A Radical Generation: High Temperature Ammonia Treatments of Carbon Felt Electrodes for Vanadium Redox Flow Batteries

The vanadium redox flow battery (VRFB) is a promising candidate for grid-scale energy storage. Modifying VRFB electrodes is one approach to improve overall battery performance and decrease costs. Research into improving these electrodes has included a focus of adding metallics or functional groups to the surface, even though they are easily swept away through physiochemical forces. This dissertation explores a variety of physical characterization and experimental techniques and analyses to gain insight into the mechanisms around an effective and robust high temperature ammonia treatment on carbon felt electrodes for VRFBs. Initial work focused on the treatment time and temperature ranges of effectiveness and identifying the importance of the induced surface area of the electrode on performance. The work continued, focusing on pinpointing the mechanism behind the increase in surface area. It was found that at higher temperatures the ammonia gas decomposes into radicals which gasify the carbon. With this knowledge, methods of increasing rates of decomposition were developed with the goal of optimizing this approach to modification of electrodes for durable high-performance operation. The main outcome of this dissertation is the determination of the mechanism of the ammonia treatment and a path to building upon it. The successful implementation of the radical theory through improving the kinetics of the radical generation and carbon removal with rough surfaces and nickel foam, resulting in improved battery performance beyond the baseline ammonia treatment, demonstrates the efficacy of the theory. This also opens avenues of research to improve electrodes by material removal rather than solely adding material, though combining the two methods is also a viable path. Experiments with high temperature nitrogen gas following high temperature ammonia also show promise. Revitalizing the optimization efforts for this component will increase the viability of VRFB technology. This scalable treatment could also be useful for carbon applications where higher porosity and surface area is beneficial, such as purification and poison control.