Researchers at UCLA say they have come up with a method for converting electrical energy into a liquid fuel, in a development that could lead to regular petrol cars being powered by electricity.
The process, which uses carbon dioxide (CO2), was recently discovered by James Liao of UCLA’s Ralph M. Parsons Foundation Chair in Chemical Engineering.
Liao and his team genetically engineered a microorganism inside an electro-bioreactor to produce the liquid fuel isobutanol and 3-methyl-1-butanol. CO2 was also present while electricity provided the sole energy input.
Currently, electrical energy is still difficult to store efficiently. Chemical batteries, hydraulic pumping and water splitting either lead to low energy-density storage or else are not easily compatible with current transportation infrastructure.
However, Liao said his new process offered a number of advantages.
“The current way to store electricity is with lithium ion batteries, in which the density is low, but when you store it in liquid fuel, the density could actually be very high,” Liao said in a press statement.
In addition, he said the liquid fuel could be introduced at the pumps as a direct replacement to gas, meaning there would be no need to change the way cars are produced.
The UCLA team’s method actually mimics photosynthesis – the process by which plants convert sunlight into energy.
Photosynthesis is divided into two parts – a light and a dark reaction. The light reaction converts light energy to chemical energy and needs sunlight. The dark reaction, which converts CO2 to sugar, can occur in the absence of sunlight.
“We’ve been able to separate the light reaction from the dark reaction and instead of using biological photosynthesis, we are using solar panels to convert the sunlight to electrical energy, then to a chemical intermediate, and using that to power carbon dioxide fixation to produce the fuel,” Liao said. “This method could be more efficient than the biological system.”
He said the use of solar panels offered an advantage over biofuels since the panels could be located out in the desert or on rooftops and would not need to take up valuable farmland, a common complaint against biofuels which require large areas of agricultural land to grow the plants needed to make them.
In theory the hydrogen generated by solar electricity can drive CO2 conversion in lithoautotrophic microorganisms but because of the low solubility and low mass-transfer rate and the safety issues surrounding hydrogen, the researchers did not consider using the gas. Instead they found that formic acid was a favorable substitute and efficient energy carrier.
Liao said the next step would be to see if the electricity-driven bioconversion of CO2 could be used to make a variety of chemicals.
“We’ve demonstrated the principle, and now we think we can scale up,” he said.