Semiconductor Surface Transformations for Photoelectrochemical Energy Conversion

Abstract

The issue of photoelectrode stability, while simultaneously maintaining efficient operation in aqueous solutions, is addressed for energy converting half cells and complete photoelectrocatalytic structures. The historical development of stability concepts, their realization and recent advances are described. Examples are presented that span the time from the inception of photoelectrochemical energy conversion to present day's renewed interest in storable solar energy. The application of (photo)corrosion processes for in-situ synthesis of protective coatings is described and chemical and electronic analyses of the interphases formed are given. Future development and innovation routes will be discussed. The early days of light-induced processes at the solid-electrolyte interface were characterized by a series of fascinating effects. They encompass fundamental investigations of semiconductor-electrolyte junctions, 1,2 the first light-assisted water splitting, 3 photoemission from metals into solution, 4,5 hot electron processes 6,7 and the first carbon dioxide reduction at illuminated semiconductors. 8,9 The conceptual basis of energy conversion at the solid-liquid junction was provided by Gerischer in 1975 when the rectifying nature of the semiconductor-redox electrolyte contact was outlined.1 The elegance of formation of a conformal contact, simply by immersion of the samples into solution, was, however, neutralized by interfacial reactivity that gives rise to photocorrosion. 10,11 In the early assessment of stability of semiconductors at electrolyte junctions, thermodynamic decomposition potentials were introduced and their energy relation relative to the semiconductor band edges was analyzed.10,12 It soon turned out that stability is a predominant and major issue in photoelectrochemical energy conversion in both the photovoltaic and photoelectrocatalytic modes. Early development of stable photoelectrodes, based on the group VIb transition metal dichalcogenides, [13][14][15] which are also characterized by high absorptivity, was compromised by the problem of scalable preparation of efficient electrodes. Technologically advanced semiconductors from the III-V and II-VI groups typically showed rather high conversion efficiencies [16][17][18] but, also, often pronounced photocorrosion.19 A promising approach for stabilization was developed by the Bell Laboratories group where ∼ 10% efficient InP photocathodes had been operated for extended time in aqueous solution. 20The employed conditioning method resulted in the formation of interfacial films 21 that enabled electron transfer but that blocked access of solution components to the absorber surface thereby suppressing the corrosion reactions.In this text, fundamental aspects and recent developments and advances of this method will be outlined and discussed. Basic concepts on stability and photocorrosion are presented first, followed briefly by a discussion of carrier transport across interfacial films. A subsequent section describes the chronological development of ...

Strategies for stable water splitting via protected photoelectrodes

“…However calculations by Lewerenz show that the charge transfer was probably not due to a Poole-Frenkel type mechanism. 162 While the Lewis group has shown amorphous 'Leaky' TiO 2 to be highly conductive to charge, the McIntyre's group has shown that their amorphous TiO 2 creates a barrier for conduction of charge. 148 While both their ALD processes appear quite similar, small difference must account for the discrepancies and further studies are needed to clarify this situation.…”

Long-Term Stability Metrics of Photoelectrochemical Water Splitting

“…III-V compounds, like GaAs, also go through corrosion reactions (see Eq. 2) due to either accumulation of a large surface hole concentration in the dark or light illumination, generating holes at the surface (Lewerenz, 2014). However, p-type III-arsenide semiconductors have shown remarkable stability under conditions where an As 0 enriched surface provides passivation against corrosion (Young et al, 2016).…”

Kinetic Competition between Water‐Splitting and Photocorrosion Reactions in Photoelectrochemical Devices

“…For this reason, the applicationo fp rotectivef ilms, nanoparticles, and fusiblea lloys at the SC-electrolytei nterface are often used to enhance the durability and robustness of SCs that are prone to photocorrosion. [8][9][10][11] Generally,t he photocorrosion of SCs immersed in liquid electrolytes is studied on the basis of thermodynamic aspects, by comparing the quasi-Fermi levels of chargec arrierst ot he decomposition potentials of the SC. [12,13] Pourbaixd iagrams can also be used to investigate the stability and phase composition of the SCs at differentp otentials and pH.…”