Work-function-induced electron rearrangement of in-plane FeP@CoP heterojunction enhances all pH range and alkaline seawater hydrogen evolution reaction

Generally, the pH dependence of electrocatalytic hydrogen evolution reaction (HER) often limits its practical application. Herein, we design in-plane FeP@CoP heterojunctions with rich coupling interfaces and unique electronic structures. The 3D self-supporting structure of in-plane FeP@CoP heterojunctions confers high mechanical stability and electrical conductivity. The work function balances the electronic states of FeP and CoP, suggesting that no additional electron loss is required to adjust the Fermi energy. This facilitates the improvement of the interfacial charge distribution state, promotes the adsorption/dissociation of H2O, and reduces the free energy of hydrogen adsorption (ΔGH* = -0.02 eV). In situ Raman spectroscopy under alkalinity revealed the H-down conformation of water, enhancing the binding energy between active site and H, and a favorable OH- adsorption site through catalyst reconfiguration. Therefore, FeP@CoP satisfies the high requirements of HER under different pH conditions, requiring only low overpotentials of 40, 33, 66, and 37 mV to drive 10 mA cm−2 in acidic, alkaline, neutral and alkaline seawater electrolytes, respectively. In particular, the FeP@CoP/CC demonstrates outstanding durability in a wide pH medium and alkaline seawater, indicating the potential for large-scale hydrogen production. This work provides deep insights into inexpensive and efficient in-plane heterojunction catalysts for pH-universal HER.