Ultrathin nickel-iron carbonate hydroxides nanosheets/sulfides (denoted as NixFeyS/CH) are fabricated by sulfurizing treatment of nickel-iron carbonate hydroxide (NixFeyCH). The partial sulfuration of NiFe carbonate hydroxides by replacing the CO3/OH groups with the S group can well remain the hexagonal morphology, regulate the electronic structure and expose more electrochemical active sites. Benefiting from the ultrathin-layered sheet with mesoporous structure for more available active sites, the strong coupling between metal carbonate hydroxides/sulfides, as well as bimetal synergism for modulation the composition and electronic structure, the optimal NixFeyS/CH exhibits excellent OER catalytic performance, which reaches 20 mA cm(-2) at an ultra-small overpotential of 261 mV, lower Tafel slope (103 mV dec(-1)) and outstanding stability. This work highlights the importance regarding the modulation of composition and electronic structure by the interface coupling and bimetal synergism for boosting OER performance. (C) 2019 Elsevier Ltd. All rights reserved.