(557e) Performance and Durability of Vapor-Fed Unitized Regenerative Fuel Cells

As the global demand for electrical energy increases and the drive toward carbon-free electricity generation intensifies, it is necessary to develop energy storage devices to compensate for the inherent intermittencies of renewable energy sources, such as wind and solar. One such device is a unitized regenerative fuel cell (URFC), which is effectively a hydrogen battery. The URFC has two modes of operation: water electrolysis mode, which utilizes renewable electrons to produce carbon-free hydrogen, and fuel cell mode, which generates electrical energy for on-demand electricity. The URFC system thus operates with both liquid and gas phases, which complicates water management within the cell, increases transition time between modes, and produces wet hydrogen gas that will need to be dried downstream.

In this study, a URFC using a water vapor feed (vapor-URFC) in electrolysis mode is presented as an alternative option. Using water vapor allows the vapor-URFC to operate exclusively in gas phase, which reduces transition times between the two operating modes. We compare the performance of the vapor-URFC to a traditional URFC operating in the constant gas configuration, in which hydrogen reactions (oxidation and evolution) occur at one electrode, and oxygen reactions (reduction and evolution) occur at the other electrode. Performance and durability of the cell are assessed by measuring polarization curves and performing accelerated stress tests. Preliminary results show that a vapor-URFC is able to obtain current densities of 2 A/cm² at 0.2 V and at 2 V during fuel cell and electrolysis operation, respectively. A vapor-URFC is also able to achieve a round trip efficiency of 60% at 1 A/cm². Furthermore, we present a parametric study of different ion exchange membranes and porous transport layers to determine the optimal architecture for the vapor-URFC cell. Finally, we analyze the performance of the vapor-URFC over a range of relative humidities and using varying carrier gases to demonstrate the viability of this device in a variety of operating conditions.