Transparent porous polymer sheets for efficient product separation in solar water splitting

Efficient product separation is an essential requirement for the safe operation and implementation of solar water splitting devices. Ion exchange membranes are typically used, but for a device that requires sunlight illumination to travel from one electrode to the other, these membranes may introduce parasitic absorption and reduce the achievable device efficiency. Here, we investigate the feasibility of utilizing transparent polymer sheets as separators in solar water splitting devices. Porosity is introduced into the polymer sheets by femtosecond laser-patterned micropore arrays with various diameters and pitch distances. Our experimental data and numerical simulation results show that these polymer sheets not only have low parasitic absorption, but also lower resistances as compared to a commercial anion exchange membrane. Finally, product crossover through the transparent porous separators is evaluated using a particle tracing model under the realistic operation conditions of solar water splitting devices. Minimal crossover can be obtained by optimizing the separator as well as the operational parameters.