Abstract

The development of stable and efficient electrocatalysts is essential for the advancement of water splitting technologies. Herein, we present a simple strategy for directly growing nanoscale cobalt selenide (CoSe) on a macroporous conducting carbon substrate (PCS) to form binder-free electrocatalysts. Notably, the nanoscale phases and morphologies of CoSe can be readily adjusted by altering the electrodeposition process. Through repeated chronoamperometry, tetragonal phase CoSe (t-CoSe) was obtained, whereas hexagonal-phase CoSe (h-CoSe) is achieved using cyclic voltammetry. Optimized t-CoSe@PCS demonstrated superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance, achieving overpotentials of 59.4 and 290 mV with Tafel slopes of 40 and 44.9 mV dec^–1, respectively. For overall water splitting, a cell voltage of only 1.76 V was required at 10 mA cm^–2, with excellent stability maintained for over 25 h. Density functional theory (DFT) calculations indicated that hydrogen adsorption was more favorable on h-CoSe; however, the enhanced activity of t-CoSe was attributed to its porous structure, higher electrochemical surface area, and increased Co³⁺content, which promoted charge transfer and active site accessibility. These findings underscore the significance of phase engineering and structural design in enhancing the electrocatalyst performance for efficient overall water splitting.