Driving Chemical Transformations Through the Power of Solar Energy

Researchers combine solar energy, electrochemistry, and thermal catalysis to remove the need for fossil fuel-driven chemical conversions.

Conversion of CO2 to butene via a solar-driven tandem process. First, CO2 is converted to ethylene using an electrochemical reactor and solar-derived electricity. Next, ethylene is converted to butene via thermal catalysis with heat from solar irradiation. — Image credit: Yap, K.M.K., *et al.*, CO ₂ Conversion to Butene via a Tandem Photovoltaic–Electrochemical/Photothermocatalytic Process: A Co-Design Approach to Coupled Microenvironments. *ACS Energy Letters* 9, 9 (2024).

The Science

Sunlight is a powerful energy source that scientists can leverage to unlock important chemical conversions. In this study, researchers used solar energy to convert carbon dioxide (CO₂), a potent greenhouse gas, into a valuable chemical commodity with a two-step process. First, electricity from solar energy combined with electrochemistry converts CO₂ to ethylene. The ethylene gas stream that exits this process then feeds directly to a thermal catalytic reactor. This reactor uses heat derived from the sun to convert ethylene to butene.

The Impact

To enable a transition to clean energy and sustainable production of chemicals, we need scientific advances that lead to technologies that recycle greenhouse gases into valuable products. Powering these technologies with renewable energy will help us reach net-zero emissions. Butene is a building block for plastics and other products. Industry currently derives butene from fossil fuels. Its generation is energy intensive and emits significant amounts of greenhouse gases. The Liquid Sunlight Alliance process converts CO₂ to butene using only energy drawn directly from the sun. This allows butene production to bypass the electrical grid and operate in a stand-alone system. This research shows that solar energy can directly enable chemical conversion to multicarbon products—complex carbon molecules useful for industry. It thus unlocks the potential for innovating other chemical transformations driven directly by renewable energy.

Summary

Solar fuels enable a pathway for sustainable generation of platform chemicals such as butene directly from solar energy, using CO₂ as a feedstock. In this study, researchers developed a two-step chemical cascade process for the single-pass conversion of CO₂ to butene, using simulated solar irradiation as the only energetic input. In the first step, electrochemical CO₂ reduction converts CO₂ to ethylene using a gas diffusion electrode functionalized with a copper-based catalyst. This reaction uses electricity from an integrated photovoltaic system to drive the chemical reaction. Without separation, ethylene in the outlet gas stream feeds directly to a thermo-catalytic reactor, where a nickel-based catalyst transforms ethylene into butene. The thermo-catalytic reactor is powered by a selective solar absorber that is directly and efficiently heated by solar irradiation.

This research demonstrates the potential for designing modular, solar-driven components and processes to synthesize net-zero carbon fuels, chemicals, and materials that displace carbon intensive fossil fuels in our industrial cycle. In the future, tandem solar fuels reactions could be a key player for the transition to sustainable, decentralized chemicals production.

Contact

Harry Atwater
California Institute of Technology
[email protected]

Funding

This material is based on work performed by the Liquid Sunlight Alliance, which is supported by the Department of Energy Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub.