Effect of the nitrogen/carbon ratio in the organic ligand of a nickel single-atom catalyst on its electrochemical activity in CO2 reduction

Abstract

Simple, large-scale synthesis of metal single-atom catalysts (SACs) is limited by the aggregation of metal atoms on the support material surface. The N atoms in small organic ligands (SOLs) can anchor single metal atoms, affording abundant surface-active sites. In this study, we investigated the effect of the nitrogen/carbon ratio (N/C) in SOLs on the properties of the resultant Ni single-atom confined nitrogen-doped carbon black (Ni-NCB). The N/C ratio affected the thermal stability of Ni-NCB_N/Cs during carbonization, and the optimal Ni-NCB (Ni-NCB_0.5) was synthesized with the SOL 2-methylimidazole. Ni-NCB_0.5 achieved a CO partial current density of >？500？mA？cm？2 and high CO Faradaic efficiency (96.4？%) in the CO2 reduction reaction. The 3- and 4-cell stack systems with Ni-NCB_0.5 (25？cm2 area per unit cell) exhibited an overall current of 10？A, high CO selectivity (>？96.0？%), and long-term stability (50？h). This synthetic strategy for SACs can be commercialized and even extended to other industrial electrocatalysts.