Electrocatalytic CO2 Research Articles

Symmetry Breaking Enhancing the Activity of Electrocatalytic CO2 Reduction on an Icosahedron‐Kernel Cluster by Cu Atoms Regulation

AbstractRecently, CO2 hydrogenation had a new breakthrough resulting from the design of catalysts to effectively activate linear CO2 with symmetry‐breaking sites. However, understanding the relationship between symmetry‐breaking sites and catalytic activity at the atomic level is still a great challenge. In this study, a set of gold‐copper alloy Au13Cux (x=0–4) nanoclusters were used as research objects to show the symmetry‐controlled breaking structure on the surface of nanoclusters with the help of manipulability of the Cu atoms. Among them, Au13Cu3 nanocluster displays the highest degree of symmetry‐breaking on its crystal structure compared with the other nanoclusters in the family. Where the three copper atoms occupying the surface of the icosahedral kernel unevenly with one copper atom is coordinately unsaturated (CuS2 motif relative to CuS3 motif). As expected, Au13Cu3 has an excellent hydrogenation activity of CO2, in which the current density is as high as 70 mA cm−2 (−0.97 V) and the maximum FECO reaches 99 % at −0.58 V. Through the combination of crystal structures and theoretical calculations, the excellent catalytic activity of Au13Cu3 is revealed to be indeed closely related to its asymmetric structure.

Connecting Biological and Synthetic Approaches for Electrocatalytic CO2 Reduction

AbstractElectrocatalytic CO2 reduction has developed into a broad field, spanning fundamental studies of enzymatic ‘model’ catalysts to synthetic molecular catalysts and heterogeneous gas diffusion electrodes producing commercially relevant quantities of product. This diversification has resulted in apparent differences and a disconnect between seemingly related approaches when using different types of catalysts. Enzymes possess discrete and well understood active sites that can perform reactions with high selectivity and activities at their thermodynamic limit. Synthetic small molecule catalysts can be designed with desired active site composition but do not yet display enzyme‐like performance. These properties of the biological and small molecule catalysts contrast with heterogeneous materials, which can contain multiple, often poorly understood active sites with distinct reactivity and therefore introducing significant complexity in understanding their activities. As these systems are being better understood and the continuously improving performance of their heterogeneous active sites closes the gap with enzymatic activity, this performance difference between heterogeneous and enzymatic systems begins to close. This convergence removes the barriers between using different types of catalysts and future challenges can be addressed without multiple efforts as a unified picture for the biological‐synthetic catalyst spectrum emerges.

Active Sites of Cobalt Phthalocyanine in Electrocatalytic CO2 Reduction to Methanol

AbstractMany metal coordination compounds catalyze CO2 electroreduction to CO, but cobalt phthalocyanine hybridized with conductive carbon such as carbon nanotubes is currently the only one that can generate methanol. The underlying structure–reactivity correlation and reaction mechanism desperately demand elucidation. Here we report the first in situ X‐ray absorption spectroscopy characterization, combined with ex situ spectroscopic and electrocatalytic measurements, to study CoPc‐catalyzed CO2 reduction to methanol. Molecular dispersion of CoPc on CNT surfaces, as evidenced by the observed electronic interaction between the two, is crucial to fast electron transfer to the active sites and multi‐electron CO2 reduction. CO, the key intermediate in the CO2‐to‐methanol pathway, is found to be labile on the active site, which necessitates a high local concentration in the microenvironment to compete with CO2 for active sites and promote methanol production. A comparison of the electrocatalytic performance of structurally related porphyrins indicates that the bridging aza‐N atoms of the Pc macrocycle are critical components of the CoPc active site that produces methanol. In situ X‐ray absorption spectroscopy identifies the active site as Co(I) and supports an increasingly non‐centrosymmetric Co coordination environment at negative applied potential, likely due to the formation of a Co−CO adduct during the catalysis.

Anchoring of Metal Complexes on Au25 Nanocluster for Enhanced Photocoupled Electrocatalytic CO2 Reduction

AbstractAtomically precise Au nanoclusters (NCs) with discrete energy levels can be used as photosensitizers for CO2 reduction. However, tight ligand capping of Au NCs hinders CO2 adsorption on its active sites. Here, a new hybrid material is obtained by anchoring of thiol functionalized terpyridine metal complexes (metal=Ru, Ni, Fe, Co) on Au NCs by ligand exchange reactions (LERs). The anchoring of Ru and Ni complexes on Au25 NC (Au25−Ru and Au25−Ni) leads to adequate CO2 to CO conversion for photocoupled electrocatalytic CO2 reduction (PECR) in terms of high selectivity, with Faradaic efficiency of CO (FECO) exceeding 90 % in a wide potential range, remarkable activity (CO production rate up to two times higher than that for pristine Au25PET18) and extremely large turnover frequencies (TOFs, 63012 h−1 at −0.97 V for Au25−Ru and 69989 h−1 at −1.07 V vs. RHE for Au25−Ni). Moreover, PECR stability test indicates the excellent long‐term stability of the modified NCs in contrast with pristine Au NCs. The present approach offers a novel strategy to enhance PECR activity and selectivity, as well as to improve the stability of Au NCs under light illumination, which paves the way for highly active and stable Au NCs catalysts.

Effect of Feature Shape and Dimension of a Confinement Geometry on Selectivity of Electrocatalytic CO2 Reduction

AbstractThe local confinement effect, which can generate a high concentration of hydroxide ions and reaction intermediates near the catalyst surface, is an important strategy for converting CO2 into multi‐carbon products in electrocatalytic CO2 reduction. Therefore, understanding how the shape and dimension of the confinement geometry affect the product selectivity is crucial. In this study, we report for the first time the effect of the shape (degree of confinement) and dimension of the confined space on the product selectivity without changing the intrinsic property of Cu. We demonstrate that geometry influences the outcomes of products, such as CH4, C2H4, and EtOH, in different ways: the selectivity of CH4 and EtOH is affected by shape, while the selectivity of C2H4 is influenced by dimension of geometry predominantly. These phenomena are demonstrated, both experimentally and through simulation, to be induced by the local confinement effect within the confined structure. Our geometry model could serve as basis for designing the confined structures tailored for the production of specific products.

Enhancing CO diffusion for selective acetate production via CO reduction on copper catalyst

The productivity of multi-carbon products in electrocatalytic CO reduction is greatly influenced by the local concentration of CO. Herein, we present a facile strategy for modulating the local concentration of CO under atmospheric pressure via polymer coating, which enables selective, active and stable production of acetate on a Cu model-catalyst. Specifically, we coat the Cu-catalyst with a fluorinated polymer, forming an optimized gas-involving reaction interface. This approach enhances the CO diffusion to catalyst surfaces and increases the hydrophobicity of the catalyst layer, resulting in enhanced acetate selectivity of over 50% with a high partial current density of −0.65 A cm−2 on Cu-catalyst. This represents an over 3 folders of enhancement compared to the pristine Cu-catalyst. Furthermore, this optimized reaction interface led to a stable COR electrolysis over a duration of 70 h. Our strategy offers valuable insights for designing efficient catalytic interface in various electrochemical reactions that involve gas diffusion.

Perylenediimide-Incorporated Covalent Triazine Framework: A Highly Conductive Carbon Support for Copper Single-Atom Catalysts in Electrocatalytic CO2 Conversion

Perylenediimide-Incorporated Covalent Triazine Framework: A Highly Conductive Carbon Support for Copper Single-Atom Catalysts in Electrocatalytic CO₂ Conversion

Selective CO2 -to-Syngas Conversion Enabled by Bimetallic Gold/Zinc Sites in Partially Reduced Gold/Zinc Oxide Arrays.

Electrocatalytic CO2 -to-syngas (gaseous mixture of CO and H2 ) is a promising way to curb excessive CO2 emission and the greenhouse gas effect. Herein, we present a bimetallic AuZn@ZnO (AuZn/ZnO) catalyst with high efficiency and durability for the electrocatalytic reduction of CO2 and H2 O, which enables a high Faradaic efficiency of 66.4 % for CO and 26.5 % for H2 and 3 h stability of CO2 -to-syngas at -0.9 V vs. the reversible hydrogen electrode (RHE). The CO/H2 ratios show a wide range from 0.25 to 2.50 over a narrow potential window (-0.7 V to -1.1 V vs. RHE). In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy combined with density functional theory calculations reveals that the bimetallic synergistic effect between Au and Zn sites lowers the activation energy barrier of CO2 molecules and facilitates electronic transfer, further highlighting the potential to control CO/H2 ratios for efficient syngas production using the coexisting Au sites and Zn sites.

Sandwiched Epitaxy Growth of 2D Single-Crystalline Hexagonal Bismuthene Nanoflakes for Electrocatalytic CO2 Reduction.

Two-dimensional (2D) bismuthene is predicted to possess intriguing physical properties, but its preparation remains challenging due to the high surface energy constraint. Herein, we report a sandwiched epitaxy growth strategy for the controllable preparation of 2D bismuthene between a Cu foil substrate and a h-BN covering layer. The top h-BN layer plays a crucial role in suppressing the structural transformation of bismuthene and compensating for the charge transfer from the bismuthene to the Cu(111) surface. The bismuthene nanoflakes present a superior thermal stability up to 500 °C in air, attributed to the passivation effect of the h-BN layer. Moreover, the bismuthene nanoflakes demonstrate an ultrahigh faradaic efficiency of 96.3% for formate production in the electrochemical CO2 reduction reaction, which is among the highest reported for Bi-based electrocatalysts. This study offers a promising approach to simultaneously synthesize and protect 2D bismuthene nanoflakes, which can be extended to other 2D materials with a high surface energy.

Continuous Production of Formic Acid Solution from Electrocatalytic CO 2 Reduction Using Mesoporous Bi 2 O 3 Nanosheets as Catalyst

Continuous Production of Formic Acid Solution from Electrocatalytic CO ₂ Reduction Using Mesoporous Bi ₂ O ₃ Nanosheets as Catalyst

Customizing Highly Asymmetrical Coordination Microenvironment into P‐Block Metal Single‐Atom Sites to Boost Electrocatalytic CO2 Reduction

AbstractThe coordination microenvironment modulation of single‐atom catalysts (SACs) based on p‐block metals holds promise for excavating their enormous potential in electrochemical CO2‐to CO conversion. Guided by the instructive theoretical calculations over serial asymmetric coordination microenvironments, herein, a novel Pb SAC with highly asymmetric coordination microenvironment (Pb‐N2SV) is developed. Namely, the Pb atom is coordinated with two N atoms, one S atom and one vacancy nearby. With the breaking of coordination symmetry, the obtained Pb‐N2SV shows excellent ECR performance with 97.3% Faradaic efficiency of CO at −0.47 V, and long‐term stability of 33 h, which exceeds the vast majority of main‐group SACs. More importantly, in situ spectroscopy and density functional theory (DFT) studies unveil that the S doping in Pb SAC can significantly improve electron localization around Pb sites to facilitate *COOH intermediate adsorption, while the introduction of vacancy defect nearby the Pb sites can function as a synergistic modulation on the electronic structure for favorable *CO intermediate desorption, which jointly contributes to achieve the suitable adsorption energy for reaction intermediates to boost the ECR process. As an expandability, this approach will be widely used to construct SACs with unique coordination microenvironment for other challenging catalysis.

A Bismuth‐Based Zeolitic Organic Framework with Coordination‐Linked Metal Cages for Efficient Electrocatalytic CO2 Reduction to HCOOH

AbstractZeolitic metal–organic frameworks (ZMOFs) have emerged as one of the most promsing catalysts for energy conversion, but they suffer from either weak bonding between metal‐organic cubes (MOCs) that decrease their stability during catalysis processes or low activity due to inadequate active sites. In this work, through ligand‐directing strategy, we successfully obtain an unprecedented bismuth‐based ZMOF (Bi‐ZMOF) featuring a ACO topological crystal structure with strong coordination bonding between the Bi‐based cages. As a result, it enables efficient reduction of CO2 to formic acid (HCOOH) with Faradaic efficiency as high as 91 %. A combination of in situ surface‐enhanced infrared absorption spectroscopy and density functional theory calculation reveals that the Bi−N coordination contributes to facilitating charge transfer from N to Bi atoms, which stabilize the intermediate to boost the reduction efficiency of CO2 to HCOOH. This finding highlights the importance of the coordination environment of metal active sites on electrocatalytic CO2 reduction. We believe that this work will offer a new clue to rationally design zeolitic MOFs for catalytic reaction

Calix[8]arene‐Based Manganese Complexes for Electrocatalytic CO2 Reduction

AbstractTransition metal catalysts with modified second‐coordination sphere employed in the electrocatalytic CO2 can result in increased activity or directed product selectivity. Calixarenes can form metal complexes and potentially catalyze reactions within its cavity, taking advantage of the surrounding phenols groups to tune the reactivity by second‐coordination sphere effects. Here, we present a Mn(I) bromotricarbonyl complex with phenanthroline‐functionalized calix[8]arene ligands capable of electrocatalytically reducing CO2 into different products with 2,2,2‐trifluoroethanol as proton donor. The selectivity of the reaction seems to be affected by the calixarene cavity: two calixarene‐free analogous complexes reduce CO2 to CO almost exclusively, while the calixarene complexes produce primarily CO, H2. Interestingly, in some cases the less frequently observed CH4 was also detected, albeit with low Faradaic efficiency. Thus, the manganese center placed within the calixarene cavity promotes the formation of reduced CO2 products by more than two electrons and two protons, affording CH4 in some cases.

Rational Design of Advanced Metal Organic Framework‐Based Nanostructured Catalysts toward Electrocatalytic CO2 Conversion: A Mini Review

Carbon dioxide emission into the atmosphere, which originates from fossil fuels consumption, has led to a serious environmental and energy crisis. Electrochemical CO2 reduction reaction (CO2RR) into valuable chemicals such as carbon monoxide, ethanol, ethylene, and methane not only help lower the CO2 concentration in the atmosphere but is also beneficial for sustainable energy production. Therefore, numerous works are assigned to improving efficient electrocatalytic materials for the selective CO2RR. Metal–organic framework (MOF)‐derived catalytic materials mostly based on transition metals demonstrate permissible CO2RR owing to their specific composition, tunable surface nanostructure and texture, and affordable market prices. In this work, the best effort is put to describe the most basic concept of electrochemical CO2RR to provide a consensus. The effect of MOF structure and surface analysis are discussed. This is reason that MOFs as catalysts for electrochemical CO2RR offers several advantages over traditional catalysts, such as tunable surface structure, multifunctionality, selectivity control, and stability under CO2RR operation. And then, some of the most recent reported works on MOF‐based catalysts are summarized, to provide and inspire further investigations and ideas in this research field. However, despite these advantages, there are still research gaps that need to be addressed. Some of these gaps include being cost‐effective and economical process for preparing MOF‐based catalysts, long‐term stability for industrial usage, and scalability of the catalyst. Thereby, further studies are essential to fully exploit the potential of MOFs in advancing CO2RR technologies.

Multiscale CO2 Electrocatalysis to C2+ Products: Reaction Mechanisms, Catalyst Design, and Device Fabrication.

Electrosynthesis of value-added chemicals, directly from CO2, could foster achievement of carbon neutral through an alternative electrical approach to the energy-intensive thermochemical industry for carbon utilization. Progress in this area, based on electrogeneration of multicarbon products through CO2 electroreduction, however, lags far behind that for C1 products. Reaction routes are complicated and kinetics are slow with scale up to the high levels required for commercialization, posing significant problems. In this review, we identify and summarize state-of-art progress in multicarbon synthesis with a multiscale perspective and discuss current hurdles to be resolved for multicarbon generation from CO2 reduction including atomistic mechanisms, nanoscale electrocatalysts, microscale electrodes, and macroscale electrolyzers with guidelines for future research. The review ends with a cross-scale perspective that links discrepancies between different approaches with extensions to performance and stability issues that arise from extensions to an industrial environment.

Mechanistic understanding of the electrocatalytic conversion of CO into C2+ products by double-atom catalysts

Electrocatalytic CO reduction reaction (CORR) has gained increasing attentions to generate valuable multi-carbon (C2+) products, and designing high-performance electrocatalysts for CORR presents a great challenge for realizing its practical application. With the unique dual-atom site, double-atom catalyst (DAC) can provide enough geometric space to bind two CO molecules simultaneously for the key C–C coupling reaction. Herein, taking the typical 3d transition metal (TM) dimer anchored N-doped graphene (denoted as M1M2@NG) as representative, using first-principles calculations we theoretically investigate the catalytic mechanism and activity origin of CORR on DACs. It is found that the metal sites with higher d-band centers can effectively bind CO molecule, and further the d-band centers can be used as descriptors to predict the coupling free energy and coupling energy barrier for the key C–C coupling step of CO dimers. Intriguingly, among 21 candidates, CrCo and MnCo@NG DACs exhibit excellent performance for selectively generating ethanol (CH3CH2OH), with small C–C coupling energy barriers of 0.52 and 0.57 eV and ultralow limiting potentials of only −0.20 and −0.34 V, respectively, which has been further confirmed by the constant-potential simulations. Moreover, both heteronuclear CrCo and MnCo@NG exhibit significantly enhanced CORR performance compared with their homonuclear counterparts, which is ascribed to the unique d orbital synergy effect of the two different TM atoms. Our work provides rational guidelines for the design of efficient DACs for CORR, and brings useful insights into the boosted CORR performance enabled by the electronic synergy effect of the heteronuclear dual-atom site.

Enhanced electrocatalytic CO2 reduction performance of Co‐porphyrin derivatives supported on CNTs with methylation of the hydroxyl and carboxyl groups

Metal‐porphyrin complexes with a well‐defined M‐N4 structure are a class of electrocatalyst materials that can be reasonably designed to exhibit high electrochemical carbon dioxide reduction (CO2RR) performance. The substituent effect of metal‐porphyrin complexes plays an important role in CO2RR. Herein, Co‐porphyrins with different substituents of ‐COOCH3, ‐OCH3, ‐COOH, and ‐OH (denoted as CoTCMePP, CoTOMePP, CoTCPP, and CoTOPP) were prepared and uniformly anchored on carbon nanotubes. CoTCMePP/CNTs exhibited a higher FE (CO) of 94.5% with a current density of 12.9 mA cm−2 and a TOF of 705 h−1 at −0.77 V versus RHE in 0.5 M KHCO3 than that of CoTCPP/CNTs. Meanwhile, the performance of CoTOMePP/CNTs was superior to CoTOPP/CNTs in FE (CO) and stability. The methylated derivatives exhibited enhanced electrocatalytic CO2 reduction performance, for the methylation of the hydroxyl and carboxyl might increase the solubility and suppress the aggregation of metal‐porphyrin, helping Co‐porphyrins disperse on the carbon nanotubes better.

Self-Standing Pd-Based Nanostructures for Electrocatalytic CO Oxidation: Do Nanocatalyst Shape and Electrolyte pH Matter?

Tailoring the shape of Pd nanocrystals is one of the main ways to enhance catalytic activity; however, the effect of shapes and electrolyte pH on carbon monoxide oxidation (COOxid) is not highlighted enough. This article presents the controlled fabrication of Pd nanocrystals in different morphologies, including Pd nanosponge via the ice-cooling reduction of the Pd precursor using NaBH4 solution and Pd nanocube via ascorbic acid reduction at 25 °C. Both Pd nanosponge and Pd nanocube are self-standing and have a high surface area, uniform distribution, and clean surface. The electrocatalytic CO oxidation activity and durability of the Pd nanocube were significantly superior to those of Pd nanosponge and commercial Pd/C in only acidic (H2SO4) medium and the best among the three media, due to the multiple adsorption active sites, uniform distribution, and high surface area of the nanocube structure. However, Pd nanosponge had enhanced COOxid activity and stability in both alkaline (KOH) and neutral (NaHCO3) electrolytes than Pd nanocube and Pd/C, attributable to its low Pd-Pd interatomic distance and cleaner surface. The self-standing Pd nanosponge and Pd nanocube were more active than Pd/C in all electrolytes. Mainly, the COOxid current density of Pd nanocube in H2SO4 (5.92 mA/cm2) was nearly 3.6 times that in KOH (1.63 mA/cm2) and 10.3 times that in NaHCO3 (0.578 mA/cm2), owing to the greater charge mobility and better electrolyte-electrode interaction, as evidenced by electrochemical impedance spectroscopy (EIS) analysis. Notably, this study confirmed that acidic electrolytes and Pd nanocube are highly preferred for promoting COOxid and may open new avenues for precluding CO poisoning in alcohol-based fuel cells.

High-Performance Electrocatalytic CO2 Reduction for CO Generation Using Hydrophobic Porous Carbon Supported Au

High-Performance Electrocatalytic CO₂ Reduction for CO Generation Using Hydrophobic Porous Carbon Supported Au

Phosphine‐Triggered Structural Defects in Au44 Homologues Boost Electrocatalytic CO2 Reduction

AbstractThe systematic induction of structural defects at the atomic level is crucial to metal nanocluster research because it endows cluster‐based catalysts with highly reactive centers and allows for a comprehensive investigation of viable reaction pathways. Herein, by substituting neutral phosphine ligands for surface anionic thiolate ligands, we establish that one or two Au3 triangular units can be successfully introduced into the double‐stranded helical kernel of Au44(TBBT)28, where TBBT=4‐tert‐butylbenzenethiolate, resulting in the formation of two atomically precise defective Au44 nanoclusters. Along with the regular face‐centered‐cubic (fcc) nanocluster, the first series of mixed‐ligand cluster homologues is identified, with a unified formula of Au44(PPh3)n(TBBT)28−2n (n=0–2). The Au44(PPh3)(TBBT)26 nanocluster having major structural defects at the bottom of the fcc lattice demonstrates superior electrocatalytic performance in the CO2 reduction to CO. Density functional theory calculations indicate that the active site near the defects significantly lowers the free energy for the *COOH formation, the rate‐determining step in the whole catalytic process.