A single device that creates both fuel and oxidant from water and then transforms the fuel and oxygen into electricity and water when a switch is turned offers a number of advantages for terrestrial, space, and military applications. For years, researchers have been working on building efficient unitized regenerative fuel cells, or URFCs, with little environmental effect and high energy density.
However, bifunctional catalysts are required for a URFC to be really efficient. This implies that in an electrolyzer, catalysts should aid in the breakdown of water into hydrogen and oxygen, and in a fuel cell, catalysts should aid in the recombination of hydrogen and oxygen back into water. A team of researchers working at Vijay Ramani’s lab, the Roma B. and Raymond H. Wittcoff Distinguished University Professor, has discovered an effective bifunctional catalyst for the oxygen electrode.
The results of their research were published in the Proceedings of the National Academy of Sciences.
“Unlike the hydrogen electrode, where platinum is an effective bifunctional catalyst, identifying a suitable catalyst for the oxygen electrode is extremely difficult due to the sluggish kinetics of oxygen reduction and oxygen evolution,” said Pralay Gayen, a postdoctoral research associate in Ramani’s lab at Washington University’s McKelvey School of Engineering.
Sulay Saha, a postdoctoral research associate in Ramani’s lab, and Gayen’s study was led by first principles, which included considering the fundamental characteristics of several compounds before traveling to the lab to test prospective catalysts.
The team eventually found and produced Pt-Pyrochlore, a combination of platinum and a lead ruthenate pyrochlore with strong bifunctionality, alongside former undergraduate researcher and co-author Xinquan Liu.
The “bifunctionality index” is a metric that assesses a catalyst’s capacity to enable both forward and backward reactions. Kritika Sharma, a Ph.D. engineering student, remarked, “We want the index to be low.” “Ideally, zero.” The bifunctionality index of this novel catalyst is 0.56 volts, which is quite low when compared to previous catalysts described. The catalyst enabled a round-trip energy efficiency (RTE) of 75% in a URFC device built by the laboratory, which is the highest recorded RTE in this type of URFC.
The URFCs created are ideally suited for applications such as submersibles, drones, spacecrafts, and space stations, as well as off-grid energy storage, due to their high efficiency.