Atomic-level dispersed nickel sites embedded in carbon support for efficient electrochemical CO2 reduction

Single-atom catalysts have shown exceptional activity and selectivity for CO₂ electrochemical reduction reaction (CO₂ERR) owing to the clearly defined and accessible active metallic sites. However, the role of Ni dispersion state (atomic vs. aggregated) on catalytic performance has remained elusive. Herein, we report the exploration of dispersion state effects on activities by synthesizing catalysts embedded with Ni single atoms or aggregated particles. The catalyst with highly-dispersed Ni single atoms shows the highest Faradaic efficiency (FE_CO) for CO (96 % at -0.75 V vs. RHE) and the FE_CO could be retained for 12 h without a significant decay. While the catalyst with crystalline Ni particles shows a decreased FE_CO of 80 % and the catalyst with no Ni shows a least FE_CO of 38 % towards CO. The above experiments indicate that Ni metallic sites are the active centers for CO₂ERR and atomic dispersion of Ni metallic sites plays a vital role in CO₂ERR performance. Density functional theory (DFT) calculations reveal that the energy barrier of CO₂ERR is reduced when Ni is in atomic dispersion rather than aggregation. The findings here have significant implications on a broad field of energy catalysis.