Directional Elements Migration in Bulkphase Promoting Surface Sulfur Fixation for Highly Stable Water Splitting

Transition metal chalcogenides have been considered as one kind of the most potential candidate catalysts for oxygen evolution reaction (OER). However, the inevitable sulfur loss during reconstruction process destructs the chemical and electronic structure of catalysts. Herein, we proposed directional metal element migration to fix sulfur on near-surface region, and evaluated the effect of lattice oxygen compensation on the stability of surface sulfur. Besides, an ‘etching-compensation factor’ of lattice oxygen is defined as a descriptor on the OER stability with coupled O─O as the key intermediates. It is found that the migration of Fe and S in opposite directions enables high voltage-dependent reversibility of Ni─O─Fe units during OER for self-healing of electrode. The further produced full gradient NiFe-sulfide electrode can stably work for more than 50 000 CV cycles at the scan rate of 50 mV s −1 , and 800 h of chronopotentiometric at current density of 100 mA cm −2 .