Electrochemical Reduction of CO₂ on Molecular Catalyst: Unfolding Operation Parameters Influence on Product Selectivity

The electrochemical reduction of CO₂ (eCO₂R) using renewable electricity offers a promising way to convert waste CO₂ into valuable chemicals and fuels, achieving a negative carbon emission footprint. Industrializing eCO₂R for chemical production requires durable, selective, and active electrocatalysts capable of generating high current density at low overpotentials. This thesis focuses on the design and development of a cobalt tetraphenyl porphyrin/multi-walled carbon nanotube (CoTPP/MWCNT) composite for eCO₂R to one-carbon (C₁) chemicals and fuels, and the evaluation of this composite in various electrochemical cells. The electrochemical reduction of CO₂ on CoTPP/MWCNT was investigated in two electrochemical cells: H-cell and industrially relevant flow cell. In both electrochemical cells, selected potential values and a temperature range of 20-50°C were investigated in a 0.1 M KHCO3 electrolyte. The local reaction environment during eCO₂R on the composite was investigated using a differential electrochemical mass spectrometry (DEMS) technique. A similar temperature range as in previous studies was employed. The H-cell studies reveal that the composite produces a mixture of liquid and gas products. The product selectivity strongly depends on the applied potentials and temperatures. At lowest applied temperature, CO₂ is mainly converted to CO and CH3OH while H2 production remains minimal. As the temperature increases H2 production becomes dominant over eCO₂R related products. Flow cell studies reveal that composite mainly produces gas products such as CO and H2 at all applied potentials and temperature. Like H-cell, product selectivity strongly depends on the applied potentials and temperatures. Interestingly, at 20°C and highest applied negative potential, the composite is highly selective for CO formation, reaching a Faradaic efficiency (FE) of 98%. However, increasing the temperature significantly reduces CO selectivity while increasing H2 production. Furthermore, this study demonstrates that the syngas (a mixture of CO and H2) ratio can be controlled by adjusting the temperature. DEMS studies identify key fragments of reaction products evolving from the electrode/electrolyte interface. Experimental results reveal that onset potential of reaction products is strongly affected by temperature, particularly onset potential of CH3OH formation decreased approximately 300 mV at highest temperature. The reduction of onset potential is economically beneficial for large-scale industrial chemicals production. Overall, DEMS studies enhance our knowledge on the mechanisms of CH3OH and CH4 production on the CoTPP/MWCNT composite.