**10.1 Modern carbon-based anodes**

*Environmental Issues and Sustainable Development*

Geobacter and Shewanella sp. use a direct electron transport mechanism where the electrons are dispatched directly to the electrode surface. The outer C-type cytochrome membrane is associated with the direct dispatch of NADH-produced

Some species of bacteria like Shewanella and Pseudomonas secrete certain shuttle molecules like flavins, to pass electrons to electrodes via the cell membrane

Genera of Geobacter and Shewanella are evident to use conductive auxiliaries for transporting the electrons outside of the cell [57, 58]. Such conductive networks, called nanowires, are cellular outgrowths for as long as 20 μm. These nanowires are claimed to have a substantially higher electrical conductivity than the synthetic

Choosing and designing an anode has a direct effect on the performance parameters which includes the microbial adhesion, transfer of electrons, and oxidation of fuels. An MFC system's achievable power density depends on the selection of an anode that significantly affects the output of an MFC system [60]. As a consequence, achieving higher power density requires the ability to facilitate the improved transfer of electrons from the bacterial cells to the external circuit, thus the anode is of prime importance towards attaining this objective [61]. The electron transfer process necessitates the donation of an electron using extracellular electron transfer (EET) towards the anode surface by the anode respiring bacteria or ARB and, consequently, the current flow in the circuit externally. This mechanism has been interpreted as being similar to transfer electrons to the anode surface from the cell through direct electron transfer mechanism, soluble electron shuttles diffusion, and the transfer of electrons from biofilm via solid component (pili) [61]. Essential features for the anode to attain the best performance include biocompatibility [62–64], corrosion-resistant, low electrical resistance, and high conduction of electricity [62]. The anode must also be of chemically inert in nature that can function in an environment containing diverse biodegradable wastewater composed of variety of organic and inorganic components that are able to react with the anode

Lots of anode materials have been used in the last five years to create various anodes for MFCs. The choice of material for the construction of anode, in particular, is significantly influenced by improvement in different MFC system structures. On a particular note, various exotic carbonaceous materials' use is on a hike. This new category includes stainless steel, stainless steel with modified surface, and anodes based on graphene-based carbonaceous anodes. In many recent studies the graphene-based anodes are found very encouraging [65–68]. The grapheme composite anodes have been stated for higher power production [69–71]. Similarly, the use of carbon nanofibers, carbon nanotubes single and multi-walled anodes has also been documented for high-performance MFCs [72]. This chapter has categorized a few

**9.1 Direct transfer of electrons**

**9.2 Mediator based electron transfer**

**9.3 Nanowires based electron transfer**

electrons [54].

of the bacteria [55, 56].

metallic nanostructure [59].

**10. Anode materials for MFCs**

material causing its deterioration inefficiency.

**108**

In MFC systems, various anode materials based on carbon have been used over the last decade. These include carbon cloth, carbon paper, or sheet or graphite plates and graphite rod. Using carbon-based anode materials has the advantages of cost-effectiveness, biocompatible nature, efficient electrical conductivity, and chemical stability [73]. Due to their potentially high-performance enhancement and excellent properties, these have been recognized as being very useful for building MFCs. Accessible surface area is an essential factor that affects the efficiency of these anode materials [74, 75]. Such anodes comprises of natural or synthetic anode materials which are as follows:
