Reconstruction of Thiospinel to Active Sites and Spin Channels for Water Oxidation

Water electrolysis is a promising technique for carbon neutral hydrogen production. A great challenge remains at developing robust and low-cost anode catalysts. Many pre-catalysts are found to undergo surface reconstruction to give high intrinsic activity in the oxygen evolution reaction (OER). The reconstructed oxyhydroxides on the surface are active species and most of them outperform directly synthesized oxyhydroxides. The reason for the high intrinsic activity remains to be explored. Here, a study is reported to showcase the unique reconstruction behaviors of a pre-catalyst, thiospinel CoFe₂S₄, and its reconstruction chemistry for a high OER activity. The reconstruction of CoFe₂S₄ gives a mixture with both Fe–S component and active oxyhydroxide (Co(Fe)O_xH_y) because Co is more inclined to reconstruct as oxyhydroxide, while the Fe is more stable in Fe–S component in a major form of Fe₃S₄. The interface spin channel is demonstrated in the reconstructed CoFe₂S₄, which optimizes the energetics of OER steps on Co(Fe)O_xH_y species and facilitates the spin sensitive electron transfer to reduce the kinetic barrier of O–O coupling. The advantage is also demonstrated in a membrane electrode assembly (MEA) electrolyzer. This work introduces the feasibility of engineering the reconstruction chemistry of the precatalyst for high performance and durable MEA electrolyzers.