New reactor turns sunlight into fuel

Plant-like reactor beats previous efficiency records for sunlight into fuel

Have you ever basked in the warm summer sun and wondered whether we could mimic plants – combining the power of its rays with carbon dioxide to produce energy?

If so, you’re not the first. The technology to harness the sun’s energy for creating syngas out of CO2 has been around for a while [see ‘CO2: the new green fuel?']. But high energy demands and low efficiency have kept it from being more than a commercial daydream.

Until now, that is. Researchers at the California Institute of Technology (CIT) have found a way to smash previous records for CO2 dissociation in a new prototype reactor.

CIT’s prototype concentrates the sun’s energy onto ceria, a ‘rare earth’ metal catalyst that is actually about as common as copper. When CO2 and water vapour are rapidly passed over it, they break down into smaller particles of carbon monoxide, hydrogen and oxygen. The O is allowed to escape, but the CO and H are harnessed as a syngas – a precursor of liquid hydrocarbon fuels. The reaction requires temperatures of up to 3,000°C to work, and so the team took it to Switzerland, where a High-Flux Solar Simulator can generate heat output equivalent to that of 1,500 suns.

The current prototype has gross inefficiencies: less than 1% of the solar energy is actually harnessed directly to create the syngas. However, the researchers claim that a number of technical improvements currently under investigation (better insulation, for one) could increase the reactor’s efficiency to as much as 19% – enough to make it commercially viable.

According to the paper, published in Science, the fuel produced “offer[s] exceptional energy density and convenience for transportation”. Dave Reay, Senior Lecturer in Carbon Management at Edinburgh University, describes the technology as “exciting”, but adds that it’s “no silver bullet for energy supply or greenhouse gas emissions”. However, he adds, “if it becomes a useful new part of the energy security tool kit, [that would be] fantastic”.

For lead researcher Sossina Haile, the commercial viability is “very much tied to policy. If [the US] had a carbon policy, something like this would move forward a lot more quickly,” she says.

- Lucy Tooher

Image credit: California Institute of Technology