Recently, microbial electrosynthesis (MESs) has been highlighted for the purpose of biological CO 2 reduction with simultaneous production of intermediates and value-added chemicals. The bioelectrochemical system (BES), which employs microorganisms and a bacterial community as a biocatalyst, has been developed to convert CO 2 , a greenhouse gas, into liquid biofuels, such as ethanol and butanol, as well as platform chemicals [1]. Several bacterial species, called cathodophilic microorganisms (e.g., Sporomusa ovata and Clostridium ljungdahlii) were reported to interact with a carbon electrode by accepting electrons supplied externally from a power supply [2][3][4]. Through this process, oxidized chemical molecules, such as CO 2 , can be converted to more reduced products, such as acetate and ethanol [4,5]. Since the first report of MESs with S. ovata [3,4], performance has been improved by efforts to optimize the reactor design, regulate the applied potential, and improve the bacterial enrichment method [6][7][8]. On the other hand, the interaction between microorganism and carbon materials is still unknown, which is the main factor limiting further improvement of the performance of the MES process. For example, insufficient information about microbecarbon interactions is delaying the advance of the process significantly when the input potential is <−410 mV vs standard hydrogen electrode (SHE), which is the theoretical minimum potential for hydrogen production [9].Carbon has been recognized as the best material for fuel cell applications owing to its good electrical conductivity, its potential for the impregnation of catalysts, and its cost effectiveness [10,11]. For the same reasons, a range of morphologies of carbon materials have been utilized as anode and cathode electrodes in BES in the form of carbon paper, cloth, graphite rod, and felt in BES systems [12]. The porous structure of carbon can also provide sufficient surface area for bacterial attachment, allowing the establishment of an electron transport system to the electrode, and good stability (i.e., resistant to oxidation and reduction). Modified carbon electrodes with chitosan and cyanuric chloride improved their electrosynthetic performance more than 6-fold compared to an untreated carbon electrode [12]. The excellent formation of biofilm on the carbon electrode, acting as a catalyst for MESs, can provide a novel application platform of carbon materials for useful chemical production and reduction of greenhouse gas with biotechnology.The electrochemical properties of microorganisms on the carbon electrode were investigated by cyclic voltammetry (CV), linear sweep voltammetry, and electrochemical impedance spectroscopy (EIS) to elucidate the electron transfer mechanisms between the bacteria and the electrode surface [13,14]. These analyses provided information on how electro-active bacteria interact with the carbon electrode, and the appropriate range of applied potentials in BES [6,8]. For the first demonstration of electromethanogenesis, methane was...
