Efficient Electrocatalysts For CO2 Reduction Research Articles

Pd-intercalated black phosphorus: An efficient electrocatalyst for CO2 reduction.

Nanoconfined catalysts enhance stabilization of reaction intermediates, facilitate electron transfer, and safeguard active centers, leading to superior electrocatalytic activity, particularly in CO2 reduction reactions (CO2RR). Despite their effectiveness, crafting nanoconfined catalysts is challenging due to unclear formation mechanisms. In this study, we introduce an electrochemical method to grow Pd clusters within the interlayers of two-dimensional black phosphorus, creating Pd cluster-intercalated black phosphorus (Pd-i-BP) as an electrocatalyst. Using in situ electrochemical liquid phase transmission electron microscopy (EC-TEM), we revealed the synthesis mechanism of Pd-i-BP, involving electrochemically driven Pd ion intercalation followed by reduction within the BP layers. The Pd-i-BP electrocatalyst exhibits exemplary CO2-to-formate conversion, achieving 90% Faradaic efficiency for formate production, owing to its distinct nanoconfined structure that stabilizes intermediates and enhances electron transfer. Density functional theory (DFT) calculations underscore the structural benefits for enhancing intermediate adsorption and catalyzing the reaction. Our insights deepen understanding of nanoconfined material synthesis, promising advanced, high-efficiency catalysts.

Boosting electrochemical conversion of CO2 to ethanol through the confinement of pyridinic N-B layer on copper nanoparticles

Developing efficient electrocatalysts for CO2 reduction has gained significant attention in the field of sustainable energy, especially the Cu-based catalysts for CO2 conversion to valuable alcohols. In this study, we developed Cu nanoparticles supported on pyridinic N-B doped graphene nanoribbons/amorphous carbon (Cu/BNC-1) as an electrocatalyst for CO2 reduction, exhibiting substantially improved ethanol (EtOH) conversion rate in terms of activity, selectivity, and stability. The Cu/BNC-1 achieved a remarkable 58.64 % Faradaic efficiency (FE) for producing EtOH at −1.0 V vs. RHE with a current density of 20.4 mA cm−2 in 0.5 M KHCO3 electrolyte. In-situ Raman, FT-IR, and density functional theory (DFT) calculations demonstrated that the high C2+ product selectivity of Cu/BNC-1 attributed to the pyridinic N-B modulation, lowering the CO dimerization barrier. Moreover, the synergistic confinement effect of Cu and BNC can stabilize the C-O bond of the *HOCCH intermediate, thereby increasing the yield of EtOH.

NHC-CDI Ligands Boost Multicarbon Production in Electrocatalytic CO2 Reduction by Increasing Accumulated Charged Intermediates and Promoting *CO Dimerization on Cu.

Copper-based materials exhibit significant potential as catalysts for electrochemical CO2 reduction, owing to their capacity to generate multicarbon hydrocarbons. The molecular functionalization of Cu electrodes represents a simple yet powerful strategy for improving the intrinsic activity of these materials by favoring specific reaction pathways through the creation of tailored microenvironments around the surface active sites. However, despite its success, comprehensive mechanistic insights derived from experimental techniques are often limited, leaving the active role of surface modifiers inconclusive. In this work, we show that N-heterocyclic carbene-carbodiimide-functionalized Cu catalysts display a remarkable activity for multicarbon product formation, surpassing bare Cu electrodes by more than an order of magnitude. These hybrid catalysts operate efficiently using an electrolyzer equipped with a gas diffusion electrode, achieving a multicarbon product selectivity of 58% with a partial current density of ca. -80 mA cm-2. We found that the activity for multicarbon product formation is closely linked to the surface charge that accumulates during electrocatalysis, stemming from surface intermediate buildup. Through X-ray photoelectron spectroscopy, we elucidated the role of the molecular additives in altering the electronic structure of the Cu electrodes, promoting the stabilization of surface CO. Additionally, in situ Raman measurements established the identity of the reaction intermediates that accumulate during electrocatalysis, indicating preferential CO binding on Cu step sites, known for facilitating C-C coupling. This study underscores the significant potential of molecular surface modifications in developing efficient electrocatalysts for CO2 reduction, highlighting surface charge as a pivotal descriptor of multicarbon product activity.

Revealing the Lattice Carbonate Mediated Mechanism in Cu2(OH)2CO3 for Electrocatalytic Reduction of CO2 to C2H4.

Understanding the CO2 transformation mechanism on materials is essential for the design of efficient electrocatalysts for CO2 reduction. In aconventional adsorbate evolution mechanism (AEM), the catalysts encounter multiple high-energy barrier steps, especially CO2 activation, limiting the activity and selectivity. Here, lattice carbonate from Cu2(OH)2CO3 is revealed to be a mediator between CO2 molecules and catalyst during CO2 electroreduction by a 13C isotope labeling method, which can bypass the high energy barrier of CO2 activation and strongly enhance the performance. With the lattice carbonate mediated mechanism (LCMM), the Cu2(OH)2CO3 electrode exhibited ten-fold faradaic efficiency and 15-fold current density for ethylene production than the Cu2O electrode with AEM at a low overpotential. Theoretical calculations and in situ Raman spectroscopy results show that symmetric vibration of carbonate is precisely enhanced on the catalyst surface with LCMM, leading to faster electron transfer, and lower energy barriers of CO2 activation and carbon-carbon coupling. This work provides a route to develop efficient electrocatalysts for CO2 reduction based on lattice-mediated mechanism.

Pyrolysis-free synthesis of a high-loading single-atom Cu catalyst for efficient electrocatalytic CO2-to-CH4 conversion.

Electrocatalytic CO2-to-CH4 conversion provides a promising means of addressing current carbon resource recycling and intermittent energy storage. Cu-based single-atom catalysts have attracted extensive attention owing to their high intrinsic activity toward CH4 production; however, they suffer from uncontrollable metal loading and aggregation during the conventional pyrolysis process of carbon-based substrates. Herein, we developed a pyrolysis-free method to prepare a single-atom Cu catalyst anchored on a formamide polymer substrate with a high loading amount and well atomic dispersion through a mild polycondensation reaction. Owing to the isolation of copper active sites, efficient CO2-to-CH4 conversion is achieved over the single-atom Cu catalyst, along with the significant suppression of C-C coupling. As a result, the optimal single-atom catalyst with 5.87 wt% of Cu offers high CH4 faradaic efficiencies (FEs) of over 70% in a wide current density range from 100 to 600 mA cm-2 in the flow cell, together with a maximum CH4 partial current density of 415.8 mA cm-2. Moreover, the CH4 FE can reach 74.2% under optimized conditions in a membrane electrode assembly electrolyzer. This work provides new insights into the subtle design of highly efficient electrocatalyst for CO2 reduction.

Intramolecular electrostatic effects on reduction of CO2 to CO by iron porphyrin complexes: Insights from DFT calculations

Iron porphyrin (Por) complexes were found to be highly efficient molecular catalysts for electrocatalytic CO2 reduction and the catalytic performance can be modulated by the modification of ligands. Herein, density functional theory calculations were employed to investigate how the presence of second-sphere anionic carboxylate groups influences the CO2-to-CO conversion by Fe porphyrins. The kinetics and thermodynamics of individual chemical steps in the reaction cycle were systematically studied. Computations indicated that the catalytic active species is the ferrous complex with the two extra electrons being stored in the π system of porphyrin and the rate-determining step is the CO2 binding. The synchronization of the Fe-to-CO2 and ligand-to-Fe electron transfers leads to the formation of FeIII(CO22−)(Por•−). The experimentally observed activity trend could be rationalized by the Brønsted-Evans-Polanyi principle. The electrostatic repulsive between the negatively charged hanging group and the CO2 moiety destabilizes the CO2 adduct and thereby raises the binding energy. Then, the two-step protonation occurs easily to give Fe(II)-CO. The further one-electron reduction triggers the dissociation of CO to regenerate of the formal Fe(I) porphyrin catalyst. The insights gained from this study may be helpful in designing efficient electrocatalysts for CO2 reduction.

Spectroelectrochemical Investigation of the Local Alkaline Environment on the Surface-Nanostructured Au for the Conversion of CO2 to CO

The electrocatalytic conversion of carbon dioxide (CO2) into fuels could potentially achieve a sustainable carbon-based economy. The engineering of nanostructured metal electrodes can enhance their activity and selectivity by controlling their local chemical environment; however, direct observation is challenging. In this study, we investigate the molecular-level reaction mechanism of a nanoporous-structured Au electrode for the conversion of CO2 to carbon monoxide (CO) using surface-enhanced infrared absorption spectroscopy (SEIRAS). We designed a well-structured nanoporous Au layer (with a depth distribution of 56.3 nm) on a Si prism using a high-temperature non-aqueous anodization process and characterized the nanoporous Au electrode using atomic force microscopy (AFM) and X-ray absorption spectroscopy (XAS). The in situ SEIRAS results demonstrated that the nanoporous Au electrode has a dominant active site, promoting the linear CO intermediate and suppressing the bridging CO intermediate when compared with the non-structured Au electrode. We also revealed a high local pH at a reaction potential of −0.9 V and the slow diffusion kinetics of local CO32– at an open-circuit potential. These findings provide deeper insights into the electrochemical kinetics and corresponding mechanisms occurring in the electric double layers and highlight the potential for the design of efficient electrocatalysts for CO2 reduction.

Facile fabrication of Sn/SnOx electrode as an efficient electrocatalyst for CO2 reduction to formate

Producing valuable hydrocarbons via electrochemical reduction of CO2 has been a promising active research area. In this study, it was aimed to develop a low-cost and efficient Sn-based electrode reducing CO2 to formate with high selectivity. SnOx thin-film electrode was prepared via potentiostatic electrodeposition at the potentials of −0.5 V, −0.6 V, −0.7 V, and −0.8 V vs. Ag/AgCl on a pure Sn plate for 300 s in an acidic media. The Sn/SnOx electrode which was prepared at −0.6 V was found to have the highest Faradaic efficiency. Electrochemical reduction of CO2 was carried out on this Sn/SnOx electrode in aqueous CO2-saturated 0.1 M KHCO3 solution. The optimum values for the parameters which have significant impacts on Faradaic efficiency for producing formate namely, electrolysis potential and electrolysis time were determined. The maximum Faradaic efficiency of formate on the Sn/SnOx electrode was obtained as 74.7 % at the applied potential of −1.8 V in an H-type cell. The maximum Faradaic efficiency of formate obtained on the Sn/SnOx electrode reached about twice the value obtained on the Sn plate (39.7 %). The results also indicated that the Sn/SnOx electrode has higher catalytic stability and electrochemically active surface area (2.08 cm2) than the bare Sn plate (0.82 cm2). This study showed that an efficient Sn/SnOx electrode can be developed with a simple method that involves only a SnSO4/H2SO4 solution and as short as 300 s plating duration via electrodeposition at a lower overpotential of −0.6 V. The novelty of this study can be attributed to the combination of simple and unique electrocatalyst preparation procedure with less energy consumption and chemical/additive use, short deposition time, and relatively low overpotential for developing an efficient Sn/SnOx electrocatalyst ensuring a high Faradaic efficiency for formate production. Thus, producing formate from the conversion of CO2 which is a waste carbon source, was achieved by a quite simple and economic method.

In situ reconstructed AgZn3 nanoparticles supported on zinc nanoplates for efficient CO2 electroreduction to tunable syngas.

Developing efficient electrocatalysts for CO2 reduction to syngas with tunable H2/CO ratios and high total faradaic efficiency is challenging. Herein, we report an effective catalyst composed of in situ reconstructed AgZn3 nanoparticles and Zn nanoplates for syngas synthesis, showing nearly 100% Faraday efficiency to syngas with a tunable H2/CO ratio from 2 : 1 to 1 : 2. Moreover, the in situ electrochemical measurements coupled with theoretical calculations disclose that the Zn site in AgZn3 nanoparticles and the hollow site between Ag and Zn in AgZn3 are the possible active sites for CO and H2 generation, respectively. This work has guiding significance for designing dual site catalysts for CO2 electroreduction to tunable syngas.

Modulating the Electronic Structures of Dual-Atom Catalysts via Coordination Environment Engineering for Boosting CO2 Electroreduction.

Dual-atom catalysts (DACs) have emerged as efficient electrocatalysts for CO2 reduction owing to the synergistic effect between the binary metal sites. However, rationally modulating the electronic structure of DACs to optimize the catalytic performance remains a great challenge. Herein, we report the electronic structure modulation of three Ni2 DACs (namely, Ni2 -N7 , Ni2 -N5 C2 and Ni2 -N3 C4 ) by the regulation of the coordination environments around the dual-atom Ni2 centres. As a result, Ni2 -N3 C4 exhibits significantly improved electrocatalytic activity for CO2 reduction, not only better than the corresponding single-atom Ni catalyst (Ni-N2 C2 ), but also higher than Ni2 -N7 and Ni2 -N5 C2 DACs. Density functional theory (DFT) calculations revealed that the high electrocatalytic activity of Ni2 -N3 C4 for CO2 reduction could be attributed to the electronic structure modulation to the Ni centre and the resulted proper binding energies to COOH* and CO* intermediates.

Modulating the Electronic Structures of Dual‐Atom Catalysts via Coordination Environment Engineering for Boosting CO2Electroreduction

AbstractDual‐atom catalysts (DACs) have emerged as efficient electrocatalysts for CO2reduction owing to the synergistic effect between the binary metal sites. However, rationally modulating the electronic structure of DACs to optimize the catalytic performance remains a great challenge. Herein, we report the electronic structure modulation of three Ni2DACs (namely, Ni2−N7, Ni2−N5C2and Ni2−N3C4) by the regulation of the coordination environments around the dual‐atom Ni2centres. As a result, Ni2−N3C4exhibits significantly improved electrocatalytic activity for CO2reduction, not only better than the corresponding single‐atom Ni catalyst (Ni−N2C2), but also higher than Ni2−N7and Ni2−N5C2DACs. Density functional theory (DFT) calculations revealed that the high electrocatalytic activity of Ni2−N3C4for CO2reduction could be attributed to the electronic structure modulation to the Ni centre and the resulted proper binding energies to COOH* and CO* intermediates.

Concentration Optimization of Localized Cu0 and Cu+ on Cu-Based Electrodes for Improving Electrochemical Generation of Ethanol from Carbon Dioxide.

Copper-based electrodes can catalyze electroreduction of CO2 to two-carbon products. However, obtaining a specific product with high efficiency depends on the oxidation state of Cu for the Cu-based materials. In this study, Cu-based electrodes were prepared on fluorinated tin oxide (FTO) using the one-step electrodeposition method. These electrodes were used as efficient electrocatalysts for CO2 reduction to ethanol. The concentration ratio of Cu0 and Cu+ on the electrodes was precisely modulated by adding monoethanolamine (MEA). The results of spectroscopic characterization showed that the concentration ratio of localized Cu+ and Cu0 (Cu+/Cu0) on the Cu-based electrodes was controlled from 1.24/1 to 1.54/1 by regulating the amount of MEA. It was found that the electrode exhibited the best electrochemical efficiency and ethanol production in the CO2 reduction reaction at the optimal concentration ratio Cu+/Cu0 of 1.42/1. The maximum faradaic efficiencies of ethanol and C2 were 48% and 77%, respectively, at the potential of −0.6 V vs. a reversible hydrogen electrode (RHE). Furthermore, the optimal concentration ratio of Cu+/Cu0 achieved the balance between Cu+ and Cu0 with the most favorable free energy for the formation of *CO intermediate. The stable existence of the *CO intermediate significantly contributed to the formation of the C–C bond for ethanol production.

Cobalt telluride electrocatalyst for selective electroreduction of CO2 to value-added chemicals

Recent emphasis on carbon dioxide utilization has necessitated the exploration of different catalyst compositions other than copper-based systems that can significantly improve the activity and selectivity towards specific CO2 reduction products at low applied potential. In this study, a binary CoTe has been reported as an efficient electrocatalyst for CO2 reduction in aqueous medium under ambient conditions at neutral pH. CoTe showed high Faradaic efficiency and selectivity of 86.83 and 75%, respectively, for acetic acid at very low potential of − 0.25 V vs RHE. More intriguingly, C1 products like formic acid was formed preferentially at slightly higher applied potential achieving high formation rate of 547.24 μmol cm−2 h−1 at − 1.1 V vs RHE. CoTe showed better CO2RR activity when compared with Co3O4, which can be attributed to the enhanced electrochemical activity of the catalytically active transition metal center as well as improved intermediate adsorption on the catalyst surface. While reduced anion electronegativity and improved lattice covalency in tellurides enhance the electrochemical activity of Co, high d-electron density improves the intermediate CO adsorption on the catalyst site leading to CO2 reduction at lower applied potential and high selectivity for C2 products. CoTe also shows stable CO2RR catalytic activity for 50 h and low Tafel slope (50.3 mV dec–1) indicating faster reaction kinetics and robust functionality. Selective formation of value-added C2 products with low energy expense can make these catalysts potentially viable for integration with other CO2 capture technologies thereby, helping to close the carbon loop.

Tin Sulfide Chalcogel Derived SnSx for CO2 Electroreduction

A new class of aerogels based exclusively on metal chalcogenide frameworks has been developed, opening up a series of novel properties and applications. Further expanding the application of such chalcogels in electrocatalytic CO2 reduction is of significance for mitigating the rise of atmospheric CO2 concentration. Herein, the tin sulfide chalcogel was employed as a pre-catalyst for the construction of efficient electrocatalysts for CO2 reduction. SnS0.09 and SnS0.55 supported on carbon cloth (SnS0.09/CC and SnS0.55/CC) were obtained with different amounts of sulfur by cyclic voltammetry activation of the tin sulfide chalcogel at different potential intervals. Compared to SnS0.09/CC, SnS0.55/CC with higher S content exhibited higher formate Faraday efficiency of 93.1% at -1.1 V vs. RHE, and the partial current density of formate was 28.4 mA/cm2. The difference in performance between SnS0.09/CC and SnS0.55/CC could be attributed to the varying sulfur which could favor the formation of formate.

N, O Coordinated Ni/Porous Bamboo Carbon as an Efficient Electrocatalyst for Co2 Reduction and Application in Zn-Co2 Batteries

N, O Coordinated Ni/Porous Bamboo Carbon as an Efficient Electrocatalyst for Co2 Reduction and Application in Zn-Co2 Batteries

Substituents and Cocatalyst Effect on the Catalytic Response and Overpotential of Re(I) Catalysts for CO2 Reduction

To design an efficient electrocatalyst for CO2 reduction, a comprehensive understanding of the catalytic architecture and the reaction mechanism is required. Herein, we synthesized and analyzed a series of fac-[Re(bpy-X) (CO)3Cl] (abbreviated as ReI(bpy-X); bpy-X = 4,4′-disubstituted-2,2′-bipyridine; X = tBu, CH3, mesityl, H, phenyl, and methyl ester) catalysts for electrocatalytic CO2 reduction with and without adding the cocatalyst [Zn(cyclam)]2+ (cyclam = 1,4,6,11-tetraazacyclotetradecane). Both computational and experimental results show that in the experiments bearing the [Zn(cyclam)]2+ cocatalyst, the Re(I) catalysts require less energy input to reduce the CO2, indicating that the CO2-to-CO conversion occurs at a lower overpotential. Interestingly, in the Re(I) electrocatalyst bearing a strong electron-withdrawing group (methyl ester), [Zn(cyclam)]2+ does not improve the CO2 reduction activity. These results emphasize the importance of how the electronic distribution throughout the molecular architecture can enhance or suppress the nucleophilicity of ReI(bpy-X) electrocatalysts, even in the presence of a cocatalyst.

Surface regulated Ni nanoparticles on N-doped mesoporous carbon as an efficient electrocatalyst for CO2 reduction

Low cost, highly selective and efficient electrocatalysts for CO2 reduction reaction (CO2RR) is crucial for lowering the global carbon footprint and mitigating energy shortages. Here, we first report a highly selective and efficient electrocatalyst for CO2RR to CO using a surface-regulated Ni nanoparticles supported on N-doped CMK-3 (N,O-Ni/CMK3). Compared with most Ni metal catalysts previously reported with severe competitive hydrogen evolution during the CO2RR, the N,O-Ni/CMK3 catalyst presents a superior CO faradaic efficiency of about 97%, a high CO partial current density (13.01 mA cm−1) and turnover frequency (4.25 s−1). The comprehensive characterization provides evidence that the N,O co-regulated Ni acts as the active center. Taking advantage of the N, O co-regulated chemical environment, N,O-Ni/CMK3 also displays a decent stability at negative potentials. Our work paves a novel approach for developing transition metal catalysts for CO2RR with enhanced activity and selectivity via regulating surface chemical environment.

The bismuth architecture assembled by nanotubes used as highly efficient electrocatalyst for CO2 reduction to formate

Electrochemical conversion of CO2 into valuable chemical fuels is a promising technology for addressing climate change and energy issues, but the progress of it has been hampered by the lack of selective and stable electrocatalysts. In this work, metallic bismuth (Bi) architecture electrocatalyst was synthesized by in situ electrochemical reduction of two-dimensional (2D) bismuth oxyiodide (BiOI) architecture, which was composed by one-dimensional (1D) BiOI nanotubes using structural assembly method. Owning to the enhanced active sites from this unique morphology, this Bi electrocatalyst exhibited high activity, excellent selectivity (Formate Faradaic efficiency is 97.1% with a partial current density of 31.1 mA cm−2 at an overpotential of only 790 mV), and excellent durability (65 h at a current density of 10 mA cm−2) for CO2 reduction reaction (CO2RR). For deeply understanding the factors governing the activity of this Bi catalyst, density functional theory (DFT) computations are employed, and the OCHO* intermediate preferentially adsorbs on the edge sites. When the rich edges sites were covered by oleylamine molecules, this step was impeded, and formate production obviously decreased. This work shows the importance of metallic Bi with unique nanostructure for catalyzing CO2RR towards formate with high efficiency and selectivity.

Carbon nanosheets supporting Ni–N3S single-atom sites for efficient electrocatalytic CO2 reduction

Of various atomically dispersed metal catalysts, those based on single Ni atoms are among the most efficient electrocatalysts for CO2 reduction. However, the activity of these catalysts is determined by the coordination environment of Ni sites. Here, N and S co-coordinated Ni sites were successfully prepared using a nickel phosphorus trisulfide two-dimensional template to form a sandwich-like conjugated microporous polymer. As-prepared Ni single atom–based porous carbon nanosheets were proved to possess N/S co-coordination via X-ray absorption spectroscopy. As electrocatalysts for CO2 reduction, the prepared porous carbon nanosheets achieved over 95% CO selectivity rate and −7.8 mA cm−2 current density (−0.8 V vs. reversible hydrogen electrode). This performance could be attributed to the sheet-like morphology of the nanosheets with long-distance conductivity and the rich single N/S-coordinated Ni atoms with high activity. The fundamental understanding of manipulating such a coordination environment revealed in this study can be used to create versatile single-metal atom–based catalysts for high-efficient energy conversion.

Atomic-level-designed copper atoms on hierarchically porous gold architectures for high-efficiency electrochemical CO2 reduction

Electrochemical CO2 reduction is a promising technology for solving the CO2 emission problems and producing value-added products. Here, we report a hierarchically porous Cu1Au single-atom alloy (SAA) as an efficient electrocatalyst for CO2 reduction. Benefiting from the hierarchically porous architectures with abundant vacancies as well as three-dimensional accessible active sites, the as-prepared nanoporous Cu1Au SAA catalyst shows remarkable CO2 reduction performance with nearly 100% CO Faraday efficiency in a wide potential range (−0.4 to −0.9 V vs. reversible hydrogen electrode. The in-situ X-ray absorption spectroscopy studies and density functional theory calculations reveal that the Cu-Au interface sites serve as the intrinsic active centers, which can facilitate the activated adsorption of CO2 and stabilize the *COOH intermediate.