High-efficiency Steam Electrolyzer

We are developing a novel high-efficiency, high-temperature steam electrolyzer. Although water or steam electrolysis is well known to be one of the cleanest ways to produce hydrogen, widespread utilization is hindered by high operational costs because of high electricity consumption. To decrease the electrical power input requirements in electrolysis, our approach uses natural gas as an anode depolarizer. This approach essentially replaces one unit of electricity with one equivalent-energy unit of natural gas at much lower cost. The direct use of natural gas on the electrolyzer enables very high system efficiency with respect to primary energy. Experiments performed on single cells have shown a voltage reduction as much as 1 V when compared to conventional electrolyzers. System efficiency has been estimated to be 50 to 80%, depending on the electrolytic current density. During FY02, we have accomplished several major milestones, including the development of a metal-to-ceramic seal that withstands 150 psi differential, the fabrication of the electrolyzer tubes of up to 16 inches in length, the improvement of single tube performance and the demonstration of the first electrolyzer stack. Introduction Currently, most hydrogen demand is met by hydrogen production from fossil fuels, i.e., by steam reforming of natural gas and by coal gasification. However, most of these central plants are located in remote areas. The hydrogen produced must then be delivered to the users either by truck or via hydrogen pipelines. Because of the inherently low energy density of hydrogen, transportation by truck is not a viable option. Hydrogen delivery using pipelines is not costeffective either because of the high cost of the pipelines. Therefore, hydrogen production for a future hydrogen economy is likely to be accomplished using a distributed system where 1 Proceedings of the 2002 U.S. DOE Hydrogen Program Review NREL/CP-610-32405