Department Chair and Campaign for Excellence Professor
Amol Ajinkya Memorial Fund Lecture
Department of Chemical Engineering
University of South Carolina
Advances in fuel-cell technology and an increasing demand for hydrogen are driving the need for the development of more efficient methods to produce hydrogen. The main methods for hydrogen production include reforming of hydrocarbons such as natural gas, coal gasification, biological processes, water electrolysis, and thermo-chemical cycles. The processes involving hydrocarbons contribute to CO2 emissions, and biological processes may not be cost effective on a large scale. Electrolysis is commercially viable but too inefficient for large-scale applications. Hence the interest in using thermochemical cycles for large-scale hydrogen production. Thermochemical cycles produce hydrogen through a series of chemical reactions that result in the splitting of water at much lower temperatures (~500-1000ºC) than direct thermal dissociation (>2500oC). All other chemical species in these reactions are recycled resulting in the consumption of only heat and water to produce hydrogen and oxygen. Since water rather than hydrocarbons are used as the source of hydrogen in these thermochemical cycles, no carbon dioxide emissions are produced and the hydrogen is highly pure.
Although there are hundreds of possible thermochemical cycles, the hybrid-sulfur (HyS) process is the only practical, all-fluid, two-step thermochemical cycle. More importantly, economic analysis has shown that hydrogen could be produced via the HyS process for approximately $1.50/kg if electrolyzer-performance targets are reached. In a solar-driven process, solar radiation is used in a solar receiver/reactor to provide the energy needed to vaporize and decompose sulfuric acid. The resulting sulfur dioxide (SO2) is used in the second step consisting of an SO2-depolarized electrolyzer (SDE) that electrochemically oxidizes SO2 with water to form sulfuric acid at the anode and hydrogen at the cathode (blue reaction). All sulfur species are recycled and the overall reaction is the splitting of water to form hydrogen and oxygen. Excess SO2 is stored during daylight operation and used at night to permit continuous electrolyzer operation and hydrogen production. Electricity is supplied from a companion solar-electric plant or obtained from the grid. Approximately 80% of the energy input to the process is solar-thermal energy, and 20% is electricity for the electrolyzer and auxiliaries.
We have developed and patented a gas-fed SDE that we tested over a range of operating conditions (e.g., current, temperature, SO2 flow rate) and design variations (e.g., catalyst type and loading, membrane type and thickness) that significantly outperformed a liquid-fed cell. I will present the results of our research and the challenges that remain in making this an economically viable process for large-scale hydrogen production.
John W. Weidner is Department Chair and Campaign for Excellence Professor of Chemical Engineering at the University of South Carolina (USC). He received his BS degree in chemical engineering from the University of Wisconsin-Madison in 1986 and his PhD in chemical engineering from NC State University under the direction of Dr. Peter S. Fedkiw in 1991. Professor Weidner has published over 100 refereed journal articles in the field of electrochemical engineering, particularly in the synthesis and characterization of electrochemically active materials, and the mathematical modeling of advanced batteries, fuel cells, and hydrogen production processes. He has been a visiting scientist at NASA’s Jet Propulsion Laboratory, the University of California-Berkeley, Los Alamos National Laboratory, and the Fraunhofer Institute for Solar Energy Systems. As a graduate student he received an Electrochemical Society (ECS) Energy Research Summer Fellowship and the Student Research Award from the Battery Division. In 2008 he received the Energy Research Award from the E.ON International Research Initiative and in 2010 he received the Research Award from the Energy Technology Division of ECS, both for his work on solar-hydrogen production. Also in 2010 he received the Research Achievement Award from the USC College of Engineering and Computing. In 2013 Professor Weidner received the USC Educational Foundation Award for Research in Science, Mathematics and Engineering. In 2016 he received the Education Leader Award at the Energy Inc. Summit in Charlotte, NC and last spring he was recognized by the University with a Breakthrough Leadership in Research Award. Dr. Weidner was inagual editor of ECS Transactions and past Technical Editor for the Journal of the Electrochemical Society. He is a Fellow of ECS and the American institute of Chemical Engineers (AIChE), and he has a joint appointment at the Savannah River National Laboratory.