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/InS 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)) could be evolved from the initial NiS/InS via both electrochemical and chemical-driven methods. The electrochemical-driven phase featured abundant bridging oxygen-deficient [NiO]-[InO] units at the interfaces of NiOOH/In(OH), 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) exhibited exceptional performance, achieving HO 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 was sustained over 20 h, together with an impressive Faradaic efficiency of ~90 % during the whole cycle process.