Boosting the oxygen evolution electrocatalysis of high-entropy hydroxides by high-valence nickel species regulation.

The addition of an extra metal source induces the transformation from crystalline α-Ni(OH) 2 to an amorphous NiCoFeCrMo-based high-entropy hydroxide (HEH) and maximizes the high-valence Ni 3+ content in HEH. For OER electrocatalysis, the quinary HEH possesses an overpotential of 292 mV at 10 mA cm -2 , a Tafel slope of 54.31 mV dec -1 and the boosted intrinsic activity, surpassing other subsystems.