Soobhankar Pati

May 2010
Electrochemical Characterization of Solid Oxide Membrane (SOM) Electrolyzer for Production of High Purity Hydrogen
Committee Members: Co-Advisor: Uday Pal, MSE/ME; Co-Advisor: Srikanth Gopalan, MSE/ME; Soumendra N. Basu, MSE/ME; Adam C. Powell, IV; Appointed Chair: Dan Cole, ME

Abstract: Concerns about the depletion of fossil fuel reserves and increase in atmospheric carbon dioxide and temperature make hydrogen based energy systems an attractive alternative energy source. However, cleaner, reliable, and cheaper hydrogen production route, which is independent of fossil fuel, is necessary for hydrogen to be used extensively as a fuel. In this work, the performance of a novel, energy-efficient, solid oxide membrane (SOM) electrolyzer for production of high purity hydrogen from steam and various reductants including hydrocarbon waste is analyzed and modeled to assist in scale-up of the technology.

The SOM electrolyzer consists of an oxygen-ion-conducting yttria-stabilized zirconia (YSZ) electrolyte with a dip coated Ni-YSZ cermet cathode on one side and liquid metal anode on the other side. The SOM electrolyzer is operated at 800-1100oC by feeding a steam-rich gas to the Ni-YSZ cermet cathode and a reductant (coal, natural gas, hydrocarbon waste) into the liquid metal anode. Along with electrolytic production of hydrogen, AC impedance spectroscopy and potentiodynamic scans are performed to characterize the various polarization losses (ohmic and non-ohmic) in the electrolyzer and understand the fundamental nature of the electrode reactions. The long term performance of the SOM electrolyzer is evaluated using chronoamperometric measurements. Further, the durability of the liquid metal anode and Ni-YSZ cathode are evaluated employing symmetrical half cells.

Based on the results obtained from the experimental study and theoretical modeling, the design of a cathode- supported commercial SOM electrolyzer producing 25 kg/day of hydrogen is proposed. Energy analysis of the proposed electrolyzer shows that hydrogen can be generated at an efficiency of nearly 75% employing carbon as reductant. Finally, future research is proposed for successful implementation of the SOM electrolyzer technology utilizing different types of wastes.