Abstract
Materials at the nanoscale show exciting and different properties. In this review, the applications of nanomaterials for modifying the main components of microbial fuel cell (MFC) systems (i.e., electrodes and membranes) and their effect on cell performance are reviewed and critically discussed. Carbon and metal-based nanoparticles and conductive polymers could contribute to the growth of thick anodic and cathodic microbial biofilms, leading to enhanced electron transfer between the electrodes and the biofilm. Extending active surface area, increasing conductivity, and biocompatibility are among the significant attributes of promising nanomaterials used in MFC modifications. The application of nanomaterials in fabricating cathode catalysts (catalyzing oxygen reduction reaction) is also reviewed herein. Among the various nanocatalysts used on the cathode side, metal-based nanocatalysts such as metal oxides and metal-organic frameworks (MOFs) are regarded as inexpensive and high-performance alternatives to the conventionally used high-cost Pt. In addition, polymeric membranes modified with hydrophilic and antibacterial nanoparticles could lead to higher proton conductivity and mitigated biofouling compared to the conventionally used and expensive Nafion. These improvements could lead to more promising cell performance in power generation, wastewater treatment, and nanobiosensing. Future research efforts should also take into account decreasing the production cost of the nanomaterials and the environmental safety aspects of these compounds.
Highlights
➢Nanomaterials and their roles in improving microbial fuel cells (MFCs) are reviewed. ➢Significant effects of nanomaterials on growing active biofilm and electron transfer are discussed. ➢Nanomaterials lead to higher catalytic activity for electrodes, and higher proton conductivity, and less biofouling for membranes. ➢Inexpensive and high-performance nanocomposites for more practical MFC applications are presented and discussed. ➢Future perspectives of using nanomaterials in MFCs are explained
Zhong et al (2019) introduced a Zr-based metal-organic frameworks (MOFs) as an excellent template for a nitrogen- and cobalt co-doped naocomposite oxygen reduction reaction (ORR) catalyst. They showed that the MOF-based catalyst could enhance MFC output to near the value reached by Pt-coated cathode (300 mW/m2 vs. 313 mW/m2, respectively) (Zhong et al, 2019)
Among various nanomaterials used in MFC modifications, cellulosic nanomaterials and their application in fabricating cellulose-based electrodes have attracted a great deal of attention
Summary
Microorganisms utilized in MFCs are classified into two main groups: exoelectrogens on the anode and electrotrophs on the cathode (biocathode) (Fig. 1a) (Logan et al, 2006 and 2019). Exoelectrogens are vital and form a biofilm on the anode surface to decompose organic substrates like glucose, acetate, and waste materials to generate electrons and protons. This group is necessary for electricity generation. These microorganisms can transport electrons from electron donors (substrate) to electrode surfaces by various mechanisms, including direct contact, nano-wires, and mediators produced by them (Logan, 2009). Electrotrophs (electrotrophic microorganisms) need electrons as feed to grow and use various electron acceptors like carbon dioxide. These microorganisms (Fig. 1c) are instrumental in the reactions taking place on the cathode. Electrotrophs play a vital role as a biocathode in microbial electrosynthesis (MES) systems
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