Insight into the Activity and Selectivity of Nanostructured Copper Titanates during Electrochemical Conversion of CO₂ at Neutral pH via In Situ X-ray Absorption Spectroscopy

The electrochemical conversion of carbon dioxide (CO₂) to useful chemical fuels is a promising route toward the achievement of carbon neutral and carbon negative energy technologies. Copper (Cu)- and Cu oxide-derived surfaces are known to electrochemically convert CO₂ to high-value and energy-dense products. However, the nature and stability of oxidized Cu species under reaction conditions are the subject of much debate in the literature. Herein, we present the synthesis and characterization of copper-titanate nanocatalysts, with discrete Cu–O coordination environments, for the electrochemical CO₂ reduction reaction (CO₂RR). We employ real-time in situ X-ray absorption spectroscopy (XAS) to monitor Cu species under neutral-pH CO₂RR conditions. Combination of voltammetry and on-line electrochemical mass spectrometry with XAS results demonstrates that the titanate motif promotes the retention of oxidized Cu species under reducing conditions for extended periods, without itself possessing any CO₂RR activity. Additionally, we demonstrate that the specific nature of the Cu–O environment and the size of the catalyst dictate the long-term stability of the oxidized Cu species and, subsequently, the product selectivity.