Identification of Ni–N4 Active Sites in Atomically Dispersed Ni Catalysts for Efficient Chlorine Evolution Reaction

Chlorine (Cl₂) is one of the most important chemicals in the chemical industry, which is primarily produced by the electrochemical chlorine evolution reaction (CER) in the chlor-alkali process. While platinum-group metal (PGM)-based dimensionally stable anodes (DSAs) have dominated over the last half century, atomically dispersed catalysts (ADCs) have recently emerged as a promising class of CER catalysts; however, they still rely on PGMs. In this work, we prepared a series of non-PGM (Fe, Co, Ni, and Cu)-based ADCs and investigated their CER reactivity trends. Among these, the Ni ADC exhibited the best CER activity and kinetics. Notably, its CER activity exceeded those of commercial DSA and reported non-PGM-based catalysts. In situ X-ray absorption spectroscopy and X-ray photoelectron spectroscopy analyses combined with density functional theory calculations revealed that the Ni-N₄ motif serves as a major active site for the CER. The Ni-loading-controlled Ni ADCs confirmed the involvement of Ni-N₄ sites as active sites in the formation of Cl₂. Overall, our findings pave the way for extending ADC-based CER catalysts to non-PGM compositions.