New aspects of improving the performance of WO₃ thin films for photoelectrochemical water splitting by tuning the ultrathin depletion region

Abstract

Surface modulation approach offers an effective and scalable method for high-performance WO3 photoanodes.

The role of oxygen vacancies in water splitting photoanodes

“…There are several studies where the population of oxygen vacancies is optimized to improve the nal PEC performance of WO 3 photoanodes. 147,148 In a very recent study, 149 the performance of WO 3 photoanodes was analyzed as a function of the concentration of bulk OVs from a kinetic perspective, since apart from all the thermodynamic effects detailed above, such as narrowing the bandgap, introducing defect levels and shiing the VB maximum, oxygen vacancies in WO 3 photoanodes also induce kinetic effects. In this work, four different concentrations of OVs were studied, "very high" ($5.8% oxygen atoms), "high" ($2.3% oxygen atoms), "medium" ($2% oxygen atoms) and "low" ($0.5% oxygen atoms), using transient absorption spectroscopy (TAS) to analyze their impact on the charge carrier recombination kinetics over different time scales, from picoseconds to seconds.…”

Model‐Based Investigation of Trap‐Assisted Recombination in Photoelectrodes for Water Splitting

“…To relate the above results with the available literature data, we sought for measurements on bare (unprotected, no catalyst) photoelectrodes such as Fe 2 O 3 , [40] BiVO 4 , [41] and WO 3 . [26] Photocurrent-voltage measurements are mostly reported in linear scale in the literature and we found only two studies on Fe 2 O 3 with semilogarithmic JV data with slope of 60 mV decade −1 for small anodic voltage, [42,43] in rough agreement with diode-like model in Equation (2). We remark that the energetic position of the SRH recombination state in the middle of the bandgap is a reasonable assumption for Fe 2 O 3 , since midgap Fe d-d states were identified as the main trapping and recombination mechanism in Fe 2 O 3 by femtosecond transient absorption.…”

“…[22,23] Moreover, the charge transfer to electrolyte is slow in many metal oxides, leading to the buildup of minority charges in the depletion layer and making recombination in the depletion layer important, e.g. BiVO 4 , [24] Fe 2 O 3 , [25] WO 3 , [26] ZnO, [27] and SrTiO 3 . [28] Recent numerical studies investigated the effect of surface recombination in GaAs, [29] organic polymer, [30] or functionalized silicon, [31] they included recombination in the depletion layer yet did not focus to provide analytical recipe to approximate the numerical results.…”

Ferro-photocatalytic Enhancement of Photoelectrochemical Water Splitting Using the WO3/BiFeO3 Heterojunction

“…Among the myriad of metal oxide semiconductor photocatalysts, such as BiVO 4 , 11,12 TiO 2 , 13,14 CZTSSe, 15 Fe 2 O 3 , 16 SnO 2 , 17 CuWO 4 , 18 and ZnO, 19,20 tungsten oxide (WO 3 ) takes into consideration as an n-type oxide semiconductor. 21 its photosensitivity, suitable electron transport properties, superior stability, abundance, and uncomplicated nanostructuring capability. WO 3 shows at least five different crystalline structures in the temperature range of −180 to 900 °C, in which monoclinic is the most stable phase at room temperature among them with an indirect band gap energy (E g ) of 2.5−3.2 eV that can be conducive to the absorption of solar radiation in the visible region.…”

“…PEC water splitting photocatalysts are examined in two distinct types of semiconductors: p-type and n-type semiconductors. Among the myriad of metal oxide semiconductor photocatalysts, such as BiVO 4 , , TiO 2 , , CZTSSe, Fe 2 O 3 , SnO 2 , CuWO 4 , and ZnO, , tungsten oxide (WO 3 ) takes into consideration as an n-type oxide semiconductor . It is the most widely used for its photosensitivity, suitable electron transport properties, superior stability, abundance, and uncomplicated nanostructuring capability.…”