Untangling the Effect of Carbonaceous Materials on the Photoelectrochemical Performance of BaTaO 2 N.

The water oxidation reaction is a rate-determining step in solar water splitting. The number of surviving photoexcited holes is one of the most influencing factors affecting the photoelectrochemical water oxidation efficiency of photocatalysts. The solar-to-hydrogen energy conversion efficiency of BaTaO 2 N is still far below the benchmark efficiency set for practical applications, notwithstanding its potential as a 600 nm-class photocatalyst in solar water splitting. To improve its efficiency in photoelectrochemical water splitting, this study offers a straightforward route to develop photocatalytic materials based on the combination of BaTaO 2 N and carbonaceous materials with different dimensions. The impact of diverse carbonaceous materials, such as fullerene, g-C 3 N 4 , graphene, carbon nanohorns, and carbon nanotubes, on the photoelectrochemical behavior of BaTaO 2 N has been examined. Notably, the use of graphene and g-C 3 N 4 remarkably improves the photoelectrochemical performance of the composite photocatalysts through a higher photocurrent and acting as electron reservoirs. Consequently, a marked reduction in recombination rates, even at low overpotentials, leads to a higher accumulation of photoexcited holes, resulting in 2.6- and 1.7-fold increased BaTaO 2 N photocurrent densities using graphene and g-C 3 N 4 , respectively. The observed trends in the dark for the oxygen reduction reaction (ORR) potential align with the increase in the photocurrent density, revealing a good correlation between opposite phenomena. Importantly, the enhancement observed implies an underlying accumulation phenomenon. The verification of this concept lies in the evidence provided by oxygen reduction and is in line with photoredox flux matching during photocatalysis. This research underscores the intricate interplay between carbonaceous materials and oxynitride photocatalysts, offering a strategic approach to enhancing various photocatalytic capabilities.