Atomic-scale redox-potential-mediated engineering of 0D/2D Cu-Cu2O/MO x (OH) y heterojunctions for efficient nitrate electroreduction to ammonia.

Green synthesis of Fe-anchored N-doped biochar with highly active FeNx catalytic sites for electrochemical nitrate reduction

Synergistic dual active sites in metal-organic framework-on-metal hydroxide heterostructures for enhanced electrocatalytic nitrate reduction to ammonia.

Constructing Ru single-atomic sites through potential-induced self-reconstruction to accelerate electrocatalytic nitrate reduction for ammonia production

The conversion of CO2 into high-value-added chemicals and fuels using electricity generated from renewable energy sources is one of the most promising methods to reduce the dependence of human society on fossil fuels and to alleviate environmental problems. The performance of catalysts is one of the most important factors restricting the development of this technology, and in recent years, carbon materials have been the hot spot of research in the field of CO2 electrocatalytic reduction catalysts. In this paper, the progress of the application of carbon materials in CO2 electrocatalytic reduction reaction (ECR) is reviewed in detail. Three aspects of carbon materials directly as metal-free carbon material catalysts for CO2 reduction, metal-centered coatings in metal catalysts, and support for metals, are comprehensively described, respectively, including the preparation strategy of catalysts, the mechanism of action and structural characteristics of catalysts, the distribution of products and the catalytic performance of catalysts. Finally, the problems and challenges faced by the field are summarized, and the outlook is presented in various areas, including catalyst preparation, performance enhancement, and deepening mechanism research.

Development of CuNi immobilized Pt surface to minimize nitrite evolution during electrocatalytic nitrate reduction in neutral medium

Efficient electrocatalytic nitrate reduction via boosting oxygen vacancies of TiO2 nanotube array by highly dispersed trace Cu doping

Open AccessCCS ChemistryMINI REVIEWS28 Dec 2022Electrocatalytic CO2 Reduction over Bimetallic Bi-Based Catalysts: A Review Wei Chen, Yating Wang, Yuhang Li and Chunzhong Li Wei Chen Key Laboratory for Ultrafine Materials of Ministry of Education, Shanghai Engineering Research Center of Hierarchical Nanomaterials, Frontiers Science Center for Materiobiology and Dynamic Chemistry, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 , Yating Wang Key Laboratory for Ultrafine Materials of Ministry of Education, Shanghai Engineering Research Center of Hierarchical Nanomaterials, Frontiers Science Center for Materiobiology and Dynamic Chemistry, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 , Yuhang Li *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory for Ultrafine Materials of Ministry of Education, Shanghai Engineering Research Center of Hierarchical Nanomaterials, Frontiers Science Center for Materiobiology and Dynamic Chemistry, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 and Chunzhong Li *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory for Ultrafine Materials of Ministry of Education, Shanghai Engineering Research Center of Hierarchical Nanomaterials, Frontiers Science Center for Materiobiology and Dynamic Chemistry, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237 https://doi.org/10.31635/ccschem.022.202202357 SectionsAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Electrocatalytic reduction of carbon dioxide (CO2) to valuable fuels is an up-and-coming approach. Owing to the low cost, environmental friendliness, and high selectivity to formate single product at low overpotentials, bismuth (Bi)-based catalysts have attracted extensive research attention. In this review, the reaction mechanisms of Bi-based catalysts are first introduced, and the bimetallic Bi-based catalysts synthesized by alloying, doping, and loading strategies are reviewed from the aspects of catalyst component, morphology, synthesis procedure, and performance optimization for electrocatalytic CO2 reduction. We provide an in-depth discussion of the existing challenges and an outlook for this highly promising kind of electrocatalysis. Download figure Download PowerPoint Introduction The energy crisis and environmental pollution have been ongoing significant issues and the focus of the international community. Over the past few decades, the strong dependence and overuse of fossil fuels has resulted in a rapid increase in the concentration of carbon dioxide (CO2) in the atmosphere.1,2 When the World Meteorological Organization released its latest Greenhouse Gas Bulletin, they pointed out that the current CO2 concentration in the atmosphere is 149% of preindustrial levels.3 The Bulletin additionally noted that greenhouse gases have increased by 47% through radiative forcing, with CO2 accounting for 80% of this increase from 1990 to 2020. The emission of an oversized quantity of CO2 and other harmful gases has resulted in global warming and environmental pollution, documented in numerous studies related to the energy and environment around the world. CO2 emission reduction is urgently needed. Electrocatalytic CO2 reduction reaction In order to curtail the global warming trend, scientists conduct in-depth discussions and research on the issue of reducing CO2 emissions. There are four primary strategies: (a) developing new clean energy technologies; (b) upgrading existing processes to eliminate and replace the low-efficiency sectors and equipment in traditional technologies;1 (c) afforestation and forestation; and (d) carbon capture, utilization and storage.4,5 Research on carbon capture, carbon storage, and carbon utilization has produced many advances and breakthroughs in CO2 storage and conversion. Among them, carbon capture and storage technology have certain limitations. First of all, the technology is expensive. Second, storage equipment may leak and cause a series of other hidden safety problems, such as local seawater acidification. In contrast, carbon capture and utilization technology, which reduce CO2 and convert it into usable chemical value-added fuels, possesses greater development prospects.6–8 Not only can this technology reduce high CO2 concentrations in the atmosphere, but it also produces renewable fuels to combat the energy crisis. In recent years, numerous catalytic conversion methods have been developed successively. The methods used for CO2 reduction chiefly include biological (enzyme) catalysis, photocatalysis, thermocatalysis, and electrocatalysis.9–12 At present, electrocatalysis as an emerging energy technology for CO2 emission reduction and production of value-added fuels receives a great deal of research attention.7 Compared with traditional industrial processes, electrocatalytic CO2 reduction reaction (CO2RR) can be carried out under milder environmental conditions, improving electrochemical stability and selectivity in CO2RR via selecting appropriate electrocatalysts to manipulate reaction-tailored products.13 In this regard, reports in the literature demonstrate the exploration of various electrocatalysts and electrode reaction mechanisms for CO2RR. CO2RR also utilizes renewable energy for catalytic reactions to achieve large-scale energy storage and production of high-energy products.14 Generally, CO2RR is in a position to produce a variety of reduction products through electrocatalysis. The corresponding reduction products are different as electron-transferred numbers change. Electrocatalytic CO2RR products are categorized as formic acid (HCOOH),12 carbon monoxide (CO), methane (CH4), methanol (CH3OH) as C1, and ethanoic acid (CH3COOH), ethanol (C2H5OH)15 as C2.16,17 The above reduction products are obtained by various electron-transfer mechanisms and half-reactions, as shown in Table 1.18,19 Table 1 | Electrochemical Potentials of Several CO2 Reduction Reactions CO2 Reduction Half-Reactions Electrode PotentialV (vs SHE) Electrode PotentialV (vs RHE) CO2 + 2H+ + 2e− → CO + H2O −0.52 −0.106 CO2 + 2H+ + 2e− → HCOOH −0.61 −0.250 CO2 + 4H+ + 4e− → HCHO + H2O −0.51 −0.070 CO2 + 6H+ + 6e− → CH3OH + H2O −0.38 0.016 CO2 + 8H+ + 8e− → CH4 + 2H2O −0.24 0.169 2CO2 + 12H+ + 12e− → C2H4 + 4H2O −0.34 0.064 2CO2 + 12H+ + 12e− → C2H5OH + 3H2O −0.33 0.084 During the electrocatalytic reduction process, not solely CO2RR but also other side reactions will occur, resulting in the complexity of the reaction. For instance, the hydrogen evolution reaction (HER) competes with CO2RR to generate H2, which decreases the performance of CO2RR20–22 in order to efficiently overcome the energy barrier of electron-transfer proton coupling, accelerate the catalytic reaction rate. and suppress the occurrence of side reaction processes. The development of ideal catalysts with remarkable CO2RR selectivity and activity is the focus of current research. Several parameters of electrocatalytic performance for CO2RR catalysts can primarily be evaluated, including Faradaic efficiency (FE), overpotential, current density, Tafel slope, stability, and so on.7,12,14 FE is the charge required as a percentage of the initial charge to cross the working electrode and facilitate the electrochemical reaction. In simple terms, FE is a significant indicator to measure the selectivity of electrocatalytic CO2RR products.23 Due to the complex reaction mechanism and sluggish kinetics, the actual reduction reaction working potential is more negative than the theoretical reduction potential. High reduction overpotentials lead to wasted energy and significant HER reactions. Therefore, overpotential is an important indicator in evaluating the electrocatalytic activity of CO2RR catalysts. Studies confirm that when current density goes above 300 mA cm−2, the production cost will be reduced as much as possible.24 The equation of Tafel (η = blgj + a) is able to directly reflect the rate of reaction dominated by kinetics. The smaller the Tafel slope of b in the equation, the faster the electrochemical reaction rate and the higher the catalytic activity, which is more favorable for the electrocatalytic reaction.25 Stability is an indicator of whether an excellent electrocatalyst possesses long-term stability and efficiency.26 The stability of electrocatalysts is usually effectively assessed with potentiostatic electrolysis or cyclic voltammetry. Bismuth-based electrocatalysts Recently, P-block electrocatalysts consisting of bismuth (Bi),27–30 tin (Sn),31–33 lead (Pb),34–36 and indium (In)37,38 have inarguably facilitated electrocatalytic CO2 reduction with remarkable selectivity for C1 products, especially formic acid or formate. The advantage of electrocatalytic generation of formate lies in the high selectivity and current density achieved by prohibiting competing side reactions. Compared with other value-added products from CO2 reduction, which are difficult to solely generate and low in yield, the FE of Bi-based CO2 toward formate can reach nearly 100%.39 In addition, formate is a liquid product with excellent chemical stability at room temperature for storage and transportation compared to gas-phase products such as CO. Experts evaluate various chemicals with economic viability in CO2RR and discovered that formate has considerable marketability.13 Moreover, converting CO2 toward formate is a 2-electron transfer process, leading to a low production cost of 1$US/0.59 kg, suggesting that CO2 electrolysis of formate is more cost-competitive than the C2 product production process.40 It may be difficult to attain widespread application of Pb and In metals on a marketable scale because of toxicity or low availability. However, Bi is a dramatic and promising electrocatalyst due to its low cost, nontoxicity, environmental safety, relatively single reduction product, and high formate generation activity. Bi-based catalysts can be traced back to the Bi electrocatalyst synthesized by Komatsu's team in 1995.41 In the following decades, research on Bi-based catalysts continued to deepen. Monometallic catalysts, including metallic Bi, are currently a hot topic in the field of electrocatalysis. Recently, with in-depth exploration and development of synthesis techniques, various nanostructured monometallic Bi catalysts have been designed, such as nanoparticles, nanowires, nanotubes, nanosheets, nanodendrites, and so on, in multidimensional aspects. However, monometallic Bi catalysts may be undesirable for the breakthrough of formate electrosynthesis, owing to the limited active sites on the catalyst surface. This means that monometallic Bi catalysts usually require high overpotential to achieve high formate FE and partial current density. Compared with the monometallic Bi catalysts that use advanced synthetic strategies or tedious structural optimization to enhance their performance, bimetallic Bi-based catalysts will further involve synergistic effects. The synergistic interaction between bimetals gives the bimetallic electrocatalyst a superior catalytic performance.42 The synergistic effects in bimetallic Bi-based catalysts can be broadly viewed as Bi acting as the active site and the other metals mainly playing three roles: (1) tailoring the electronic structures of Bi sites, (2) regulating the adsorption states of the key intermediates, and (3) generating interfacial active sites to further enhance performance. Through the electronic structure modulations by the second metal, the bimetallic Bi-based catalysts will boost the formation of the key intermediate OCHO*, thus improving the performance of CO2 electroreduction to formate. The activity, selectivity, and stability will be further improved via preparing bimetallic Bi-based materials through strategies such as alloying, surface doping, defect introduction, and nanoengineering. Here, in this review, the representative reaction pathways of Bi-based electrocatalysts are first introduced, and then the reaction mechanisms of bimetallic Bi-based heterogeneous CO2RR electrocatalysts are summarized with examples from the perspective of reaction pathways. Afterward, based on the Bi-based electrocatalysts in recent development, we divide bimetallic Bi-based catalysts into three categories: (1) alloyed Bi, (2) doped Bi, and (3) supported Bi. For each category, we describe in detail its performance-enhancing strategies and provide examples of catalysts, including descriptions of their preparation process, composition, morphology, catalytic activity, and product properties. Finally, we provide an in-depth analysis of the existing challenges and the current outlook for this field. Reaction Mechanisms of the Bi-Based Electrocatalysts Bi-based catalysts have high efficiency, selectivity, and stability to form formate via electrocatalytic CO2RR in aqueous solutions. They also possess the capacity to generate CO, according to some reports.43 The pathways of the formate and CO products are comparatively simple compared to that of other CO2RR products, and the essential difference is the intermediate products. An in-depth study of the electrocatalytic CO2RR process on the surface of Bi-based catalysts is required for a good understanding of the catalytic mechanism of Bi metals. In general, there are three types of steps involving the generation of products theoretically, consisting of: (1) reactant adsorption on the electrocatalytic surface, (2) transfer of electrons and protons to the reactant, and (3) the products desorption from the electrocatalyst surface.44 Research demonstrates that the first proton coupling determines the selectivity for a catalyst, which takes place at the C or O in CO2*− radical anion. Three reaction pathways for electrocatalytic CO2RR over Bi-based catalysts are displayed in Figure 1: (a) Generally, CO2 comes into contact with the catalyst via carbon or oxygen atoms. If the carbon atom binds to the catalyst electrode surface first, *COOH intermediate will be formed, which is the first intermediate for CO2 activation in this pathway. However, *COOH intermediate will have multiple pathways in the second proton coupling electron transfer (PCET) process, which is not conducive to promoting highly selective formate production. *COOH can lose H2O to form CO, or be reduced to form HCOOH. (b) Compared to pathway a, pathway b is different in that the oxygen is bound to the electrode surface, by which CO2* − hydrogenation forms the HCOO* intermediate.19 Based on the reaction mechanism of Bi-based catalysts, the second PCET process of the HCOO* intermediate can only generate HCOOH.(c) In the pathway c, CO2 forms the OCHO* intermediate during the first PCET when only one oxygen molecule is bound to the surface electrode. Formate is the only product obtained via a subsequent second PCET process. Theoretical analyses indicate that the formation energy barrier of OCHO* intermediate is lower than that of *COOH and HCOO* intermediates, leading to the importance of OCHO* intermediates in the Bi-based electroreduction process.45 Figure 1 | Possible electrochemical reaction pathways of CO2 over Bi-based catalysts. Download figure Download PowerPoint Theoretical calculations confirm that the CO2RR process of Bi-based catalysts follows the key intermediate of OCHO* from a PCET mechanism, facilitating highly selective formate production. The specific mechanism equations (1–5) for reducing CO2 pathway in solution to HCOOH are summarized as follows:46 CO 2 ( g ) → CO 2 * (1) CO 2 * + e − → CO 2 * − (2) CO 2 * − + e − + H + → OCHO * − (3) OCHO * − + e − + H + → HCOOH * (4) HCOOH * → HCOOH ( aq ) + * (5)where * denotes the catalytic surface or adsorption site, initially the CO2 molecules are dissolved in the solution and contact the electrode surface to form adsorbed CO2*. Afterwards, single electron is transferred to CO2* that forms the CO2* − radical anion. According to HCO3 − ↔ H+ + CO32−, electron transfer and proton coupling form OCHO* − intermediates. Ultimately, OCHO* − forms formic acid solution by PCET. Since the slow kinetics of the electrocatalytic CO2RR process, HER side reactions inevitably generate H2, and some reduction reactions are accompanied by CO generation, which negatively affects the highly selective production of formate from Bi-based materials. For the purpose of obtaining more formate, the production of H2 and CO is reduced as much as possible. The catalytic mechanism may be diametrically different in the same Bi-based alloy, depending on the content of two metal elements. Therefore, the reaction mechanism is manipulated via controlling different proportions of the two metals in bimetallic Bi-based electrocatalysts. For instance, Zhang et al.47 have developed CuO/Bi(OH)3 decorated on carbon nanotubes for CO2 electroreduction. CuBi#8 and CuBi#4 are bimetallic nanoparticles obtained via a two-step hydrolysis method and adjusted the Cu/Bi ratio. CuBi#8 and CuBi#4 exhibit CO and formate FE of 96% and 60% at −0.99 V versus reversible hydrogen electrode (RHE) (VRHE), respectively. It is found that with Bi content increasing, HER is well suppressed, and the products are mainly CO. By further increasing Bi content, FEHCOOH rapidly increases accompanied by the rapid decrease of FECO. FEHCOOH reaches the maximum of 96% at 12.5 mA cm−2. The conversion of intermediates from *COOH to OCHO* via increasing Bi content further illustrates the high selectivity of OCHO* to formate. Adjusting the optimal Cu/Bi ratio suppresses the production of CO and H2, leading to efficient production of formate. In addition, defects such as oxygen vacancies or doped atoms significantly improve the catalytic performance.12 Li et al.48 have prepared Sn atom-doped Bi2O3 nanosheet (NS) electrocatalysts by constant electrolysis. Three products can be detected during the electrolysis, including H2, CO, and HCOOH. The Sn-doped Bi2O3 NSs current density is significantly increased compared to the undoped Bi2O3 NSs. The 2.5% Sn-doped Bi2O3 NSs exhibit high selectivity for formate, obtaining a supreme FE of 93.4% at the potential of −0.97 V. The HER inhibition effect is significantly enhanced compared to the undoped Bi2O3 NSs. Moreover, the catalytic capacity is optimized by coping with significant HER and expanding its specific surface area. For the first time, metallic aerogel is a three-dimensional (3D) material that has attracted enormous attention due to its abundant specific surface area, contributing to the generation of more catalytic centers.49 In addition, adjusting the partial pH can also improve the selectivity of CO2RR, and proper control of pH into acidity facilitates the formation of formate.50 Advanced Bi-Based Electrocatalysts for CO2 Reduction In recent decades, various Bi-based CO2 reduction electrocatalysts have been exhaustively studied, mainly with formate as the end product. Especially, the preparation of bimetallic catalysts via different synthetic methods is the focus of most current studies. Bimetallic Bi-based catalysts can mainly be classified into three types: (1) alloyed Bi, (2) doped Bi, and (3) supported Bi. Detailed CO2RR performances of bimetallic Bi-based electrocatalysts are summarized in Table 2. Table 2 | Performance of Bimetallic Bi-Based Catalysts in Electrocatalytic CO2RR Catalyst Electrolyte Major Products FE (%) Potential at FEMax (V) Current Density (mA cm−2) Stability (h) References Bi5Sn60 0.1 M KHCO3 Formate 94.8 −1.0 (vs RHE) 34 20 52 BixSny/Cu 0.1 M KHCO3 Formate 90.4 −0.84 (vs RHE) 30 12 53 Bi-Sn aerogel 0.1 M KHCO3 Formate 93.9 −1.0 (vs RHE) 9.3 10 57 Cu-Bi 0.1 M KHCO3 Formate 90 −0.8 (vs RHE) >2 — 60 CuBi-100 0.5 M KHCO3 Formate 94.7 −1.0 (vs RHE) 12.8 8 61 CuBi 0.5 M KHCO3 Formate 94.4 −0.97 (vs RHE) 38.5 — 62 CuBi 0.5 M KHCO3 Formate 98.3 −1.07 (vs RHE) 56.6 — 62 Bi/Cu 0.5 M KHCO3 Formate 95 −0.9 (vs RHE) 59.7 12 64 CuBi75 0.5 M KHCO3 Formate 100 −0.77 (vs RHE) 33.65 24 66 Cu1-Bi/Bi2O3@C 0.5 M KHCO3 Formate 93.4 −0.94 (vs RHE) 10.1 10 67 Pd3Bi-IMA 0.1 M KHCO3 Formate >90 −0.35 (vs RHE) 3 8 68 a-NPSB 0.1 M KHCO3 Formate 88.4 −1.15 (vs RHE) 21.2 18 70 Bi–Pt complex 0.1 M TBAPF6/THF CO 82 −1.25 (vs NHE) 0.125 — 71 Mo-Bi BMC/CP 0.5 M [Bmim]BF4 CH3OH 71.2 −0.7 (vs SHE) 12.1 — 72 Sn-doped Bi2O3 NSs 0.5 M KHCO3 Formate 93.4 −0.97 (vs RHE) 24.3 8 48 Bi/Bi(Sn)Ox NWs 1 M KOH Formate ∼100 −0.7 (vs RHE) 301.4 20 77 Cu-Bi2Se3 0.5 M NaHCO3 Formate 65.31 −1.3 (vs RHE) 24.1 24 78 Ce–[email protected]x/C 0.5 M KHCO3 Formate 96 −1.7 (vs SHE) 15.2 10 79 BiIn5[email protected] 0.5 M KHCO3 Formate 97.5 −0.86 (vs RHE) 13.5 15 81 Bi-Sn/CF 0.5 M KHCO3 Formate 96 −1.1 (vs RHE) 45 100 82 Sn0.80Bi0.20@Bi-SnOx 0.5 M KHCO3 Formate 95.8 −0.88 (vs RHE) 74.6 — 83 Bi-SnO/Cu 0.1 M KHCO3 Formate 93 −1.7 (vs Ag/AgCl) — 30 84 [email protected] 0.5 M NaHCO3 Formate 95 (vs RHE) 15 12 45 NSs 0.5 M KHCO3 Formate −0.86 (vs RHE) 8 90 0.5 M KHCO3 Formate −0.8 (vs RHE) 0.5 M KHCO3 Formate −0.8 (vs RHE) 10 [email protected] 0.5 M KHCO3 Formate (vs RHE) 10 M Formate (vs RHE) 34 Bi The is one of the methods to enhance the electrocatalytic performance of Bi-based effects facilitate the catalytic reaction by a between two different metal elements. P-block catalysts have CO2 conversion that is highly selective for Among them, Bi-Sn bimetallic is the most is a and method for the preparation of The method a of two metallic elements. Bimetallic obtained via are or and possess such as high density and can improve the catalytic activity of the catalyst Li et have two Bi and on the an In this different electrode The at different of This structure is to the surface and more catalytic When the of metal Bi and the of metal Sn 60 the catalytic performance the as the of −1.0 with mA partial current density, the FE of formate it excellent formate yield, which superior to most electrocatalysts. The of bimetallic is to the OCHO* intermediate and suppress the HER process. Li et have also electrocatalysts on and discovered that the FE of formate enhanced by the Bi content in the BixSny/Cu electrode. is an emerging in electrocatalytic due to their structure and the of the catalyst, contributing to the generation of more catalytic Bimetallic prepared by the method it to compared with methods such as or solution et have prepared Bi-Sn bimetallic under with and abundant Bi and Sn the of via controlling the ratio. with with a electron as shown in Figure abundant of that favorable for and abundant active sites during electrocatalysis. The of the Bi-Sn aerogel well with of Sn and Bi suggesting that the obtained aerogel is a Bi-Sn The that the are and corresponding to the and of Bi and This that the Sn and Bi are and more reaction sites are during the catalytic process. The the of Sn and Bi in the The electrochemical performance displayed compared with Sn and Bi catalysts, Bi-Sn aerogel excellent performance for formate with FE as high as Density that electronic between Bi and Sn the energy barrier for formate, the electrocatalytic performance In can indicate the reaction pathway of Bi-Sn aerogel bimetallic catalyst in CO2RR. shown in Figure the at at V and more as the potential increased from to V. This is to the that in the formate intermediate HCOO* is in suggesting that the synergistic effects between Bi-Sn bimetals can the generation of Figure 2 | (a) of the synthesis of Bi-Sn (b) of (c) of (d) and the corresponding of the catalytic mechanism of the of Bi-Sn with various with from Download figure Download PowerPoint is a and catalyst in the field of electrocatalysis. The product selectivity of catalysts is C1 products such as formate and CH4 and value-added fuels such as The of the Bi and to form a Cu-Bi usually formate conversion and the HER The reaction intermediates with of the between bimetallic Cu-Bi facilitate the catalytic reaction. et have synthesized bimetallic Cu-Bi electrocatalysts with Owing to the difference between Bi and the of bimetallic defect sites with high density, leading to the formation of more catalytic Cu-Bi exhibit lower current for HER and CO evolution thus the higher selectivity of Cu-Bi for formate. At −0.8 the FE of the formate product In to materials obtained by have numerous and catalytic activity will be Through the of bimetallic catalysts, the of reaction sites of electrocatalysts are increased as much as and the electrochemical of product selectivity is For instance, et have synthesized bimetallic Cu-Bi electrocatalysts by at room temperature In the by the of CuBi-100 the electrochemical performance At the potential from −0.8 V to CuBi-100 excellent selectivity for formate and FE of more than The supreme at the potential of −1.0 electron that CuBi-100 on carbon and a The of CuBi-100 has

Lean Cu-immobilized Pt and Pd films/–H+ Conducting Membrane Assemblies: Relative Electrocatalytic Nitrate Reduction Activities

Ammonia is a valuable feedstock for most chemicals, pharmaceuticals, and fertilizer products. It is a promising carbon-free energy source. Under severe experimental circumstances (high temperature and high pressure), ammonia is manufactured industrially using the standard Haber-Bosch process. This process uses a lot of energy and emits a huge amount of CO2 into the environment. One method that is seen to be promising and could eventually replace the Haber-Bosch process is the electrocatalytic production of ammonia. However, in ambient conditions, the cleavage of the nitrogen molecule is exceedingly difficult. As a result, the yield of ammonia remains modest and the study's scope is still restricted to the lab. When the catalytic performance is significantly increased, nitrate and nitrite contaminations in water systems can be effectively removed and simultaneously transformed into energy sources if nitrites or nitrates are employed as nitrogen sources instead of nitrogen gas. This may become a new substitute for the synthesis of ammonia, but nitrate and nitrite reduction are not getting enough attention. In this review, we discuss the performance of the electrocatalytic nitrate reduction reaction, which includes cycling stability, reactivity, selectivity, and faradaic efficiency. Following this summary, we look into the crucial elements, the rate-determining step, and the reaction mechanisms that govern the performance of the nitrate reduction reaction. In order to support the practical use of the electrocatalytic nitrate reduction reaction, we finally provided a summary of the challenges and future directions guiding the design of efficient catalyst and reaction systems.

Electrocatalytic nitrate reduction reaction (NO3RR) is a process that requires the participation of eight electrons and nine protons. The regulation of active hydrogen (H*) supply and a deep understanding of related processes are necessary for improving the ammonia yield rate and Faradaic efficiency (FE). Herein, we synthesized a series of atomically precise copper-halide clusters Cu2X2(BINAP)2 (X=Cl, Br, I), among which the Cu2Cl2(BINAP)2 cluster shows the optimal ammonia FE of 94.0 % and an ammonia yield rate of 373 μmol h-1 cm-2. In situ experiments and theoretical calculations reveal that halogen atoms, especially Cl in Cu2Cl2(BIANP)2, can significantly affect the distance of alkali metal-ionized water on the catalyst surface, which can promote the water dissociation to enhance the localized H* enrichment for the continues hydrogenation of nitrate to ammonia. This work explains the role of H* in the hydrogenation process of NO3RR and the importance of localized H* enrichment strategy for improving the FEs.

Electrocatalytic nitrate reduction reaction (NitRR) offers a promising route for hydroxylamine (NH 2 OH) synthesis under ambient conditions. However, the inherent activity‐selectivity trade‐off limits the overall performance. To overcome this challenge, a bimetallic NiMg‐MOF‐74 electrocatalyst is designed for NH 2 OH production via NitRR with high performance. Experimental and theoretical investigations have unraveled the synergy of dual active sites in promoting NO 3 − to NH 2 OH conversion. The electron‐sufficient Ni (2‐δ)+ site weakens the binding of *NH 2 OH intermediate and minimizes its excessive reduction to undesired NH 3 byproduct. Moreover, the electron‐deficient Mg (2+δ)+ site with higher charge density than Ni (2‐δ)+ facilitates hydration and hydrogenation steps of N─O species over proximal Ni (2‐δ)+ site, thus the overall activity for NH 2 OH formation is increased. The concurrently enhanced selectivity and activity result in a high Faradaic efficiency of 92.3% and an unprecedented NH 2 OH yield rate of 55.1 mg h −1 cm −2 in a flow reactor, which can be directly utilized for the preparation of value‐added oxime compounds. Further, the coupling of NitRR with photovoltaics in one system enables bias‐free NH 2 OH production with a high solar‐to‐NH 2 OH efficiency of 17.74%. Our work offers advanced electrocatalysts and new insights for sustainable NH 2 OH electrosynthesis.

Electrocatalytic nitrate reduction reaction (NitRR) offers a promising route for hydroxylamine (NH2OH) synthesis under ambient conditions. However, the inherent activity-selectivity trade-off limits the overall performance. To overcome this challenge, a bimetallic NiMg-MOF-74 electrocatalyst is designed for NH2OH production via NitRR with high performance. Experimental and theoretical investigations have unraveled the synergy of dual active sites in promoting NO3 - to NH2OH conversion. The electron-sufficient Ni(2-δ)+ site weakens the binding of *NH2OH intermediate and minimizes its excessive reduction to undesired NH3 byproduct.Moreover, the electron-deficient Mg(2+δ)+ site with higher charge density than Ni(2-δ)+ facilitates hydration and hydrogenation steps of N─O species over proximal Ni(2-δ)+ site, thus the overall activity for NH2OH formation is increased. The concurrently enhanced selectivity and activity result in a high Faradaic efficiency of 92.3% and an unprecedented NH2OH yield rate of 55.1mg h-1 cm-2 in a flow reactor, which can be directly utilized for the preparation of value-added oxime compounds. Further, the coupling of NitRR with photovoltaics in one system enables bias-free NH2OH production with a high solar-to-NH2OH efficiency of 17.74%. Our work offers advanced electrocatalysts and new insights for sustainable NH2OH electrosynthesis.

To advance the electrocatalytic nitrate reduction reaction (NIRR) to ammonia, it is essential to rationally regulate the kinetics of active hydrogen (H*). Nevertheless, an in-depth understanding of H* generation, transfer, and utilization remains elusive, which impedes exploring strategies for optimizing H* dynamics. In this study, a copper nanocrystalline is developed with a multiply nano-twinned structure (MNTs-Cu) using a "dual nonequilibrium" strategy to optimize H* dynamics and enhance NIRR performance. Experimental and theoretical studies show that MNTs-Cu functions as a "dual-site cooperative" catalyst, addressing the H* supply-consumption balance to boost ammonia electrosynthesis. Specifically, the Cu sites are responsible for the activation of nitrate, while the nano-twinned structure serves as an "active hydrogen hub" to facilitate the generation, transfer, and utilization of H*. The MNTs-Cu catalyst achieves a high NH3 yield of 112.03mg h-1 cm-2 at -0.7V vs RHE, and notably, it can continuously maintain a high FENH3 of >99% within the high potential range from -0.7 to -0.9V vs RHE. This work provides a novel pathway for optimizing H* behavior through structural engineering, offering insights for advancing NIRR and other hydrogenation reactions.

Electrocatalytic nitrate reduction reaction (NitRR) in neutral condition offers a promising strategy for green ammonia synthesis and wastewater treatment, the rational design of electrocatalysts is the cornerstone. Inspired by modern factory design where both machines and logistics matter for manufacturing, it is reported that cobalt phosphide (CoP) nanoparticles embedded in zinc-based zeolite imidazole frameworks (Zn-ZIF) function as a nanofactory with high performance. By selective phosphorization of ZnCo bimetallic zeolite imidazole framework (ZnCo-ZIF), the generated CoP nanoparticles act as "machines" (active sites) for molecular manufacturing (NO3 - to NH4 + conversion). The purposely retained framework (Zn-ZIFs) with positive charge promotes logistics automation, i.e., the automatic delivery of NO3 - reactants and timely discharge of NH4 + products in-and-out the nanofactory due to electrostatic interaction. Moreover, the interaction between Zn-ZIF and CoP modulates the Co sites into electron insufficient state with upshifted d-band center, facilitating the reduction/hydrogenation of NO3 - to ammonia and restricting the competitive hydrogen evolution. Consequently, the assembled CoP/Zn-ZIF nanofactory exhibits superior NitRR performances with a high Faraday efficiency of ≈97% and a high ammonia yield of 0.89mmol cm-1 h-1 in neutral condition, among the best of reported electrocatalysts. The work provides new insights into the design principles of efficient NitRR electrocatalysts.

Nitrate (NO 3 − ) pollution from industrial and agricultural sources poses significant threats to water quality and human health. The electrocatalytic nitrate reduction reaction (NIRR), which converts NO 3 − into high‐value ammonia (NH 3 ), offers an efficient approach for treating NO 3 − ‐containing wastewater while addressing energy‐related challenges. Generally, NIRR is a multi‐step reaction, and its core steps‐NO 3 − activation and hydrogenation‐correspond to the NO 3 − adsorption sites and hydrogenation sites on the catalyst, respectively. The tandem catalytic sites accelerate reaction kinetics by spatially separating NO 3 − adsorption sites from hydrogenation sites and leveraging multifunctional catalytic sites for tandem catalysis. Consequently, tandem catalytic sites have recently emerged as an effective strategy for electrocatalytic NIRR. Nevertheless, a comprehensive understanding of the underlying mechanism remains limited. This review begins by outlining the advantages of tandem catalytic sites and recent advances in representative catalysts. It then highlights in situ characterization techniques used to elucidate reaction intermediates and tandem catalytic sites. Finally, applications and economic analysis in wastewater treatment, sustainable NH 3 synthesis, and energy conversion are systematically discussed. The review concludes with a perspective on complex NO 3 − wastewater treatment, NH 3 purification, environmental catalytic flow battery, and economic feasibility analysis, emphasizing their roles in sustainable energy solutions.