Water reduction into hydrogen using Rh-doped SrTiO^sub 3^ photoelectrodes surface-modified by minute amounts of Pt: Insights from heterogeneous kinetic analysis

• Published in: Electrochimica acta 2019-02, Vol.297, p.696
• Main Authors: Antuch, Manuel, Millet, Pierre, Iwase, Akihide, Kudo, Akihiko
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Catalysis; Charge efficiency; Charge transfer; Dependence; Electrical resistivity; Hydrogen evolution reactions; N-type semiconductors; Nanoparticles; Platinum; Rate constants; Reaction kinetics; Rhodium; Space charge; Strontium titanates
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2018.11.110

In this paper, we report on the photoelectrochemical hydrogen evolution reaction (HER) from water using Rhodium-doped strontium titanate, surface-modified by the addition of minute amounts of platinum nanoparticles. Platinum has been used in an attempt to increase the charge transfer efficiency of the photoelectrode but also to investigate the balancing effect of surface co-catalysis on charge transfer versus recombination processes. The dynamics of the HER in pH-neutral aqueous solutions has been investigated by Photoelectrochemical Impedance Spectroscopy. Experimental impedance data has been analyzed using a model derived from considerations on heterogeneous kinetics. From the best experimental vs. calculation PEIS fits, microscopic rate parameters have been determined over an extended range of electrical potential. The charge transfer (kt) and recombination (kr) rate constants have been found to vary exponentially with the applied potential. The analysis of the potential dependence of kt led to a Butler-Volmer transfer coefficient of 0.21. The analysis of the potential dependence of the recombination rate constant kr led to the determination of a non-ideality factor β = 0.04 (β = 1 for ideal interfaces), demonstrating the strong non-ideal behavior of the interface. Such non-ideal behavior has been attributed to the presence of a high density of surface states. The space charge capacitance under inversion conditions, i.e. when a strong reversed bias is applied and when the surface of this p-semiconductor exhibits a n-type conductivity, has also been measured and analyzed.