Isolated Diatomic Ni‐Fe Metal–Nitrogen Sites for Synergistic Electroreduction of CO₂

Abstract

Polynary single‐atom structures can combine the advantages of homogeneous and heterogeneous catalysts while providing synergistic functions based on different molecules and their interfaces. However, the fabrication and identification of such an active‐site prototype remain elusive. Here we report isolated diatomic Ni‐Fe sites anchored on nitrogenated carbon as an efficient electrocatalyst for CO2 reduction. The catalyst exhibits high selectivity with CO Faradaic efficiency above 90 % over a wide potential range from −0.5 to −0.9 V (98 % at −0.7 V), and robust durability, retaining 99 % of its initial selectivity after 30 hours of electrolysis. Density functional theory studies reveal that the neighboring Ni‐Fe centers not only function in synergy to decrease the reaction barrier for the formation of COOH* and desorption of CO, but also undergo distinct structural evolution into a CO‐adsorbed moiety upon CO2 uptake.

Engineering Local Coordination Environments of Atomically Dispersed and Heteroatom‐Coordinated Single Metal Site Electrocatalysts for Clean Energy‐Conversion

“…Different from isolated FeN x and CoN x sites, the EXAFS analysis suggests that the FeCo site had an unusual dual metal structure composed of two adjacent, FeCo bond linked FeN 3 /CoN 3 configurations (Figure f). This method has been extended to synthesize FeNi dual‐metal sites . In addition, ZnCo dual‐metal sites with a similar structure have been synthesized through a low‐temperature pyrolysis, which leads to the incomplete volatilization of Zn atoms, followed by acid washing and a second thermal activation at 900 °C .…”

“…To simultaneously tune the relatively weak adsorption of *COOH on Ni sites and the relatively strong adsorption of CO* on Fe sites, Ni–Fe dual metal sites (Ni/Fe–N–C) have naturally been proposed for CO 2 RR ( Figure 13 ). A Ni/Fe–N–C catalyst was synthesized through the pyrolysis of Ni, Fe‐modified ZIF‐8 precursors, where Fe ions anchored onto the nodes and Ni ions were incorporated into cavities of ZIF‐8. EXAFS results suggest that Ni/Fe–N–C adopts a deformed porphyrin‐like configuration with the NiN 3 and its neighboring FeN 3 moieties linked by a detectable Ni–Fe bond (Figure d,e).…”

“…The schematic illustration of suggested catalytic mechanism. Reproduced with permission . Copyright 2019, Wiley‐VCH.…”

Heterogeneous Single Atom Electrocatalysis, Where “Singles” Are “Married”

“…or C2 chemicals (e.g., C 2 H 4 and ethanol) would be ideally a “one stone kills two birds” story, i.e., make renewable fuels from CO 2 and at the same time solve the ever worsening environmental problem . Unfortunately, direct reduction of CO 2 to liquid fuels is still at very low efficiency, due to the very stable chemical bond of CO (806 KJ mol −1 ) in CO 2 as well as the competitive water reduction reaction in the aqueous environment . Hence, to develop robust SACs with sufficiently active sites, particularly with high selectivity and reliable stability for electrochemical CO 2 reduction would be highly desired.…”

“…In addition, there can be synergistic effects between single sites, dual sites as well as poly sites, which can effectively break the limit of the scaling relations among multistep reactions of electrocatalysis and other types of catalysis. For example, although dual metal sites have been confirmed to have lower reaction barriers and better catalytic performance than single sites, much deeper insights, such as the roles of each site and their interactions played in different catalytic steps, as well as the change in coordination during the catalytic process, needs to be investigated in detail …”