Synergistic Active Heterostructure Design for Enhanced Two Electron Oxygen Reduction via Chemical and Electrochemical Reconstruction of Heterosulfides

Transition metal sulfides, particularly heterostructures, represent a promising class of electrocatalysts for two electron oxygen reduction (2e − ORR), however, understanding the dynamic structural evolution of these catalysts during alkaline ORR remains relatively unexplored. Herein, NiS 2 /In 2.77 S 4 heterostructure was synthesized as a precatalyst and through a series of comprehensive ex situ and in situ characterizations, including X‐ray absorption spectroscopy, Raman spectroscopy, transient photo‐induced voltage measurements, electron energy loss spectroscopy, and spherical aberration‐corrected electron microscopy, it was revealed that nickel/indium (oxy)hydroxides (NiOOH/In(OH) 3 ) could be evolved from the initial NiS 2 /In 2.77 S 4 via both electrochemical and chemical‐driven methods. The electrochemical‐driven phase featured abundant bridging oxygen‐deficient [NiO 6 ]‐[InO 6 ] units at the interfaces of NiOOH/In(OH) 3 , facilitating a synergistic effect between active Ni and In sites, thus enabling an enhanced alkaline 2e − ORR capability than that of chemical‐driven process. Remarkably, electrochemically induced NiOOH/In(OH) 3 exhibited exceptional performance, achieving H 2 O 2 selectivity of >90 % across the wide potential window (up to 0.4 V) with a peak selectivity of >99 %. Notably, within the three‐electrode flow cell, a current density of 200 mA cm −2 was sustained over 20 h, together with an impressive Faradaic efficiency of ~90 % during the whole cycle process.