In situ tuning of platinum 5d valence states for four-electron oxygen reduction.

The oxygen reduction reaction (ORR) catalyzed by efficient and economical catalysts is critical for sustainable energy devices. Although the newly-emerging atomically dispersed platinum catalysts are highly attractive for maximizing atomic utilization, their catalytic selectivity and durability are severely limited by the inflexible valence transformation between Pt and supports. Here, we present a structure by anchoring Pt atoms onto valence-adjustable CuO/Cu hybrid nanoparticle supports (Pt-CuO/Cu), in which the high-valence Cu (+2) in CuO combined with zero-valent Cu (0) serves as a wide-range valence electron reservoir (0‒2e) to dynamically adjust the Pt 5d valence states during the ORR. In situ spectroscopic characterizations demonstrate that the dynamic evolution of the Pt 5d valence electron configurations could optimize the adsorption strength of *OOH intermediate and further accelerate the dissociation of O = O bonds for the four-electron ORR. As a result, the Pt-CuO/Cu catalysts deliver superior ORR performance with a significantly enhanced four-electron selectivity of over 97% and long-term durability.