Activated FeS 2 @NiS 2 Core-Shell Structure Boosting Cascade Reaction for Superior Electrocatalytic Oxygen Evolution.

Unlike single-step reactions, multi-step reactions can be greatly facilitated only if all the intermediate reactions can be catalyzed simultaneously and progressively. Herein, the theoretical analysis and experiments to illustrate the superiority of the cascade oxygen evolution reaction (OER) are conducted. As different OER intermediate reactions demand Fe x Ni 1-x OOH with altered Fe/Ni ratios, gradient Fe-doped NiOOH can be an ideal electrocatalyst for the efficient cascade OER in line. Fine controlling of the nucleation sequence of iron and nickel sulfides leads to a FeS 2 @NiS 2 core-shell structure. The activated outward diffusion of Fe dopants results in the gradient Fe/Ni ratios in the Fe x Ni 1-x OOH shell, where a cascade OER can happen. Electrochemical tests suggest that the FeS 2 @NiS 2 only needs an overpotential of 237 mV to reach the current density of 10 mA cm -2 , with fast reaction kinetics and good stability.