Nitrogen-Stabilized Low-Valent Ni Motifs for Efficient CO2 Electrocatalysis

Abstract

Single-atom catalysts have found considerable applications in the field of electrochemical CO 2 reduction reaction (CO 2 RR) due to their unique coordination environments. However, during the preparation of single-atom catalysts, some metal nanoparticles (NPs) are inevitably generated, which suffer from low selectivity in CO 2 RR. In this regard, complex postprocessing solution treatments are usually conducted to remove metal NPs using acid. Herein, we fabricated Ni(NC)-based catalysts composed of single Ni atoms and Ni NPs, both of which feature local Ni–N coordination via a simple Ni-metal organic framework (MOF)-assisted strategy. Based on X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy measurements, nitrogen species in N-doped carbon have been demonstrated to be coordinated with surface nickel species to form Ni–N motifs, which makes Ni at a low-valent state for efficient CO 2 RR. Consequently, the catalyst exhibited high performances toward CO 2 RR with CO Faradic efficiencies (FE CO ) maintained over 90% from −0.65 to −0.90 V vs reversible hydrogen electrode (RHE). More importantly, the FE CO of 99% could be obtained at a considerable current density ( j ) of −160 mA cm –2 in a flow cell configuration. These findings suggest that regulating the surface environment of Ni species can activate the original inert reaction sites into active reaction sites, providing a promising avenue to design high-performance electrocatalysts for CO 2 RR.