Oxalic Acid-Assisted Vacancy Engineering Promotes Iron-Copper Sulfide Nanosheets for High-Current Density Water Oxidation.

The effective defect and interface coupling are pivotal for the promotion of the catalytic activity for the oxygen evolution reaction. Herein, we report novel hybrid nanosheets with sulfur vacancies composed of FeS 2 and Cu 39 S 28 grown on Cu foam (V s -FeS 2 /Cu 39 S 28 ). The optimal V s -FeS 2 /Cu 39 S 28 exhibits a high current output of 500 mA cm -2 at a low overpotential of 370 mV and robust stability for 60 h at 100 mA cm -2 , surpassing the values of most previously reported Cu-based catalysts. Furthermore, a two-electrode electrolyzer made by pairing the prepared catalyst with commercial Pt/C requires a low cell voltage of 1.75 V at 100 mA cm -2 and is retained over 80 h. Key to its excellent performance is the synergism between intertwined FeS 2 and Cu 39 S 28 domains, enriched by the deliberate introduction of sulfur vacancies, thus optimizing the electronic structure and causing the proliferation of catalytic active sites. This work presents a potent Cu-based electrocatalyst and emphasizes the leveraging of non-precious metals for efficient water oxidation.