Tailored Heterogeneous Catalysts via Space‐Confined Engineering for Efficient Electrocatalytic Oxygen Evolution

Abstract Enhancing the intrinsic activity and number of catalytic sites is crucial in developing high‐performing and robust electrocatalysts. Reductionism provides a material design concept that progresses from atoms to phases and then to phase sequences. Herein, the well‐recognized high‐active (CoFe)Se 2 and multi‐site (CoFe)─N─C phases are carefully selected and creatively combined by space‐confined selenization, resulting in the (CoFe)Se 2 @(CoFe)─N─C heterogeneous nanocatalyst. This design simultaneously yields “better” and “more” catalytic active sites to enable stronger reaction kinetics with a low overpotential of 238 mV at 10 mA cm −2 for the oxygen evolution reaction. The overpotential surprisingly remained almost unchanged after an ultra‐long 500 h of continuous reaction. This ideal space‐confined combination effectively optimizes the absorption capacity and alters the rate‐determining step from *O→*OOH to *OH→*O. This work effectively demonstrates the principles of reductionism and confined engineering, opening a promising avenue for designing and constructing efficient multi‐phase catalytic nanomaterials.