Room-Temperature Preparation of Cobalt-Based Electrocatalysts through Simple Solution Treatment for Selectively High-Efficiency Hydrogen Evolution Reaction in Alkaline or Acidic Medium

The versatile cobalt-phosphorus (Co-P) precursor was synthesized on Ni foam (NF) with an electrodeposition method. Simple room-temperature treatment of the precursor with 1 M NaOH and 0.5 M H2SO4 allows for the production of cobalt oxide nanorods (CoxOy/NF) and cobalt phosphate/phosphide (Co-Pi/CoP/NF), respectively. The resulting CoxOy/NF shows a low overpotential (η10) of 80 mV at −10 mA/cm2 in an alkaline electrolyte (pH = 14) for a hydrogen evolution reaction (HER) toward electrocatalytic water splitting. The Co-Pi/CoP/NF exhibits a low η10 of 112 mV in an acidic electrolyte (pH = 0), in which the synergy between Co (+2) and Co (+3) may play an important role in the reaction.