Temperature-Controlled Syngas Production via Electrochemical CO ₂ Reduction on a CoTPP/MWCNT Composite in a Flow Cell

Abstract

The mixture of CO and H ₂, known as syngas, is a building block for many substantial chemicals and fuels. Electrochemical reduction of CO ₂ and H ₂O 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 CO ₂ and H ₂O 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 H ₂/CO increases with increasing temperature. Interestingly, at −0.6 V _RHE and 40 °C, the H ₂/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.