New 'Nano-Sandwich' Photocathode Turns CO2 Into Ethanol Using Sunlight

Researchers at Charles University in Prague, led by Pavla Eliasova, have developed a photocathode that helps convert the greenhouse gas carbon dioxide into pure ethanol using sunlight. The device, described in the journal Advanced Energy Materials, solves a long-standing problem of material degradation in water and achieves a record conversion efficiency for the process.

The technology uses a solar reactor whose key element, a photocathode, absorbs light and drives the chemical reaction. Cuprous oxide has long looked like an ideal material for this because it is inexpensive, widely available and captures sunlight well, but in water under light it degrades rapidly — much like iron corroding — and loses its function within tens of minutes.

The team, working with Tomas Hrbek from the university's Faculty of Mathematics and Physics, solved this by building a "nano-sandwich": combining cuprous oxide with two-dimensional materials called MXenes, then using controlled heating to create an ultrathin layer of titanium dioxide on the surface. The modified MXenes rapidly drain electric charge away from the cuprous oxide, slowing its breakdown, while using that same charge to convert carbon dioxide into liquid fuel. "The copper base enables maximum utilization of light energy, while the conductive MXene framework ensures that the material remains active even after many hours of operation," Eliasova said.

In laboratory tests, the new photocathode reached a record solar-energy-to-ethanol conversion efficiency of 2.74%. A key improvement is that it forms only a single liquid product, pure ethanol, while other systems often produce a mixture of byproducts that complicate industrial use.

"This is a major step forward for us," Eliasova said. "At the laboratory scale, the system works very well and produces ethanol over many hours. In the next step, we want to further reinforce the stability of the entire photocathode and begin testing on a larger scale and under real daylight conditions."