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

• Published in: Applied catalysis. B, Environmental Environmental, 2018-05, Vol.224, p.579-585
• Main Authors: Qi, Yu, Chen, Shanshan, Cui, Junyan, Wang, Zhiliang, Zhang, Fuxiang, Li, Can
• Format: Article
• Language: English
• Subjects: (Oxy)Nitride; Adsorption; Catalysis; Catalysts; Cobalt; Construction; Dispersion; Evolution; Inhibition; Iodides; Ions; Iridium; Kinetics; Overall water splitting; Oxidation; Photocatalysis; Photocatalysts; Platinum; Promotion; Reaction kinetics; Reduction; Splitting; Surface modification; Surface properties; Tantalum; Tantalum nitrides; Water; Water splitting; Z-scheme
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2017.10.041

[Display omitted] Surface modification of photocatalysts is demonstrated to be effective in inhibiting competing reactions for construction of Z-scheme overall water splitting •Surface modification strategy was applied to inhibit the competing reactions enable Z-scheme overall water splitting.•MgO modification on Ta3N5 can suppress the adsorption and oxidation of I− ions as well as promoting the O2-evolving rate.•Surface coating of Cr2O3 on Pt loaded on ZrO2/TaON can inhibit the reduction of IO3− ions and improve the H2-evolving rate. Construction of photocatalytic Z-scheme overall water splitting (OWS) using iodate/iodide (IO3−/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 (Ta3N5) and tantalum oxynitride (TaON) are employed as the O2- and H2-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 Ta3N5 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 O2-evolving rate via meliorative dispersion of loaded iridium cocatalyst. And surface coating of Cr2O3 nanolayer on the platinum cocatalyst loaded on the TaON-based photocatalyst is available to inhibit the reduction of IO3− ions (a competing reaction of proton reduction) and improve the H2-evolving rate. Only after both inhibition of competing reactions and promotion of H2- and O2-evolving reactions under the assistance of surface modification, the visible-light-driven Z-scheme OWS system can be achieved successfully with the mixture of IO3− 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.