Recent advancements in the field of electrochemistry reveal how oxide-derived copper electrocatalysts activate and deactivate during the electrochemical reduction of carbon dioxide (CO2). Using state-of-the-art multiscale X-ray scattering techniques, researchers have gained unprecedented insights demonstrating the delicate interplay between catalyst structure and performance.
The reduction of CO2 is pivotal for creating sustainable fuels and reducing greenhouse gas emissions. Copper stands out as one of the most promising materials for this task, due to its unique ability to produce carbon-based products like ethylene and ethanol efficiently. Nevertheless, the detailed mechanisms governing copper’s electrocatalytic activity have been poorly understood, primarily because of the dynamic morphological changes these catalysts undergo during operation.
Recent findings from collaborative research at the European Synchrotron Radiation Facility (ESRF) highlight the significance of tracking these transformations. The study utilized small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) to monitor, with millisecond-resolution precision, the morphological changes of copper catalysts under realistic electrocatalytic conditions.
Under the newly developed methodology, the research team observed the transformation of copper oxide (Cu2O) to metallic copper, which plays a significant role during CO2 reduction. "The multiscale insights highlight the dynamic and intimate relationship between electrocatalyst structure, surface-adsorbed molecules, and catalytic performance," the authors of the article stated. They noted the necessity to understand these dynamics if advancements are to be made toward efficient electrocatalytic processes.
Essentially, continual morphologic changes observed during the reduction process indicated varied electrocatalytic behavior. Immediately post-activation, the electrocatalyst demonstrated high selectivity for value-added products. This sharp selectivity transitioned over time toward less desirable products such as hydrogen, mimicking the decline often observed during prolonged operation. The detailed SAXS and WAXS data indicated not only changes in the catalyst size and shape but also the variable degree of undercoordination on the surface of the active sites.
These transformations were exhibited through direct measurements. For example, the initial Cu2O octahedral structures underwent rapid reduction to pure Cu with accompanying growth of undercoordinated site density, effectively enhancing selectivity for C2+ products. Over periods of sustained bias, the produced copper particles demonstrated restructuring—the increase of grain size led to substantial loss of selectivity and efficacy.
Raman spectroscopy played a complementary role, confirming the dynamic changes at the electrode interface with enhanced resolution. The research indicated changes were rooted primarily at the atomic level, as vibrational modes associated with adsorbed reaction intermediates evolved, aligning with the changes captured through X-ray scattering. From operational measurements, the research detected surface-bound carbon monoxide (*CO) immediately after activation, with changes manifesting toward bridged CO species implicated as potentially poisonous to catalytic action as operation time extended.
The findings draw attention to the importance of maintaining undercoordinated surface sites for optimal catalytic activity. The authors concluded, "we inferred...that undercoordinated surface sites are necessary for an active CO2 reduction catalyst, and increasing the length scale of roughness by ripening should be avoided to prevent deactivation."
With breakthrough insights, this study opens pathways for designing improved catalytic materials. The potential applications span beyond CO2 reduction, leading to vast possibilities for energy transformation processes. The ability to elucidate how electrocatalysts are activated and deactivated through multiscale X-ray scattering methodologies could lead to the advancement of more stable and efficient electrocatalysts, promoting sustainability and effective carbon management.