Cobalt phosphide embedded on interconnected ultrathin carbon nanosheets as an electrocatalyst for hydrogen evolution in alkaline medium

A highly effective hydrogen evolution reaction (HER) electrocatalyst was developed by combining Co₂P nanoparticles (Co₂P NPs) embedded on interconnected and ultrathin carbon nanosheets (CNS) through a facial in-situ thermal decomposition of the cobalt-triphenylphosphine complex. CNS were derived from the pyrolysis of sodium citrate in one step, resulting in an interconnected ultrathin nanosheet structure with a small thickness. The interaction between Co₂P NPs and CNS boosted the electron transfer rate, resulting in a remarkable electrocatalytic performance toward the HER in an alkaline solution with excellent durability. An overpotential of −200 mV vs. RHE was sufficient to afford a current density of −10 mA cm⁻² with a Tafel slope of 83.4 mV dec⁻¹ in potassium hydroxide medium (1.0 M), which are lower than that of Co₂P nanoparticles (-250 mV) with Tafel slope 93.3 mV dec⁻¹. The electrochemical impedance spectroscopy data illustrated that the mutual coupling between the Co₂P NPs and CNS supports the electrochemical HER performance and accelerates the kinetic of electron transfer. The high HER activity of the novel Co₂P NPs/CNS catalyst is ascribed to the presence of CNS robust support.