Method for the Solution Deposition of Phase-Pure CoSe₂ as an Efficient Hydrogen Evolution Reaction Electrocatalyst

We demonstrate the ability of a thiol–amine solvent mixture to deposit phase-pure marcasite-type CoSe₂ nanostructured thin films as effective hydrogen evolution reaction (HER) electrocatalysts. Electrodes are readily prepared by spin coating a precursor ink onto highly ordered pyrolytic graphite substrates followed by annealing to 350 °C. The resulting CoSe₂ films have an onset potential for HER of −117 mV vs RHE and Tafel slopes of ca. 60 mV dec^–1. Normalization based on electrochemically active surface area reveals that simple optimization of film thickness, based on the number of layers deposited, leads to electrodes with better surface utilization. Based on the electrocatalytic performance of the solution-processed CoSe₂ presented here (η_10mA/cm² = −272 mV vs RHE), this approach shows promise as a simple method to deposit a wide range of useful dichalcogenide electrocatalysts