Phase-Engineered Cobalt Selenide Nanoparticles Supported on Porous Carbon Substrate as Electrocatalyst for Water Splitting

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.