The CO2 electrochemical reduction reaction (CO2RR) has intrigued scientists for decades as a way to make fuel and chemicals from the greenhouse gas CO2. Prior research identified copper as a CO2RR catalyst, and has revealed the active sites where electrocatalysis takes place, but copper’s catalytic properties quickly degrade during CO2RR, so researchers have sought ways to prevent it.
Copper mineral (Shutterstock)
Scientists at Lawrence Berkeley National Laboratory (Berkeley, Calif.; www.lbl.gov) and the SLAC National Accelerator Laboratory (San Mateo, Calif.; www6.slac.stanford.edu) have shed light on these degradation processes by applying scattering and imaging techniques in a novel way that allowed the researchers to identify and observe two competing mechanisms that drive copper nanoparticles toward degradation in a CO2RR catalyst: particle migration and coalescence (PMC), in which smaller particles combine into larger ones; and Ostwald ripening, where larger particles grow at the expense of smaller particles.
The researchers used small-angle X-ray scattering (SAXS) to track the size and shape distributions of uniformly shaped 7-nm copper oxide nanoparticles under various electrical voltages in a custom-designed electrochemical cell. They observed that the PMC process dominates initially, before Ostwald ripening takes over.
The results “suggest various mitigation strategies to protect catalysts depending on the desired operating conditions, such as improved support materials to limit PMC, or alloying strategies and physical coatings to slow dissolution and reduce Ostwald ripening,” explains Berkeley Lab staff scientist Walter Drisdell, a co-author of the study.
The study was undertaken as part of the Liquid Sunlight Alliance (LiSA), a DOE Energy Innovation Hub led by Caltech (www.caltech.edu) and Berkeley Lab, and was published recently in the Journal of the American Chemical Society.