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

Abstract

Single-atom catalysts have found considerable applications in the field of electrochemical CO2 reduction reaction (CO2RR) 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 CO2RR. 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 CO2RR. Consequently, the catalyst exhibited high performances toward CO2RR with CO Faradic efficiencies (FECO) maintained over 90% from -0.65 to -0.90 V vs reversible hydrogen electrode (RHE). More importantly, the FECO 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 CO2RR.