Efficient Solar-Driven Water Splitting

Author: Charlotte Koschnick
Published On: April 11, 2018
Copyright: Wiley-VCH Verlag GmbH & Co. KGaA

Bismuth vanadate (BiV0₄) is a promising photoanode material for photoelectrochemical (PEC) water splitting and has applications in PEC/photovoltaic(PV) tandem systems for unbiased solar-driven water splitting. To achieve high photocurrent densities in PEC/PV tandem systems, high light adsorption, charge separation, and charge transfer efficiencies are required. However, light adsorption and charge separation efficiencies (ƞ_abs and ƞ_sep) are inversely related: thicker films generally result in higher ƞ_abs while lowering the ƞ_sep and vice versa.

Gang Liu, Chinese Academy of Sciences, Shenyang, China, Lianzhou Wang, University of Queensland, Australia, and colleagues have developed dual BiVO₄ photoanodes with both improved ƞ_sep and enhanced ƞ_abs. Transparent, thin BiVO₄ films were fabricated by electrodeposition of a bismuth precursor film followed by thermal treatments. The thin BiVO₄ films presented well controlled oxygen vacancies which increased the carrier density and electronic conductivity leading to enhanced ƞ_sep. At the same time, the researchers increased ƞ_ads by layering two identical films to make a dual photoanode that was able to more efficiently use light.

The team studied the PEC water splitting performance after depositing FeOOH/NiOOH dual oxygen evolution cathodes onto the dual BiVO₄ photoanodes. This material had a photocurrent density of 5.13 mA cm^–2 and a surface charge transfer efficiency at 1.23 V of 95.3 % when compared to the reversible hydrogen electrode.

The researchers finally evaluated the unbiased water splitting performance of the dual photoanodes by placing a sealed perovskite solar cell behind the photoanodes to form a PEC/PV tandem system. The system featured a current density of 5.27 mA cm^–2 which corresponds to a theoretical solar-to-hydrogen efficiency of 6.5 %.