Ultra-fast surface reconstruction enabled by the built-in electric field in heterostructured CoS₂/CuS for water electrolysis

Transition-metal chalcogenides (TMCs) show great potential as highly efficient and cost-effective electrocatalysts for oxygen evolution reaction (OER). Yet the electrochemical conversion into oxides/hydroxides remains poorly understood. In this work, we develop a built-in, electric-field-induced surface reconstruction strategy for ultra-fast self-activation of transition metal sites in self-supporting CoS₂/CuS heterostructures. The activated CoS₂/CuS grown on carbon cloth with oxygenated surface species displays an outstanding OER electrocatalytic activity with ultra-low overpotentials of only 136 mV at the current density of 10 mA cm⁻² and 266 mV at 100 mA cm⁻² in 1.0 M KOH. Comparative studies via synchrotron radiation X-ray absorption spectroscopy and theoretical calculations are employed to elucidate that the built-in electric field within heterointerfaces significantly promotes the reconstruction efficiency by decreasing the formation energy of (oxy)hydroxide species. We believe this work provides new perspectives to conceive catalysts with ultra-low overpotentials and complements the fundamental comprehension of TMCs’ self-reconstruction mechanism.