A future sustainable society will need low-carbon emissions supplies of hydrogen for which photoelectrochemical (PEC) water splitting is an interesting, low-cost option that so far underperforms alternatives such as electrolysis. To explore the potential of PEC water splitting in this thesis, I first use energy balance modelling to compare PEC water splitting with the more established photovoltaic (PV)-coupled electrolysis. Then I simulate the performance of PEC modules when integrated with PV cells. Finally, I conduct an experimental study of promising low-cost metal oxide photoanodes. Chapter 1 contains an introduction to these topics and the motivations for this research. Chapter 2 describes the model simulation and experimental methods.

In Chapter 3, I model net-energy balance to determine the energy return on energy invested (ERoEI) for PEC water splitting as 0.84 under favourable assumptions. PV-coupled electrolysis is determined to have an ERoEI of 5.8 in an analogous simulation. Recycling is found to improve both energy balance results by 30 %.

In Chapter 4, I investigate how PEC water splitting may be improved by coupling with PV modules. PV-PEC systems with ideal parameters have a solar-to-hydrogen conversion efficiency of 17.7 % when the bandgaps and electronic properties are optimised. This performance leads to an ERoEI of 0.94 in the model from Chapter 3.

In Chapter 5, I present experimental research using chemical vapour deposition to fabricate BiVO4-coated WO3 nanoneedle heterojunction photoanodes and FeOx and NiOx co-catalysts. The best photoanode demonstrates a solar predicted photocurrent of 2.6 mA cm-2 and STH efficiency of 3.2 %. Photoanodes with FeOx co-catalyst have improved dark current onset potential while NiOx co-catalyst improves photocurrent at low applied potentials. I finally apply my models from Chapter 4 and Chapter 3 to a theoretical PEC facility based on this material and determine that the ERoEI peaks at 0.27.