Dissolution Stability of Photoanodes and Co-Catalysts in Photoelectrochemical Water Splitting

Abstract

In the future energy scenario, production of hydrogen is a promising solution for the storage of renewables. Photoelectrochemical water splitting with integrated devices can be engaged for the production of hydrogen with the advantage of less space consumption and saving power lines to the production site. Current devices have already come close to the efficiency of an electrolyzer coupled to a solar cell [1]. However, to be profitable in commercial use several challenges have to be resolved. One of the most pressing issues is photostability of materials during operation. Even though photoelectrodes are able to reach lifetimes of several days in lab conditions, it is still a long way until real device lifespans of several years are possible.While efforts in the field of photoelectrochemical water splitting are mainly focused on achieving higher activity, research on stability is still at the very beginning. Evaluation of photostability is typically done by rather short (only few hours) chronoamperometry measurements and post mortem analysis. One option to study degradation processes in-situ is to use on-line inductively coupled plasma mass spectrometry (on-line ICP-MS) which became available recently and revealed photocorrosion of WO3 [2] and BiVO4 [3].In this study, we aim to achieve a better understanding of the key factors driving photocorrosion. It has already been shown, that WO3 exhibits significant differences in faradaic efficiency towards the oxygen evolution reaction (OER) in various electrolytes [4]. One reason behind this behavior might be degradation processes driven by the electrolyte. To study the effect of electrolytes on stability, dissolution of spray-coated WO3 films was investigated in four electrolytes (HClO4, H2SO4, HNO3 and CH3SO3H). Additionally, the influence of protective iridium co-catalyst layers on stability, synthesized in various thicknesses by atomic layer deposition (ALD) was explored. 1. Cheng, W.-H., et al., Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency. ACS Energy Letters, 2018. 3(8): p. 1795-1800.2. Knöppel, J., et al., Time-resolved analysis of dissolution phenomena in photoelectrochemistry – A case study of WO3 photocorrosion. Electrochemistry Communications, 2018. 96: p. 53-56.3. Zhang, S., et al., Dissolution of BiVO4 Photoanodes Revealed by Time-Resolved Measurements Under Photoelectrochemical Conditions. The Journal of Physical Chemistry C, 2019.4. Reinhard, S., F. Rechberger, and M. Niederberger, Commercially Available WO 3 Nanopowders for Photoelectrochemical Water Splitting: Photocurrent versus Oxygen Evolution. ChemPlusChem, 2016. 81: p. 935-940.