Electrochemical reduction of CO₂ on a CoTPP/MWCNT composite: Investigation of operation parameters influence on CH₃OH production by differential electrochemical mass spectrometry (DEMS)

Renewable electricity-driven electrochemical production of small organic molecules, such as CH₃OH, from chemical industry waste CO₂ feedstock is highly desirable for circular economy. These reactions proceed via multiple intermediate steps which causes high overpotential and poor selectivity imposing a challenge for designing techno-economically viable systems. Proper understanding of the reaction mechanism is essential to overcome those challenges. Herein, we present a simple qualitative analysis to understand the reaction mechanism during electrochemical reduction of CO₂ (eCO₂R) on a cobalt tetraphenylporphyrin / multiwalled carbon nanotube (CoTPP/MWCNT) composite in the temperature range of 20–50 °C by employing differential electrochemical mass spectrometry (DEMS) in 0.1 M and 0.5 M KHCO₃ electrolytes. Interestingly, temperature is observed to strongly affect the onset potentials for product generation in such a way that with the increase of temperature from 20 °C to 50 °C a decrease in the onset potential specifically for methanol formation is observed. Moreover, formaldehyde (HCHO) formation appears to occur at lower overpotentials before the formation of CH₃OH which suggests that on the composite electrocatalyst, HCHO is an important intermediate on a route to CH₃OH. This work offers valuable information on reaction routes to CH₃OH and temperature effects on the eCO₂R selectivity on molecular catalysts.