PEM Electrolyzer Incorporating an Advanced Low-Cost Membrane
Electrolysis of water, particularly in conjunction with renewable energy sources, is potentially a cost-effective and environmentally friendly method of producing hydrogen at dispersed forecourt sites, such as automotive fueling stations. However, state-of-the-art proton-exchange-membrane (PEM) electrolyzer systems have not been economically competitive for forecourt hydrogen production due to their high capital and operating costs, particularly the cost of the electricity used by the electrolyzer stack. The forecourt hydrogen application requires an electrolyzer that produces 1500 kg/day (62.5 kg/hr) hydrogen. At the present time, the markets for PEM electrolyzers are for much smaller units, typically less than 5 kg/hr. Although larger stacks have been developed they have not been commercialized. Thus, PEM electrolyzer systems are generally quite small. The primary feedstock for an electrolyzer is electricity, which could be produced by renewable sources such as wind or solar that do not produce carbon dioxide or other greenhouse gas emissions. In this project, Giner, Inc. (Giner) developed a low-cost, high-efficiency PEM electrolysis stack and system for hydrogen production at moderate pressures of 300 to 400 psig (2170 to 2860 kPa). The electrolyzer stack operates at differential pressure, with hydrogen produced at moderate pressure while oxygen is evolved at near-atmospheric pressure, reducing the cost of the water feed and oxygen handling subsystems. The project included research on catalysts and membranes to improve the efficiency of the electrolysis reaction, as well as development of advanced materials and component fabrication methods to reduce the capital cost of the electrolyzer stack and system. The project culminated in the delivery of a prototype electrolyzer module to the National Renewable Energy Laboratory for testing at the National Wind Technology Center. Electrolyzer stack efficiency of 74% LHV (87%HHV), meeting DOE 2012 targets, was demonstrated using an advanced high-strength membrane. Giner significantly reduced the capital cost of a PEM electrolyzer stack through development of low-cost components and fabrication methods, including a 60% reduction in stack cost. The estimated cost of the present stack design in large-scale production is less than $\$$350/kW. In addition, Giner demonstrated improved lifetimes of the advanced membrane and cell components that can exceed 60,000 hours of operation. An Economic analysis indicates that hydrogen, prior to delivery costs, could be produced for $\$$3.64 per gge (gasoline-gallon equivalent) at an electricity cost of $\$$0.04/kWh utilizing the lower-cost PEM electrolyzer developed in this project assuming high-volume production of large-scale systems.