Development of solar fuels that could transform chemical industry

The Liquid Solar Alliance looks to reimagine the chemical industry by coupling electricity from solar energy with semiconductor materials to transform carbon dioxide into ethylene.

January 21, 2025 Phoebe Skok

A diagram of how solar fuels can be produced using LiSA’s methods

Image: Liquid Solar Alliance

Pulling energy from thin air might not be so futuristic after all.

The Liquid Solar Alliance (LiSA), a consortium of national laboratories and West Coast universities, is trying to do just that. LiSA aims to scale liquid fuels generated using sunlight, also known as solar fuels.

Rather than pumping solar-generated electrons into the grid, solar fuels siphon that power into semiconductor materials to create a “redox” reaction, which generates byproducts like hydrogen that can replace the oil and gas traditionally used in chemical production.

“We essentially have to replace the entire fossil-based upstream chemical process,” explained Harry Atwater, a professor of applied physics and material science at CalTech and the director of LiSA.

Large, fossil-powered chemical plants currently generate those “platform” chemicals. Once scaled, solar fuels could replace oil and gas as the main power source for those plants.

“The aim is to develop a scalable technology that can produce the hydrocarbon feedstock and platform chemicals using clean power,” he said, adding that solar fuels could revolutionize the chemical and fuel industries. “We need to be able to start with carbon dioxide, water, and sunlight to perform electrochemical transformations.”

Atwater noted many crucial platform chemicals used in fuels and chemicals are those containing four carbon atoms including butene, the focus of a recent study published in ACS Energy Letters. The study that demonstrated that the chemical can be produced purely using solar fuels.

To do so, researchers couple electricity from solar energy with semiconductor materials to transform carbon dioxide into ethylene. The resulting gas feeds into a thermal catalytic reactor, powered by heat from a connected PV system, that accelerates the chemical reaction and converts the ethylene to butene.

The catch? When producing butene through carbon dioxide reduction, many possible byproducts can also occur. Essentially, “the entire richness of organic chemistry is an available output.” The challenge is thus creating a selective system that only produces a certain chemical.

Even so, solar fuels remain in their early days.

“One of the key reasons we have a bankable photovoltaic industry is that you can warrant the module lifetime of a panel, but you can’t do the same with a perovskite panel at this time,” he said, adding that the element of durability has shooed investors away from investing in perovskite.

It’s similar for solar fuels, which haven’t yet achieved high enough levels of durability or stability. Their production requires cells containing liquid electrolytes, meaning that it takes more to facilitate chemical transformations than simply connecting wires to a “dry” PV module. And the possibility of terawatt-level scalability remains unclear.

Even so, Atwater is bullish about the industry’s future, as he sees many parallels between PV development and how he expects solar fuels to develop. He recognizes, however, that “reimagining the entire chemical industry is an audacious vision.”

“The system looks more like a utility-scale solar field than a series of pipes and plants,” he added. “Instead of drawing electricity from the grid to do chemical processing, you’re harvesting it directly from the sun.”

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