The main challenge for acidic water electrolysis is the lack of active and stable oxygen evolution catalysts based on abundant materials, which are globally scalable. Iridium oxide is the only material, which is active and stable. However, Ir is extremely rare and far from scalable. There exist both active materials and stable materials, but those that are active are not stable and vice versa. In this work, we present a strategy for making stable materials active. The stable materials are semiconductors that cannot change oxidation state at relevant reaction conditions. Based on DFT calculations, we find that by adding an n-type dopant, semiconductor surfaces can bind oxygen. However, after oxygen is adsorbed, the material is again in a state where it cannot bind or desorb oxygen. By combining n-type and p-type dopants, the reactivity can be tuned so that oxygen can be adsorbed and desorbed under reaction conditions. It turns out that the tuning can be understood from the electrostatic interactions between the dopants as well as between the dopants and the binding site. We experimentally verify that this strategy works in TiO2 by co-doping with different pairs of n- and p-type dopants. This encourages that the co-doping approach can be used to activate stable materials, without intrinsic oxygen evolution activity, to discover new catalysts for acid water electrolysis.
Synergistic effect of p-type and n-type dopants in semiconductors for efficient electrocatalytic water splitting
