Copper Doping Boosts Electrocatalytic CO2 Reduction of Atomically Precise Gold Nanoclusters.

Electrocatalytic CO2 reduction (CO2RR) has emerged as a promising approach for converting CO2 into valuable chemicals and fuels to achieve a sustainable carbon cycle. However, the development of efficient electrocatalysts with high current densities and superior product selectivity remains a significant challenge. In this study, we present the synthesis of a porous nitrogen-doped carbon nanosheet loaded with heterostructured Ni/Ni3ZnC0.7 nanoparticles through a facile hydrothermal-calcination method (Ni/Ni3ZnC0.7-NC). Remarkably, the Ni/Ni3ZnC0.7-NC catalyst exhibits outstanding performance towards CO2RR in an H-cell, demonstrating a high CO faradaic efficiency of 92.47% and a current density (jCO) of 15.77 mA cm-2 at 0.87 V vs. RHE. To further explore its potential industrial applications, we constructed a flow cell and a rechargeable Zn-CO2 flow cell utilizing the Ni/Ni3ZnC0.7-NC catalyst as the cathode. Impressively, not only does the Ni/Ni3ZnC0.7-NC catalyst achieve an industrial high current density of 254 mA cm-2 at a voltage of -1.19 V vs. RHE in the flow cell, but it also exhibits a maximum power density of 4.2 mW cm-2 at 22 mA cm-2 in the Zn-CO2 flow cell, while maintaining excellent rechargeability. Density functional theory (DFT) calculations indicate that Ni/Ni3ZnC0.7-NC possesses more spontaneous reaction pathways for CO2 reduction to CO, owing to its heterogeneous structure in contrast to Ni3ZnC0.7-NC and Ni-NC. Consequently, Ni/Ni3ZnC0.7-NC demonstrates accelerated CO2RR reaction kinetics, resulting in improved catalytic activity and selectivity for CO2RR.

The general synthesis and control of the coordination environment of single-atom catalysts (SACs) remains a great challenge. Herein, a general host-guest cooperative protection strategy has been developed to construct SACs by introducing polypyrrole (PPy) into a bimetallic metal-organic framework. As an example, the introduction of Mg2+ in MgNi-MOF-74 extends the distance between adjacent Ni atoms; the PPy guests serve as N source to stabilize the isolated Ni atoms during pyrolysis. As a result, a series of single-atom Ni catalysts (named NiSA -Nx -C) with different N coordination numbers have been fabricated by controlling the pyrolysis temperature. Significantly, the NiSA -N2 -C catalyst, with the lowest N coordination number, achieves high CO Faradaic efficiency (98 %) and turnover frequency (1622 h-1 ), far superior to those of NiSA -N3 -C and NiSA -N4 -C, in electrocatalytic CO2 reduction. Theoretical calculations reveal that the low N coordination number of single-atom Ni sites in NiSA -N2 -C is favorable to the formation of COOH* intermediate and thus accounts for its superior activity.

Developing efficient and stable electrocatalysts within a wide potential range is vital for the mature applications of the electrocatalytic CO2 reduction reaction (CO2RR) into value-added chemical products. Herein, we engineered a NC@Ni/C nano-composite featuring a core–shell structure of a pyridinic-N-rich carbon layer encapsulating Ni nanoparticles (NPs) as a highly effective electrocatalyst for CO2RR to CO over a wide potential range. The catalyst demonstrates a high CO Faradaic efficiency (FECO) of >90% in a wide potential range from −0.65 to −1.45 V [vs reversible hydrogen electrode (RHE)] with the maximum FECO of 97% at −1.05 V (vs RHE). Strikingly, it exhibits an excellent stability with a constant current density and a FECO > 95% for 92 h at −1.05 V (vs RHE). Structural studies and DFT calculations further reveal that pyridinic-N doping in the carbon shell of Ni NPs plays a dual role in promoting the CO2RR activity. It not only alleviates the mass transfer limitation of CO2 by enhancing the CO2 adsorption capacity, but it also lowers the reaction energy barrier of the *COOH formation rate-determining step with the electronic structure modulation by Ni. This work may shed more light on the seeking of practical catalysts for high-efficiency electrochemical CO2 reduction over a broad potential window.

We report the synthesis, structure analysis, and electrocatalytic CO2 reduction application of Ag19Cu2(CCArF)12(PPh3)6Cl6 (abbreviated as Ag19Cu2, CCArF: 3,5-bis(trifluoromethyl)phenylacetylene) nanoclusters. Ag19Cu2 has characteristic absorbance features and is a superatomic cluster with 2 free valence electrons. Single-crystal X-ray diffraction (SC-XRD) revealed that the metal core of Ag19Cu2 is composed of an Ag11Cu2 icosahedron connected by two Ag4 tetrahedra at the two terminals of the Cu-Ag-Cu axis. Notably, Ag19Cu2 exhibited excellent catalytic performance in the electrochemical CO2 reduction reaction (eCO2RR), manifested by a high CO faradaic efficiency of 95.26% and a large CO current density of 257.2 mA cm-2 at -1.3 V. In addition. Ag19Cu2 showed robust long-term stability, with no significant drop in current density and FECO after 14 h of continuous operation. Density functional theory (DFT) calculations disclosed that the high selectivity of Ag19Cu2 for CO in the eCO2RR process is due to the shedding of the -CCArF ligand from the Ag atom at the very center of the Ag4 unit, exposing the active site. This study enriches the potpourri of alkynyl-protected bimetallic nanoclusters and also highlights the great advantages of using atomically precise metal nanoclusters to probe the atomic-level structure-performance relationship in the catalytic field.

Electrocatalytic reduction of carbon dioxide over reduced nanoporous zinc oxide

Electrocatalytic CO2 reduction reaction (CO2RR) using membrane electrode assembly (MEA) systems requires complex regulation of protons, hydroxyls, carbonate ions and alkali-metal ions across both electrodes to efficiently produce multicarbon products. In acid-fed CO₂RR MEAs, excessive proton migration and accumulation on the catalyst surface suppress CO₂ adsorption and promote hydrogen evolution, leading to low Faradaic and energy efficiencies. Sluggish hydroxide transport further triggers carbonate precipitation, undermining system stability. Here we report an acid-fed membrane electrode assembly system for highly efficient CO2RR by integrating hydrazone-linked covalent organic framework (COF) and catalyst on the anion-exchange membrane to enable bidirectional pathway for hydroxide and potassium ions diffusion, while enhancing transport of CO2 to the catalyst surface. As a result, the scaled-up MEA operates at a full-cell voltage of ~4.5 V under a total current of 10 A (current density of 204 mA cm⁻²), delivering a Faradaic efficiency of ~50% for CO₂-to-C₂H₄ conversion and maintaining stability for over 300 hours.

Unsaturated Ni single-atom catalysts (SACs), Ni-Nx (x=1,2,3), have been investigated to break the conventional Ni-N4 structural limitation and provide more unoccupied 3d orbitals for CO2 reduction reaction (CO2RR) intermediates adsorption, but their intrinsically low structural stability has seriously hindered their applications. Here, we developed a strategy by integrating Ni nanoclusters to stabilize unsaturated Ni-N3 atomic sites for efficient CO2 electroreduction to CO at industrial-level current. Density Functional Theory (DFT) calculations revealed that the incorporation of Ni nanocluster effectively stabilizes the unsaturated Ni-N3 atomic sites and modulates their electronic structure to enhance the adsorption of the key intermediate *COOH during CO2RR. Guided by these insights, we prepared an optimal composite catalyst, Ni6@Ni-N3, which features a Ni6N6 nanocluster surrounded by six Ni-N3 single atoms sites, through low-temperature pyrolysis. The morphology and coordinative structure of Ni6@Ni-N3 were confirmed by an aberration-corrected transmission electron microscope (AC-TEM) and X-ray absorption spectroscopy (XAS). As a result, Ni6@Ni-N3 demonstrated a remarkably high CO Faradaic efficiency (FECO) of 99.7 % and a turnover frequency (TOF) of 83984.2 h-1 at 500 mA cm-2 under -1.15 VRHE, much better than those of Ni-N4 with a lower FECO of 86 % at 100 mA cm-2 and a TOF of 39309.9 h-1under identical potential. XAS analyses of Ni6@Ni-N3 before and after long-term CO2RR testing confirmed the excellent stability of its coordinative environment. This work highlights a generalizable approach for stabilizing unsaturated single-atom catalysts, paving the way for their application in high-performance CO2RR.

Developing diatomic catalysts (DACs) for the CO2 reduction reaction (CO2RR) has emerged as a promising leading-edge research area owing to their maximum atomic utility and more sophisticated functionalities. However, the proper design of DACs at an atomic level and an understanding of the synergistic mechanism of binary sites remain challenging. Herein, an N-rich carbon matrix with precisely controlled Ni/Cu dual sites is synthesized through the assistance of metal–organic frameworks. The as-prepared catalyst presents high CO Faradaic efficiency of over 95% from −0.39 to −1.09 V vs reversible hydrogen electrode (RHE) with the maximum value of 99.2% at −0.79 V vs RHE and long-term durability of 60 h electrolysis. Density functional theory studies reveal that the electronic redistribution and band gap narrowing induced by the adjacent NiN4 and CuN4 moieties enhance the electron conductivity and strengthen the bonding interactions between *COOH intermediates and Ni centers, thus lowering the overall reaction barriers and promoting CO generation.

Enhanced OH− conductivity and stability of polybenzimidazole membranes for electrocatalytic CO2 reduction via grafting and crosslinking strategies

Atomically dispersed iron immobilized on nitrogen-doped carbon catalyst has attracted enormous attention for CO2 electroreduction, but still suffers from low current density and poor selectivity. Herein, atomically dispersed FeN5 active sites supported on defective N-doped carbon successfully formed by a multistep thermal treatment strategy with the aid of dicyandiamide are reported. This dual-functional strategy can not only construct intrinsic carbon defects by selectively etching pyridinic-N and pyrrolic-N, but also introduces an additional N from the neighboring carbon layer coordinating to the commonly observed FeN4 , thus creating an FeN5 active site supported on defective porous carbon nanofibers (FeN5 /DPCF) with a local 3D configuration. The optimized FeN5 /DPCF achieves a high CO Faradaic efficiency (>90%) over a wide potential range of -0.4 to -0.6V versus RHE with a maximal FECO of 93.1%, a high CO partial current density of 9.4mAcm-2 at the low overpotential of 490mV, and a remarkable turnover frequency of 2965 h-1 . Density functional theory calculations reveal that the synergistic effect between the FeN5 sites and carbon defects can enhance electronic localization, thus reducing the energy barrier for the CO2 reduction reaction and suppressing the hydrogen evolution reaction, giving rise to the superior activity and selectivity.

Carbon dioxide electroreduction over imidazolate ligands coordinated with Zn(II) center in ZIFs

Hydroxyl-engineered Ag nanoparticles achieves almost 100% faradaic efficiency in electrocatalytic CO2 reduction to CO over wide potential windows.

Transition metal nitrogen carbon based single‐atom catalysts (SACs) have exhibited superior activity and selectivity for CO2 electroreduction to CO. A favorable local nitrogen coordination environment is key to construct efficient metal‐N moieties. Here, a facile plasma‐assisted and nitrogen vacancy (NV) induced coordinative reconstruction strategy is reported for this purpose. Under continuous plasma striking, the preformed pentagon pyrrolic N‐defects around Ni sites can be transformed to a stable pyridinic N dominant Ni‐N2 coordination structure with promoted kinetics toward the CO2‐to‐CO conversion. Both the CO selectivity and productivity increase markedly after the reconstruction, reaching a high CO Faradaic efficiency of 96% at mild overpotential of 590 mV and a large CO current density of 33 mA cm‐2 at 890 mV. X‐ray adsorption spectroscopy and density functional theory (DFT) calculations reveal this defective local N environment decreases the restraint on central Ni atoms and provides enough space to facilitate the adsorption and activation of CO2 molecule, leading to a reduced energy barrier for CO2 reduction.

Silica-nickel catalyst interfaces promote highly efficient CO2 electroreduction to CO with a wide potential range

The selectivity between CO and HCOOH in the 2e- CO2 reduction reaction on heterogeneous single-atom catalysts (SACs) remains mechanistically contested. We propose a novel selectivity-determining step using ab initio molecular dynamics with slow-growth sampling method, taking p-block bismuth SACs as an example. The complete free energy calculation results demonstrate the second proton-coupled electron transfer step (COOH protonation) dictates both the rate-determining kinetics and ultimate product selectivity, contrary to the prevailing paradigm focusing on initial *COOH vs *OCHO formation. The alkali metal cation identity (AM+ = Li+, Na+, K+, Cs+) critically modulates this step; Li+ promotes C atom protonation of *COOH, leading to HCOOH. Na+/K+/Cs+ favor O atom protonation to yield CO with activity increasing following cation radius (Li+ < Na+ < K+ < Cs+). Specifically, K+/Cs+ enables the proton preadsorption in one of four N sites of the BiN4/G without energy barrier, simultaneously boosting CO2RR kinetics and suppressing HER, which matches well with experimental measurements by high CO Faradaic efficiency (92%) at the -0.5 V vs reversible hydrogen electrode. This work puts forward an innovative selectivity mechanism toward the strategic design of a CO or HCOOH product on the basis of distinct AM+ cation identity, which can also apply to other electrochemical interface systems, such as the metal-water system.