High Temperature Alkaline Electrolysis Cells with Metal Foam Based Gas Diffusion Electrodes

Alkaline electrolysis cells operating at 250 degrees C and 40 bar are able to convert electrical energy into hydrogen at very high efficiencies and power densities. In the present work we demonstrate the application of a PTFE hydrophobic network and Ag nanowires as oxygen evolution electrocatalyst in the metal foam based gas diffusion electrodes. A novel cell production method, based on tape casting and hot pressing, was developed which allows to increase the cell size from lab scale (1 cm(2)) to areas of 25 cm(2) or larger. The thickness of the electrolyte matrix could be adjusted to only 200 mu m, achieving a serial resistance and total area specific resistance of only 60 m Omega cm(2) and 150 m Omega cm(2), respectively, at 200 degrees C and 20 bar, yielding a record high current density of 3.75 A cm(-2) at a cell voltage of 1.75 V. Encouraging long-term stability was obtained over 400 h of continuous electrolysis. This novel cell concept promises more than a 10-fold improvement in power density, compared to conventional alkaline electrolysis cells, and thereby equivalent reduction in stack size and cost. (C) The Author(s) 2016. Published by ECS. All rights reserved.