Efficient BiVO₄ Thin Film Photoanodes Modified with Cobalt Phosphate Catalyst and W‐doping

Abstract

Bismuth vanadate (BiVO4) thin film photoanodes for light‐induced water oxidation are deposited by a low‐cost and scalable spray pyrolysis method. The resulting films are of high quality, as indicated by an internal quantum efficiency close to 100 % between 360 and 450 nm. However, its performance under AM1.5 illumination is limited by slow water oxidation kinetics. This can be addressed by using cobalt phosphate (Co‐Pi) as a water oxidation co‐catalyst. Electrodeposition of 30 nm Co‐Pi catalyst on the surface of BiVO4 increases the water oxidation efficiency from ≈30 % to more than 90 % at potentials higher than 1.2 V vs. a reversible hydrogen electrode (RHE). Once the surface catalysis limitation is removed, the performance of the photoanode is limited by low charge separation efficiency; more than 60 % of the electron‐hole pairs recombine before reaching the respective interfaces. Slow electron transport is shown to be the main cause of this low efficiency. We show that this can be remedied by introducing W as a donor type dopant in BiVO4, resulting in an AM1.5 photocurrent of ≈2.3 mA cm−2 at 1.23 V vs. RHE for 1 % W‐doped Co‐Pi‐catalyzed BiVO4.

Photoanodes on titanium substrates: one-step deposited BiVO4 versus two-step nano-V2O5 films impregnated with Bi3+

“…Substantially lower photocurrents were reported for example by Chatchai et al using FTO/SnO2/BiVO4 and FTO/BiVO4 film photoanodes [19]. The photocurrent observed in this work is larger than most results reported in the literature for pure BiVO4 films [19][20][21] and consistent with high-quality films with good electrical contact to the underlying substrate.…”

Enhancing Charge Carrier Lifetime in Metal Oxide Photoelectrodes through Mild Hydrogen Treatment

“…We confirm that this improvement is a result of bulk modification of the BiVO4 film by calculating the charge separation and charge injection efficiencies ( Figure S4), using methods well described in the literature. [34,35] The charge separation efficiency increases with hydrogen treatment and matches the improvement in photocurrent. In contrast, the charge injection efficiency is found to decrease.…”

“…Along with Mo, W is the most common effective donor dopant in BiVO4. [30,34,44] The TRMC signals and the extracted carrier properties of 1% W:BiVO4 are shown in Figure 3 and Table 1. Consistent with our earlier report [17] and in contrast with the results on hydrogen-treated BiVO4, Wdoping in BiVO4 results in a significantly smaller carrier mobility and lifetime.…”

Efficient Water‐Splitting Device Based on a Bismuth Vanadate Photoanode and Thin‐Film Silicon Solar Cells

“…We believe that the reason for this decrease is related to the competing effects of enhanced light absorption and poorer carrier collection efficiency (h col , sometimes also referred as carrier separation efficiency, h sep ) in thicker films. [20] The performance decrease indicates that the detrimental influence on carrier collection efficiency apparently outweighs the improvement in light absorption upon increasing the film thickness from 250 to 300 nm.…”