Ultrasmall Nickel Nanoclusters Accelerating Protonation for Efficient CO ₂ Electroreduction towards CO

Abstract

Abstract Proton‐coupled electron transfer (PCET), particularly the protonation step is widely recognized as the kinetic bottleneck in electrochemical CO 2 reduction (CO 2 RR). Modulating catalyst microstructures to accelerate protonation has thus emerged as a promising strategy to boost from CO 2 to CO selectivity. Here, we report ultrasmall Ni nanocluster catalysts (denoted as Ni 3 ─N─C) prepared via one‐step pyrolysis of Ni‐containing precursors under H 2 atmosphere. Compared to conventional Ni─N─C with symmetric Ni─N 4 motifs, Ni 3 ─N─C displays similar physicochemical characteristics—Ni loading, defect density, surface area—yet exhibits distinct local Ni coordination environments. These sub‐nanoclusters markedly enhance CO 2 RR performance, delivering > 90% CO Faradaic efficiency (FE CO ) across −0.6 to −1.0 V versus RHE, with a peak FE CO of ∼95% at −0.8 V. Density functional theory calculations reveal that Ni 3 ─N─C substantially lowers the energy barrier for *COOH formation owing to altered adsorption configurations, thereby facilitating the rate‐limiting protonation step. In situ FTIR measurements further confirm the accelerated *COOH formation on Ni 3 ─N─C surfaces. This work highlights the critical role of Ni sub‐nanoclusters in PCET modulation and establishes a rational design principle for nanocluster‐based catalysts in CO 2 RR.