Co–Fe–Mo Phosphides’ Triphasic Heterostructure Loaded on Nitrogen-Doped Carbon Nanofibers by Electrospinning as Efficient Bifunctional Electrocatalysts for Overall Water Splitting

The rational design of efficient and stable bifunctional electrocatalysts for the hydrogen evolution reactions (HER) and oxygen evolution reactions (OER) poses a significant challenge in realizing environmentally friendly hydrogen production through electrocatalytic water splitting. The construction of heterostructure catalysts, coexisting of multiple components, represents a favorable approach for increasing active sites, modulating electronic structure, accelerating charge transfer, decreasing reaction energy barriers, and synergistically enhancing electrocatalytic performance. In this study, a triphasic metal phosphides' heterostructure among CoP, FeP, and MoP4 loaded on nitrogen-doped carbon nanofibers (labeled as CoP-FeP-MoP4@NC) was successfully synthesized through electrospinning and other subsequent steps as a bifunctional electrocatalyst material for water splitting. Benefiting from the strong interaction and synergistic effect among these components, CoP-FeP-MoP4@NC exhibits facile kinetics and high electrocatalytic activity under alkaline conditions with overpotentials (η) of 222 and 75 mV at a current density of 10 mA cm-2 for OER and HER, respectively, as well as a low cell voltage of 1.47 V at 10 mA cm-2 for overall water splitting. Moreover, the catalyst shows great long-term stability at a high current density of about 100 mA cm-2. The density functional theory calculations revealed that the CoP-FeP-MoP4 heterostructure can reduce the Gibbs free energy associated with the H2O dissociation and hydrogen adsorption during HER, as well as the rate-determining step for the OER, increase the electronic states near the Fermi level, and optimize the work function of the electrons, improving electrical conductivity and reaction capacity. This study presents an efficient and stable electrocatalytic material for water splitting, and the design concept provides insights for future rational construction of advanced electrocatalysts.