Proton-Exchange Effect of Rb₄Ta₆O₁₇ Crystal on Nitridation Efficiency to Ta₃N₅

(Oxy)nitrides are photocatalysts that can split water under visible-light irradiation. Thus, Ta3N5 is a promising photocatalyst for water splitting. Ta3N5 is typically produced by the nitridation of oxides. However, complete nitridation requires time, and even if it is achieved, the photocatalytic performance is lower than that of a mixture nitrided in the middle. A reason for this is the long-term nitridation, which may induce stepwise nitridation from the surface to the core of the reactant, resulting in overnitridation of the surface composition. To solve this problem, we hypothesized that interlayer interactions in layered oxides affect the nitridation efficiency. This study aimed to verify the role of interlayer interactions in the nitridation of oxides. We demonstrated proton-exchange in Rb4Ta6O17·nH2O (RTO) as a model material and its nitridation to Ta3N5. Consequently, proton-exchange could improve the nitridation efficiency by a factor of 7 compared to nonproton-exchanged RTO. Experimental and theoretical reaction analyses revealed that this improvement was achieved by a change in the reaction pathway and the subsequent structural relaxation of RTO derived from proton exchange. These findings provide new guidelines for developing fast nitridation protocols using ion-exchanged layered oxides.