Achieving advanced hydrogen evolution under large current density using an amorphous/crystalline core-shell electrocatalyst of a-NiCoP/Co 2 P.

Non-precious transition metal-based electrocatalysts with high activities are promising candidates for substituting Pt- or Ru-based electrocatalysts in hydrogen evolution. In this study, we propose core-shell engineering to combine the amorphous NiCoP and crystalline Co ₂ P (a-NiCoP/Co ₂ P@NF), which requires an ultra-low overpotential of only 26 mV to achieve the benchmark current density of 10 mA cm ^-2 . Furthermore, it achieves an industrial-level hydrogen evolution current density of 500 mA cm ^-2 with excellent stability. The superior catalytic performance and stability can be attributed to the hierarchical amorphous/crystalline interface and the electron-rich interfacial Co sites. The amorphous NiCoP shell can not only protect the internal Co ₂ P from corrosion, but also provide a larger electrochemically active area. Together, the Co ₂ P core provides fast electron transport and promotes H ₂ emission from the interfacial electron-rich Co sites. This work provides inspiration to the rational design of an advanced core-shell structure between amorphous and crystalline states.