Synthesis of CoP nanoarrays by morphological engineering for efficient electrochemical hydrogen production

•A method that regulates morphology by controlling ionic coordination is proposed.•CoP nanoarrays are designed by morphological engineering for alkaline HER.•CoP-NS and CoP-NN are synthesized with and without EDTA·4Na, respectively.•More exposed active sites on CoP-NS endows it higher HER activity than CoP-NN.•Fast electronic transport and mass transfer make CoP-NS catalyze HER well. Transition metal phosphides have been regarded as excellent electrocatalysts for hydrogen evolution reaction (HER), and the morphological engineering on them is one of the most effective methods to boost their HER activity. Here, the morphology of CoP nanoarrays supported on the nickel foam (NF) is controlled by morphological engineering using sodium edetate (EDTA·4Na) as a regulating factor. Through the hydrothermal-phosphating process, a self-supported electrode (NF/Ni2P/CoP-NS) with a tertiary structure of NF, Ni2P layer and CoP nanosheets is obtained. Due to the abundant exposed active sites, as well as superior conductivity and mass transfer capabilities of the nanosheets, NF/Ni2P/CoP-NS exhibits excellent hydrogen evolution reaction activity in 1.0 M KOH. It merely needs an overpotential of 64 mV to supply the current density of 10 mA cm−2, far better than the 90 mV of NF/Ni2P/CoP-NN with a nanoneedle-like morphology. The morphological engineering of introducing modifiers (such as EDTA·4Na) to control ionic coordination is expected to develop diverse two-dimensional materials for catalysis and energy storage. [Display omitted] Morphological engineering on CoP nanoarrays endows the nanosheets better HER performance than the nanoneedles.