Temperature dependent product distribution of electrochemical CO2 reduction on CoTPP/MWCNT composite

M.N Hossain,P Prslja,C Flox,N Muthuswamy,J Sainio,A.M Kannan,M Suominen,N Lopez,T Kallio

doi:10.1016/j.apcatb.2021.120863

M.N Hossain, P Prslja + Show 7 more

Open Access

https://doi.org/10.1016/j.apcatb.2021.120863

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Abstract

Electrochemical reduction of CO2 to valuable products on molecular catalysts draws attention due to their versatile structures allowing tuning of activity and selectivity. Here, we investigate temperature influence on CO2 conversion product selectivity over a Cobalt(II)-tetraphenyl porphyrin (CoTPP)/multiwalled carbon nanotube (MWCNT) composite in the range of 20–50 ℃. Faradaic efficiency of products changes with temperature and potential so that two-electron transfer product CO formation is enhanced at low potentials and temperatures while the competing hydrogen formation shows an opposite trend. Multi-electron transfer product methanol formation is more favorable at low temperatures and potentials whereas reverse applies for methane. Activity and selectivity are analyzed with DFT simulations identifying the key differences between the binding energies of CH2O and CHOH, the binding strength of CO, and the protonation of CHO intermediate. This novel experimental and theoretical understanding for CO2 reduction provides insight in the influence of the various conditions on the product distribution.

Highlights

Anthropogenic CO2 emissions are one of the biggest contributors to global climate change
The Cobalt(II)-tetraphenyl porphyrin (CoTPP)/multiwalled carbon nanotube (MWCNT) composite morphology was characterized by scanning electron microscopy (SEM)
CoTPP is in a planar configu ration: When deposited on the nanotube, phenyl groups are in perpendicular configuration, where hydrogen atoms of the aromatic phenyl rings interact with the π electron system of MWCNT forming multiple CH–π interactions [41,42,43]

Summary

Introduction

Anthropogenic CO2 emissions are one of the biggest contributors to global climate change. Several techniques have been suggested for lowering atmospheric CO2, e.g., sequestering, enhanced weathering, direct air capture, and biochar [3] Besides these methods, electrochemical reduction of CO2 (eCO2R) is one of the promising techniques for converting CO2 waste emissions into valuable commodity chemicals and closing the carbon cycle and enhancing the circular economy design. The coordinated metal atoms are isolated from each other and behaving as single active sites with high activity and selectivity towards CO production [15,17,18,19]. The selectivity of these molecular catalysts has been demonstrated to depend on the experimental conditions, e.g., cobalt protoporphyrin can produce

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