Nanostructured Co₂P electrocatalyst for the hydrogen evolution reaction and direct comparison with morphologically equivalent CoP

Metal phosphides have emerged as promising Earth-abundant alternatives to platinum for catalyzing the hydrogen evolution reaction (HER) in acidic aqueous solutions. Here, Co₂P nanoparticles having a hollow, multifaceted, crystalline morphology have been evaluated as HER electrocatalysts at a mass loading of 1 mg cm^-2 on Ti foil substrates. The Co₂P/Ti electrodes required low overpotentials of -95 and -109 mV to produce operationally relevant cathodic current densities of -10 and -20 mA cm^-2, respectively. These values establish Co₂P nanoparticles as highly active Earth-abundant HER catalyst materials. Importantly, the Co₂P nanoparticles are morphologically equivalent to previously reported CoP nanoparticle HER catalysts, allowing a direct side-by-side evaluation of their HER activities. Such comparisons of different metal phosphide HER catalysts with the same constituent elements and morphologies are important for identifying the key materials characteristics that lead to high activity.