Optical optimization considerations of a potential cell system for upscaled photoelectrochemical reactors

The need for sustainable renewable energy is urgent, and harnessing solar energy to produce green hydrogen is promising. Hydrogen is a versatile energy carrier that can be stored and converted into various forms of energy. The FreeHydroCells project aims to create a novel, wireless tandem, monolithic photoelectrochemical (PEC) cell for water splitting, offering a cheap, efficient, and modular hydrogen-generating solution. However, scaling up PEC technology presents significant challenges, with performance losses occurring as systems reach industrial dimensions. Optimizing light energy capture and reducing parasitic light absorption are key to maximizing performance. This study investigates light attenuation in a monolithic PEC water-splitting system, providing guidance on material selection regarding optical properties, scalability, and cost. The assembled device was characterized using both laboratory-grade and portable spectrophotometers, showing a total transmitted flux of roughly 63%. A simple optical model underestimated the transmitted flux by 11%. The global optical efficiency of the device is estimated to be about 14%, but limited to 9% without a reflector. The study highlights substantial optical losses, approximately 33%, from the windows and electrolyte alone. These findings emphasize the importance of holistic optical design and rigorous experimental validation in developing scalable PEC systems.