An interface-engineered Co2P/CoMoP2 heterojunction with greatly improved electrocatalytic activity in water/seawater splitting†

It is essential to design and synthesize non-noble metal-based electrocatalysts for the highly efficient hydrogen evolution reaction (HER). In this study, we have successfully prepared a self-supporting phosphide heterostructured electrocatalyst, where CoMoP₂ nanosheets are well distributed on the surface of Co₂P hollow nanobricks on Ni foam. The testing results demonstrated that the as-prepared Co₂P/CoMoP₂ exhibited excellent HER performance with an overpotential of 36 mV and 43 mV (at 10 mA cm⁻²) in alkaline water and seawater electrolyte, respectively. Meanwhile, it also showed good oxygen evolution reaction (OER) activity at 10 mA cm⁻² with an overpotential of 254 mV in alkaline water and 268 mV in alkaline seawater electrolyte, respectively. Theoretical research studies have verified that the activation energy barrier of H₂O on the surface of CoMoP₂ was 0.63 eV, while that on the surface of Co₂P was 0.73 eV, indicating that CoMoP₂ can promote the Volmer step. Also, the electronic redistribution at the interface enabled the Co₂P/CoMoP₂ heterojunction to achieve the ideal Gibbs free energy of hydrogen adsorption (0.16 eV). Interface engineering provides a simple and efficient approach for designing highly efficient Co₂P-based electrocatalysts.