Inhibiting competing reactions of iodate/iodide redox mediators by surface modification of photocatalysts to enable Z-scheme overall water splitting

Abstract Construction of photocatalytic Z-scheme overall water splitting (OWS) using iodate/iodide (IO 3 − /I − ) redox mediator commonly confronts challenges of competing reactions and slow reaction kinetics. Here we address the aforementioned key issues using surface modification strategy. Visible-light-responsive tantalum nitride (Ta 3 N 5 ) and tantalum oxynitride (TaON) are employed as the O 2 - and H 2 -evolving photocatalysts, respectively. It is found that the inhibition of competing reactions and promotion of half reactions are indispensable for the successful construction of Z-scheme OWS system, both of which are directly related to the surface property of the photocatalysts. Specifically, the magnesia modification on the surface of Ta 3 N 5 is demonstrated to be effective not only in suppressing the adsorption and oxidation of I − ions (a competing reaction of water oxidation), but also in promoting the charge separation and O 2 -evolving rate via meliorative dispersion of loaded iridium cocatalyst. And surface coating of Cr 2 O 3 nanolayer on the platinum cocatalyst loaded on the TaON-based photocatalyst is available to inhibit the reduction of IO 3 − ions (a competing reaction of proton reduction) and improve the H 2 -evolving rate. Only after both inhibition of competing reactions and promotion of H 2 - and O 2 -evolving reactions under the assistance of surface modification, the visible-light-driven Z-scheme OWS system can be achieved successfully with the mixture of IO 3 − and I − ions as a redox mediator. This work sheds light on the availability and importance of surface modification strategy in fabricating Z-scheme OWS system.