Stability of Cu/TiO₂ Nanoparticle Model Catalysts under Electrochemical CO₂ Reduction Conditions

Abstract

Investigations of catalysts for electrochemical CO2 reduction have mainly focused on improving their activity and selectivity, while studies on the stability of these catalysts are less scrutinized and generally lacking. In this study, we investigate the stability of a model catalyst system consisting of CuO x nanoparticles selectively deposited on TiO2 nanoparticles on a highly oriented pyrolytic graphite (HOPG) substrate under electrochemical CO2 reduction conditions. X-ray photoelectron spectroscopy (XPS) was used to study changes in the chemical composition and approximate amount of the nanoparticles after electrochemical reduction. Scanning electron microscopy (SEM) was used to track the structure and movement of specific particles after electrochemical reduction, and atomic force microscopy (AFM) was used to monitor morphological changes on the substrate surface. Herein, we show that sufficiently reducing potentials lead to mobility of some (approximately 30%) of the TiO2 nanoparticles. The TiO2 nanoparticle mobility results in some agglomeration and vertical growth of the nanoparticles, as the mobile nanoparticles tend to attach to the top of the stationary particles. It is also shown that, upon agglomeration, the mobile TiO2 nanoparticles undergo a reduction in diameter, while the diameter of the stationary particles remains unchanged. These results highlight the importance of stability studies in order to understand the degradation mechanisms of model electrochemical catalysts in an effort to mitigate catalyst deactivation and maintain activity and selectivity over long periods of time.

Dynamic Evolution of Active Sites in Electrocatalytic CO2 Reduction Reaction: Fundamental Understanding and Recent Progress

“…[32,41] The surface protection can be achieved by adding another thin layer of 2D material or organic compounds on Cu particles or films. [156][157][158][159][160][161] For example, Cu nanowires wrapped by graphene layers behaved much better preservation of morphology after 5 C of CO 2 electrolysis, while evident disintegration, fracturing and particle formation were observed on naked wire. The production toward CH 4 was also well-maintained on wrapped nanowires, with negligible shifting of selectivity from CH 4 to other products like C 2 H 4 .…”

CO2 Activation on Cu/TiO2 Nanostructures: Importance of Dual Binding Site

“…The Cu/TiO 2 support is of particular interest for CO 2 reduction. [14][15][16][17] The final aspect considered is the role of surface reduction on the catalytic properties of supported Cu nanocatalysts. Titania is a reducible oxide, and it is hardly produced in stoichiometric form.…”

“…Thus, we considered both single Cu atoms and Cu 10 clusters deposited on the most stable rutile, r‐TiO 2 (110), and anatase, a‐TiO 2 (101), surfaces. The Cu/TiO 2 support is of particular interest for CO 2 reduction [14–17] …”

Stabilizing Cu Catalysts for Electrochemical CO2 Reduction Using a Carbon Overlayer

“…One major issue is the structure evolution of Cu catalysts during CO 2 RR, which could influence not only their activities but also selectivities toward the formation of a certain product. − Cu catalysts tend to reconstruct quickly from sphere to cubes and then agglomerate into irregular dendrites during the reaction, causing a decline in FE of C 2+ products. ,− Researchers investigated possible reasons for reconstruction and decreased durability. − The reaction intermediate *CO was reported to induce the formation of Cu clusters on the close-packed Cu(111) surface. , In addition, hydroxide was also suggested to induce the formation of the surface reconstruction and the ejection of excess Cu atoms onto the surface . Moreover, CO adsorption was also found to enhance hydroxide adsorption on metal catalyst surface .…”