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Purposely Designed Hierarchical Porous Electrodes for High Rate Microbial Electrosynthesis of Acetate from Carbon Dioxide
journal contribution
posted on 2020-01-28, 19:46 authored by Victoria Flexer, Ludovic JourdinConspectusCarbon-based products are crucial to our society, but their production
from fossil-based carbon is unsustainable. Production pathways based
on the reuse of CO2 will achieve ultimate sustainability.
Furthermore, the costs of renewable electricity production are decreasing
at such a high rate, that electricity is expected to be the main energy
carrier from 2040 onward. Electricity-driven novel processes that
convert CO2 into chemicals need to be further developed.
Microbial electrosynthesis is a biocathode-driven process in which
electroactive microorganisms derive electrons from solid-state electrodes
to catalyze the reduction of CO2 or organics and generate
valuable extracellular multicarbon reduced products. Microorganisms
can be tuned to high-rate and selective product formation. Optimization
and upscaling of microbial electrosynthesis to practical, real life
applications is dependent upon performance improvement while maintaining
low cost. Extensive biofilm development, enhanced electron transfer
rate from solid-state electrodes to microorganisms and increased chemical
production rate require optimized microbial consortia, efficient reactor
designs, and improved cathode materials.This Account is about
the development of different electrode materials
purposely designed for improved microbial electrosynthesis: NanoWeb-RVC
and EPD-3D. Both types of electrodes are biocompatible, highly conductive
three-dimensional hierarchical porous structures. Both chemical vapor
deposition (CVD) and electrophoretic deposition were used to grow
homogeneous and uniform carbon nanotube layers on the honeycomb structure
of reticulated vitreous carbon. The high surface area to volume ratio
of these electrodes maximizes the available surface area for biofilm
development, i.e., enabling an increased catalyst loading. Simultaneously,
the nanostructure makes it possible for a continuous electroactive
biofilm to be formed, with increased electron transfer rate and high
Coulombic efficiencies. Fully autotrophic biofilms from mixed cultures
developed on both types of electrodes rely on CO2 as the
sole carbon source and the solid-state electrode as the unique energy
supply.We present first the synthesis and characteristics of
the bare
electrodes. We then report the outstanding performance indicators
of these novel biocathodes: current densities up to −200 A
m–2 and acetate production rates up to 1330 g m–2 day–1, with electron and CO2 recoveries into acetate being very close to 100% for mature
biofilms. The performance indicators are still among the highest reported
by either purposely designed or commercially available biocathodes.
Finally, we made use of the titration and off-gas analysis sensor
(TOGA) to elucidate the electron transfer mechanism in these efficient
biocathodes. Planktonic cells in the catholyte were found irrelevant
for acetate production. We identified the electron transfer to be
mediated by biologically induced H2. H2 is not
detected in the headspace of the reactors, unless CO2 feeding
is interrupted or the cathodes sterilized. Thus, the biofilm is extremely
efficient in consuming the generated H2. Finally, we successfully
demonstrated the use of a synthetic biogas mixture as a CO2 source. We thus proved the potential of microbial electrosynthesis
for the simultaneous upgrading of biogas, while fixating CO2 via the production of acetate.
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performance indicatorssurface area-3DTOGAExtensive biofilm developmentelectron transfer rateacetate production ratesuniform carbon nanotube layerselectron transfer mechanismElectricity-driven novel processeselectrodeEPDreticulated vitreous carbonCO 2Carbon Dioxide ConspectusCarbon-based productsfixating CO 2electrosynthesiCO 2 sourcecathode materials.This AccountHierarchical Porous ElectrodesH 2biocathodeCVDchemical production ratechemical vapor depositionCO 2 recoveriesHigh Rate Microbial Electrosynthesisoff-gas analysis sensor
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