Hydrogen membrane fuel cells (HMFCs) employ a thin palladium-based hydrogen purification membrane as the anode. The palladium membrane serves simultaneously as the hydrogen oxidation catalyst and current collector. Protons pass through the palladium and then through a thin proton conducting ceramic layer that acts as the fuel cell electrolyte. Electrons are collected from the palladium anode and travel an external circuit to the cathode layer where they react with protons to form water. By incorporating the palladium membrane in the fuel cell, HMFCs can work directly on impure hydrogen in gas mixtures formed by steam reforming or other processes. HMFCs have shown to be the most effective fuel cell to date in the intermediate temperature range of 300-600 Celsius.
This talk highlights our recent work on developing proton conducting apatite membranes for use in HMFCs. A novel three step synthesis technique is used to form fully dense apatite thin films on the surface of palladium. Synthesis conditions are designed to align proton conducting channels and eliminate resistive grain boundaries within the apatite layer. The microstructural engineering of the apatite results in remarkable enhancement in proton transport. The transport properties and thermal stability of the apatite films on palladium will be described, as well as efforts to deposit compatible cathode layers for testing in working fuel cells.