The secret of renewable solar fuels is an intermittent relationship

They say it is better to have had something special and to have lost it than never to have had it. Who would have thought that the sentiment holds true for metal oxide catalysts? According to scientists at the Lawrence Berkeley National Laboratory (Berkeley Lab) and Caltech, copper that was once bound to oxygen is better at converting carbon dioxide into renewable fuels than copper that was never bound to oxygen.

For your study, now published in the journal. ACS catalysisScientists performed X-ray spectroscopy on working solar fuel generator prototypes to demonstrate that catalysts made of copper oxide are superior to catalysts of purely metallic origin when it comes to producing ethylene, a two-carbon gas with a wide range of industrial applications – even after there are no detectable oxygen atoms left in the catalyst.

“Many researchers have shown that oxide-derived copper catalysts are better for making combustible products from CO_twoHowever, there is debate about why this is happening, “said co-director of research Walter Drisdell, a chemist at Berkeley Lab and a member of the Joint Center for Artificial Photosynthesis (JCAP). JCAP’s mission is to develop energy-efficient technologies solar that can convert atmospheric CO_two in alternative fuels derived from petroleum. Drisdell and his colleagues say their discovery is an important advance toward that goal.

He explained that under operating conditions for fuel generation, which implies first converting CO_two in carbon monoxide and then building hydrocarbon chains: oxygen bound to copper is naturally depleted in the catalyst. However, some researchers believe that small amounts of oxygen remain in the metal structure, and that this is the source of the greatest efficiency.

To resolve the debate, the team brought a gas chromatography (GC) system to the X-ray line so that they could detect ethylene production in real time. “Our Caltech collaborators drove the GC from Pasadena and installed it at the X-ray facility in Palo Alto,” said Soo Hong Lee, a postdoctoral researcher at Berkeley Lab and co-author of the study. With this, we demonstrate that there is no correlation between the amount of oxygen (‘oxide’) in the catalyst and the amount of ethylene produced. Therefore, we believe that oxide-derived catalysts are good, not because they have oxygen remaining while they reduce carbon monoxide, but because the oxygen removal process creates a copper metal structure that is better at forming ethylene. “

The team further demonstrated that although the efficiency of oxide-derived catalysts decreases over time, they can be ‘reactivated’ regularly by adding and removing oxygen again during a simple maintenance process. Their next step is to design a fuel-generating cell that can operate with X-ray scattering instruments, allowing them to directly map the changing structure of the catalyst while converting carbon monoxide to ethylene.

The research team also included Ian Sullivan and Chengxiang Xiang at Caltech, and David Larson, Guiji Liu and Francesca Toma at Berkeley Lab. This work was supported by the Office of Science of the United States Department of Energy (DOE). JCAP is a DOE energy innovation center.