Abstract
A series of WO3, BiVO4 and WO3/BiVO4 heterojunction coatings were deposited on fluorine-doped tin oxide (FTO), by means of reactive radio frequency (RF) plasma (co)sputtering, and tested as photoanodes for water splitting under simulated AM 1.5 G solar light in a three-electrode photoelectrochemical (PEC) cell in a 0.5 M NaSO4 electrolyte solution. The PEC performance and time stability of the heterojunction increases with an increase of the WO3 innermost layer up to 1000 nm. A two-step calcination treatment (600 °C after WO3 deposition followed by 400 °C after BiVO4 deposition) led to a most performing photoanode under back-side irradiation, generating a photocurrent density of 1.7 mA cm−2 at 1.4 V vs. SCE (i.e., two-fold and five-fold higher than that generated by individual WO3 and BiVO4 photoanodes, respectively). The incident photon to current efficiency (IPCE) measurements reveal the presence of two activity regions over the heterojunction with respect to WO3 alone: The PEC efficiency increases due to improved charge carrier separation above 450 nm (i.e., below the WO3 excitation energy), while it decreases below 450 nm (i.e., when both semiconductors are excited) due to electron–hole recombination at the interface of the two semiconductors.
Highlights
With the rapid increase in the global energy demand and the tremendous climate concerns due to combustion of the limited fossil fuels reserves, there is an urgent need for clean and renewable energy sources [1,2]
The incident photon to current efficiency (IPCE) measurements reveal the presence of two activity regions over the heterojunction with respect to WO3 alone: The PEC efficiency increases due to improved charge carrier separation above 450 nm, while it decreases below
Reactive radio frequency (RF) plasmasputtering demonstrates to be an effective technique for the deposition of Reactive RF plasmasputtering demonstrates to be an effective technique for the deposition multilayered WO3 /BiVO4 heterojunction photoanodes for solar-driven water splitting
Summary
With the rapid increase in the global energy demand and the tremendous climate concerns due to combustion of the limited fossil fuels reserves, there is an urgent need for clean and renewable energy sources [1,2]. To date, most of its production is based on steam reforming of natural gas which still involves massive amounts of CO2 emission, resulting environmentally unsustainable [5] In this context, photoelectrochemical (PEC) water splitting is considered one of the most promising and green routes to harvest and convert solar energy through the production of H2 [6]. Among plenty of semiconductor materials suitable for the PEC water splitting reaction, BiVO4 has received significant attention in the last years due to its remarkable theoretical efficiency under visible light irradiation [7,8]. This is due to its narrow band gap of 2.4 eV, that extends its photoactivity up to 510 nm, and favorable band edges position.
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