Bioelectrosynthetic Conversion of CO2 Using Different Redox Mediators: Electron and Carbon Balances in a Bioelectrochemical System

Hyeon Sung Im,Chulhwan Park,Shuwei Li,Minsoo Kim,Young Eun Song,Booki Min,Jiyun Baek,Jung Rae Kim,Mutyala Sakuntala

doi:10.3390/en13102572

Hyeon Sung Im, Chulhwan Park + Show 7 more

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https://doi.org/10.3390/en13102572

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Abstract

Microbial electrosynthesis (MES) systems can convert CO2 to acetate and other value-added chemicals using electricity as the reducing power. Several electrochemically active redox mediators can enhance interfacial electron transport between bacteria and the electrode in MES systems. In this study, different redox mediators, such as neutral red (NR), 2-hydroxy-1,4-naphthoquinone (HNQ), and hydroquinone (HQ), were compared to facilitate an MES-based CO2 reduction reaction on the cathode. The mediators, NR and HNQ, improved acetate production from CO2 (165 mM and 161 mM, respectively) compared to the control (without a mediator = 149 mM), whereas HQ showed lower acetate production (115 mM). On the other hand, when mediators were used, the electron and carbon recovery efficiency decreased because of the presence of bioelectrochemical reduction pathways other than acetate production. Cyclic voltammetry of an MES with such mediators revealed CO2 reduction to acetate on the cathode surface. These results suggest that the addition of mediators to MES can improve CO2 conversion to acetate with further optimization in an operating strategy of electrosynthesis processes.

Highlights

Global greenhouse gas emissions were estimated to be 3.38 × 104 million tons and increased by 2.0%in 2018 [1]
This study examines the Microbial electrosynthesis (MES) process for acetate production from CO2 with different redox mediators, such as 2-hydroxy-1,4-naphthoquinone (HNQ), neutral red (NR), and hydroquinone (HQ), which have different standard reduction potentials and chemical properties
The MES with the NR and HNQ mediators showed the highest level of acetate accumulation in comparison with the control without mediators, but the difference was insignificant, whereas the MES with HQ produced a relatively low acetate level

Summary

Introduction

Global greenhouse gas emissions were estimated to be 3.38 × 104 million tons and increased by 2.0%in 2018 [1]. Global greenhouse gas emissions were estimated to be 3.38 × 104 million tons and increased by 2.0%. Efforts to reduce emissions have been made in industry and academia. The capture and reutilization of CO2 have attracted considerable attention in the international research community. Chemoautotrophic and heterotrophic microorganisms use hydrogen, iron, and sulfur compounds as reducing reagents to metabolize and transform CO2 to organic carbon and the building blocks of cells [4,5,6]. These chemical reagents are expensive and unsustainable, and may not apply

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