Abstract
Recombination of photo-generated charges is one of the most significant challenges in designing efficient photo-anode for photo electrochemical water oxidation. In the case of TiO2, mixed phase (anatase-rutile) junctions often shown to be more effective in suppressing electron-hole recombination compared to a single (anatase or rutile) phase. Here, we report the study of bulk and surface recombination process in TiO2 multi-leg nanotube (MLNTs) anatase-rutile (A-R) junctions decorated with reduced graphene oxide (rGO) layers, through an analysis of the photo-current and impedance characteristics. To quantify the charge transport/transfer process involved in these junctions, holes arriving at the interface of semiconductor/electrolyte were collected by adding H2O2 to the electrolyte. This enabled us to interpret the bulk and surface recombination process involved in anatase/rutile/rGO junctions for photo-electrochemical water oxidation. We correlated this quantification to the electrochemical impedance spectroscopy (EIS) measurements, and showed that in anatase/rutile junction the increase in PEC performance was due to suppression in electron-hole recombination rate at the surface states that effectively enhances the hole transfer rate to the electrolyte. On the other hand, in rGO wrapped A-R MLNTs junction it was due to both phenomenon i.e decrease in bulk recombination rate as well as increase in hole transfer rate to the electrolyte at the semiconductor/electrolyte interface.
Highlights
An efficient production of hydrogen through the photo electrochemical water splitting requires that the semiconducting material should efficiently absorb light to generate electron hole pairs and these charges can be separated quickly to minimize recombination.[1]
We report on the study of charge recombination in TiO2 multi-leg nanotube (MLNTs) anatase-rutile (A-R) junctions decorated with reduced graphene oxide layers with the help of hole scavenger (H2O2).[20]
A comparative systematic investigations shown for charge recombination phenomenon associated with reduced graphene oxide (rGO) functionalized mixed phase TiO2 nanotubes (A/R-rGO multi-leg nanotubes (MLNTs)), rGO functionalized anatase phase TiO2 nanotubes (A-rGO MLNTs), bare anatase phase TiO2 nanotubes (A-MLNTs) and bare mixed phase TiO2 nanotubes (A/R-MLNTs) for PEC water splitting
Summary
An efficient production of hydrogen through the photo electrochemical water splitting requires that the semiconducting material should efficiently absorb light to generate electron hole pairs and these charges can be separated quickly to minimize recombination.[1]. We report on the study of charge recombination in TiO2 multi-leg nanotube (MLNTs) anatase-rutile (A-R) junctions decorated with reduced graphene oxide (rGO) layers with the help of hole scavenger (H2O2).[20] A comparative systematic investigations shown for charge recombination phenomenon associated with rGO functionalized mixed phase TiO2 nanotubes (A/R-rGO MLNTs), rGO functionalized anatase phase TiO2 nanotubes (A-rGO MLNTs), bare anatase phase TiO2 nanotubes (A-MLNTs) and bare mixed phase TiO2 nanotubes (A/R-MLNTs) for PEC water splitting Such an analysis so far has not been reported for rGO decorated mixed phase junctions of. The data obtained from the analysis of the photocurrent values have been correlated with Electrochemical Impedance Spectra (EIS) to achieve a detailed understanding of the charge recombination and transport occurring inside the semiconductor as well as at the semiconductor-electrolyte interface This comprehensive study of the charge transfer process occurring at rGO modified TiO2 mixed phase junctions show that the enhancement in photo-current corresponding to A/R-MLNTs junction is due the decrease in electronhole recombination rate at the surface states of semiconductor (ηct). In A/R-rGO MLNTs, the improvement in photocurrent is attributed to the enhancement of charge separation and transport (reduction of recombination) both in the bulk semiconductor (ηtr), as well as across at the semiconductor/electrolyte interface (ηct)
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