Temperature-Controlled Syngas Production via Electrochemical CO₂ Reduction on a CoTPP/MWCNT Composite in a Flow Cell

The mixture of CO and H₂, known as syngas, is a building block for many substantial chemicals and fuels. Electrochemical reduction of CO₂ and H₂O to syngas would be a promising alternative approach for its synthesis due to negative carbon emission footprint when using renewable energy to power the reaction. Herein, we present temperature-controlled syngas production by electrochemical CO₂ and H₂O reduction on a cobalt tetraphenylporphyrin/multiwalled carbon nanotube (CoTPP/MWCNT) composite in a flow cell in the temperature range of 20–50 °C. The experimental results show that for all the applied potentials the ratio of H₂/CO increases with increasing temperature. Interestingly, at −0.6 V_RHE and 40 °C, the H₂/CO ratio reaches a value of 1.2 which is essential for the synthesis of oxo-alcohols. In addition, at −1.0 V_RHE and 20 °C, the composite shows very high selectivity toward CO formation, reaching a Faradaic efficiency of ca. 98%. This high selectivity of CO formation is investigated by density functional theory modeling which underlines that the potential-induced oxidation states of the CoTPP catalyst play a vital role in the high selectivity of CO production. Furthermore, the stability of the formed intermediate species is evaluated in terms of the pK_a value for further reactions. These experimental and theoretical findings would provide an alternative way for syngas production and help us to understand the mechanism of molecular catalysts in dynamic conditions.