Journal of Energy Bioscience 2024, Vol.15, No.4, 233-242 http://bioscipublisher.com/index.php/jeb 234 contribute to the development of more efficient and sustainable MFC systems for practical applications in energy generation and environmental remediation. 2 Fundamentals of Microbial Fuel Cells 2.1 Working principle of MFCs Microbial Fuel Cells (MFCs) are bio-electrochemical systems that convert chemical energy stored in organic substrates directly into electrical energy through the metabolic activities of microorganisms. The fundamental working principle involves the oxidation of organic matter by microorganisms in the anode chamber, which releases electrons and protons. The electrons are transferred to the anode and flow through an external circuit to the cathode, generating electricity. Meanwhile, the protons migrate through a proton exchange membrane to the cathode, where they combine with electrons and an electron acceptor, typically oxygen, to form water (Li et al., 2018; Massaglia et al., 2020; Chen et al., 2021a). 2.2 Types of microorganisms used in MFCs The microorganisms used in MFCs, known as electricigens or exoelectrogens, play a crucial role in the electron transfer process. These microorganisms can be categorized into pure cultures and mixed communities. Pure cultures, such as Geobacter and Shewanella species, are often used to study specific electron transfer mechanisms due to their well-characterized metabolic pathways. However, mixed microbial communities are generally more robust and efficient in electricity generation and can adapt better to complex environments. Mixed communities can include a variety of bacteria that work synergistically to enhance the overall performance of the MFC (Li et al., 2018; Cao et al., 2019; Chen et al., 2021a). 2.3 Role of electrodes in MFCs Electrodes are critical components in MFCs, serving as the sites for microbial attachment and electron transfer. The anode, in particular, is where the primary conversion of organic matter into electrons occurs. The material and design of the anode significantly influence the efficiency of electron transfer and the overall performance of the MFC. Advanced materials such as carbon-based nanomaterials, metal oxides, and composite materials have been developed to enhance the electrical conductivity, biocompatibility, and surface area of the anode, thereby improving microbial attachment and electron transfer rates (Cai et al., 2020; Yang et al., 2020; Yaqoob et al., 2020a; Banerjee et al., 2022; Wang et al., 2022). The cathode also plays a vital role by facilitating the reduction reactions and completing the electrical circuit. Innovations in electrode materials and configurations continue to be a major focus of research to optimize MFC performance (Slate et al., 2019; Cai et al., 2020; Wang et al., 2022). 3 Current Electrode Materials in MFCs 3.1 Carbon-based materials (graphite, carbon cloth, carbon paper) Carbon-based materials are widely used in microbial fuel cells (MFCs) due to their favorable properties such as low cost, high conductivity, and chemical stability. Graphite, carbon cloth, and carbon paper are commonly employed as anode materials. These materials support bacterial attachment and facilitate extracellular electron transfer (EET), which is crucial for electricity generation in MFCs. For instance, carbon cloth modified with polydopamine and reduced graphene oxide (CC-PDA-rGO) has shown significant improvements in power density and electron transfer efficiency (Li et al., 2020). Additionally, carbon felt modified with nickel ferrite and MXene composites has demonstrated enhanced electrochemical performance and higher power densities (Tahir et al., 2020). 3.2 Metal-based materials (stainless steel, titanium) Metal-based materials such as stainless steel and titanium are also used in MFCs due to their excellent electrical conductivity and mechanical strength. These materials can serve as both anode and cathode components. For example, stainless steel and titanium electrodes have been utilized to improve the overall performance and durability of MFCs. However, their high cost and susceptibility to corrosion in certain environments can limit their widespread application (Slate et al., 2019) (Figure 1).
RkJQdWJsaXNoZXIy MjQ4ODYzMg==