Bio-functional metal organic framework composite as bioanode for enhanced electricity generation by a microbial fuel cell

Bifunctional electrode materials: Enhancing microbial fuel cell efficiency with 3D hierarchical porous Fe3O4/Fe-N-C structures

The rational development of high-performance anode and cathode electrodes for microbial fuel cells (MFCs) is crucial for enhancing MFC performance. However, complex synthesis methods and single-performance electrode materials hinder their large-scale implementation. Here, three-dimensional hierarchical porous (3DHP) Fe3O4/Fe-N-C composites were prepared via the hard template method. Notably, Fe3O4/Fe-N-C-0.04-600 demonstrated uniformly dispersed Fe3O4 nanoparticles and abundant Fe-Nx and pyridinic nitrogen, showing excellent catalytic performance for oxygen reduction reaction (ORR) with a half-wave potential (E1/2) of 0.74 V (vs. RHE), surpassing Pt/C (0.66 V vs. RHE). Moreover, Fe3O4/Fe-N-C-0.04-600 demonstrated favorable biocompatibility as an anode material, enhancing anode biomass and extracellular electron transfer efficiency. Sequencing results confirmed its promotion of electrophilic microorganisms in the anode biofilm. MFCs employing Fe3O4/Fe-N-C-0.04-600 as both anode and cathode materials achieved a maximum power density of 831.8 ± 27.7 mW m-2, enduring operation for 38 days. This study presents a novel approach for rational MFC design, emphasizing bifunctional materials capable of serving as anode materials for microorganism growth and as cathode catalysts for ORR catalysis.

The influence of ZIF-L in a microbial fuel cell (MFC) cathode for oxygen reduction reaction (ORR)

Microbial fuel cells (MFCs) utilize the metabolic activities of microorganisms, through which the chemical energy is directly converted into electrical energy. Bacteria produce electrons by means of oxidation of organic/inorganic substrates within the MFCs. Metal organic frameworks (MOFs) that are porous coordination polymers have gained much interest in the field of efficient catalysts due to their unique characteristics. The utilization of MOF catalysts for oxygen reduction reaction (ORR) in the MFC cathode is one of the most remarkable research areas in material science. MOF (zeolitic imidazole framework-leaf like, ZIF-L) decorated cathode system was employed for the first time in MFC to monitor the improvement in performance by taking advantages of both electrocatalytic activity and porosity of MOFs for the utilization of bioelectrons for ORR. Analysis of ORR performance of ZIF-L/carbon black (CB) composite cathode demonstrated that ZIF-L containing cathode system had an improved ORR activity compared to MFC cathode materials in the literature. The remarkable current density value of 2.1 mA cm-2 and the maximum power density value of 1,462 mW m-2 at room temperature revealed that ZIF-L decorated cathode is an excellent alternative for efficient reduction of oxygen in MFCs.

Promoted electrochemical performance by MOF on MOF composite catalyst of microbial fuel cell: CuCo-MOF@ZIF-8 and the comparison between two-step hydrothermal method and dual-solution method

The microbial fuel cell (MFC) is a device that simultaneously achieves electricity generation and sewage degradation. In this study, a novel cathode catalyst metal-organic frameworks (MOFs) have been fabricated by two-step hydrothermal and dual-solution method (CuCo-MOF@ZIF-8). The synthesized trimetal MOFs exhibited a 3D badminton-like structure morphology and porosity. The results of the characterizations showed that CuCo-MOF@ZIF-8 possesses greater surface area porosity and novel functional groups. The Trimetal MOF-on-MOF mode not only demonstrated the stability of the structure but also enhanced its mechanism. Molecular mechanism analysis revealed changes in the organic ligand and metal binding site due to the transformation of Cu2+ to Cu+, Co2+ to Co3+, and Zn-N to Zn-O organic connection. Furthermore, differences between the two fabrication methods were compared. The solid-state single preparation (CuCo-MOF@ZIF-8-1), was synthesized using the two-step hydrothermal method; the liquid mixed preparation material (CuCo-MOF@ZIF-8-2), was synthesized using the dual-solution method; they exhibited completely different chemical structures and morphologies during material testing and characterization. The maximum output power density of CuCo-MOF@ZIF-8-2-MFC was 246.38 mW/m2, about 2.49 times of ZIF-8 (98.72 mW/m2). The output voltage of CuCo-MOF@ZIF-8-1-MFC was measured at 357 mV over 10 d, while that of CuCo-MOF@ZIF-8-2-MFC reached 365 mV over 12 d.

Harnessing Pseudomonas putida in bioelectrochemical systems

Bioelectrochemical systems (BESs), a group of promising integrated systems that combine the advantages of biotechnology and electrochemical techniques, offer new opportunities to address environmental and energy challenges. Exoelectrogens capable of extracellular electron transfer (EET) are the critical factor enabling electrocatalytic activity in BESs. Pseudomonas putida, an aerobe widely used in environmental bioremediation, the biosynthesis of valuable chemicals, and energy bioproduction, has attracted much attention due to its unique application potential in BESs. This review provides a comprehensive understanding of the working principles, key factors, and applications of BESs using P. putida as the exoelectrogen. The challenges and perspectives for the development of BESs with P. putida as the exoelectrogen are also proposed and discussed.

Trace N-doped manganese dioxide cooperated with Ping-pong chrysanthemum-like NiAl-layered double hydroxide on cathode for improving bioelectrochemical performance of microbial fuel cell

Trace N-doped manganese dioxide (MnO₂) nanoparticles were attached to NiAl-layered double hydroxide (LDH) nano sheets by a simple two-step hydrothermal reaction, and N-MnO₂@NiAl-LDH was successfully prepared as cathode catalyst of microbial fuel cell (MFC). N-MnO₂@NiAl-LDH was Ping-pong chrysanthemum-like structure formed by overlapping lamellar structures, with spherical MnO₂ particles attached on. The unique Ping-pong chrysanthemum-like structure and pore size distribution provided large number of electrochemical active sites. The recombination of trace N and MnO₂ reduced the charge transfer resistance, accelerated the electron transfer rate, and N-MnO₂@NiAl-LDH showed high oxygen reduction reaction (ORR) capability. The maximum output power density of N-MnO₂@NiAl-LDH-MFC was 698 mW/m², about 4.59 times of NiAl-LDH (152.1 mW/m²). The maximum voltage was about 320 mV, and the stability was good for about 7 d. This would provide technical reference for the utilization of cathode catalyst for fuel cells.

Three-Dimensional Carbon Monolith Coated by Nano-TiO2 for Anode Enhancement in Microbial Fuel Cells

A three-dimensional (3D) anode is essential for high-performance microbial fuel cells (MFCs). In this study, 3D porous carbon monoliths from a wax gourd (WGCM) were obtained by freeze-drying and carbonization. Nano-TiO2 was further coated onto the surface of WGCM to obtain a nano-TiO2/WGCM anode. The WGCM anode enhanced the maximum power density of MFCs by 167.9% compared with the carbon felt anode, while nano-TiO2/WGCM anode additionally increased the value by 45.8% to achieve 1396.2 mW/m2. WGCM enhancement was due to the 3D porous structure, the good conductivity and the surface hydrophilicity, which enhanced electroactive biofilm formation and anodic electron transfer. In addition, nano-TiO2 modification enhanced the enrichment of Acinetobacter, an electricigen, by 31.0% on the anode to further improve the power production. The results demonstrated that the nano-TiO2/WGCM was an effective anode for power enhancement in MFCs.