparatus, it readily corrodes the equipment and requires exhaust gas treatment, increasing reaction costs. Furthermore, if the reaction apparatus is poorly sealed or the ammonia gas introduction rate is unstable, ammonia leakage may occur, leading to environmental pollution or operator poisoning. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a green electrosynthesis method for ammonium formate in a non-precious metal catalytic system, so as to at least partially solve the above-mentioned technical problems.

[0005] The technical solution adopted in this invention is as follows: This invention proposes a green electrosynthesis method for ammonium formate under a non-noble metal catalytic system, comprising the following steps: Step 1: Preparation of the anode catalyst: Copper foam was sequentially cleaned with isopropanol and washed with 1 mol / L hydrochloric acid solution for 15 minutes. Then, it was placed in a three-electrode electrolytic cell as the working electrode and anodized for 20 minutes in 2 mol / L KOH electrolyte at a current density of 20 mA / cm² to obtain copper foam with a light blue precursor film on the surface. The precursor film was rinsed with deionized water and then vacuum dried at 60℃ for 12 hours. It was then heated to 200℃ in a flowing argon atmosphere at a heating rate of 2℃ / min and held for 2 hours to obtain a Cu-CuO-Cu2O nanowire structure anode material composed of metallic copper, copper oxide (CuO), and cuprous oxide (Cu2O). Step 2: Preparation of cathode catalyst: Another copper foam is sequentially subjected to ultrasonic treatment with hydrochloric acid solution for 30 minutes, rinsed with deionized water, ultrasonicated in acetone / ethanol mixture for 30 minutes, and then dried; the treated copper foam is taken, and the required mass of CuO and Cu2O mixed powder is calculated according to the ratio of its unit area loading of 200%. An ethanol dispersion containing Nafion is prepared according to the mass ratio of catalyst powder to Nafion of 95:5. The dispersion is coated on the surface of the copper foam and dried to form a cathode catalyst layer; Step 3: Prepare the electrolyte: Inject a mixed solution containing 1M methanol and 1M KOH into the anode chamber, and inject a mixed solution containing 1M KOH and 2000ppm KNO3 into the cathode chamber; Step 4: Assemble the electrolytic cell: A sealed H-type dual-chamber electrolytic cell is adopted, with a volume ratio of 1:1 between the two chambers, separated by a FumasepFAA-3-50 anion exchange membrane that has been pretreated with 1.0 MkOH solution for 24 hours and then washed with deionized water; the Cu-CuO-Cu2O nanowire anode obtained in Step 1 and the cathode obtained in Step 2 are placed in the anode chamber and cathode chamber, respectively; Step 5: Conduct the electrolysis reaction at a constant current density of 400 mA / cm², and stop the reaction after the set time. Step 6: Combine the reaction solutions in the cathode and anode chambers, concentrate by evaporation, cool and crystallize, filter and dry to obtain ammonium formate product.

[0006] In one embodiment of the present invention, the diameter of the Cu-CuO-Cu2O nanowires in the anode catalyst is 30-80 nm, and the three phases are distributed in a gradient along the nanowire axis. The side near the copper foam substrate is dominated by metallic Cu, and the outer layer is successively enriched with Cu2O and CuO, forming a heterojunction structure with interfacial synergistic effect.

[0007] In one embodiment of the present invention, the mass ratio of CuO to Cu2O mixed powder in the cathode catalyst is 1:1 to 3:1, and the powder particle size is controlled in the range of 50-200 nm.

[0008] In one embodiment of the present invention, the thickness of the anion exchange membrane is 50.0±2μm, and it undergoes the following pretreatment before use: first, it is immersed in 1.0M KOH solution for 24 hours to activate the OH⁻ conduction channel, then it is repeatedly rinsed with deionized water until the pH of the washing solution is ≤8.5, and finally it is soaked in deionized water for storage until assembly.

[0009] In one embodiment of the present invention, the sealed H-type dual-chamber electrolytic cell is made of plexiglass, each chamber has an independent gas outlet and liquid inlet / outlet, and the anode and cathode chambers are airtightly connected by a flange interface and a rubber sealing ring.

[0010] In one embodiment of the present invention, the electrolysis reaction is carried out at room temperature and pressure, the reaction temperature is controlled at 20-35°C, no additional inert gas is introduced for protection during the electrolysis process, and the carbon dioxide generated at the anode and the ammonium ions generated at the cathode spontaneously combine in the solution to form an ammonium formate precursor.

[0011] In one embodiment of the present invention, the methanol concentration in the anolyte is 0.8-1.2M and the KOH concentration is 0.9-1.1M; the KNO3 concentration in the catholyte is strictly controlled at 1800-2200ppm (calculated as NO3⁻), and the KOH concentration is also 0.9-1.1M, in order to maintain the balance of ionic conductivity in the two chambers and optimize the Faraday efficiency.

[0012] In one embodiment of the invention, the electrolysis current density is limited to 350-450 mA / cm², preferably 400 mA / cm²; within this current density window, the Faradaic efficiency of ammonium formate is higher than 85%, and the selectivity of the byproduct ammonia is lower than 5%.

[0013] In one embodiment of the present invention, both the cathode and the anode use 2×2cm² copper foam as a conductive substrate, with a porosity of 85-95PPI and a pore size of 0.3-0.8mm.

[0014] In one embodiment of the present invention, after electrolysis, before merging the cathode and anode liquids, the pH of the cathode liquid is adjusted to 6.5-7.5 to neutralize excess OH⁻ and promote the ion association of NH⁺ and HCOO⁻; then, it is concentrated to 1 / 3-1 / 2 of the original volume by vacuum rotary evaporation at 50-60°C, and then cooled to 0-5°C and allowed to stand for crystallization for ≥12 hours to finally obtain ammonium formate crystals with a purity of ≥98%.

[0015] The beneficial effects of the technical solution of this invention are as follows: This invention utilizes an in-situ constructed Cu-CuO-Cu2O gradient heterojunction nanowire structure at the anode, with a diameter controlled between 30 and 80 nm. The axial phase distribution exhibits an ordered gradient of "inner metal Cu—middle Cu2O—outer CuO." A synergistic catalytic system is formed through electrochemical oxidation and low-temperature thermal treatment: metallic Cu provides an excellent electron conduction channel, ensuring rapid charge transfer at high current densities; Cu2O, as an intermediate phase, regulates the adsorption strength of methanol dehydrogenation intermediates (such as HCHO and HCO), avoiding catalyst poisoning caused by strong adsorption; the outermost CuO undertakes a strong oxidation function, efficiently oxidizing formic acid intermediates to CO2 at a high current density of 400 mA / cm², and rapidly capturing and generating HCOO⁻ in an alkaline environment.

[0016] This invention utilizes a cathode made of mixed nanoparticles with a particle size of 50–200 nm and a CuO / Cu2O mass ratio of 1:1–3:1 loaded onto copper foam. This achieves optimal balance in the 8-electron reduction pathway of nitrate: CuO enriches surface oxygen vacancies, facilitating the initial adsorption and activation of NO3⁻; Cu2O provides a moderate reducing environment, promoting the continuous hydrogenation of *NO and *NH2OH intermediates. The coexistence of these two components forms micro-regional redox coupling sites, effectively suppressing N–N coupling side reactions (such as N2 generation) and over-reduction (such as NH3 escape), ensuring that the NH4⁺ Faradaic efficiency remains stable above 85%, and the selectivity of the byproduct ammonia is less than 5%.

[0017] In this invention, during electrolysis, OH⁻ migrates directionally from the cathode to the anode, precisely compensating for the OH⁻ consumed at the anode (due to CO₂ + 2OH⁻ → HCOO⁻ + H₂O) and balancing the OH⁻ generated at the cathode (NO₃⁻ reducing OH⁻), achieving dynamic pH self-stabilization in both chambers and avoiding selectivity decreases caused by localized acidification or alkalization. The entire electrolysis is carried out at ambient temperature and pressure (20–35℃) without inert gas protection, eliminating the need for heating / cooling equipment or gas cylinders, thus reducing energy consumption and operational complexity. The anolyte uses 0.8–1.2M methanol + 0.9–1.1M KOH, and the catholyte uses 1800–2200ppm KNO₃ + 0.9–1.1M KOH. The consistent KOH concentration in both chambers ensures matched ionic conductivity and minimizes ohmic losses; the KNO₃ concentration is precisely controlled within the optimal window, satisfying nitrogen source requirements while preventing a surge in side reactions. Under these conditions, almost all of the CO2 generated at the anode is captured by the alkaline solution and converted into HCOO⁻, while the NH4⁺ generated at the cathode remains stable in the solution. Although the two are physically isolated, they spontaneously associate into ammonium formate precursors through solution mixing after the reaction, achieving "cathode-anode coupling". This results in high atom utilization and no waste gas or waste liquid emissions.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a method framework diagram of the green electrosynthesis method of ammonium formate under a non-precious metal catalytic system proposed in the embodiments of the present invention; Figure 2 This is a first extension method framework diagram of the green electrosynthesis method of ammonium formate under a non-precious metal catalytic system proposed in the embodiments of the present invention; Figure 3 This is a second extension method framework diagram of the green electrosynthesis method of ammonium formate under a non-precious metal catalytic system proposed in the embodiments of the present invention. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] The following describes a green electrosynthesis method for ammonium formate in a non-precious metal catalytic system according to an embodiment of the present invention, with reference to the accompanying drawings.

[0022] like Figures 1 to 3 As shown, this embodiment of the invention provides a green electrosynthesis method for ammonium formate under a non-noble metal catalytic system, comprising the following steps: Step 1: Preparation of the anode catalyst: Copper foam was sequentially cleaned with isopropanol and washed with 1 mol / L hydrochloric acid solution for 15 minutes. Then, it was placed in a three-electrode electrolytic cell as the working electrode and anodized for 20 minutes in 2 mol / L KOH electrolyte at a current density of 20 mA / cm² to obtain copper foam with a light blue precursor film on the surface. The precursor film was rinsed with deionized water and then vacuum dried at 60℃ for 12 hours. It was then heated to 200℃ in a flowing argon atmosphere at a heating rate of 2℃ / min and held for 2 hours to obtain a Cu-CuO-Cu2O nanowire structure anode material composed of metallic copper, copper oxide (CuO), and cuprous oxide (Cu2O). Step 2: Preparation of cathode catalyst: Another copper foam is sequentially subjected to ultrasonic treatment with hydrochloric acid solution for 30 minutes, rinsed with deionized water, ultrasonicated in acetone / ethanol mixture for 30 minutes, and then dried; Take the treated copper foam, calculate the required mass of CuO and Cu2O mixed powder based on its unit area loading ratio of 200%, and prepare an ethanol dispersion containing Nafion according to the mass ratio of catalyst powder to Nafion of 95:5. Coat the dispersion onto the surface of the copper foam, and after drying, form a cathode catalyst layer; Step 3: Prepare the electrolyte: Inject a mixed solution containing 1M methanol and 1M KOH into the anode chamber, and inject a mixed solution containing 1M KOH and 2000ppm KNO3 into the cathode chamber; Step 4: Assemble the electrolytic cell: A sealed H-type dual-chamber electrolytic cell is adopted, with a volume ratio of 1:1 between the two chambers, separated by a FumasepFAA-3-50 anion exchange membrane that has been pretreated with 1.0 MkOH solution for 24 hours and then washed with deionized water; the Cu-CuO-Cu2O nanowire anode obtained in Step 1 and the cathode obtained in Step 2 are placed in the anode chamber and cathode chamber, respectively; Step 5: Conduct the electrolysis reaction at a constant current density of 400 mA / cm², and stop the reaction after the set time. Step 6: Combine the reaction solutions in the cathode and anode chambers, concentrate by evaporation, cool and crystallize, filter and dry to obtain ammonium formate product.

[0023] In specific applications, this invention utilizes in-situ electrochemical and thermal treatment processes to prepare Cu-CuO-Cu2O nanowire anode materials with a multiphase heterogeneous structure. The anode forms a nanowire array on a copper foam framework, consisting of three phases: metallic copper, cuprous oxide, and copper oxide. Its surface exhibits a gradient-distributed electronic structure and abundant interfacial active sites, effectively promoting the deep oxidation of methanol during electrolysis. In alkaline media, methanol is first partially dehydrogenated at the Cu / Cu2O interface to generate formaldehyde or formic acid intermediates, and then further oxidized to carbon dioxide at the strong oxidation sites dominated by CuO. Due to the high current density (400 mA / cm²) operating state of the anode, the local pH rapidly decreases, and the generated CO2 reacts with OH⁻ in the system to convert into HCOO⁻ (formate ions). Metallic Cu provides good conductivity and electron transport channels, Cu2O regulates the adsorption energy of intermediates, and CuO undertakes the strong oxidation function. All three are indispensable, working together to ensure the highly selective generation of formate and inhibit excessive oxidation to carbonates.

[0024] Meanwhile, on the cathode side, a supported CuO / Cu2O mixed powder catalyst is coated onto the pretreated copper foam to form a cathode catalyst layer with a high specific surface area. The cathode efficiently and selectively reduces nitrate ions (NO3⁻) in the electrolyte to ammonium ions (NH4⁺). In this process, KNO3 is introduced into the cathode chamber as a nitrogen source, and its concentration is controlled at 2000 ppm (approximately 32 mM). This ensures sufficient nitrogen supply while avoiding an increase in side reactions (such as the generation of N2 or NH2OH) due to excessive concentration. The ratio of CuO to Cu2O in the cathode catalyst (preferably 1:1 to 3:1) and its nanoscale (50-200 nm) endow it with a moderate adsorption capacity for *NO2⁻ intermediates, making the nitrate reduction pathway tend to be a continuous hydrogenation process via NO2⁻→NO→N2O→NH2OH→NH4⁺. Furthermore, the Nafion binder (comprising 5% of the total catalyst mass) not only fixes the powder but also, through its sulfonic acid groups, creates a slightly acidic environment locally, which is beneficial for proton supply and thus enhances the selectivity of NH4⁺ generation. Experiments show that at a current density of 400 mA / cm², the cathode can achieve a nitrate conversion rate exceeding 90%, and the NH4⁺ Faraday efficiency remains stable above 85%, with minimal ammonia (free NH3) as a byproduct.

[0025] The anode and cathode are placed in a sealed H-type dual-chamber electrolytic cell. The two chambers are of phase volume and separated by a FumasepFAA-3-50 anion exchange membrane. Before use, the membrane is activated for 24 hours with 1.0 MkOH solution to fully convert it to the OH⁻ conductive form and thoroughly wash away residual impurities, ensuring high OH⁻ conductivity and good chemical stability. During electrolysis, HCOO⁻ generated at the anode and NH₄⁺ generated at the cathode are enriched in their respective chambers. To maintain charge balance, OH⁻ migrates from the cathode to the anode through the anion exchange membrane. Although the two chambers are physically isolated, the entire system achieves electrochemical coupling through ion migration: the anode consumes OH⁻ (due to CO₂ + 2OH⁻ → HCOO⁻ + H₂O), and the cathode generates OH⁻ (due to NO₃⁻ + 6H₂O + 8e⁻ → NH₄⁺ + 9OH⁻). Under ideal conditions, internal circulation of OH⁻ can be achieved, significantly reducing changes in electrolyte alkalinity and improving process stability. Electrolysis is carried out at room temperature (20-35℃), atmospheric pressure, and without inert gas protection. Only a constant current density of 400mA / cm² is required, and the reaction time is set according to the target yield (usually 2-6 hours). Under these conditions, methanol is continuously converted to formate at the anode, and nitrate is simultaneously converted to ammonium ions at the cathode. No external ammonia or high-pressure CO is needed, fundamentally avoiding the high-risk operation and high carbon emission problems of traditional ammonium formate production processes.

[0026] After electrolysis, the reaction solutions from the anode and cathode chambers are combined. At this point, the solution contains molar amounts of HCOO⁻ and NH₄⁺, as well as a small amount of unreacted KOH and K⁺ salts. To obtain high-purity ammonium formate crystals, the pH of the combined solution is first adjusted to the neutral range (6.5-7.5) to neutralize excess OH⁻ and promote the formation of stable ion pairs between NH₄⁺ and HCOO⁻. Subsequently, the solution is concentrated to 1 / 3-1 / 2 of its original volume by rotary evaporation under reduced pressure at 50-60℃ to increase the ion concentration. Then, it is cooled to 0-5℃ and allowed to stand for crystallization for at least 12 hours to allow ammonium formate to fully precipitate. Finally, after filtration and low-temperature drying, white needle-like or flaky crystals with a purity of over 98% are obtained.

[0027] In one specific embodiment, the diameter of the Cu-CuO-Cu2O nanowires in the anode catalyst is 30-80 nm, and the three phases are distributed in a gradient along the nanowire axis. The side near the copper foam substrate is dominated by metallic Cu, and the outer layer is successively enriched with Cu2O and CuO, forming a heterojunction structure with interfacial synergistic effect. The mass ratio of CuO to Cu2O mixed powder in the cathode catalyst is 1:1 to 3:1, and the powder particle size is controlled in the range of 50-200 nm.

[0028] In specific applications, the Cu-CuO-Cu2O nanowire array grown in situ on a copper foam substrate on the anode side constitutes a heterojunction structure with an axial gradient phase distribution. The ordered hierarchy formed through electrochemical oxidation and thermal treatment processes is as follows: the inner layer near the conductive copper substrate is dominated by highly conductive metallic Cu, ensuring rapid electron transfer from the reaction interface to the external circuit; the intermediate transition layer is enriched with Cu2O, whose semiconductor properties and moderate oxygen vacancy concentration provide suitable adsorption energy for methanol dehydrogenation intermediates (such as CH2O or HCO), preventing excessive adsorption of intermediates and catalyst poisoning; the outermost layer is dominated by CuO, whose strong oxidizing ability effectively promotes the further oxidation of formic acid intermediates to CO2 at high current densities (400 mA / cm²), and rapidly converts them into formate ions (HCOO⁻) in a locally alkaline environment. Because the nanowire diameter is strictly controlled within the range of 30-80 nm, a high specific surface area is ensured to expose sufficient active sites while maintaining good structural stability, preventing aggregation or peeling during long-term electrolysis.

[0029] Meanwhile, on the cathode side, the CuO and Cu2O mixed nanoparticles loaded on pretreated copper foam are controlled within the 50-200 nm range. This ensures high dispersibility and abundant edge / step sites while avoiding agglomeration and deactivation due to excessively small particle size or mass transfer resistance due to excessively large particle size. Furthermore, the mass ratio of CuO to Cu2O is optimized between 1:1 and 3:1, determined based on the thermodynamic and kinetic requirements of the nitrate multi-electron reduction pathway. CuO is rich in surface lattice oxygen and Lewis acidic sites, which is beneficial for the initial adsorption and activation of NO3⁻; while Cu2O provides a suitable reducing environment and hydrogen species supply capacity, promoting the continuous hydrogenation of *NO2 and *NO intermediates. When the two coexist in a specific ratio, micro-regional redox coupling sites can be formed on the catalyst surface, causing the NO3⁻ reduction pathway to tend towards the octet transfer process of NO2⁻→NO→NH2OH→NH4⁺, rather than N / N coupling to generate N2 or remaining at the NO2⁻ stage. Experiments show that the cathode in the specified ratio can achieve a NO3⁻ conversion rate of >95% at a current density of 400 mA / cm², and the NH4⁺ Faraday efficiency is stable at 85-90%, with extremely low ammonia (NH3) byproduct emission.

[0030] During the entire electrolysis process, HCOO⁻ generated at the anode and NH₄⁺ generated at the cathode accumulate in their respective chambers. Ion conduction and charge balance are achieved between the anode and cathode through an anion exchange membrane. The anode reaction consumes OH⁻ (CO₂ + 2OH⁻ → HCOO⁻ + H₂O), while the cathode reaction produces OH⁻ (NO₃⁻ + 6H₂O + 8e⁻ → NH₄⁺ + 9OH⁻). Under ideal conditions, the two are close to material matching, resulting in small fluctuations in the OH⁻ concentration within the system, eliminating the need for frequent alkali replenishment and improving process stability. The nanostructure of the catalyst is a prerequisite for achieving this dynamic balance: if the anode selectivity is insufficient, excessive CO₃²⁻ will be produced, consuming additional OH⁻ and lowering the pH, affecting the generation of NH₄⁺ at the cathode; if the cathode side reaction is severe, generating N₂ or NH₃, the NH₄⁺ yield will be insufficient and unable to combine with HCOO⁻ molarly.

[0031] Finally, after electrolysis is complete and the solutions in the two chambers are combined, HCOO⁻ and NH4⁺ spontaneously associate under near-neutral conditions to form ammonium formate, and a high-purity product is obtained by evaporation-cooling crystallization.

[0032] In one specific embodiment, the thickness of the anion exchange membrane is 50.0±2μm. Before use, it undergoes the following pretreatment: first, it is immersed in 1.0M KOH solution for 24 hours to activate the OH⁻ conduction channels, then it is repeatedly rinsed with deionized water until the pH of the washing solution is ≤8.5, and finally it is soaked in deionized water for storage until assembly. The sealed H-type dual-chamber electrolytic cell is made of plexiglass. Each chamber has an independent gas outlet and liquid inlet and outlet, and the anode and cathode chambers are airtightly connected by a flange interface and a rubber sealing ring.

[0033] In specific applications, each chamber of the electrolytic cell is equipped with an independent liquid inlet / outlet and a gas outlet, allowing the anolyte (containing methanol and KOH) and catholyte (containing KNO3 and KOH) to be injected, circulated, or replaced separately. Simultaneously, it allows trace amounts of gas generated during the reaction (such as trace amounts of O2 escaping from the anode or N2 generated at the cathode) to be safely discharged, preventing internal pressure buildup from affecting operational safety. The two chambers are connected in a completely airtight manner via a machined flange interface and an alkali-resistant rubber sealing ring. This not only ensures no cross-leakage of liquids during long-term electrolysis but also completely prevents direct mixing of anode and cathode products. If NH4⁺ enters the anode chamber prematurely, it will be oxidized to N2 or NO3⁻ by the strong oxidizing environment; if HCOO⁻ diffuses into the cathode chamber, it will decompose under reducing conditions or participate in competing reactions, reducing the overall Faraday efficiency.

[0034] Before assembly, the membrane must undergo standardized pretreatment: First, it must be completely immersed in a 1.0 M KOH solution for 24 hours to fully convert the quaternary ammonium groups that originally existed in the form of Cl⁻ or other counterions into OH⁻, thereby opening and stabilizing its anion conduction channels; then, it must be repeatedly rinsed with a large amount of deionized water until the pH of the rinsing solution drops below 8.5 to completely remove residual free KOH and prevent it from causing drastic local pH fluctuations in the early stages of electrolysis, which would interfere with the reaction kinetics on the catalyst surface; finally, the membrane must be stored in deionized water to maintain its full swelling state, ensuring that it can immediately establish an efficient OH⁻ migration pathway after being loaded into the electrolytic cell.

[0035] In actual electrolysis operation, the pretreated anion exchange membrane not only prevents HCOO⁻ and NH4⁺ from combining prematurely or interfering with each other during the reaction stage, but also, as an ion conductor, selectively allows OH⁻ to migrate from the cathode chamber to the anode chamber to maintain the electroneutrality of the entire circuit. Since the anode reaction (methanol oxidation to HCOO⁻) consumes OH⁻, while the cathode reaction (NO3⁻ reduction to NH4⁺) generates OH⁻, the directional migration of OH⁻ precisely achieves a dynamic balance of alkalinity between the two chambers. This avoids a sudden drop in pH at the anode due to OH⁻ depletion, which would lead to CO2 escape (rather than conversion to HCOO⁻), and also prevents excessively high pH at the cathode due to OH⁻ accumulation, which would cause NH4⁺ to convert into volatile NH3.

[0036] In one specific embodiment, the electrolysis reaction is carried out at ambient temperature and pressure, with the reaction temperature controlled at 20-35℃. No additional inert gas is introduced for protection during the electrolysis process. The carbon dioxide generated at the anode and the ammonium ions generated at the cathode spontaneously combine in the solution to form an ammonium formate precursor. The methanol concentration in the anolyte is 0.8-1.2M, and the KOH concentration is 0.9-1.1M. The KNO3 concentration in the catholyte is strictly controlled at 1800-2200ppm (calculated as NO3⁻), and the KOH concentration is also 0.9-1.1M, in order to maintain the balance of ionic conductivity between the two chambers and optimize the Faraday efficiency.

[0037] In specific applications of this invention, methanol on the anode side is selectively oxidized to carbon dioxide in an alkaline environment, while nitrate on the cathode side is efficiently reduced to ammonium ions. Although the two are physically isolated in a two-chamber electrolytic cell, they spontaneously associate in the later stages of the reaction through solution chemistry and ion migration kinetics to form an ammonium formate precursor, which is then post-processed to obtain the target product.

[0038] Specifically, electrolysis is carried out at ambient temperature (20-35℃) and normal pressure, without the need for any external heating or cooling devices, nor for the introduction of nitrogen or argon inert gases for atmosphere protection. The anodic reaction (methanol oxidation) and the cathodic reaction (nitrate reduction) both have sufficiently fast kinetic rates within the temperature window, especially under a high current density of 400 mA / cm², the reaction efficiency is not limited by low temperature. At the same time, since the entire system is in a strongly alkaline environment (KOH concentration maintained at 0.9-1.1M), the reduction potential of dissolved oxygen in the solution is much lower than that of nitrate reduction. Therefore, even if there is a trace amount of air, it will not significantly interfere with the cathodic selectivity and can be ignored.

[0039] In the anode chamber, the methanol concentration is controlled within the range of 0.8-1.2 M. Too low a concentration leads to decreased anode current efficiency because some current is used for the oxygen evolution side reaction; too high a concentration causes intermediate accumulation, increases the risk of carbonate formation, and exacerbates mass transfer resistance. A KOH concentration of 0.9-1.1 M provides sufficient OH⁻ to promote methanol dehydrogenation and CO₂ capture (CO₂ + OH⁻ → HCO₃⁻; HCO₃⁻ + OH⁻ → HCOO⁻ + H₂O) while maintaining high ionic conductivity and reducing ohmic losses. Under these conditions, the CO₂ generated at the anode is almost immediately absorbed by the alkaline environment and converted into formate (HCOO⁻), with very little escaping in gaseous form, thus achieving efficient carbon utilization.

[0040] Meanwhile, in the cathode chamber, potassium nitrate (KNO3) serves as the nitrogen source, with its concentration limited to 1800-2200 ppm (approximately 28-35 mM as NO3⁻). If the concentration is too low, the NH4⁺ production will be insufficient to match the molar ratio of HCOO⁻ generated at the anode, resulting in limited product yield. If the concentration is too high, local saturation of reducing capacity will trigger side reactions (such as the generation of N2, NO2⁻, or hydroxylamine), reducing Faraday efficiency and increasing the difficulty of subsequent separation. Similarly, the KOH concentration in the catholyte is maintained at 0.9-1.1 M, providing the necessary proton acceptor for nitrate reduction (indirectly supplying H⁺ through water molecule dissociation) while maintaining consistent ionic strength and conductivity with the anolyte. This minimizes the migration potential difference across the membrane, reduces unnecessary voltage loss, and improves overall energy efficiency.

[0041] Meanwhile, although the anode and cathode chambers are physically separated by anion exchange membranes, the alkalinity of the electrolytes in both chambers is highly consistent, minimizing the resistance to OH⁻ migration and allowing the system to maintain a near-steady-state pH distribution during long-term operation. After electrolysis, when the solutions from the two chambers are combined, HCOO⁻ in the anolyte and NH⁺ in the catholyte rapidly undergo ion association in a near-neutral mixed environment, forming a hydrated precursor of ammonium formate (HCOONH₄).

[0042] In one specific embodiment, the electrolysis current density is limited to 350-450 mA / cm², preferably 400 mA / cm². Within this current density window, the Faraday efficiency of ammonium formate is higher than 85%, and the selectivity of the byproduct ammonia is lower than 5%. Both the cathode and anode use 2×2 cm² copper foam as the conductive substrate, with a porosity of 85-95 PPI and a pore size of 0.3-0.8 mm.

[0043] After electrolysis, before merging the cathode and anode solutions, the pH of the cathode solution is adjusted to 6.5-7.5 to neutralize excess OH⁻ and promote the association of NH⁺ and HCOO⁻ ions. Then, the solution is concentrated to 1 / 3-1 / 2 of its original volume by rotary evaporation under reduced pressure at 50-60℃, and then cooled to 0-5℃ and allowed to stand for crystallization for ≥12 hours to finally obtain ammonium formate crystals with a purity of ≥98%.

[0044] In specific applications of this invention, the electrolysis process is carried out within a current density window of 350-450 mA / cm². Within this range, the rate of methanol oxidation at the anode to formate (HCOO⁻) and the rate of nitrate reduction at the cathode to ammonium ions (NH₄⁺) are essentially in stoichiometric equilibrium, resulting in a molar ratio of products in both chambers close to 1:1. The current density is sufficient to overcome the activation energy barrier, promoting rapid multi-electron transfer processes (such as NO₃⁻→NH₄⁺ requiring 8e⁻), while not being high enough to trigger significant oxygen or hydrogen evolution side reactions. Experimental data show that within this window, the overall Faraday efficiency of ammonium formate is consistently above 85%, with over 85% of the charge effectively used for the formation of the target product; simultaneously, the selectivity of the cathode byproduct ammonia (NH₃) is controlled below 5%. The substrate possesses a high porosity of 85-95 PPI (pores per inch) and a uniform pore size of 0.3-0.8 mm, forming a three-dimensional interconnected porous network structure. This provides a large specific surface area for loading active catalysts (whether in-situ grown Cu-CuO-Cu2O nanowires or coated CuO / Cu2O mixed powders), constructing efficient mass transfer channels: reactants (methanol, NO3⁻) can rapidly diffuse to the catalyst surface, and products (HCOO⁻, NH4⁺) can also leave the active sites in a timely manner, avoiding side reactions caused by excessively high local concentrations or pore blockage. Simultaneously, the high conductivity and mechanical strength of the copper foam itself ensure uniform current distribution at high current densities, without local overheating or electrode deformation, guaranteeing stability during long-term operation.

[0045] Once the electrolysis reaction reaches the predetermined time, the system enters the product recovery stage. At this point, the anolyte is rich in HCOO⁻ and a small amount of K⁺, while the catholyte contains NH⁺, excess OH⁻, and incompletely converted KNO₃. If directly combined, the strongly alkaline environment (pH>13) will cause some of the NH⁺ to be converted into volatile NH₃, resulting in nitrogen loss and reduced yield. Therefore, before combining, the pH of the catholyte must be adjusted by using dilute acid (such as dilute HNO₃ or CO₂ bubbling) to control its pH within the weakly acidic to neutral range of 6.5-7.5.

[0046] Subsequently, the pH-adjusted mixed solution was placed in a vacuum rotary evaporator and concentrated to 1 / 3-1 / 2 of its original volume at a mild temperature of 50-60℃. Vacuuming lowers the boiling point of water, preventing the decomposition of ammonium formate (its thermal decomposition temperature is approximately 180℃, but it degrades prematurely in the presence of alkaline or acidic impurities) due to high temperatures. The 50-60℃ temperature accelerates water evaporation without causing product deterioration. After concentration, the concentration of ammonium formate in the solution significantly increases, reaching a supersaturated state. At this point, the solution is rapidly transferred to a low-temperature environment of 0-5℃ and allowed to stand for at least 12 hours. This low temperature further reduces the solubility of ammonium formate and provides sufficient time for crystal nucleation and growth. Under these conditions, ammonium formate precipitates as high-purity white crystals, while impurity ions (such as K⁺ and NO₃⁻) remain mostly in the mother liquor due to their low concentration and high solubility. Finally, after filtration, washing with cold deionized water, and low-temperature drying, ammonium formate crystals with a purity ≥98% are obtained, meeting the requirements for industrial or pharmaceutical applications.

[0047] In practical application, the anode, cathode, and catalyst are prepared as follows: Anode: Cu-CuO-Cu2O nanowires were prepared via electro-oxidation and thermal treatment of copper foam. First, 2×2 cm nanowires were pretreated with isopropanol. 2 The copper foam was then washed with 1 mol / L HCl for 15 minutes to clean the surface. Next, an electro-oxidation process was performed in a three-electrode cell, using the pretreated copper foam as the anode, platinum foil as the cathode, and 2 mol / L KOH as the electrolyte. The electro-oxidation process was carried out at 20 mA / cm². -2 Anodizing was performed at a current density of [value missing] for 20 minutes. After oxidation, a light blue film formed on the copper foam, which can be simply defined as the precursor. The precursor was washed with deionized water, then vacuum dried at 60°C for 12 hours, and finally anodized at 2°C / min in a flowing Ar atmosphere at 200°C. -1 The heating rate was annealed for 2 hours to obtain Cu-CuO-Cu2O nanowires, which were used as the anode in the electrochemical reaction for the synthesis of ammonium formate.

[0048] Cathode: Copper foam was impregnated with a mixture of CuO and Cu2O powders and Nafion's ethanol solution. A 2×2 cm copper foam was immersed in hydrochloric acid solution and sonicated for 30 min to remove the surface oxide layer. It was then rinsed with deionized water, immersed in acetone / ethanol solution, sonicated for 30 min, dried, and stored in ethanol for later use. The pretreated copper foam was dried and weighed to its initial mass m0. Taking a loss of 200%, the catalyst mass m was calculated. CB =1*1*1*200%, according to m n :m CB =5:95 Determine the mass m of Nafion n Then, the mass of the sample vial was measured using a 10 mL sample bottle, and the result was m(n,l) = m n A 5% Nafion solution was prepared, and its actual mass m(n,l) was recorded. The actual catalyst mass m was then calculated using the formula. CB Then, the Nafion solution and ethanol were added to a 50 mL beaker at a ratio of 1:1 (mg:mL), and sonicated for 5 min. The mass of the mixture was then measured as m. CB The catalyst was added to the sonicated Nafion-ethanol mixture. The mixture was then sonicated for another 30 minutes to obtain the impregnation solution. The catalyst was then loaded onto copper foam using an impregnation method. The copper foam was impregnated in the catalyst solution for 1 minute and then dried with a hairdryer. The result was recorded as m. x , Δm=m x -m0, repeat until approximately Δm = 1mg / 95% = 1.05mg, and finally calculate the actual catalyst loading m. loading =Δm*95%. This catalyst-supported copper foam serves as the cathode in the electrochemical reaction for the synthesis of ammonium formate.

[0049] Specifically, the anode and cathode solutions are prepared as follows: a mixture of 1 M KOH and 2000 ppm KNO3 is used as the cathode solution, and a mixture of 1 M KOH and 1 M methanol is used as the anolyte. The nitrate ions participate in the reaction at the cathode, while the methanol ions participate in the reaction at the anode.

[0050] Specifically, the pretreatment of the ion exchange membrane: The membrane used is FumasepFAA-3-50, with OH- as the charge carrier and a coarse thickness of 50.0 μm, serving as an anion exchange membrane (AEM). Before use, the AEM needs to be pretreated: the membrane is immersed in a prepared 1.0 MkOH solution for 24 hours, then washed with deionized water to remove all contaminants, and finally placed in deionized water for later use.

[0051] Specifically, the electrolysis reaction is carried out as follows: Equal amounts of the prepared anode and cathode solutions are taken and placed in a sealed H-type double-chamber electrolytic cell, with the two chambers separated by an AEM FumasepFAA-3-50 membrane. Equal amounts of the prepared anode and cathode solutions are injected into the cathode and anode chambers, respectively. The cathode and anode working electrodes are respectively made of catalyst-supported copper foam and Cu-CuO-Cu2O nanowires. Subsequently, the electrolysis is performed at 400 mA / cm². 2 Electrolysis is carried out at a current density (at which the Faraday efficiency is optimal) and the reaction continues for a sufficient duration.

[0052] Specifically, after the electrolysis reaction is completed, the anode and cathode reaction solutions are mixed, and then subjected to evaporation and concentration, cooling and crystallization, filtration and drying to obtain the ammonium formate product.

[0053] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0054] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A green electrosynthesis method for ammonium formate under a non-precious metal catalytic system, characterized in that, Includes the following steps: Step 1: Preparation of the anode catalyst: Copper foam was sequentially cleaned with isopropanol and washed with 1 mol / L hydrochloric acid solution for 15 minutes. Then, it was placed in a three-electrode electrolytic cell as the working electrode and anodized for 20 minutes in 2 mol / L KOH electrolyte at a current density of 20 mA / cm² to obtain copper foam with a light blue precursor film on the surface. The precursor film was rinsed with deionized water and then vacuum dried at 60℃ for 12 hours. It was then heated to 200℃ in a flowing argon atmosphere at a heating rate of 2℃ / min and held for 2 hours to obtain a Cu-CuO-Cu2O nanowire structure anode material composed of metallic copper, copper oxide (CuO), and cuprous oxide (Cu2O). Step 2: Preparation of cathode catalyst: Another copper foam is sequentially subjected to ultrasonic treatment with hydrochloric acid solution for 30 minutes, rinsed with deionized water, ultrasonicated in acetone / ethanol mixture for 30 minutes, and then dried; the treated copper foam is taken, and the required mass of CuO and Cu2O mixed powder is calculated according to the ratio of its unit area loading of 200%. An ethanol dispersion containing Nafion is prepared according to the mass ratio of catalyst powder to Nafion of 95:

5. The dispersion is coated on the surface of the copper foam and dried to form a cathode catalyst layer; Step 3: Prepare the electrolyte: Inject a mixed solution containing 1M methanol and 1.0M KOH into the anode chamber, and inject a mixed solution containing 1M KOH and 2000ppm KNO3 into the cathode chamber; Step 4: Assemble the electrolytic cell: A sealed H-type dual-chamber electrolytic cell is adopted, with a volume ratio of 1:1 between the two chambers, separated by a FumasepFAA-3-50 anion exchange membrane that has been pretreated with 1.0 MkOH solution for 24 hours and then washed with deionized water; the Cu-CuO-Cu2O nanowire anode obtained in Step 1 and the cathode obtained in Step 2 are placed in the anode chamber and cathode chamber, respectively; Step 5: Conduct the electrolysis reaction at a constant current density of 400 mA / cm², and stop the reaction after the set time. Step 6: Combine the reaction solutions in the cathode and anode chambers, concentrate by evaporation, cool and crystallize, filter and dry to obtain ammonium formate product.

2. The green electrosynthesis method of ammonium formate under a non-precious metal catalytic system according to claim 1, characterized in that, The diameter of the Cu-CuO-Cu2O nanowires in the anode catalyst is 30-80 nm, and the three phases are distributed in a gradient along the nanowire axis. The side near the copper foam substrate is dominated by metallic Cu, while the outer layer is successively enriched with Cu2O and CuO, forming a heterojunction structure with interfacial synergistic effect.

3. The green electrosynthesis method of ammonium formate under a non-precious metal catalytic system according to claim 1, characterized in that, The mass ratio of CuO to Cu2O mixed powder in the cathode catalyst is 1:1 to 3:1, and the powder particle size is controlled within the range of 50-200 nm.

4. The green electrosynthesis method of ammonium formate under a non-precious metal catalytic system according to claim 1, characterized in that, The thickness of the anion exchange membrane is 50.0±2μm. Before use, it undergoes the following pretreatment: first, it is immersed in 1.0M KOH solution for 24 hours to activate the OH⁻ conduction channel, then it is repeatedly rinsed with deionized water until the pH of the washing solution is ≤8.5, and finally it is soaked in deionized water for storage until assembly.

5. The green electrosynthesis method of ammonium formate under a non-precious metal catalytic system according to claim 1, characterized in that, The sealed H-type dual-chamber electrolytic cell is made of plexiglass. Each chamber has an independent gas outlet and liquid inlet / outlet, and the anode and cathode chambers are airtightly connected by a flange interface and a rubber sealing ring.

6. The green electrosynthesis method of ammonium formate under a non-noble metal catalytic system according to claim 1, characterized in that, The electrolysis reaction is carried out at room temperature and pressure, with the reaction temperature controlled between 20-35℃. No additional inert gas is introduced for protection during the electrolysis process, and the carbon dioxide generated at the anode and the ammonium ions generated at the cathode spontaneously combine in the solution to form an ammonium formate precursor.

7. The green electrosynthesis method of ammonium formate under a non-precious metal catalytic system according to claim 1, characterized in that, The anolyte has a methanol concentration of 0.8-1.2M and a KOH concentration of 0.9-1.1M; the catholyte has a KNO3 concentration strictly controlled at 1800-2200ppm (calculated as NO3⁻) and a KOH concentration of 0.9-1.1M, in order to maintain the balance of ionic conductivity between the two chambers and optimize the Faraday efficiency.

8. The green electrosynthesis method of ammonium formate under a non-precious metal catalytic system according to claim 1, characterized in that, The electrolysis current density is limited to 350-450 mA / cm², preferably 400 mA / cm²; within this current density window, the Faradaic efficiency of ammonium formate is higher than 85%, and the selectivity of the byproduct ammonia is lower than 5%.

9. The green electrosynthesis method of ammonium formate under a non-noble metal catalytic system according to claim 1, characterized in that, Both the cathode and anode use 2×2cm² copper foam as the conductive substrate, with a porosity of 85-95 PPI and a pore size of 0.3-0.8 mm.

10. The green electrosynthesis method of ammonium formate under a non-noble metal catalytic system according to claim 1, characterized in that, After electrolysis, before merging the cathode and anode solutions, the pH of the cathode solution is adjusted to 6.5-7.5 to neutralize excess OH⁻ and promote the association of NH⁺ and HCOO⁻ ions. Then, the solution is concentrated to 1 / 3-1 / 2 of its original volume by rotary evaporation under reduced pressure at 50-60℃, and then cooled to 0-5℃ and allowed to stand for crystallization for ≥12 hours to finally obtain ammonium formate crystals with a purity of ≥98%.

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