Activity For Electrochemical Reduction Of CO2 Research Articles

Plastron effect enhanced electrochemical CO2 reduction activity over hydrophobic three-dimensional nanoporous silver.

The electrochemical reduction of CO2 on catalyst surfaces is hindered by the inefficient mass transfer of CO2 in aqueous solutions. In this study, we employed an electrochemical reduction approach to fabricate a hydrophobic three-dimensional nanoporous silver catalyst with a plastron effect, aiming to enhance the CO2 diffusion. The resulting catalyst exhibited an exceptional performance with the FECO peaking at 95% at -0.65 V (vs. RHE) and demonstrated remarkable stability during continuous electrolysis for 48 hours. Control experiments, together with Tafel analysis, EIS measurements, and contact angle results, confirmed that the notable enhancement of performance was attributed to the hydrophobic porous structure that facilitated efficient storage and rapid mass transfer of low-solubility CO2 gas reactants.

The influence of exogenous amines on the electrochemical CO2 reduction activity of a cobalt-pyridyldiimine catalyst.

Studying the interactions between CO2 sorbents and electrocatalysts for the electrochemical CO2 reduction reaction (e-CO2RR) can offer viable strategies to advance the development of the Reactive Capture of CO2 (RCC). In this report we studied the effect of amines on the performance of the [Co(PDI-Py)] catalyst for the e-CO2RR. The presence of amines shifts the onset potential for the e-CO2RR more positive and increases the catalytic activity while maintaining the high Faradaic efficiency (≥90%) for CO production.

Synergistic effects of interface and valence state on boosting electrochemical CO2 reduction activity of La2CuO4

The electrochemical CO2 reduction reaction (CER) to methane (CH4) has received great attention. Here, we proposed an efficient method to facilitate the conversion of CO2-to-CH4 by creating a two-phase interface over urea-modified La2CuO4 catalyst. The most optimized one exhibits the highest selectivity (22%) for CH4 and the best activity (14 mA cm−2) and stability (5 h) at the potential of −1 V vs. reversible hydrogen electrode. The enhanced CER performance can be attributed to the establishment of interfacial effect within the two-phase, which facilitates the reduction of Cu2+ and promotes the active sites concentration.

Anion-Driven Nanostructuring of Copper Electrodeposits for Tuning the Selectivity of Electrocatalytic CO2 Reduction Reaction

Electrochemical CO2 reduction (ECR) to value-added products is one of the potential ways to utilise CO2 as a feedstock, thereby decreasing its level in the atmosphere as it has harmful repercussions on planet earth. Copper (Cu)-nanostructures have demonstrated a great potential to convert CO2 into valuable higher-end hydrocarbons electrochemically, but with poor selectivity1. Therefore, novel strategies to tune Cu-based electrocatalysts' activity and selectivity toward multi-carbon products, particularly at low overpotential, are highly desirable. At the same time, keeping in mind the growing concerns regarding the environmental impact of the synthetic procedures and atom-economy among chemists, the synthesis methods employing reagents with multiple characteristics are equally essential to ensure minimal use of undesirable and excess reagents. In the present work, we report an atom-economic strategy to tune the physicochemical properties and the electrocatalytic activity of Cu-nanostructures towards ECR. The Cu-nanostructures namely CA, CN, CS and CC were synthesized via pulse electrodeposition from an electrolyte bath containing Cu-precursor salts with varying anions viz. acetate, nitrate, sulphate, and chloride respectively and are investigated for the effect of anions on the physicochemical properties and ECR performance. In the case of Cu electrodeposition process, when the pH is low as in the case of sulphate and acetate ions, electrodeposition is accompanied by hydrogen evolution reaction2 which results in the formation of nondendritic structures as in the case of CS and CA. But the presence of nitrate ions in the electrolyte bath causes nitrate reduction reaction to take place as a side reaction as well, as Cu is a well-known catalyst for nitrate reduction. Thus, this simultaneous redox reaction at the surface of the Cu electrodeposit causes an additional dissolution of the Cu nuclei3. This results in a smoother morphology as seen in CN as the dendrite formation is overridden. The very distinct cubic morphology of CC is due to Chloride ions in the bath.The presence of chloride ions during the electrodeposition of CC samples results in the formation of nanocubes by reducing Cu2+ via the formation of CuCl which is known to exist in cubic form when it precipitates4. The intermediate CuCl then quickly forms Cu2O through an equilibrium reaction in the presence of H2O when the concentration of chloride ions is not so high. The Cu-nanostructures electrodeposited from Cu-chloride demonstrated the best ECR performance with the highest total faradaic efficiency for carbon products and good selectivity for ethylene formation (30% at -0.93V vs RHE). The presence of chloride ions in the electrolyte bath strongly affects the active sites of the Cu deposits as the cubic morphology of CC catalyst exposes large number of Cu (100) faces5. Cu (100) are highly selective towards ethylene formation with very low overpotential due to the lower barrier for Cu-CO* which leads to greater CO coverage favouring CO*-CO* coupling at low bias59. In addition to that the electrochemically active surface area, the higher Cu+ content can be rationalized as the reasons for relatively higher ECR activity of CC.

Surface engineering of ZnO electrocatalyst by N doping towards electrochemical CO2 reduction

The discovery of efficient, selective, and stable electrocatalysts can be a key point to produce the large-scale chemical fuels via electrochemical CO2 reduction (ECR). In this study, an earth-abundant and nontoxic ZnO-based electrocatalyst was developed for use in gas-diffusion electrodes (GDE), and the effect of nitrogen (N) doping on the ECR activity of ZnO electrocatalysts was investigated. Initially, a ZnO nanosheet was prepared via the hydrothermal method, and nitridation was performed at different times to control the N-doping content. With an increase in the N-doping content, the morphological properties of the nanosheet changed significantly, namely, the 2D nanosheets transformed into irregularly shaped nanoparticles. Furthermore, the ECR performance of ZnO electrocatalysts with different N-doping content was assessed in 1.0 M KHCO3 electrolyte using a gas-diffusion electrode-based ECR cell. While the ECR activity increased after a small amount of N doping, it decreased for higher N doping content. Among them, the N:ZnO-1 h electrocatalysts showed the best CO selectivity, with a faradaic efficiency (FECO) of 92.7% at −0.73 V vs. reversible hydrogen electrode (RHE), which was greater than that of an undoped ZnO electrocatalyst (FECO of 63.4% at −0.78 VRHE). Also, the N:ZnO-1 h electrocatalyst exhibited outstanding durability for 16 h, with a partial current density of −92.1 mA cm−2. This improvement of N:ZnO-1 h electrocatalyst can be explained by density functional theory calculations, demonstrating that this improvement of N:ZnO-1 h electrocatalyst comes from (i) the optimized active sites lowering the free energy barrier for the rate-determining step (RDS), and (ii) the modification of electronic structure enhancing the electron transfer rate by N doping.

Modulating the degree of O vacancy defects to achieve selective control of electrochemical CO2 reduction products

Conversion of CO2 into high-value products using electrochemical CO2 reduction (ECR) technology is an effective way to alleviate global warming and reach carbon neutrality. The oxygen vacancies in heterogenous catalysis are generally considered as a powerful method to enhance the performance of ECR by promoting CO2 adsorption and activation. However, the extent of defects in oxygen vacancies-activity relation has rarely been studied. Herein, we prepared Cu–Cd bimetallic catalysts with adjustable oxygen defect degree by controlling the amount of cadmium addition. Fourier transform infrared spectroscopy characterization results reveal that the formation of oxygen vacancies is attributed to the asymmetric stretching of Cu–O by the addition of cadmium. Electrochemical results show that the oxygen defect degree can modulate the selectivity of ECR products. A low degree of oxygen defects (CuO) is generally associated with lower product Faraday efficiency (FEC2/FEC1 ≈ 114%), but overabundant oxygen vacancies (CuO2.625–CdO0.375) are not entirely favorable to improving ECR activity (FEC2/FEC1 ≈ 125%) and single selectivity, while an appropriate degree of oxygen vacancies (CuO2.75–CdO0.25) can facilitate the ECR process toward single product selective production (FEC2/FEC1 ≈ 296%). The theoretical calculation showed that the O vacancy formed on CuO and the interface between CdO and CuO were conducive to enhancing the formation of *COOH intermediate and promoting the generation of ethylene products. This study provides a new approach and insight into the selective production of single products for future industrial applications of ECR.

Regulating the coordination environment of single-atom catalysts for electrocatalytic CO2 reduction

Electrochemical CO2 reduction (ECR) through single-atom catalysts (SACs) consisting of transition metals (TMs) anchored on nitrogenated carbon (TM–N–C) has shown promise for carbon neutralization. However, high overpotentials and low selectivity are still issues. Regulating the coordination environment of anchored TM atom is important to address these problems. In this study, we evaluated nonmetal atom (NM = B, O, F, Si, P, S, Cl, As and Se) modified TM (TM = Fe, Co, Ni, Cu and Zn)@N4–C catalysts for their ECR to CO performance using density functional theory (DFT) calculations. NM dopants can induce active center distortion and tune electron structure, promoting intermediate formation. Doping heteroatoms can improve ECR to CO activity on Ni and Cu@N4 but worsen it on Co@N4 catalysts. Fe@N4–F1(I), Ni@N3–B1, Cu@N4–O1(III), and Zn@N4–Cl1(II) have excellent activity for ECR to CO, with overpotentials of 0.75, 0.49, 0.43, and 0.15 V, respectively, and improved selectivity. The catalytic performance is related to the intermediate binding strength, as evidenced by d band center, charge density difference, crystal orbital Hamilton population (COHP), and integrated COHP (ICOHP). It is expected that our work can be used as the design principle to guide the synthesis of the high-performance heteroatoms modified SACs for ECR to CO.

Quantitative Structure–Electrochemistry Relationship (QSER) Studies on Metal–Amino–Porphyrins for the Rational Design of CO2 Reduction Catalysts

The quantitative structure-electrochemistry relationship (QSER) method was applied to a series of transition-metal-coordinated porphyrins to relate their structural properties to their electrochemical CO2 reduction activity. Since the reactions mainly occur within the core of the metalloporphyrin catalysts, the cluster model was used to calculate their structural and electronic properties using density functional theory with the M06L exchange-correlation functional. Three dependent variables were employed in this work: the Gibbs free energies of H*, C*OOH, and O*CHO. QSER, with the genetic algorithm combined with multiple linear regression (GA-MLR), was used to manipulate the mathematical models of all three Gibbs free energies. The obtained statistical values resulted in a good predictive ability (R2 value) greater than 0.945. Based on our QSER models, both the electronic properties (charges of the metal and porphyrin) and the structural properties (bond lengths between the metal center and the nitrogen atoms of the porphyrin) play a significant role in the three Gibbs free energies. This finding was further applied to estimate the CO2 reduction activities of the metal-monoamino-porphyrins, which will prove beneficial in further experimental developments.

Hollow carbon spheres with isolated Ni atoms on both external and internal surfaces for efficient CO2 electroreduction

Electrochemical CO2 reduction is a promising method to mitigate excessive CO2 emission and realize CO2 valorization. However, the lacking of efficient catalysts hinders the practical applications of this important process. Here, we report a new type of hollow carbon spheres containing isolated Ni atoms on both external and internal surfaces by an integrated bottom-up and top-down strategy. For such unique structure, the material exhibits good activity for electrochemical CO2 reduction with much higher current density and Faradaic efficiency for CO production than the materials with common structures (i.e., the solid spheres with Ni sites only on external surface). The enhanced activity of the material is attributed to the favored mass transport and charge transfer guaranteed by the presence of hollow structure as well as active Ni sites on both external and internal surfaces. Furthermore, we demonstrate that a secondary pyrolysis of the material can improve its activity and stability for CO2 reduction. Such treatment can increase the degree of graphitization and reaction kinetics of the material during electrocatalysis. The final material exhibits a large current density (150 mA cm−2) and a high Faradaic efficiency for CO production (94%) in a flow cell, showing good potential for practical applications. This work extends the concept of structural regulation of catalysts and provides the guidance for the design of high-performance catalysts for electrochemical CO2 reduction.

One-step synthesis of N-doped carbon nanotubes-encapsulated Ni nanoparticles for efficient electrochemical CO2 reduction to CO

Electrochemical CO2 reduction (ECR) into high value-added chemicals has attracted continuous attentions in the field of environment and energy storage. Synthesizing stable and efficient electrocatalyst through facile method continues to be a major challenge for ECR. Herein, we produced a carbon nanotubes-encapsulated Ni nanoparticles catalyst through a one-step chemical vapor deposition approach for ECR. Compared with Ni@C and N-C catalysts, the Ni@N-C shows the optimal CO Faraday efficiency (FECO%) of 90% at −0.77 V vs. RHE in the H-type cell. Notably, it shows a high FECO% over 93% within the scope of −0.37 to −0.77 V vs. RHE in the flow cell. The excellent catalytic performance of Ni@N-C demonstrates that N-doped carbon nanotubes coated on Ni nanoparticles are considered as the key step to promoting ECR activity. This work may provide some ideas on the seeking of electrocatalyst in a simple process for efficient ECR.

Sustainable Conversion of Harmful Algae Biomass into a CO2 Reduction Electrocatalyst for Two-Fold Carbon Utilization.

Harmful algae blooms (HABs) frequently occur all over the world and cause great harm to the environment, human health, and aquatic ecosystems. However, owing to their great growth rate and large nutrient intake capacity, algae can enrich a large amount of carbon (CO2) and nutritional elements (N and P) in their biomass. Thus, this could be applied as a robust approach to battle global warming and water eutrophication if the harmful algae biomass was effectively harvested and utilized. Herein, we propose a thermochemical approach to convert algae biomass into a nitrogen-doped electrocatalyst for CO2 reduction. The as-synthesized carbon catalyst exhibits a favorable electrochemical CO2 reduction activity. The key drivers of the environmental impacts in the thermochemical conversion approach with a comparison with the commonly used landfilling approach are identified with life cycle assessment. The former presents much lower environmental burdens in terms of impacts such as freshwater/terrestrial ecotoxicity and human toxicity than the latter. Moreover, if the thermochemical conversion process was successfully applied for biomass conversion worldwide, 2.17 × 108 tons of CO2-eq, 8.42 × 106 tons of N, and 1.21 × 106 tons of P could be removed from the global carbon and other element cycles. Meanwhile, the thermochemical approach is also similar to landfilling in terms of costs. The results from this work provide a brand-new perspective for achieving twofold CO2 utilization and efficiently battling harmful algae blooms.

Molecularly dispersed nickel complexes on N-doped graphene for electrochemical CO2 reduction.

In this work, new hybrid catalysts based on molecularly dispersed nickel complexes on N-doped graphene were developed for electrochemical CO2 reduction (ECR). Nickel(II) complexes (1-Ni, 2-Ni), and a new crystal structure ([2-Ni]Me), featuring N4-Schiff base macrocycles, were synthesized and investigated for their potential in ECR. Cyclic voltammetry (CV) in NBu4PF6/CH3CN solution demonstrated that the nickel complexes bearing N-H groups (1-Ni and 2-Ni) showed a substantial current enhancement in the presence of CO2, while the absence of N-H groups ([2-Ni]Me) resulted in an almost unchanged voltammogram. This indicated the necessity of the N-H functionality towards ECR in aprotic media. All three nickel complexes were successfully immobilized on nitrogen-doped graphene (NG) via non-covalent interactions. All three Ni@NG catalysts exhibited satisfactory CO2-to-CO reduction in aqueous NaHCO3 solution with the faradaic efficiency (FE) of 60-80% at the overpotential of 0.56 V vs. RHE. The ECR activity of [2-Ni]Me@NG also suggested that the N-H moiety from the ligand is less important in the heterogeneous aqueous system owing to viable hydrogen-bond formation and proton donors from water and bicarbonate ions. This finding could pave the way for understanding the effects of modifying the ligand framework at the N-H position toward fine tuning the reactivity of hybrid catalysts through molecular-level modulation.

Non-negligible Axial Ligand Effect on Electrocatalytic CO2 Reduction with Iron Porphyrin Complexes

Iron(III) porphyrin complexes have been demonstrated as one of the efficient molecular catalysts for the electrochemical reduction of CO2. However, the role of axial ligands coordinated with a metal center in the complex on the electrochemical CO2 reduction activity has not been fully explored yet. Herein, iron(III) tetraphenylporphyrin thiocyanate (FeTPP-SCN) is synthesized from a commercially available catalyst of FeTPP-Cl by a counteranion exchanging reaction. Cyclic voltammetry measurements showed that the catalytic activity of FeTPP-SCN is noticeably suppressed in the DMF solutions. The structural dynamics of the axial ligand in FeTPP-SCN are further examined by the FTIR and ultrafast IR spectroscopies, where the SCN ligand is employed as the local vibrational probe. Vibrational relaxation measurements showed that the reorientational dynamics of SCN ligands was strongly restricted in DMF solution, suggesting that the subtle electrostatic interaction between the ligands and metal center in the complex can have a non-negligible effect on its catalytic activity.

(Digital Presentation) Multi-Regression Analysis for Metal Sulfide-Based CO2 Reduction

The electrochemical reduction of carbon dioxide (CO2) is a promising approach towards the utilization of CO2 as a carbon feedstock, which is desirable for mitigating global warming and closing the carbon cycle. Despite the desire to develop metal-based electrocatalysts for CO2 reduction, CO2 reduction activity on metal electrodes is limited largely by the scaling relationship of intermediate binding energies. To fabricate efficient electrocatalysts, the adsorption energy of the target intermediate species in each reaction process should be optimized; however, such optimization becomes difficult when intermediate species have similar adsorption properties, resulting in an unavoidable overpotential. Multi-component compounds, such as metal sulfides, have the potential to break this scaling relationship because they possess multiple adsorption sites. Further, the investigation of electrochemical CO2 reduction activity on metal sulfides could provide insights into the origins of life, as metal sulfides have been hypothesized as proto-catalysts of extant CO2 reduction enzymes.Catalyst informatics is an effective approach for predicting the relationship between the physicochemical parameters and catalytic activity of materials. Here, we performed multi-regression analysis of electrochemical CO2 reduction catalyzed by metal sulfides to gain insight into the activity-determining properties of these electrocatalytic materials using following 14 physicochemical parameters as explanatory variables: metal-sulfur bonding length, nearest metal-metal distance, absolute negativity, standard redox potential of metals, band gap, first ionic energy, maximum radius of s-orbital, d-electron number, molar capacity of heat, formation enthalpy, metal-sulfur-metal angle, maximum radius of d-orbital, position of conduction band edge, and electron affinity. To avoid the effect of collinearity among explanatory variables, we applied partial least squares (PLS) analysis for the multi-regression process. PLS extracts the main components and uses the principal component as the explanatory variable. As the correlation between the main components is set to zero, collinearity can be avoided. Further, the number of main components can be controlled, allowing for regression to be performed with fewer samples. In addition, we applied the least absolute shrinkage and selection operator (LASSO) regression analysis.To obtain objective variable for regression analysis, the synthesized metal sulfides were subjected to electrochemical CO2 reduction. After applying an electrochemical potential of -1.2 V vs. SHE for 1 h, CO and HCOO- were obtained as CO2 reduction products for several of the metal sulfide samples. Among the 14 samples examined (Ag2S, CdS, CoS2, CuS, Fe3S4, In2S3, MnS, MoS2, NiS2, Ni3S2, SnS2, TiS2, WS2, and ZnS), CdS and Ag2S exhibited the highest CO production activity, with Faradaic efficiencies of 37.2% and 29.5%, respectively, in a 0.1 M KHCO3 aqueous solution, whereas CuS maximized formate (HCOO-) production, with a FE of 4.5%. PLS and Lasso analyses revealed that CO production was largely affected by the structural parameter of metal-sulfur bond length; however, HCOO- generation was influenced by the electronic parameters of the metal centers, particularly absolute electronegativity. These findings are distinct from those of metal electrodes, for which the generation of CO and HCOO- is predominantly influenced by electronic parameters, demonstrating that CO2 reduction on metal sulfides proceeds by a different mechanism compared to that of the corresponding metal electrodes. As demonstrated in the present study, changing the structural parameters, such as metal-sulfur bond length, alters the adsorption characteristics of the intermediate species to optimize the CO/HCOO- production activity. We anticipate that the key parameters identified through multi-regression analysis of metal sulfides will prompt further study of the factors influencing the specificity of these unique electrochemical CO2 reduction catalysts.

Tertiary amine-functionalized Co(II) porphyrin to enhance the electrochemical CO2 reduction activity

Tertiary amine-functionalized Co(II) porphyrin to enhance the electrochemical CO2 reduction activity

Molecular engineering to introduce carbonyl between nickel salophen active sites to enhance electrochemical CO2 reduction to methanol

The electrochemical reduction of CO2 to methanol is a potentially cost-effective strategy to reduce the concentration of this greenhouse gas while at the same time producing a value-added chemical. Herein, we detail a highly efficient 2D nickel organic framework containing a large density of highly dispersed salophen NiN2O2 active sites toward electrochemical CO2RR to methanol. By tuning the ligand environment of the salophen NiN2O2, the electrocatalytic activity of the material toward CO2 reduction can be significantly improved. We prove that by introducing a carbonyl group at the ligand environment of the Ni active sites, the electrochemical CO2 reduction activity is highly promoted and its product selectivity reaches a Faradaic efficiency of 27% toward the production of methanol at − 0.9 V vs RHE. The salophen-based π-d conjugated metal-organic framework presented here thus provides the best performance toward CO2 reduction to methanol among the previously developed nickel-based electrocatalysts.

Electroreduction of CO2 to ethanol by electrochemically deposited Cu-lignin complexes on Ni foam electrodes

A low cost, non-toxic and highly selective catalyst based on a Cu-lignin molecular complex is developed for CO2 electroreduction to ethanol. Ni foam (NF), Cu–Ni foam (Cu–NF) and Cu-lignin-Ni foam (Cu-lignin-NF) were prepared by a facile and reproducible electrochemical deposition method. The electrochemical CO2 reduction activity of Cu-lignin-NF was found to be higher than Cu–NF. A maximum faradaic efficiency of 23.2% with current density of 22.5 mA cm−2 was obtained for Cu-lignin-NF at −0.80 V (versus RHE) in 0.1 M Na2SO4 towards ethanol production. The enhancement of catalytic performance is attributed to the growth of the number of active sites and the change of oxidation states of Cu and NF due to the presence of lignin.

Electronic Regulation of Bismuth Oxide Via Sulfur Doping for Efficient CO2 Electroreduction to Formate

Electrochemical CO2 reduction (ECR) to value-added fuels and chemical feedstocks driven by renewable energy sources is one promising approach to alleviating the ever-increasing atmospheric CO2 concentration and the rapid fossil fuels consumption.1,2 Among various products formed, formate is a very attractive product due to its wide applications in textile and pharmaceutical industries, and in fuel cells as the hydrogen carrier. Bi in particular has been widely investigated as advanced catalyst for formate production because of their cost-effectiveness, low toxicity, and high activity. Up to date, various strategies including size, morphology, defect, grain boundary, and heterostructure engineering have been developed to improve the catalytic performances of Bi-based catalysts. Despite some exciting achievements, the performances over Bi-based catalysts still fall behind the commercial requirements. Most existing catalysts suffer from low formate production rate (in H-type cell) because high standard of catalytic activity and product selectivity could be hardly achieved simultaneously. On the other side, desirable formate faradaic efficiency (FE) of ˃90 % can be only achieved in a narrow potential window owing to the competing hydrogen evolution reaction (HER) at high potential. Therefore, developing Bi-based catalysts for formate production via ECR with high formation rate and current density over a broad potential window is a top priority but remains as great challenges. Electronic regulation of electrocatalysts via element doping has been regarded as a powerful strategy to enhance the electrochemical activity of ECR. The introduction of heteroatoms can regulate the electron density and thus, precisely modify the electronic structures of the active sites, resulting in optimal adsorption energy of the reaction intermediates. S modification of catalysts can modulate the electronic structure of catalysts, thus boosting the electrocatalytic activity for HER, 3 oxygen evolution reaction (OER),4 and oxygen reduction reaction (ORR).5 Moreover, S doping can increase the adsorption capacity of CO2 and decrease the energy barrier for the formation of *HCOO intermediate.6 To that end, S doping is expected to be an effective strategy to improve the catalytic performance of ECR by tuning the electronic structure. However, the studies on fine-tuning the electronic structure of Bi-based catalysts for ECR by S doping have rarely been reported so far; a comprehensive understanding of the S doping effect on the ECR activity is also lacking. The study demonstrates S doped Bi2O3 nanosheets coupled with carbon nanotube (S-Bi2O3-CNT) as catalyst for ECR to formate production. The prepared S2-Bi2O3-CNT with the S doping amount of 0.7 at % achieved high FE over a wide potential range, and also achieved high partial current density (48.6 mA cm-2) and good long-term stability. Experimental results and a series of characterizations highlighted the advantages of S doping which facilitates electron transfer, increases the adsorption of CO2 and offers more undercoordinated Bi sites. Moreover, DFT results reveal that S doping induced the electronic delocalization of Bi sites, which optimized the adsorption of *CO2 and *HCOO intermediates while hindering the adsorption of *H. Therefore, S doped Bi2O3 promotes the ECR to formate by supressing the competitive HER simultaneously. This work opens up an attractive avenue for developing highly efficient electrocatalyst for ECR at atomic level.References Nielsen, D. U.; Hu, X.-M.; Daasbjerg, K.; Skrydstrup, T., Chemically and electrochemically catalysed conversion of CO2 to CO with follow-up utilization to value-added chemicals. Nat. Catal. 2018, 1, 244-254.Ross, M. B.; De Luna, P.; Li, Y.; Dinh, C.-T.; Kim, D.; Yang, P.; Sargent, E. H., Designing materials for electrochemical carbon dioxide recycling. Nat. Catal. 2019, 2, 648-658.Yu, J.; Guo, Y.; Miao, S.; Ni, M.; Zhou, W.; Shao, Z., Spherical ruthenium disulfide-sulfur-doped graphene composite as an efficient hydrogen evolution electrocatalyst. ACS Appl. Mater. Interfaces 2018, 10, 34098-34107. Yu, L.; Wu, L.; McElhenny, B.; Song, S.; Luo, D.; Zhang, F.; Yu, Y.; Chen, S.; Ren, Z., Ultrafast room-temperature synthesis of porous S-doped Ni/Fe (oxy) hydroxide electrodes for oxygen evolution catalysis in seawater splitting. Energy Environ. Sci. 2020, 13, 3439-3446.Wang, Y. C.; Lai, Y. J.; Song, L.; Zhou, Z. Y.; Liu, J. G.; Wang, Q.; Yang, X. D.; Chen, C.; Shi, W.; Zheng, Y. P., S‐doping of an Fe/N/C ORR catalyst for polymer electrolyte membrane fuel cells with high power density. Angew. Chem., Int. Ed. 2015, 54, 9907-9910. 6. Tian, W.; Zhang, H.; Sun, H.; Suvorova, A.; Saunders, M.; Tade, M.; Wang, S., Heteroatom (N or N‐S)‐Doping Induced Layered and Honeycomb Microstructures of Porous Carbons for CO2 Capture and Energy Applications. Adv. Funct. Mater. 2016, 26, 8651-8661.

A Tandem Strategy for Enhancing Electrochemical CO2 Reduction Activity of Single-Atom Cu-S1 N3 Catalysts via Integration with Cu Nanoclusters.

We developed a tandem electrocatalyst for CO2 -to-CO conversion comprising the single Cu site co-coordinated with N and S anchored carbon matrix (Cu-S1 N3 ) and atomically dispersed Cu clusters (Cux ), denoted as Cu-S1 N3 /Cux . The as-prepared Cu-S1 N3 /Cux composite presents a 100 % Faradaic efficiency towards CO generation (FECO ) at -0.65 V vs. RHE and high FECO over 90 % from -0.55 to -0.75 V, outperforming the analogues with Cu-N4 (FECO only 54 % at -0.7 V) and Cu-S1 N3 (FECO 70 % at -0.7 V) configurations. The unsymmetrical Cu-S1 N3 atomic interface in the carbon basal plane possesses an optimized binding energy for the key intermediate *COOH compared with Cu-N4 site. At the same time, the adjacent Cux effectively promotes the protonation of *CO2 - by accelerating water dissociation and offering *H to the Cu-S1 N3 active sites. This work provides a tandem strategy for facilitating proton-coupled electron transfer over the atomic-level catalytic sites.

Quick and Easy Method to Dramatically Improve the Electrochemical CO2 Reduction Activity of an Iron Porphyrin Complex

AbstractThe development of artificial molecular catalysts for CO2 reduction is the key to solving energy and environmental problems. Although chemical modifications can generally improve the catalytic activity of this class of compounds, they often require complicated synthetic procedures. Here, we report a simple procedure that dramatically enhances electrochemical CO2 reduction activity. A one‐step counteranion‐exchange reaction increased the solubility of a commercially available catalyst, iron(III) tetraphenylporphyrin chloride, in a variety of solvents, allowing the investigation of its catalytic performance under various conditions. Surprisingly, the turnover frequency for CO evolution in acetonitrile (MeCN) reached 7 300 000 s−1, which is the highest among those of current best‐in‐class molecular catalysts. This excellent catalytic activity originates from the unique reaction between the generated FeI species and CO2 in MeCN during catalysis. The present study offers a “quick and easy” method for obtaining an efficient catalytic system for electrochemical CO2 reduction.