Photoelectrochemical water splitting suffers from limited light absorption, low charge separation and transport. To deal such challenges alkali metals (Li, Na, K) doping in BiVO4 was carried out systematically to demonstrate enhanced light absorption, high diffusion length of electron-hole pairs, enhanced charge separation in the bulk and charge transport at the surface, with their unique placements in the crystal structure. The nanostructured porous grain of alkali metals doped BiVO4 thin film photoanodes exhibited 8-20 times photocurrent density higher than pristine BiVO4. Li:BiVO4, Na:BiVO4 achieved 4.2 ± 0.18 mAcm-2 and 3.2 ±0.15 mAcm-2 with OER catalyst in 0.1 M K2HPO4 electrolytes at 1.23 V under 1 sun illumination. Through XPS analysis, it was noticed that the bond formation between alkali metals and oxygen are significant. From that, it was speculated that alkali metals are getting placed in the interstitial void of the BiVO4 crystal structure. Diffusion length of charge particles was measured by implementing a positron at the surface of the thin films. It was observed that diffusion length of positron increased ~ 4 times in Na:BiVO4 and 6 times in Li:BiVO4 compared to pristine BiVO4. It is also concluded that the Bi and V based defects density is minimum in Na:BiVO4. The density functional theory calculations confirm this through interbands formation (Figure 1) on Li and Na doping along with the reduction in the optical bandgap.

Effect of alkali metals placement in the interstitial void of BiVO4 structure

ACS Fall 2020 Virtual Meeting

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