Thermal Management for Optimal Performance of Unitized Regenerative Fuel Cells

As the race to net zero energy intensifies around the world, hydrogen production and fuel cell technologies are attracting more attention, and the technologies are growing rapidly. Together, hydrogen production and fuel cell technologies hold potential for a reliable, green, and sustainable energy system. Hydrogen is an excellent energy carrier and can be produced from various sources, especially green and renewable sources. Fuel cells generate electricity and water from hydrogen and oxygen. In reverse mode, fuel cells operate as electrolyzers to produce hydrogen and oxygen from electricity and water. However, the major drawback that keeps hydrogen and fuel cells from dominating the commercial energy market and replacing fossil fuels is cost, including capital and operating costs. The cost of producing, storing, and transporting hydrogen, as well as the cost of building a regenerative fuel cell system, are still much higher than fossil fuel and traditional energy generation and storage systems. Unitized regenerative fuel cells (URFC) offer advantages of space (volume), weight, and maximized utilization of high-cost cells and their components, thus, lowering system capital costs. Improving the URFC energy efficiency is an effective way to lower URFC operating cost. This study evaluates a thermal management strategy with waste heat recovery for secondary use to improve system efficiency of Proton Exchange Membrane (PEM) URFC. By building a 3-D software model for simulation of the PEM URFC, the study also offers an in-depth understanding of cell behaviors and characteristics during operation with 3-D visualization and analysis. A 3-D model of 25 cm2 5-cell PEM URFC stack was built in COMSOL Multiphysics® to simulate the URFC operation under current density from 0A/cm2 to 1A/cm2 . The results show that the employed thermal management strategy recovers 76% and 78% of waste heat when the URFC operates in fuel cell mode and in reverse water electrolyzer mode, respectively. With waste heat recovery, the PEM URFC round-trip efficiency is improved from 32% to 81%.