1 Introduction
1.1 Electrochemical/Bioelectrochemical Advantages
The search for solutions towards atmospheric CO 2 reduction/mitigation has
increased dramatically, in recent years, driven by the global awareness of the climate change effects, including Institutional boost to find solutions, such as the 2030
Agenda for Sustainable Development, namely in its goal 13 goals (Climate Action).
A multitude of past and on-going research projects propose different approaches
towards the CO 2 transformation into added-value products, simultaneously reducing CO 2 atmospheric levels. Still, most of those have shown low efficiencies and the
research intensively continues. Amongst the proposals, it is possible to find photochemical, biochemical, thermochemical, electrochemical and mixed methodologies [1]. The difficulties to find an efficient approach are associated to the known
properties of CO 2 molecule, namely its stability and also to its low solubility in
water [2, 3]. The electrochemical approach for reducing CO 2 seems to present
advantages since can be considered a “greener” route by the possibility to use the
excess of electricity generated by other renewable sources (considering the different
demands throughout the days), such as solar or wind. Another gain is the possible
estimation and selection of the reaction products through the applied conditions,
namely the current density, amongst other parameters [4]. Several possible CO 2
electro-synthesized products can be formed such as carbon monoxide, hydrocarbons, alcohols, urea and formic acid. The later has received particular attention
since has been considered as the most valuable (in terms of its market value) [3, 5].
Although studies have demonstrated that electroreduction of CO 2 to formic acid, for
instance, can be economically viable when compared with traditional industrial
methods [5], the energetics and catalysts needed are still issues to be overcome.
These issues can, however, be surpassed by merging biochemical and electrochemical methods. In fact, in Nature enzymes are known to easily use (by reducing
or oxidizing or by acid–base reactions) and convert CO 2 to value-added products
using mild conditions (room temperature, 1 atm, physiological pH values) and
some mixed methods are being pursued [6, 7]. Our ability to use Natures’ solutions
together with our technological developments seems to be the key to a more sustainable world.
2 Enzymatic Systems and CO 2
2.1 Enzymes Catalysing CO 2 Reactions
Currently, it is well established that human activity altered the carbon cycle, leading
to perturbation in the fluxes between atmospheric, land, water and geological
carbon reservoirs with consequently enhanced levels of atmospheric CO 2 [8]. The
most known carbon processes/pools are related to photosynthesis, organic
Carbon Dioxide Utilization—Bioelectrochemical Approaches
85
1.1 Electrochemical/Bioelectrochemical Advantages
The search for solutions towards atmospheric CO 2 reduction/mitigation has
increased dramatically, in recent years, driven by the global awareness of the climate change effects, including Institutional boost to find solutions, such as the 2030
Agenda for Sustainable Development, namely in its goal 13 goals (Climate Action).
A multitude of past and on-going research projects propose different approaches
towards the CO 2 transformation into added-value products, simultaneously reducing CO 2 atmospheric levels. Still, most of those have shown low efficiencies and the
research intensively continues. Amongst the proposals, it is possible to find photochemical, biochemical, thermochemical, electrochemical and mixed methodologies [1]. The difficulties to find an efficient approach are associated to the known
properties of CO 2 molecule, namely its stability and also to its low solubility in
water [2, 3]. The electrochemical approach for reducing CO 2 seems to present
advantages since can be considered a “greener” route by the possibility to use the
excess of electricity generated by other renewable sources (considering the different
demands throughout the days), such as solar or wind. Another gain is the possible
estimation and selection of the reaction products through the applied conditions,
namely the current density, amongst other parameters [4]. Several possible CO 2
electro-synthesized products can be formed such as carbon monoxide, hydrocarbons, alcohols, urea and formic acid. The later has received particular attention
since has been considered as the most valuable (in terms of its market value) [3, 5].
Although studies have demonstrated that electroreduction of CO 2 to formic acid, for
instance, can be economically viable when compared with traditional industrial
methods [5], the energetics and catalysts needed are still issues to be overcome.
These issues can, however, be surpassed by merging biochemical and electrochemical methods. In fact, in Nature enzymes are known to easily use (by reducing
or oxidizing or by acid–base reactions) and convert CO 2 to value-added products
using mild conditions (room temperature, 1 atm, physiological pH values) and
some mixed methods are being pursued [6, 7]. Our ability to use Natures’ solutions
together with our technological developments seems to be the key to a more sustainable world.
2 Enzymatic Systems and CO 2
2.1 Enzymes Catalysing CO 2 Reactions
Currently, it is well established that human activity altered the carbon cycle, leading
to perturbation in the fluxes between atmospheric, land, water and geological
carbon reservoirs with consequently enhanced levels of atmospheric CO 2 [8]. The
most known carbon processes/pools are related to photosynthesis, organic
Carbon Dioxide Utilization—Bioelectrochemical Approaches
85