Reviewed by Danielle Ellis, B.Sc.Nov 26 2024
Researchers have developed a new photocatalytic system that can convert carbon dioxide into carbon monoxide without external electrical input. By studying the role of copper in this system, scientists have discovered that copper acts as an oxidant, facilitating the transfer of electrons from the gold nanoparticles to the carbon dioxide molecules, ultimately leading to the formation of carbon monoxide. The study was published in the journal ACS Nano.
Copper X-ray absorption spectroscopy measurements of catalysts in action demonstrate light-driven oxidation of copper nanoparticles under photocatalytic operating conditions. Image Credit: Image courtesy of Levi Palmer, California Institute of Technology and Amy Cordones-Hahn, SLAC National Accelerator Laboratory
Copper is a promising catalyst for the sustainable conversion of carbon dioxide into compounds with more electrons (known as reduced species). In the process of turning carbon dioxide into fuels, this stage is crucial. Although electrical energy is frequently used to start this reaction, solar energy can also be used to create solar fuels.
The chemical makeup of the copper catalyst during the solar reaction is still unclear to scientists. In this study, researchers employed X-rays to examine the changes that occur in copper catalysts when they are just exposed to light and no electricity.
Copper plays an unexpected role, as evidenced by changes in its composition during the reaction. Copper creates a more oxidized chemical species than a more reduced one.
The Impact
To employ copper catalysts to collect carbon and transform it for use in other applications, it is essential to comprehend how they function when exposed to sunlight. This study found that when copper is mixed with a common plasmonic light-absorbing substance, more oxidized species are formed.
The coordinated vibration of metal electrons is known as plasmonics. This new work provides important guidelines for the design and optimization of future light-based catalytic systems.
Summary
Researchers recently proved the photocatalytic conversion of carbon dioxide to carbon monoxide under unaided (electrically unbiased) conditions. The catalysts utilized in the study were copper co-catalysts (p-GaN/Al2O3/Au/Cu), plasmonic gold light absorbers, and a p-type gallium-nitrogen (GaN) semiconductor.
Researchers at the Liquid Sunlight Alliance (LiSA) Fuels from Sunlight Energy Innovation Hub examined the mechanistic function of the Cu catalyst in this system. This study employed Cu K-edge X-ray absorption spectroscopy observations at the Stanford Synchrotron Radiation Lightsource (SSRL), a user facility of the Department of Energy Office of Science.
The researchers determined that copper is composed of a mixture of Cu(I) and Cu(II) oxide, hydroxide, and carbonate compounds without metallic Cu after subjecting the material to gas-phase carbon dioxide and water vapor reaction conditions. The scientists noticed more Cu oxidation during photocatalytic operation conditions with visible light irradiation.
This suggests that hole transfer from Au-to-Cu is initiated by light. First principles simulations of the band alignments of the oxidized Cu compositions with plasmonic Au particles, which show that light-driven hole transfer from Au-to-Cu is thermodynamically favorable, corroborated this observation.
These results revealed that when combined with plasmonic Au particles for light absorption, Cu plays an oxidative rather than a reductive role in photocatalysis under unsupported gas-phase reaction circumstances.
The Liquid Sunlight Alliance, with assistance from the Department of Energy Office of Science, Office of Basic Energy Sciences, and Fuels from Sunlight Hub, is largely responsible for the work that this content is based on.
Journal Reference:
Zoric, M. R., et al. (2024) Oxidizing Role of Cu Cocatalysts in Unassisted Photocatalytic CO2 Reduction Using p-GaN/Al2O3/Au/Cu Heterostructures. ACS Nano. doi.org/10.1021/acsnano.4c02088.