Hierarchically Structured SnO/NiCo2O4/CC Catalysts with Stability and Superior Faradaic Efficiency for Electrocatalytic CO2 Reduction to Formic Acid

SnO-based catalysts are among the most common and promising catalysts for electrocatalytic CO2 conversion, while their feature of easy deactivation greatly hinders the industrial application. Here, we developed highly stable SnO/NiCo2O4/CC catalysts by constructing SnO/NiCo2O4 hierarchical structures with a large number of complex pores on carbon cloth (CC). Through a series of characterization, we found that the solid oxide pairs (Ni3+/Co3+) contained in the SnO/NiCo2O4/CC catalysts could protect the SnO from being reduced to Sn monomers during the electrocatalytic process, greatly enhancing the stability of the electrocatalysts. The SnO/NiCo2O4/CC catalyst remained constant in current density during the 30 h CO2 conversion process, and the loss resistance activity is more than 300% of the SnO/CC catalyst. In addition, the SnO/NiCo2O4/CC catalyst presented a high faradaic efficiency of 91.87% in the CO2 electroreduction process, much higher than most of the SnO-based catalysts. The DFT calculations and analysis show that the superior faradaic efficiency is mainly attributed to the heterostructure of SnO(001)/NiCo2O4 on CC plane, which significantly reduces the Gibbs free energy of producing the *OOCH intermediates. This study provides an effective strategy in designing SnO-based electrocatalysts with high performance for CO2 reduction.