One-step preparation of eggplant-derived hierarchical porous graphitic biochar as efficient oxygen reduction catalyst in microbial fuel cells

Effects of Co3O4 modified with MoS2 on microbial fuel cells performance

In this study, Co3O4@MoS2 is prepared as anodic catalytic material for microbial fuel cells (MFCs). As the mass fraction of MoS2 is 20%, the best performance of Co3O4@MoS2 composite catalytic material is achieved, and the addition of MoS2 enhances both the electrical conductivity and catalytic performance of the composite catalyst. Through the structural characterization of Co3O4@MoS2 composite catalytic material, nanorod-like Co3O4 and lamellar MoS2 interweaved and stacked each other, and the agglomeration of Co3O4 is weakened. Among the four groups of single-chamber MFCs constructed, the Co3O4@MoS2-MFC shows the best power production performance with a maximum stable output voltage of to 539 mV and a maximum power density of up to 2221 mW/m2. Additionally, the ammonia nitrogen removal rate of the MFCs loaded with catalysts is enhanced by about 10% compared with the blank carbon cloth MFC. Overall, the findings suggest that Co3O4@MoS2 composite catalysts can significantly improve the performance of MFCs, making them more effective for both energy production and wastewater treatment.

Graphene and biochar-based cathode catalysts for microbial fuel cell: Performance evaluation, economic comparison, environmental and future perspectives

Microbial fuel cells (MFCs) have been the prime focus of research in recent years because of their distinctive feature of concomitantly treating and producing electricity from wastewater. Nevertheless, the electrical performance of MFCs is hindered by a protracted oxygen reduction reaction (ORR), and often a catalyst is required to boost the cathodic reactions. Conventional transition metals-based catalysts are expensive and infeasible for field-scale usage. In this regard, carbon-based electrocatalysts like waste-derived biochar and graphene are used to enhance the commercialisation prospects of MFC technology. These carbon-catalysts possess unique properties like superior electrocatalytic activity, higher surface area, and high porosity conducive to ORR. Theoretically, graphene-based cathode catalysts yield superior results than a biochar-derived catalyst, though at a higher cost. In contrast, the synthesis of waste-extracted biochar is economical; however, its ability to catalyse ORR is debatable. Therefore, this review aims to make a side-by-side techno-economic assessment of biochar and graphene-based cathode catalyst used in MFC to predict the relative performance and typical cost of power recovery. Additionally, the life cycle analysis of the graphene and biochar-based materials has been briefly discussed to comprehend the associated environmental impacts and overall sustainability of these carbo-catalysts.

Fe/N codoped porous graphitic carbon derived from macadamia shells as an efficient cathode oxygen reduction catalyst in microbial fuel cells

In this study, Fe/N codoped porous graphitic carbon derived from macadamia shells was prepared at different temperatures as cathodic catalysts for microbial fuel cells (MFCs), with K2FeO4 as a bifunctional catalyst for porosity and graphitization. The catalyst prepared at 750 °C (referred to as MSAC-750) showed a large specific surface area (1670.3 m2 g-1), graphite structure, and high pyridine-N and Fe-N X contents. Through the electrochemical workstation test, MSAC-750 shows excellent oxygen reduction reaction (ORR) activity, with an onset potential of 0.172 V and a half-wave potential of -0.028 V (vs. Ag/AgCl) in a neutral medium, and the ORR electron transfer number is 3.89. When applied to the MFCs as cathodic catalysts, a higher maximum power density and voltage of 378.68 mW m-2 and 0.425 V were achieved with the MSAC-750 catalyst and is superior to that of the Pt/C catalyst (300.85 mW m-2 and 0.402 V). In this case, a promising method is hereby established for the preparation of an excellent electrochemical catalyst for microbial fuel cells using inexpensive and easily available macadamia shells.

Sulfidised nanoscale zerovalent iron-modified pitaya peel-derived carbon for enrofloxacin degradation and swine wastewater treatment: Combination of electro-Fenton and bio-electro-Fenton process

In this study, a new Fenton system combining electro-Fenton and bio-electro-Fenton (EF-BEF) processes was proposed for ENR degradation and swine wastewater treatment, and pitaya peel-derived carbon modified with sulfidised nanoscale zerovalent iron (SnZVI) was developed as a catalyst for the system. The as-prepared PPC-800 carbon displayed a hierarchical porous structure (693.5 m²/g), abundant oxygen-containing groups, and carbon defects, which endowed it with a good adsorption capacity, high H₂O₂ generation capacity (151.9 ± 10.5 mg/L) during the EF period, and good power production performance (194.3 ± 12.50 mW/m²) during the BEF period. When modified with SnZVI, despite the decrease in the adsorption capacity and power output (102.05 ± 4.05 mW/m²), the SnZVI@PPC-2 exhibited the best ENR removal performance with that of 98.9 ± 0.2% in the EF period and 86.2 ± 5.6% during the BEF period. An increase in the current intensity and air flow rate promoted ENR degradation. Finally, swine wastewater was treated using the SnZVI@PPC-2 EF-BEF system, and 97.9 ± 1.3% of the TOC was removed using the combined system.

Cedar Wood-Based Biochar: Properties, Characterization, and Applications as Anodes in Microbial Fuel Cell

In this study, the relationship between pyrolysis temperature of woody biomass and physicochemical properties of derived biochar was investigated for microbial fuel cell (MFC) application. Physical and chemical properties of biochar were characterized for different pyrolysis temperatures. Results showed that biochar obtained at 400 °C was not conductor, while biochars prepared at 600 °C, 700 °C, and 900 °C exhibited decreased electrical resistivity of (7 ± 6) × 10³ Ω.m, (1.8 ± 0.2) Ω.m, and (16 ± 3) × 10^-3 Ω.m, respectively. Rising pyrolysis temperature from 400 to 700 °C exhibited honeycomb-like macroporous structures of biochar with an increase in the specific surface area from 310 to 484 m².g^-1. However, the production of biochar at 900 °C reduced its specific surface area to 136 m².g^-1 and caused the loss of the ordered honeycomb structure. MFCs using anodes based on biochar prepared at 900 °C produced maximum power densities ((9.9 ± 0.6) mW.m^-2) higher than that obtained with biochar pyrolyzed at 700 °C ((5.8 ± 0.1) mW.m^-2) and with conventional carbon felt anodes ((1.9 ± 0.2) mW.m^-2). SEM images of biochar-based anodes indicated the clogging of macropores in honeycomb structure of biochar prepared at 700 °C by growth of electroactive biofilms, which might impede the supply of substrate and the removal of metabolites from the inside of the electrode. These findings highlight that electrical conductivity of biochar is the major parameter for ensuring efficient anodes in microbial fuel cell application. Schematic representation of cedar wood-based biochar and its application as anode in MFC.

Nano-Biochar as a Sustainable Catalyst for Anaerobic Digestion: A Synergetic Closed-Loop Approach

Nowadays, the valorization of organic wastes using various carbon-capturing technologies is a prime research area. The anaerobic digestion (AD) technology is gaining much consideration in this regard that simultaneously deals with waste valorization and bioenergy production sustainably. Biochar, a well-recognized carbonaceous pyrogenic material and possessing a broad range of inherent physical and chemical properties, has diverse applications in the fields of agriculture, health-care, sensing, catalysis, carbon capture, the environment and energy. The nano-biochar-amended anaerobic digestion approach has intensively been explored for the past few years. However, an inclusive study of multi-functional roles of biochar and the mechanism involved for enhancing the biogas production via the AD process still need to be evaluated. The present review inspects the significant role of biochar addition and the kinetics involved, further focusing on the limitations, perspectives, and challenges of the technology. Additionally, the techno-economic analysis and life-cycle assessment of biochar-aided AD process for the closed-loop integration of biochar and AD and possible improvement practices are discussed.

Plant microbial fuel cell: Opportunities, challenges, and prospects

Microbial fuel cells (MFCs) are considered as greener technologies for generation of bioenergy and simultaneously treatment of wastewater. However, the major drawback of these technologies was, rapid utilization of substrate by the microbes to generate power. This drawback is solved to a great extent by plant microbial fuel cell (PMFC) technology. Therefore, this review critically explored the challenges associated with PMFC technology and approaches to be employed for making it commercially feasible, started with brief introduction of MFCs, and PMFCs. This review also covered various factors like light intensity, carbon dioxide concentration in air, type of plant used, microbial flora in rhizosphere and also electrode material used which influence the efficiency of PMFC. Finally, this review comprehensively revealed the possibility of future intervention, such as application of biochar and preferable plants species which improve the performance of PMFC along with their opportunities challenges and prospects.

Trends in renewable energy production employing biomass-based biochar

Tremendous population growth and industrialization have increased energy consumption unprecedentedly. The depletion of fossil-based energy supplies necessitates the exploration of solar, geothermal, wind, hydrogen, biodiesel, etc. as a clean and renewable energy source. Most of these energy sources are intermittent, while bioelectricity, biodiesel, and biohydrogen can be produced using abundantly available organic wastes regularly. The production of various energy resources requires materials that are costly and affect the applicability at a large scale. Biomass-derived materials (biochar) are getting attention in the field of bioenergy due to their simple method of synthesis, high surface area, porosity, and availability of functional groups for easy modification. Biochar synthesis using various techniques is discussed and their use as an electrode (anodic/cathodic) in a microbial fuel cell (MFC), catalysts in transesterification, and anaerobic digestion for energy production are reviewed. Renewable energy production using biochar would be a sustainable approach to create an energy secure world.

Use of Biochar-Based Cathodes and Increase in the Electron Flow by Pseudomonas aeruginosa to Improve Waste Treatment in Microbial Fuel Cells

In this paper, we tested the combined use of a biochar-based material at the cathode and of Pseudomonas aeruginosa strain in a single chamber, air cathode microbial fuel cells (MFCs) fed with a mix of shredded vegetable and phosphate buffer solution (PBS) in a 30% solid/liquid ratio. As a control system, we set up and tested MFCs provided with a composite cathode made up of a nickel mesh current collector, activated carbon and a single porous poly tetra fluoro ethylene (PTFE) diffusion layer. At the end of the experiments, we compared the performance of the two systems, in the presence and absence of P. aeruginosa, in terms of electric outputs. We also explored the potential reutilization of cathodes. Unlike composite material, biochar showed a life span of up to 3 cycles of 15 days each, with a pH of the feedstock kept in a range of neutrality. In order to relate the electric performance to the amount of solid substrates used as source of carbon and energy, besides of cathode surface, we referred power density (PD) and current density (CD) to kg of biomass used. The maximum outputs obtained when using the sole microflora were, on average, respectively 0.19 Wm−2kg−1 and 2.67 Wm−2kg−1, with peaks of 0.32 Wm−2kg−1 and 4.87 Wm−2kg−1 of cathode surface and mass of treated biomass in MFCs with biochar and PTFE cathodes respectively. As to current outputs, the maximum values were 7.5 Am−2 kg−1 and 35.6 Am−2kg−1 in MFCs with biochar-based material and a composite cathode. If compared to the utilization of the sole acidogenic/acetogenic microflora in vegetable residues, we observed an increment of the power outputs of about 16.5 folds in both systems when we added P. aeruginosa to the shredded vegetables. Even though the MFCs with PTFE-cathode achieved the highest performance in terms of PD and CD, they underwent a fouling episode after about 10 days of operation, with a dramatic decrease in pH and both PD and CD. Our results confirm the potentialities of the utilization of biochar-based materials in waste treatment and bioenergy production.

Sustainable Syntheses and Sources of Nanomaterials for Microbial Fuel/Electrolysis Cell Applications: An Overview of Recent Progress

The use of microbial fuel cells (MFCs) is quickly spreading in the fields of bioenergy generation and wastewater treatment, as well as in the biosynthesis of valuable compounds for microbial electrolysis cells (MECs). MFCs and MECs have not been able to penetrate the market as economic feasibility is lost when their performances are boosted by nanomaterials. The nanoparticles used to realize or decorate the components (electrodes or the membrane) have expensive processing, purification, and raw resource costs. In recent decades, many studies have approached the problem of finding green synthesis routes and cheap sources for the most common nanoparticles employed in MFCs and MECs. These nanoparticles are essentially made of carbon, noble metals, and non-noble metals, together with a few other few doping elements. In this review, the most recent findings regarding the sustainable preparation of nanoparticles, in terms of syntheses and sources, are collected, commented, and proposed for applications in MFC and MEC devices. The use of naturally occurring, recycled, and alternative raw materials for nanoparticle synthesis is showcased in detail here. Several examples of how these naturally derived or sustainable nanoparticles have been employed in microbial devices are also examined. The results demonstrate that this approach is valuable and could represent a solid alternative to the expensive use of commercial nanoparticles.