Co3S4 nanosheets on Ni foam (NS/NF) were prepared by sulfurization for various time after calcination of electrodeposited Co(OH)(2). In our FE-SEM images, we observed that Co3S4 NS was vertically, or obliquely, deposited on the Ni foam. As a result, the structure contained more active sites, and active sites were highly accessible to the electrolyte for the hydrogen evolution reaction (HER). Furthermore, results of XPS and XRD analysis confirmed S-conversion from Co3O4 to Co3S4 during sulfurization. 3-Co3S4 NS/NF with sulfurization for 3 h exhibited the highest sulfur content, while Co3S4 began to desulfurize to Co9S8 after sulfurization for 4 h. The 3-Co3S4 NS/NF electrocatalyst showed a lowest overpotential of 93 mV at -10 mA/cm(2), with a Tafel slope of -55.1 mV/dec in N-2-purged 1 M KOH. Also, the single cell anion exchange membrane water electrolyzer (AEMWE) showed a high current density of 431 mA/cm(2) with cell voltage 2.0 V-cell at 40-45 degrees C. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.