Scientists have invented a new device for turning carbon dioxide into a liquid fuel that can efficiently store energy in fuel cells. The fuel could potentially be the future of green transport, packing more energy into the tank than the same volume of hydrogen while also serving as a building block for a whole chemical production industry.
In recent years, a new innovative technology based on formic acid has attracted attention as the next generation of fuel cells. Formic acid isn’t typically a primary choice for the fuel of the future. This formidable energy carrier is found naturally contributing to the pain of bee and ant stings. Currently, it takes a lot of effort to get concentrated into a useful form.
Engineers at Rice University in Houston, Texas, reconsidered the entire production process and developed a clever method to trim out some fatiguing steps to make the process far more efficient.
Chemist Haotian Wang said, “Usually people reduce carbon dioxide in a traditional liquid electrolyte like salty water”.
These dissolved salts aid conversion of the gas into a molecule that stores energy. But along with the fuel, we also end up with thick briny soup and sifting out the formic acid from this is painstaking work.
Wang explains, “So we employed solid electrolytes that conduct protons and can be made of insoluble polymers or inorganic compounds, eliminating the need for salts”.
One vital improvement was replacing the electrolyte with a solid matrix and the second was finding a robust catalyst to speed up the conversion process. A common challenge is keeping a catalyst in the right state, without it degrading and needing to be replaced over time. Bismuth is the ideal catalyst for the job as its bulkier than other metals capable of the same task and it also doesn’t move about as easily. The only need is to stock enough material to turn a lab-test into an industry.
The research team found a solution which was published in Nature Energy.
The investigation’s lead author, Chuan Xia described, “Currently, people produce catalysts on the milligram or gram scales. We developed a way to produce them at the kilogram scale.”
The resultant device is engineered to channel the carbon dioxide through the catalyst where it transforms into a negatively charged molecule named formate. From here it diffuses into the solid electrolyte core, where it comes in contact with the hydrogen ions released from a second catalytic reaction with water, resulting in the formation of a highly concentrated solution of formic acid.
Up to now, the process has reportedly converted about 42% of the electricity from a power source into a chemical form that is usable in fuel cells. This electricity can be easily sourced from a renewable source like a photovoltaic cell or a wind turbine, providing a clean method to store energy from otherwise variable power supplies.
Wang says, “It’s also fundamental in the chemical engineering industry as a feedstock for other chemicals, and a storage material for hydrogen that can hold nearly 1,000 times the energy of the same volume of hydrogen gas, which is difficult to compress. That’s currently a big challenge for hydrogen fuel-cell cars.”
Taking out carbon dioxide from the atmosphere in order to satisfy our growing energy demands sounds like a winning solution amid the problems of climate change. Technology is leaping ahead in finding solutions that use our excess in greenhouse gases to phase out polluting fuels and tap it to charge batteries and improve the natural process of photosynthesis itself.
In the meantime, other researchers are keen to turn it into a solid material resource. It is easy to simply bury it deep underground in rock form again but such a step may not be viable environmentally.