Researchers at Caltech have developed an artificial photosynthesis system that converts sunlight and carbon dioxide into hydrocarbon fuels at 18 percent efficiency — more than ten times the efficiency of natural photosynthesis and nearly double the previous record for artificial systems. The breakthrough, published in Science, could provide a pathway to producing carbon-neutral liquid fuels at scale using only sunlight, water, and captured CO2.
The system uses a novel two-stage catalytic process. In the first stage, a perovskite-silicon tandem solar cell generates electrical current with high efficiency. This current drives a copper-indium catalyst that selectively converts CO2 into ethanol and propanol — liquid fuels that can be used directly in existing engines and infrastructure without modification. Previous artificial photosynthesis systems primarily produced simpler molecules like hydrogen or methane, which are harder to store and transport.
Scalability Potential
"The key breakthrough is not just the efficiency — it's the selectivity," explained lead researcher Professor Harry Atwater. "Our catalyst produces multi-carbon liquid fuels with 85 percent selectivity, meaning very little energy is wasted on unwanted byproducts. This makes the economics of scaling up dramatically more favorable."
The technology addresses a critical challenge in the clean energy transition: the need for carbon-neutral liquid fuels for applications where electrification is impractical, including aviation, long-haul shipping, and heavy industry. These sectors account for approximately 30 percent of global emissions and have few viable alternatives to liquid hydrocarbon fuels.
At current efficiency levels, the system could produce fuel at approximately $6 per gallon equivalent — not yet competitive with fossil fuels but approaching the threshold where policy support could make it economically viable. The research team is working with industry partners to develop pilot-scale prototypes and projects that further improvements in catalyst durability and efficiency could bring costs below $4 per gallon within five years. The Department of Energy has awarded a $50 million grant to support commercialization efforts.
