Electrochemical Reduction
of Carbon Dioxide in an
MFC–MEC System with a Layer-by-Layer Self-Assembly Carbon Nanotube/Cobalt
Phthalocyanine Modified Electrode
- Publication date
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Abstract
Electrochemical reduction of carbon dioxide (CO<sub>2</sub>) to
useful chemical materials is of great significance to the virtuous
cycle of CO<sub>2</sub>. However, some problems such as high overpotential,
high applied voltage, and high energy consumption exist in the course
of the conventional electrochemical reduction process. This study
presents a new CO<sub>2</sub> reduction technique for targeted production
of formic acid in a microbial electrolysis cell (MEC) driven by a
microbial fuel cell (MFC). The multiwalled carbon nanotubes (MWCNT)
and cobalt tetra-amino phthalocyanine (CoTAPc) composite modified
electrode was fabricated by the layer-by-layer (LBL) self-assembly
technique. The new electrodes significantly decreased the overpotential
of CO<sub>2</sub> reduction, and as cathode successfully reduced CO<sub>2</sub> to formic acid (production rate of up to 21.0 ± 0.2
mg·L<sup>–1</sup>·h<sup>–1</sup>) in an MEC
driven by a single MFC. Compared with the electrode modified by CoTAPc
alone, the MWCNT/CoTAPc composite modified electrode could increase
the current and formic acid production rate by approximately 20% and
100%, respectively. The Faraday efficiency for formic acid production
depended on the cathode potential. The MWCNT/CoTAPc composite electrode
reached the maximum Faraday efficiency at the cathode potential of
ca<i>.</i> −0.5 V vs Ag/AgCl. Increasing the number
of electrode modification layers favored the current and formic acid
production rate. The production of formic acid was stable in the MFC–MEC
system after multiple batches of CO<sub>2</sub> electrolysis, and
no significant change was observed on the performances of the modified
electrode. The coupling of the catalytic electrode and the bioelectrochemical
system realized the targeted reduction of CO<sub>2</sub> in the absence
of external energy input, providing a new way for CO<sub>2</sub> capture
and conversion