This Small Business Innovation Research (SBIR) Phase I project addresses global energy concerns by enabling reduced dependence on energy derived from fossil fuels. A major limitation of many renewable energy sources is the intermittent nature of the source, such as solar or wind. As the percentage of energy applied to the grid from these sources grows, energy storage systems must be developed to store energy during peak generation periods, and provide power during lower generation periods. Hydrogen-based regenerative fuel cells are an ideal candidate for these applications due to their high energy density, fast response times, and carbon-free footprint when the hydrogen is generated by electrolysis using the renewable power source. However, materials for the electrolysis and fuel cell stacks are still too expensive to make this solution cost effective. The goal of this project is to develop bifunctional electrodes for operation in both fuel cell and electrolysis mode, enabling a single stack to serve the function of both the electrolyzer and fuel cell and eliminating significant cost.
The broader/commercial impacts of this research are applicable to consumer, industrial, and military customers. All of the United States armed services branches have identified energy storage as a critical need for assuring troop safety and operational energy security. Higher energy density for longer unmanned missions, reduction in fuel needs for forward operating bases, and reduced power signatures are key concerns to be addressed. The proposed energy storage system can provide power for military surveillance vehicles, forward operating bases, and consumer homes. Japan is already leading the effort in distributed energy generation and has deployed thousands of residential energy storage systems. However, most of the current systems are based on natural gas, which still relies on fossil fuel sources and contributes to the problem of increasing global carbon dioxide levels. Hydrogen-based systems enable a fully reversible chemical cycle of hydrogen and oxygen to water and back. Advances in these areas will find immediate commercial interest, and will address a specific capability that enables clean, sustainable energy solutions.
Project Outcomes In Phase 1 of this project, Proton Energy Systems (d/b/a Proton OnSite) demonstrated improvements in round trip efficiency for a reversible fuel cell, converting water and electricity to hydrogen and oxygen for storage, and then converting these stored fuels back to electricity within a single device. As the percentage of delivered energy from the grid becomes higher in renewable content, energy storage becomes a critical factor in supply reliability, due to the high variability of intermittent renewable energy sources such as solar and wind. Power fluctuations can be over 80% for these sources, on minutes to hour time scales. For this large variation, grid buffering is needed for ensuring power needs are continuously met, without significantly oversizing the primary energy source. From a technology standpoint, regenerative fuel cells are an ideal choice for capturing the excess capacity during periods of high wind or peak sunlight hours, and feeding it back during deficit periods. These devices have high energy density, excellent load-following characteristics, and long cycle life. In this approach, excess electricity is captured in the form of hydrogen via electrolysis of water, and stored until needed. The hydrogen is then fed through a fuel cell to generate electricity. The cell stacks which perform the chemical conversions represent the largest cost component of the system, especially since typically separate stacks are utilized for the electrolysis and fuel cell functions. Given that the materials of construction are very similar, the concept of a unitized device has been considered very attractive. However, traditionally, electrolyzers have utilized very thick membranes due to the higher mechanical stress in the cell, which result in poor fuel cell performance. In addition, the traditional oxygen catalysts used in each device are not very reversible. These two effects reduce the overall round trip efficiency significantly vs. two separate stacks, creating additional cost and energy losses. In this project, materials advances in membrane and catalyst technology were leveraged to remove some of the roadblocks to using a combined fuel cell-electrolysis stack. Thinner, reinforced membranes have recently shown promise in electrolysis cells, with over 66% reduction in thickness. In addition, recent catalyst work has shown promise in improving bifunctionality for the unitized application. These materials were integrated into electrodes for testing in both modes to demonstrate feasibility of a combined device. Specific accomplishments of the Phase 1 project included: Fabrication of novel nanoengineered catalysts for oxygen evolution and reduction which showed good activity and stability for both modes; Development of novel membranes with improved mechanical strength required for electrolysis but similar thickness to standard fuel cells; Modification of testing equipment to achieve the desired operating protocol; Building a single cell prototype and characterizing performance in both operating modes; and Cost and efficiency modeling of the final configuration vs. traditional discrete devices. The cost modeling demonstrated a cost savings range of 15-25% for the unitized device vs. the discrete version. This analysis considers the stack only as the highest single cost element in the system, and does not include savings in balance of plant components due to the integrated system, which can also be significant. The work completed in this project also has market applications in the hydrogen generator alone, due to the improvements in membrane efficiency.