Researchers from the University of California, Riverside, are examining the other uses of ammonia borane – a chemical used in electric vehicle batteries – and they suggested that the chemical could also give us carbon-free fuel for space flight. According to their research, this chemical also has several advantages over other types of rocket fuels: higher energy, lower costs, and no requirement for frozen storage.
Ammonia borane is currently used for storing hydrogen in fuel cells that power electric vehicles. UCR researchers now understand how this combination of boron and hydrogen can release enough energy to also launch rockets and satellites.
Conventional rocket fuels are based on hydrocarbons refined from fossil fuels and are known to have a variety of negative environmental impacts, including poisoning the soil for decades, causing cancer, and leading to the production of acid rain, ozone holes, and greenhouse gases. In contrast, once burned, ammonia borane releases the benign compounds boron oxide and water, which are much less harmful to the environment. It also releases more energy, potentially resulting in cost savings because less of it is required to power the same flight.
To release energy from traditional hydrocarbon-based rocket fuels and enable combustion, catalysts and oxidizers are added to supply extra oxygen to the fuel. They enhance the rate of combustion, but they also stay in the same form both before and after the reaction.
The inherent chemistry of ammonia borane decomposition hinders the release of its total energy when it reacts with most oxidizers, which is why it hasn’t been widely considered as an option for rocket fuel until now. However, the researchers found an oxidizer that alters the decomposition and oxidation mechanisms of this fuel, leading to the extraction of its total energy content.
“This is analogous to the use of catalytic converters to enable the complete combustion of hydrocarbon fuels,” said Pankaj Ghildiyal, University of Maryland chemistry Ph.D. student and study co-author, currently working at UCR. “Here, we were able to create more complete combustion of the chemicals and increase the energy of the entire reaction by using the chemistry of the oxidizer itself, without needing a catalyst.”
Some rocket fuels also require storage at sub-freezing temperatures. By contrast, ammonia borane fuel is stable at room temperature and is resistant to high heat. In their research, the team created very fine, nanoscale particles of ammonium borane, which could degrade over the course of a month in very humid environments.
They are now studying the way ammonium borane particles of various sizes age in different environments and also developing methods of encapsulating particles of the fuel a protective coating to enhance their stability in moist conditions.
“We’ve determined the fundamental chemistry that powers this fuel and oxidizer combination,” said Prithwish Biswas, UCR chemical engineer and first author of the new study. “Now, we are looking forward to seeing how it performs at a large scale.”