Towards Highly Efficient Bias-Free Solar Water Splitting

Towards Highly Efficient Bias-Free Solar Water Splitting

Abdi, F.F.

Dam, B. (promotor)
Van de Krol, R. (promotor)

Applied Sciences

Chemical Engineering

2013-09-10

Solar water splitting has attracted significant attention due to its potential of converting solar to chemical energy. It uses semiconductor to convert sunlight into electron-hole pairs, which then split water into hydrogen and oxygen. The hydrogen can be used as a renewable fuel, or it can serve as a feedstock material to form hydrocarbons. However, the development of an adequate semiconductor material for solar water splitting still remains a challenge. This thesis work aimed at developing new, multinary metal oxides: bismuth vanadate (BiVO4). BiVO4 was synthesized using a low-cost spray deposition process. By systematically optimizing the deposition parameters, high quality thin films of BiVO4 photoanodes with quantum efficiencies close to 90% were reproducibly produced. To further increase the performance, a thorough analysis was performed to determine its performance limiting factors, which are poor catalytic activity and slow carrier transport. Cobalt-phosphate catalyst was then deposited on BiVO4 surface to solve the first limitation, and a gradient concentration of tungsten as a dopant was introduced to solve the latter problem. As a result, the photocurrent of BiVO4-based photoanode has been increased up to 4.0 mA/cm2 under 1 sun irradiation, which is the highest value ever reported for this material. Considering that only a photocurrent of <0.2 mA/cm2 was achieved prior to the start of this thesis work, this is a significant ~20-fold improvement of the performance. This state-of-the-art BiVO4 photoanode was then combined with a thin film amorphous silicon solar cell to fabricate a complete solar water splitting device. As a result, a device with ~5% solar-to-hydrogen (STH) efficiency was produced, which is the current world-record for a device based on a metal-oxide photoanode. Finally, the significant progress achieved through this thesis shows that the ideal semiconductor material for solar water splitting, which is cheap, abundant, stable, and showing the 10% efficiency target, could be developed within the next few years.

solar water splitting
bismuth vanadate
spray pyrolysis
photoelectrochemistry

https://doi.org/10.4233/uuid:e81e5ed8-1608-47c0-a668-3be25e04c039

2013-08-24

9789064646935

Institutional Repository

doctoral thesis

(c) 2013 Abdi, F.F.