Carbon supported nickel-phthalocyanine/MnOx as novel cathode catalyst for microbial fuel cell application

Multi-metal ferrite as a promising catalyst for oxygen reduction reaction in microbial fuel cell

Improving catalytic activity of cathode with noble metal-free catalysts can significantly establish microbial fuel cells (MFCs) as a sustainable and economically affordable technology. This investigation aimed to assess the viability of utilizing tri-metal ferrite (Co0.5Cu0.5 Bi0.1Fe1.9O4) as an oxygen reduction reaction (ORR) catalyst to enhance the performance of cathode in MFCs. Trimetallic ferrite was synthesized using a sol-gel auto-combustion process. Electrochemical evaluations were conducted to assess the efficacy of as-synthesized composite as an ORR catalyst, employing electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). This evaluation revealed that the impregnation of bismuth in the Co-Cu-ferrite structure improves the reduction current response and reduces the charge transfer resistance. Further experiments were conducted to test the performance of this catalyst in an MFC. The MFC with tri-metal ferrite catalyst generated a power density of 11.44 W/m3 with 21.4% coulombic efficiency (CE), which was found to be comparable with commercially available 10% Pt/C used as cathode catalyst in MFC (power density of 12.14 W/m3 and CE of 23.1%) and substantially greater than MFC having bare carbon felt cathode without any catalyst (power density of 2.49 W/m3 and CE of 7.39%). This exceptionally inexpensive ORR catalyst has adequate merit to replace commercial costlier platinum-based cathode catalysts for upscaling MFCs.

A review of microbial fuel cell and its diversification in the development of green energy technology

The advancement of microbial fuel cell technology is rapidly growing, with extensive research and well-established methodologies for enhancing structural performance. This terminology attracts researchers to compare the MFC devices on a technological basis. The architectural and scientific successes of MFCs are only possible with the knowledge of engineering and technical fields. This involves the structure of MFCs, using substrates and architectural backbones regarding electrode advancement, separators and system parameter measures. Knowing about the MFCs facilitates the systematic knowledge of engineering and scientific principles. The current situation of rapid urbanization and industrial growth is demanding the augmented engineering goods and production which results in unsolicited burden on traditional wastewater treatment plants. Consequently, posing health hazards and disturbing aquatic veracity due to partial and untreated wastewater. Therefore, it's sensible to evaluate the performance of MFCs as an unconventional treatment method over conventional one to treat the wastewater. However, MFCs some benefits like power generation, stumpy carbon emission and wastewater treatment are the main reasons behind the implementation. Nonetheless, few challenges like low power generation, scaling up are still the major areas needs to be focused so as to make MFCs sustainable one. We have focused on few archetypes which majorities have been laboratory scale in operations. To ensure the efficiency MFCs are needed to integrate and compatible with conventional wastewater treatment schemes. This review intended to explore the diversification in architecture of MFCs, exploration of MFCs ingredients and to provide the foreseen platform for the researchers in one source, so as to establish the channel for scaling up the technology. Further, the present review show that the MFC with different polymer membranes and cathode and anode modification presents significant role for potential commercial applications after change the system form prototype to pilot scale.

Iron/iron carbide coupled with S, N co-doped porous carbon as effective oxygen reduction reaction catalyst for microbial fuel cells

As a novel energy device, microbial fuel cells (MFCs) have attracted much attention for their dual functions of electricity generation and sewage treatment. However, the sluggish oxygen reduction reaction (ORR) kinetic on the cathode have hindered the practical application of MFCs. In this work, metallic organic framework derived carbon framework co-doped by Fe, S, N tri-elements was used as alternative electrocatalyst to the conventional Pt/C cathode catalyst in pH-universal electrolytes. The amount of thiosemicarbazide from 0.3 to 3 g determined the surface chemical property, and therefore the ORR activity of FeSNC catalysts. The sulfur/nitrogen doping and Fe/Fe₃C embedded in carbon shell was characterized by X-ray photoelectron spectroscopy and transmission electron microscopy. The synergy of iron salt and thiosemicarbazide contributed to the improvement of nitrogen and sulfur doping. Sulfur atoms were successfully doped into the carbon matrix and formed a certain amount of thiophene- and oxidized-sulfur. The optimal FeSNC-3 catalyst synthesized with 1.5 g of thiosemicarbazide exhibited the highest ORR activity with a positive half wave potential of 0.866 V in alkaline and 0.691 V (vs. Reversible Hydrogen Electrode) in neutral electrolyte, which both outperformed the commercial Pt/C catalyst. However, as the amount of thiosemicarbazide surpassed 1.5 g, the catalytic performance of FeSNC-4 was lowered, and this could be assigned to the decreased defects and low specific surface area. The excellent ORR performance in neutral medium urged FeSNC-3 as good cathode catalyst in single chambered MFC (SCMFC). It showed the highest maximum power density of 2126 ± 100 mW m^-2, excellent output stability of 8.14% decline in 550 h, chemical oxygen demand removal of 90.7 ± 1.6% and coulombic efficiency of 12.5 ± 1.1%, all superior to those of benchmark SCMFC-Pt/C (1637 ± 35 mW m^-2, 15.4%, 88.9 ± 0.9%, and 10.2 ± 1.1%). These outstanding results were associated to the large specific surface area and synergistic interaction of multiple active sites, like Fe/Fe₃C, Fe-N₄, pyridinic N, graphite N and thiophene-S.

Microbial electrolysis cells for the production of biohydrogen in dark fermentation - A review

To assess biohydrogen for future green energy, this review revisited dark fermentation and microbial electrolysis cells (MECs). Hydrogen evolution rate in mesophilic dark fermentation is as high as 192 m³ H₂/m³-d, however hydrogen yield is limited. MECs are ideal for improving hydrogen yield from carboxylate accumulated from dark fermentation, whereas hydrogen production rate is too slow in MECs. Hence, improving anode kinetic is very important for realizing MEC biohydrogen. Intracellular electron transfer (IET) and extracellular electron transfer (EET) can limit current density in MECs, which is proportional to hydrogen evolution rate. EET does not limit current density once electrically conductive biofilms are formed on anodes, potentially producing 300 A/m². Hence, IET kinetics mainly govern current density in MECs. Among parameters associated with IET kinetic, population of anode-respiring bacteria in anode biofilms, biofilm density of active microorganisms, biofilm thickness, and alkalinity are critical for current density.

Synergistically enhanced oxygen reduction reaction and oxytetracycline mineralization by FeCoO/GO modified cathode in microbial fuel cell

The widespread application of antibiotics have aroused serious pollution over the world. Microbial fuel cell (MFC) air cathode was able to simultaneously recover electricity and perform advanced oxidation of pollutions through electro-Fenton (EF). This study synthesized an iron‑cobalt oxide and graphene composite (FeCoO/GO), which possessed high electrochemical activity and ORR catalytic performance. The uniform decoration of FeCoO/GO in MFC air cathode distinctly increased the electricity generation (4.5 times higher than carbon felt) and oxytetracycline (OTC) degradation and detoxification (1.33 times higher). FeCoO/GO boosted the H₂O₂ generation from ORR (1.14 times higher than CF) and mineralization efficiency of OTC (2.63 times higher than CF). UPLC-QTOF-MS verified that OTC was degraded and mineralized through decarboxylation, demethylation, and carbon ring cleavage by the oxidation of ·OH. The enhanced degradation of OTC was not only benefited from the increased ORR catalytic performance, but also the excellent H₂O₂ catalytic activity by Fe and Co for ·OH generation. This study demonstrated an effective strategy by decorating FeCoO/GO in MFC air cathode for the synergistically enhanced ORR and OTC degradation and detoxification, giving promising guidance for the deep removal of antibiotic pollutants in the environment.

Critical insights into psychrophilic anaerobic digestion: Novel strategies for improving biogas production

Anaerobic digestion (AD) under psychrophilic temperature has only recently garnered deserved attention. In major parts of Europe, USA, Canada and Australia, climatic conditions are more suited for psychrophilic (<20 ℃) rather than mesophilic (35 - 37 ℃) and thermophilic (55 - 60 ℃) AD. Low temperature has adverse effects on important cellular processes which may render the cell biology inactive. Moreover, cold climate can also alter the physical and chemical properties of wastewater, thereby reducing the availability of substrate to microbes. Hence, the use of low temperature acclimated microbial biomass could overcome thermodynamic constraints and carry out flexible structural and conformational changes to proteins, membrane lipid composition, expression of cold-adapted enzymes through genotypic and phenotypic variations. Reduction in organic loading rate is beneficial to methane production under low temperatures. Moreover, modification in the design of existing reactors and the use of hybrid reactors have already demonstrated improved methane generation in the lab-scale. This review also discusses some novel strategies such as direct interspecies electron transfer (DIET), co-digestion of substrate, bioaugmentation, and bioelectrochemical system assisted AD which present promising prospects. While DIET can facilitate syntrophic electron exchange in diverse microbes, the addition of organic-rich co-substrate can help in maintaining suitable C/N ratio in the anaerobic digester which subsequently can enhance methane generation. Bioaugmentation with psychrophilic strains could reduce start-up time and ensure daily stable performance for wastewater treatment facilities at low temperatures. In addition to the technical discussion, the economic assessment and future outlook on psychrophilic AD are also highlighted.

Simultaneous sulfamethoxazole degradation with electricity generation by microbial fuel cells using Ni-MOF-74 as cathode catalysts and quantification of antibiotic resistance genes

Antibiotic wastewater presents serious challenges in water treatment. Metal-organic frameworks (MOFs) have received significant attention as promising precursors and sacrificial templates in the preparation of porous carbon-supported catalysts. Herein, we investigated the sulfamethoxazole (SMX) degradation and electrochemical performance of microbial fuel cells (MFCs) that applied as-prepared Ni-MOF-74 and Ni-N-C (Ni-MOF-74 underwent pyrolysis treatment at different temperatures) as air-cathode catalyst. Firstly, the electrocatalytic activity towards oxygen reduction reaction (ORR) of the catalyst was investigated by rotating disk electrode. The results showed that electron transfer number for Ni-MOF-74 was 2.12, while that of 800Ni-N-C was 3.44, which was close to four-electron reduction. Applying Ni-MOF-74 in MFCs, a maximum power density of 446 mW/m² was obtained, which was close to that of 800Ni-N-C. Besides, using Ni-MOF-74 as cathode catalyst, a chemical oxygen demand removal rate of about 84% was obtained, and the degradation rate of 10 mg/L SMX was 61%. The degradation rate decreased with increasing antibiotic concentration, but the average degradation efficiency increased stepwise. Additionally, the relative abundance of resistant gene sul1 in the reactors of the new catalytic material was about 62% lower than that of sul1 in the control (Pt/C) reactors, and the relative abundance of sul2 was about 73% lower. Moreover, cost assessments related to the catalyst performance are presented. The findings of this study demonstrated that Ni-MOF-74 could be considered as a two-electron transfer ORR catalyst, and offers a promising technique for preparation of Ni-N-C for use as four-electron transfer ORR catalysts. In comparison, Ni-MOF-74 could be a promising ORR catalyst of MFCs for antibiotic degradation.

A microbial fuel cell system with manganese dioxide/titanium dioxide/graphitic carbon nitride coated granular activated carbon cathode successfully treated organic acids industrial wastewater with residual nitric acid

To meet the urgent demands for sustainable and efficient, environmental-friendly wastewater treatment, a Microbial fuel cell reactor system with MnO₂/TiO₂/g-C₃N₄ (manganese dioxide/ titanium dioxide/graphitic carbon nitride) @GAC (granular activated carbon) electrode was developed. It was both efficient and energy-saving in treating organic acid wastewater generated in Nylon production, with high-concentration COD and residual nitric acid. The MnO₂/TiO₂/g-C₃N₄ catalyst was deposited on GAC via in-situ growth and sol-gel method. The COD, NH₄⁺-N and NO₃^--N was efficiently removed (respectively 98%, 99% and 99%). The COD removal capacity (17.77 kg COD m^-3d^-1) and the maximum power density (1176.47 mW m^-3) was respectively 36.83% and 65.29% higher than the GAC cathode system. The anodic and cathodic microbial consortiums in MFC were analyzed and compared. The MnO₂/TiO₂/g-C₃N₄@GAC MFC system is technically feasible and cost-effective in treating industrial wastewater.

Biofouling effects on the performance of microbial fuel cells and recent advances in biotechnological and chemical strategies for mitigation

The occurrence of biofouling in MFC can cause severe problems such as hindering proton transfer and increasing the ohmic and charge transfer resistance of cathodes, which results in a rapid decline in performance of MFC. This is one of the main reasons why scaling-up of MFCs has not yet been successfully accomplished. The present review article is a wide-ranging attempt to provide insights to the biofouling mechanisms on surfaces of MFC, mainly on proton exchange membranes and cathodes, and their effects on performance of MFC based on theoretical and practical evidence. Various biofouling mitigation techniques for membranes are discussed, including preparation of antifouling composite membranes, modification of the physical and chemical properties of existing membranes, and coating with antifouling agents. For cathodes of MFC, use of Ag nanoparticles, Ag-based composite nanoparticles, and antifouling chemicals is outlined in considerable detail. Finally, prospective techniques for mitigation of biofouling are discussed, which have not been given much previous attention in the field of MFC research. This article will help to enhance understanding of the severity of biofouling issues in MFCs and provides up-to-date solutions. It will be beneficial for scientific communities for further strengthening MFC research and will also help in progressing this cutting-edge technology to scale-up, using the most efficient methods as described here.

Utilisation of waste medicine wrappers as an efficient low-cost electrode material for microbial fuel cell

Waste generation from healthcare facilities now has become a concerning issue as it contain plastic and metals. Medicine wrappers are one of the major portions of healthcare solid waste, which impel intensive solid waste management practice due to fewer possibilities of deriving by-products. However, it can be recycled and used as an electrode material in microbial fuel cells (MFCs). An electrode material for application in MFCs is a crucial component, which governs total fabrication cost as well as power recovery, thus a cost-effective, stable and durable electrode is essential. In this endeavour, a new metallic (aluminium) waste material, a waste medicine wrapper (WMW), was evaluated for feasibility to be used as anode/cathode in MFCs. Based on the stability test under corrosive environment (1 N KCl), the WMW electrode sustained a maximum current of 46 mA during cyclic voltammetry (CV) and noted only 14% reduction in current at an applied voltage of +0.4 V after 2500 s in chronoamperometry, indicating its good stability. Power recovery from MFC using WMW was higher than the MFC using bare carbon felt as an anode (27 vs. 21 mW/m²). The entire analytical test results viz. CV, electrochemical impedance spectroscopy and power performance established WMW as an excellent anode rather than cathode material.

Low-cost nanowired α-MnO2/C as an ORR catalyst in air-cathode microbial fuel cell

In this work, low cost α-MnO₂ nanowires and α-MnO₂ nanowires supported on carbon Vulcan (α-MnO₂/C) have been synthesized via a simple and facile hydrothermal method for application in microbial fuel cells. The prepared samples have been characterized by X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FE-SEM). Electrocatalytic activities of the samples have been evaluated by means of cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in a neutral phosphate buffer solution. EIS was performed at different potentials to gain further insight into the kinetic properties of α-MnO₂/C. Both catalysts were used in air cathode microbial fuel cells to achieve power densities of 180 and 111 mWm^-2 for α-MnO₂/C and pristine α-MnO₂ nanowires, respectively. α-MnO2/C functions as a good and economical alternative for Pt free catalysts in practical MFC applications, as shown by the findings of stability test and voltage generation cycles in long-term operation of MFC.