Unlocking synergy between multi-valence rhodium species for promoted methanol photoreforming.

Solar-powered photocatalytic methanol dehydrogenation to produce hydrogen (H2) and formaldehyde provides a promising approach for storable H2 fuel without carbon emissions. However, the different properties of C-H and O-H bonds in methanol molecules make it challenging to cleave both bonds effectively on a single catalytic active site during the methanol dehydrogenation process. This work proposes a strategy that constructs multi-valence metal species in the co-catalyst to address this challenge. In the case study of multi-valence rhodium species (Rh0 and Rh3+) on titanium dioxide (RhO x /TiO2) photocatalysts, an apparent turnover frequency (TOF, the H2 evolution rate as a function of the co-catalyst amount) of 1236 h-1 is achieved, outperforming that of most reported co-catalysts. Detailed investigations unveil that the synergy between Rh0 and Rh3+ not only facilitates the cleavage of both C-H and O-H bonds in methanol molecules but also facilitates the desorption of H2 molecules, leading to improved efficiency. This work showcases an effective strategy for engineering co-catalysts to promote photocatalytic methanol dehydrogenation and provides insights into the mechanism of this reaction catalyzed by heterogeneous photocatalysts.