Covalent sulfur–oxygen linkages enhanced the localized acidic environment coupled with the hydrogen spillover effect for boosting hydrogen evolution reaction kinetics

CuFe 2 O 4 @CuFeS 2 heterostructure electrodes with covalent S–O bonds are synthesized. H 3 O + intermediates accumulate at electron-rich O δ − sites, forming a localized acidic microenvironment and accelerating the hydrogen spillover process.