Photocorrosion of WO3 Photoanodes in Different Electrolytes.

Julius Knöppel,Julien Bachmann,Britta Mayerhöfer,Markus Bierling,André Hofer,Attila Kormányos,Serhiy Cherevko,Simon Thiele

doi:10.1021/acsphyschemau.1c00004

Abstract

Photocorrosion of an n-type semiconductor is anticipated to be unfavorable if its decomposition potential is situated below its valence band-edge position. Tungsten trioxide (WO3) is generally considered as a stable photoanode for different photoelectrochemical (PEC) applications. Such oversimplified considerations ignore reactions with electrolytes added to the solvent. Moreover, kinetic effects are neglected. The fallacy of such approaches has been demonstrated in our previous study dealing with WO3 instability in H2SO4. In this work, in order to understand parameters influencing WO3 photocorrosion and to identify more suitable reaction environments, H2SO4, HClO4, HNO3, CH3O3SH, as electrolytes are considered. Model WO3 thin films are fabricated with a spray-coating process. Photoactivity of the samples is determined with a photoelectrochemical scanning flow cell. Photostability is measured in real time by coupling an inductively coupled plasma mass spectrometer to the scanning flow cell to determine the photoanode dissolution products. It is found that the photoactivity of the WO3 films increases as HNO3 < HClO4 ≈ H2SO4 < CH3O3SH, whereas the photostability exhibits the opposite trend. The differences observed in photocorrosion are explained considering stability of the electrolytes toward decomposition. This work demonstrates that electrolytes and their reactive intermediates clearly influence the photostability of photoelectrodes. Thus, the careful selection of the photoelectrode/electrolyte combination is of crucial importance in the design of a stable photoelectrochemical water-splitting device.

Highlights

In light of the current climate crisis, our dependency on the efficient utilization of renewable energy becomes inevitable
In PEC devices, semiconducting photoelectrodes are used to drive the relevant hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and CO2 reduction reaction (CO2RR) directly using sunlight as a primary energy source.[1−4] They are usually formed from inexpensive transition metals or their oxides,[5,6] opening up possibilities for widespread application of the PEC technologies
To prepare WO3 thin films, a new synthesis method based on a peroxotungstic acid route, but more suitable for upscaling, was suggested

Summary

■ INTRODUCTION

In light of the current climate crisis, our dependency on the efficient utilization of renewable energy becomes inevitable. As promising approaches toward energy storage, generation of hydrogen and other value-added products via photoelectrochemical (PEC) water splitting and CO2 reduction are commonly discussed. In PEC devices, semiconducting photoelectrodes are used to drive the relevant hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and CO2 reduction reaction (CO2RR) directly using sunlight as a primary energy source.[1−4] They are usually formed from inexpensive transition metals or their oxides,[5,6] opening up possibilities for widespread application of the PEC technologies. Considering PEC water splitting, promising solar-tohydrogen efficiencies of up to 30% have been reported so far.[7] it is unsurprising that research interest in photoelectrochemistry is growing steadily.[8−10] Commercialization, on the other hand, has progressed only slowly. A more detailed description of the PEC-SFC system can be found in the literature.[26] less positive potential than the water oxidation potential; in

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ REFERENCES