Fe3O4 nanospheres decorated reduced graphene oxide as anode to promote extracellular electron transfer efficiency and power density in microbial fuel cells

Fabrication of a Molybdenum Dioxide/Multi-Walled Carbon Nanotubes Nanocomposite as an Anodic Modification Material for High-Performance Microbial Fuel Cells

A nanocomposite of multi-walled carbon nanotubes (MWCNTs) decorated with molybdenum dioxide (MoO2) nanoparticles is fabricated through the reduction of phosphomolybdic acid hydrate on functionalized MWCNTs in a hydrogen-argon (10%) atmosphere in a tube furnace. The MoO2/MWCNTs composite is proposed as an anodic modification material for microbial fuel cells (MFCs). MWCNTs have outstanding physical and chemical peculiarities, with functionalized MWCNTs having substantially large electroactive areas. In addition, combined with the exceptional properties of MoO2 nanoparticles, the synergistic advantages of functionalized MWCNTs and MoO2 nanoparticles give a MoO2/MWCNTs anode a large electroactive area, excellent electronic conductivity, enhanced extracellular electron transfer capacity, and improved nutrient transfer capability. Finally, the power harvesting of an MFC with the MoO2/MWCNTs anode is improved, with the MFC showing long-term repeatability of voltage and current density outputs. This exploratory research advances the fundamental application of anodic modification to MFCs, simultaneously providing valuable guidance for the use of carbon-based transition metal oxide nanomaterials in high-performance MFCs.

Pore-Matched Sponge for Microorganisms Pushes Electron Extraction Limit in Microbial Fuel Cells

Microbial fuel cells (MFCs) are of great potential for wastewater remediation and chemical energy recovery. Nevertheless, limited by inefficient electron transfer between microorganisms and electrode, the remediation capacity and output power density of MFCs are still far away from the demand of practical application. Herein, a pore-matching strategy is reported to develop uniform electroactive biofilms by inoculating microorganisms inside a pore-matched sponge, which is assembled of core-shell polyaniline@carbon nanotube (PANI@CNT). The maximum power density achieved by the PANI@CNT bioanode is 7549.4 ± 27.6 mW m-2 , which is higher than the excellent MFCs with proton exchange membrane reported to date, while the coulombic efficiency also attains a considerable 91.7 ± 1.2%. The PANI@CNT sponge enriches the exoelectrogen Geobacter significantly, and is proved to play the role of conductive pili in direct electron transfer as it down-regulates the gene encoding pilA. This work exemplifies a practicable strategy to develop excellent bioanode to boost electron extraction in MFCs and provides in-depth insights into the enhancement mechanism.

Mechanism and application of modified bioelectrochemical system anodes made of carbon nanomaterial for the removal of heavy metals from soil

Bioelectrochemical techniques are quick, efficient, and sustainable alternatives for treating heavy metal soils. The use of carbon nanomaterials in combination with electroactive microorganisms can create a conductive network that mediates long-distance electron transfer in an electrode system, thereby resolving the issue of low electron transfer efficiency in soil remediation. As a multifunctional soil heavy metal remediation technology, its application in organic remediation has matured, and numerous studies have demonstrated its potential for soil heavy metal remediation. This is a ground-breaking method for remediating soils polluted with high concentrations of heavy metals using soil microbial electrochemistry. This review summarizes the use of bioelectrochemical systems with modified anode materials for the remediation of soils with high heavy metal concentrations by discussing the mass-transfer mechanism of electrochemically active microorganisms in bioelectrochemical systems, focusing on the suitability of carbon nanomaterials and acidophilic bacteria. Finally, we discuss the emerging limitations of bioelectrochemical systems, and future research efforts to improve their performance and facilitate practical applications. The mass-transfer mechanism of electrochemically active microorganisms in bioelectrochemical systems emphasizes the suitability of carbon nanomaterials and acidophilic bacteria for remediating soils polluted with high concentrations of heavy metals. We conclude by discussing present and future research initiatives for bioelectrochemical systems to enhance their performance and facilitate practical applications. As a result, this study can close any gaps in the development of bioelectrochemical systems and guide their practical application in remediating heavy-metal-contaminated soils.

Simultaneous boost of anodic electron transfer and exoelectrogens enrichment by decorating electrospinning carbon nanofibers in microbial fuel cell

Microbial fuel cell (MFC) is a promising technology in wastewater recovery driven by microbial metabolism. However, the low power output resulting from the sluggish extracellular electron transfer (EET) between the anode surface and exoelectrogens dramatically restricted the further application. This study fabricated a high-performance anode by decorating porous and conductive electrospinning carbon nanofibers (CNFs). The maximum power density in MFC modified with 14 wt% polyacrylonitrile CNFs (M-CNF14, 9.6 ± 0.2 W m^-3) was 1.9 and 2.7 times higher than carbon black modified MFC (M-CB, 5.1 ± 0.1 W m^-3) and the blank (M-BA, 3.6 ± 0.1 W m^-3), respectively. Denser biofilm and more microbial nanowires were observed in the M-CNF14 anode than in other conditions. Furthermore, the redox peak current of c-type cytochrome was 1.7-21 times higher in M-CNF14 than in the blank control, verifying the preferable EET activity. Several exoelectrogens like Petrimonas and Comamonas were enriched in M-CNF14 and showed a positive correlation to power generation. Besides, more simplified and modular interrelations among exoelectrogens and other bacteria were obtained in M-CNF14. This study revealed the microbial-related mechanism for simultaneously improving EET and exoelectrogens enrichment by CNFs modified anode, providing guidelines for high-performance wastewater recovery.

Magnetite Nanoparticles In-Situ Grown and Clustered on Reduced Graphene Oxide for Supercapacitor Electrodes

Fe₃O₄ nanoparticles with average sizes of 3–8 nm were in-situ grown and self-assembled as homogeneous clusters on reduced graphene oxide (RGO) via coprecipitation with some additives, where RGO sheets were expanded from restacking and an increased surface area was obtained. The crystallization, purity and growth evolution of as-prepared Fe₃O₄/RGO nanocomposites were examined and discussed. Supercapacitor performance was investigated in a series of electrochemical tests and compared with pure Fe₃O₄. In 1 M KOH electrolyte, a high specific capacitance of 317.4 F g⁻¹ at current density of 0.5 A g⁻¹ was achieved, with the cycling stability remaining at 86.9% after 5500 cycles. The improved electrochemical properties of Fe₃O₄/RGO nanocomposites can be attributed to high electron transport, increased interfaces and positive synergistic effects between Fe₃O₄ and RGO.

Boosting microfluidic microbial fuel cells performance via investigating electron transfer mechanisms, metal-based electrodes, and magnetic field effect

The presented paper fundamentally investigates the influence of different electron transfer mechanisms, various metal-based electrodes, and a static magnetic field on the overall performance of microfluidic microbial fuel cells (MFCs) for the first time to improve the generated bioelectricity. To do so, as the anode of microfluidic MFCs, zinc, aluminum, tin, copper, and nickel were thoroughly investigated. Two types of bacteria, Escherichia coli and Shewanella oneidensis MR-1, were used as biocatalysts to compare the different electron transfer mechanisms. Interaction between the anode and microorganisms was assessed. Finally, the potential of applying a static magnetic field to maximize the generated power was evaluated. For zinc anode, the maximum open circuit potential, current density, and power density of 1.39 V, 138,181 mA m^-2 and 35,294 mW m^-2 were obtained, respectively. The produced current density is at least 445% better than the values obtained in previously published studies so far. The microfluidic MFCs were successfully used to power ultraviolet light-emitting diodes (UV-LEDs) for medical and clinical applications to elucidate their application as micro-sized power generators for implantable medical devices.

Enhancing microbial fuel cell performance using anode modified with Fe3O4 nanoparticles

Low electricity generation efficiency is one of the key issues that must be addressed for the practical application of microbial fuel cells (MFCs). Modification of microbial electrode materials is an effective method to enhance electron transfer. In this study, magnetite (Fe₃O₄) nanoparticles synthesized by co-precipitation were added to anode chambers in different doses to explore its effect on the performance of MFCs. The maximum power density of the MFCs doped with 4.5 g/L Fe₃O₄ (391.11 ± 9.4 mW/m²) was significantly increased compared to that of the undoped MFCs (255.15 ± 24.8 mW/m²). The COD removal efficiency of the MFCs increased from 85.8 ± 2.8% to 95.0 ± 2.1%. Electrochemical impedance spectroscopy and cyclic voltammetry tests revealed that the addition of Fe₃O₄ nanoparticles enhanced the biocatalytic activity of the anode. High-throughput sequencing results indicated that 4.5 g/L Fe₃O₄ modified anodes enriched the exoelectrogen Geobacter (31.5%), while control MFCs had less Geobacter (17.4%). Magnetite is widely distributed worldwide, which provides an inexpensive means to improve the electrochemical performance of MFCs.

Improving the anode performance of microbial fuel cell with carbon nanotubes supported cobalt phosphate catalyst

Microbial fuel cell (MFC) is a sustainable technology that can convert waste to energy by harnessing the power of exoelectrogenic bacteria. However, the poor biocompatibility and low electrocatalytic activities of surface usually cause weak bacterial adhesion and low electron transfer efficiency, which seriously hampers the development of MFCs. Herein, a novel carbon nanotube supported cobalt phosphate (CNT/Co-Pi) electrode is fabricated by assembling CNTs on carbon cloth, followed by the electrodeposition of Co-Pi catalyst. The deposited amorphous Co-Pi thin film contains phosphate and the cobalt ions of multiple oxidation states. The hydrophilic phosphate can promote the adhesion of microorganisms on electrode. The strong conversion ability of multiple states of cobalt offers excellent electrocatalytic activity for the electron transfer across biotic/abiotic interface. Therefore, the highly conductive CNTs substrate, along with the Co-Pi catalyst, provide an effective electron transfer between the electrogenic bacteria and the electrode, which endows MFC high power densities up to 1200 mW m^-2. Our work has demonstrated for the first time that CNT/Co-Pi catalyst can promote the interfacial electron transfer between electrogenic bacteria and electrode, and highlighted the application potentials of Co-Pi as an anode catalyst for the fabrication of high performance MFC anodes.

Modified cobalt-manganese oxide-coated carbon felt anodes: an available method to improve the performance of microbial fuel cells

The novel MnCo₂O₄ (MCO/CF), CNTs-MnCo₂O₄ (CNTs-MCO/CF) and MnFe₂O₄-MnCo₂O₄ (MFO-MCO/CF) electrodes were prepared on carbon felt (CF) by simple hydrothermal and coating method as anodes for MFC. The modified anodes combine the electrocatalytic properties of transition metal oxides (TMOs), the high electrical conductivity of CNTs and the good biocompatibility of CF. These anodes play a synergistically role in the synthesis of structural, to realize high-efficiency electron transfer, low resistance and sufficient space for microbial colonization, while also ensuring high power density. The maximum power density of the composite electrodes CNTs-MCO/CF and MFO-MCO/CF were 4268 mW/m³ and 3660 mW/m³, respectively. The synergistic effect of multi-component effectively improves the performance of MFC. This work not only offers a good design and preparation concept for functional TMOs composite electrodes, but also provides an important guide for the fabrication of CNTs-doped MFC anodes.