Heterostructured Mo and Co-based phosphides as high-performance bifunctional electrocatalysts for overall water splitting

Abstract

Transitional metal phosphides are efficient and durable electrocatalysts for water splitting. In this work, Mo-CoP/Co₂P/NF heterostructures are reported to exhibit bifunctional electrocatalyst properties in various electrolytes. The Co phosphides were found to be possessing a hydrogenase-like structure in these heterostructures with P as the proton-acceptor site and Co as the hydride-acceptor site, making them highly active during the HER process. Moreover, the electronic structure of Co ions could be modified, or the transfer of electrons could be accelerated due to the different valence states of Mo. Additionally, the Mo centers possessed superior adsorption properties toward hydrogen. Consequently, excellent performance for the electrocatalytic HER was exhibited by the Mo-CoP/Co₂P/NF-300 heterostructure with small overpotentials of 86.6 mV and 48 mV at a current density of 10 mA cm⁻² in 1.0 M KOH and 0.5 M H₂SO₄ solutions, respectively. Furthermore, it also exhibited efficient OER activity in an alkaline solution with a low overpotential of 245 mV at 30 mA cm⁻². Post-analysis revealed the changes in the surface and the formation of Co oxyhydroxide during the OER process, and the formation of Co–P–O during the HER process. The high HER and OER performances are attributed to these transformations of morphologies and compositions. Consequently, a two-electrode electrolyzer based on Mo-CoP/Co₂P/NF-300 required voltages of 1.59 V and 1.703 V at 20 mA cm⁻² and 100 mA cm⁻², respectively, and maintained long-term stability.