Performance of III-V Photoelectrochemical Devices in Neutral Electrolyte

Photoelectrochemical (PEC) cells separate water molecules into oxygen and hydrogen gasses using sunlight to extract hydrogen for fuel or feedstocks. Tandem III-V photoelectrodes, used in PEC devices, are known to have high efficiency but low durability. They are normally placed in acidic conditions and last between a few minutes to 10 hours. An acidic electrolyte is hazardous on a large scale and corrodes electrodes quickly, creating a barrier for commercialization. This work evaluated safer, neutral buffers for their potential to extend device lifetime. Nafion membranes and separators were also evaluated to separate oxygen and hydrogen gas products to prevent explosive mixtures of hydrogen and oxygen. Both Nafion and porous separators isolate products but were found to require different operating schemes. When using Nafion, a pH gradient built up between the anolyte and catholyte which decreased the performance by creating a greater overpotential for water splitting. When using a porous separator, a pH gradient was not observed, but their ability to prevent dissolved gas crossover requires further investigation. Using neutral electrolytes and a membrane in a PEC cell allowed for approximately a 10x increase in lifetime but at a decreased efficiency, which may be recovered with additional device and component optimization.

This research was supported by the Department of Energy: Office of Science as part of Science Undergraduate Laboratory Internship program.