(643b) Membrane-Encapsulated Solar Fuel Generators

Membrane-encapsulated devices are attractive for solar-driven hydrogen production, as their design mitigates problems with concentration overpotentials, gas bubbles, and safety inherent in liquid electrolyte water-splitting devices.^1-4 However, the competing processes such as heat, water, gas, and ion transport make it nontrivial to design such devices. Here, we show analytical expressions and associated design spaces for critical membrane dimensions and material properties required for stable and efficient gas, heat, proton, and water transport. The best condition for stable gas transport in thin film or gas channels is given by the critical Damköhler number. The maximum heating of the device is governed by the Heating and Nusselt numbers, which can be tuned to the desired level. The optimal dimensions of the device, to operate under tolerable ohmic losses, correspond to the maximum value of scaled Power-loss factor. An optimal device architecture is proposed for stable and efficient operation.

References:

 (1)      Spurgeon, J. M.; Lewis, N. S., Proton exchange membrane electrolysis sustained by water vapor. Energy & Environmental Science 2011, 4, (8), 2993-2998.

(2)       Xiang, C.; Chen, Y.; Lewis, N. S., Modeling an integrated photoelectrolysis system sustained by water vapor. Energy & Environmental Science 2013, 6, (12), 3713-3721.

(3)       Haussener, S.; Xiang, C.; Spurgeon, J. M.; Ardo, S.; Lewis, N. S.; Weber, A. Z., Modeling, simulation, and design criteria for photoelectrochemical water-splitting systems. Energy & Environmental Science 2012, 5, (12), 9922-9935.

(4)       Singh, M. R.; Stevens, J. C.; Weber, A. Z., Design of Membrane-Encapsulated Wireless Photoelectrochemical Cells for Hydrogen Production. Journal of The Electrochemical Society 2014, 161, (8).