From these figures, we can conclude that many materials meet both the Λ and m * red criteria. This number decreases if we also require VIS and HER, but the real bottleneck is the combination with OER. Indeed, it is well established in the literature that the evolution of O 2 is more challenging than that of H 2 . The main reason for this is based on kinetics, where the transfer of 4 electrons involved in OER makes it a slower process than that of 2 electrons for HER. Additionally, the redox potential for OER is 1.23 eV higher than that of HER.