Tailored energy level alignment at MoOX/GaP interface for solar-driven redox flow battery application

Abstract

MoO X is commonly considered to be a high work-function semiconductor. From X-ray photoelectron spectroscopy and photo-electrochemical analysis, it is shown that MoO X can be considered as an effective holetransfer layer (HTL) for the GaP-based device. Specifically, in the absence of carbon contamination using an ionbeam cleaning step, the oxygen vacancy derived defect band located inside the band-gap becomes the main charge transfer mechanism. We demonstrate, for the first time, a device with a MoO X /GaP junction that functions as an unbiased photo-charging cell for the redox flow battery system with AQS/AQSH 2 ‖I-/I 3redox couples. This work has important implications toward enabling MoO X applications beyond the conventional solar cells, including electrochemical energy storage and chemical conversion systems. SUPPLEMENTARY MATERIAL See the supplementary material for further details on band alignment calculation method, UV-Vis transmittance, XPS survey and depth profile, LSV for n-GaP/MoO X , Pt/n-GaP, and Pt film, CV using a charged electrolyte, and the charging/discharging measurements with normalized capacity data, and Mott-Schottky analysis on the n-Gap.

Fabrication of TiVO4 photoelectrode for photoelectrochemical application

“…Hence, if these bimetallic semiconductors can be combined with other novel photoactive materials such as NiO, 16 ZnO, 17 CdO (ref. 18) etc., to construct heterojunctions such as Co 3 O 4 /TiO 2 , 19 Fe 2 O 3 /Au/ TiO 2 , 20 ZnO/Fe 2 O 3 , 21 Fe 2 O 3 /CdO, 22 MoO x /GaP 23 and ZnO/NiO 24 etc. with proper band alignment, they could serve as efficient PEC material as compared to single-phase metal oxide.…”

“…18) etc. , to construct heterojunctions such as Co 3 O 4 /TiO 2 , 19 Fe 2 O 3 /Au/TiO 2 , 20 ZnO/Fe 2 O 3 , 21 Fe 2 O 3 /CdO, 22 MoO x /GaP 23 and ZnO/NiO 24 etc. with proper band alignment, they could serve as efficient PEC material as compared to single-phase metal oxide.…”

Advances and Challenges in Photoelectrochemical Redox Batteries for Solar Energy Conversion and Storage

“…[22a,34a] Such defect is mainly due to the narrow spectrum utilization and serious recombination of photogenerated charge carriers. [70] Therefore, consideration of utilizing the fullspectrum solar energy and promoting the separation and utilization of charge carriers is largely required. [30c,71] In summary, an ideal redox couples in PRBs should possess the following properties including high reversibility with appropriate redox potential, high energy capacity, fast reaction kinetics for both charge/discharge process, long operating life cycle, low cost, and non-toxicity.…”

“…[ 22a,34a ] Such defect is mainly due to the narrow spectrum utilization and serious recombination of photogenerated charge carriers. [ 70 ] Therefore, consideration of utilizing the full‐spectrum solar energy and promoting the separation and utilization of charge carriers is largely required. [ 30c,71 ]…”

Introducing special issue on photocatalysis and photoelectrochemistry

“…Increasingly, researchers realize that a single material will unlikely deliver the desired efficiency. Instead, attention has been turned to engineer combinations of materials, where bandgap matching becomes critical (see, e.g., articles by Bae et al, 12 Yoda et al, 13 Méndez-Medrano et al, 14 and Das et al 15 ). Indeed, heterostructure is a popular idea that has been explored by multiple other papers in this virtual issue, e.g., articles by Lin et al, 16 Zhu et al, 17 and Wang et al 18 To this end, another idea is to utilize portions of the solar spectrum that are difficult to directly utilize by ideas such as plasmonic effect (see the article by Li et al 19 ) or upconversion (see the article by Jiang et al 20 ).…”