Phase-Dependent Electrochemical CO₂ Reduction Ability of NiSn Alloys for Formate Generation

Bimetallic alloys are important catalysts with enhanced catalytic activities and product selectivities. However, the phase dependence of catalytic activity in bimetallic alloys afford contradictory characters in that one phase catalyzes the main reaction and the other catalyzes the side reaction; this aspect of bimetallic alloy catalysts has not been investigated. In this study, we systematically synthesized NiSn alloys from Ni, which is catalytically active in hydrogen generation, and Sn, which is catalytically active in electrochemical CO2 reduction. The thus-prepared alloys were applied in catalyzing the phase-dependent electrochemical CO2 reduction, and the formate generation mechanism was elucidated. The Faradaic efficiency of formate was found to increase with increasing Sn atomic concentration, and Ni3Sn4 showed higher catalytic activity than only Sn for electrochemical CO2 reduction. Density functional theory calculations revealed that Ni can additionally provide catalytically active sites for formate generation in a suitable phase. Thus, our investigation brings a better understanding of the catalytic activities of bimetallic alloys prepared from metals with different characters for electrochemical CO2 reduction.