Continuous Modulation of Electrocatalytic Oxygen Reduction Activities of Single‐Atom Catalysts through p‐n Junction Rectification

Fine‐tuning single‐atom catalysts (SACs) to surpass their activity limit remains challenging at their atomic scale. Herein, we exploit p‐type semiconducting character of SACs having a metal center coordinated to nitrogen donors (MeNx) and rectify their local charge density by an n‐type semiconductor support. With iron phthalocyanine (FePc) as a model SAC, introducing an n‐type gallium monosulfide that features a low work function generates a space‐charged region across the junction interface, and causes distortion of the FeN4 moiety and spin‐state transition in the FeII center. This catalyst shows an over two‐fold higher specific oxygen‐reduction activity than that of pristine FePc. We further employ three other n‐type metal chalcogenides of varying work function as supports, and discover a linear correlation between the activities of the supported FeN4 and the rectification degrees, which clearly indicates that SACs can be continuously tuned by this rectification strategy. A p‐n junction single‐atom catalyst (SAC) was designed by exploiting the p‐type semiconducting character of the SAC having a metal center coordinated to nitrogen donors. Simply changing the n‐type support material for ones with a different work function allows continuous, controllable modification of the electronic structure and intrinsic activity of catalytically active single‐atom site.