Oxygen Reduction Reaction In Microbial Fuel Cells Research Articles

Fe, N-codoped carbon derived from different ligands for oxygen reduction reaction in air-cathode microbial fuel cells: Performance comparison and the associated mechanism

In order to clarify the effect of iron ligands on properties, catalysts with different structure through four kinds of ligands are prepared and the oxygen reduction reaction (ORR) activity and the maximum power density in microbial fuel cells (MFCs) are compared. The formed Fe single atoms, the metal-organic framework compound, the Prussia blue crystal and ethylenediamine coordination compound (Phen-Fe, PA-Fe, PB-Fe and EDA-Fe) exhibit the maximum power densities of 2041 ± 23 mW m−2, 1656 ± 32 mW m−2, 1062 ± 31 mW m−2, and 1865 ± 36 mW m−2, respectively. In addition, the electrochemical performance of four catalysts with different structures is significantly different, and the higher exchange current density and 4-electron pathway of Phen-Fe explained the kinetics of ORR. The structures and surface properties are explored through a series of characterizations. The different amounts of nitrogen functionalities, Fe ion, and high graphitization degree are thought to facilitate electron transfer, lower Rct and improve ORR activity. In sum, the iron ligands have a great influence on the structure and performance of catalysts, and the single-atom structure and ethylenediamine coordination structure are proved to be promising structures for ORR in MFCs.

The enhancement of microbial fuel cell performance by anodic bacterial community adaptation and cathodic mixed nickel–copper oxides on a graphene electrocatalyst

BackgroundAlthough microbial fuel cells (MFCs) represent a promising technology for capturing renewable energy from wastewater, their scaling-up is significantly limited by a slow-rate cathodic oxygen reduction reaction (ORR) and the development of a resilient anodic microbial community. In this study, mixed transition metal oxides of nickel and copper (Ni and Cu), supported on a graphene (G) (NiO–CuO/G) electrocatalyst, were synthesized and tested as a cost-effective cathode for ORR in MFCs. Electrochemical measurements of electrocatalyst were conducted using a rotating disk electrode (RDE) and linear sweep voltammetry (LSV) in a neutral electrolyte, and compared with a benchmark Pt/C catalyst. Furthermore, the long-term performance of the as-synthesized electrocatalyst was evaluated in a single-chamber MFC by measuring organic matter removal and polarization behavior. The successful enrichment of electroactive biofilm was also monitored using transmission electron microscopy and the Vitek2 compact system technique. ResultsWhen compared with the benchmark platinum cathode, the NiO–CuO/G electrocatalyst exhibited high selectivity toward ORR. The rotating disk electrode (RDE) experiments reveal that ORR proceeds via a 4-electron ORR mechanism. Furthermore, the NiO–CuO/G electrocatalyst also exhibited a high power density of 21.25 mW m−2 in an air-cathode MFC, which was slightly lower than that of Pt/C-based MFC (i.e., 50.4 mW m−2). Biochemical characterization of the most abundant bacteria on anodic biofilms identified four genera (i.e., Escherichia coli, Shewanella putrefaciens, Bacillus cereus, and Bacillus Thuringiensis/mycoides) that belonged to Gammaproteobacteria, and Firmicutesphyla. ConclusionsThis study demonstrates that the NiO–CuO/G cathode had an enhanced electrocatalytic activity toward ORR in a pH-neutral solution. This novel mixed transition metal oxide electrocatalyst could replace expensive Pt-based catalysts for MFC applications.

Perovskite-Based Nanocomposite Electrocatalysts: An Alternative to Platinum ORR Catalyst in Microbial Fuel Cell Cathodes

Microbial fuel cells (MFCs) are biochemical systems having the benefit of producing green energy through the microbial degradation of organic contaminants in wastewater. The efficiency of MFCs largely depends on the cathode oxygen reduction reaction (ORR). A preferable ORR catalyst must have good oxygen reduction kinetics, high conductivity and durability, together with cost-effectiveness. Platinum-based electrodes are considered a state-of-the-art ORR catalyst. However, the scarcity and higher cost of Pt are the main challenges for the commercialization of MFCs; therefore, in search of alternative, cost-effective catalysts, those such as doped carbons and transition-metal-based electrocatalysts have been researched for more than a decade. Recently, perovskite-oxide-based nanocomposites have emerged as a potential ORR catalyst due to their versatile elemental composition, molecular mechanism and the scope of nanoengineering for further developments. In this article, we discuss various studies conducted and opportunities associated with perovskite-based catalysts for ORR in MFCs. Special focus is given to a basic understanding of the ORR reaction mechanism through oxygen vacancy, modification of its microstructure by introducing alkaline earth metals, electron transfer pathways and the synergistic effect of perovskite and carbon. At the end, we also propose various challenges and prospects to further improve the ORR activity of perovskite-based catalysts.

Crafting controllable Fe-based hierarchically organic-frameworks from bacterial cellulose nanofibers for efficient electrocatalysts in microbial fuel cells

One highly hopeful strategy to supply oxygen reduction reaction (ORR) catalysts for microbial fuel cells (MFCs) is the use of supporting substrates to achieve orderly stacking of metal-organic frameworks (MOFs). In this work, a mixed hierarchically porous carbon nanofiber ([email protected]) is proposed by in-situ growth of Fe-based MOFs particles on the surface of bacterial cellulose (BC). Its superior electrocatalytic performance originates from the existence of abundant multi-stage pores in the BC substrate and MOFs after pyrolysis, with a specific surface area up to 636.5 m2/g. Apart from this, poison tests confirm that Fe-Nx sites and Fe3C species achieve synergistic catalysis. As such, [email protected] exhibits a superior ORR half-wave potential (−0.429 V vs. Hg/HgCl2), which exceeds that of commercial Pt/C. Impressively, the MFC equipped with [email protected] catalyst achieves a coulombic efficiency of 23.6%, far exceeding 20 wt% Pt/C (12.6%), showing fascinating potential in pollutants degradation and power recovery. Furthermore, the abundant hydroxyl groups on BC tightly anchor the MOFs to the fibers, thus avoiding agglomeration and migration, and ensuring the continuous and efficient occurrence of ORR in MFCs. This work can provide a new perspective for synthesis of low-cost, eco-friendliness and efficient catalysts suitable for MFCs.

N, S co-doped carbon quantum dots anchoring on copper-vacancy-rich Cu nanowires/Cu foam as the cathode in microbial fuel cells: Role of C-S-Cu active site

Oxygen reduction reaction (ORR) electrocatalysts have been considered as one of the key components in microbial fuel cells (MFCs). Heteroatom-doped carbon quantum dots (CQDs) derived from biomass have attracted wide attention due to their rich functional groups, excellent properties, and environmental friendliness. Herein, orange-peels-derived N, S co-doped carbon quantum dots (N, S-CQDs) are in-situ anchored on copper-vacancy-rich Cu nanowires/Cu foam (V-Cu NWs/CF), obtaining the N, S-CQDs/Cu2O-Cu NWs, to catalyze ORR in MFCs. The interaction between N, S-CQDs and V-Cu NWs/CF from the N, S-CQDs/Cu2O-Cu NWs is bridged by the C-S-Cu bond, which is demonstrated to be the active site towards ORR and plays an important role in promoting electron transfer by in-situ Raman and X-ray photoelectron spectroscopy characterizations. In MFCs, the maximum power density (924.5 ± 32.5 mW·m−2) of N, S-CQDs/Cu2O-Cu NWs is 1.34 times that of Pt/C (686.5 ± 28.0 mW·m−2), and its long-term stability also outperforms the Pt/C. This study provides inspiration for synthesis of efficient ORR electrocatalysts with metal-ligand active sites creating by heteroatom-doped CQDs and cationic-metal-vacancy-rich materials.

Transition metal (Fe, Co, Ni) and sulfur codoped nitrogen-enriched hydrothermal carbon as high-performance cathode catalyst for microbial fuel cell

Microbial fuel cell (MFC), a new technology, uses microorganisms to decompose and oxidize the organic matter for bioelectricity generation. However, the sluggish oxygen reduction reaction of cathode catalyst is an important factor that affects electricity generation. Herein, nitrogen-enriched hydrothermal carbon doped with transition metal and sulfur heteroatoms was prepared. Carbon doped with iron, cobalt and nickel metal particles and nitrogen and sulfur heteroatoms (Fe-NSC, Co-NSC, Ni-NSC) exhibited maximum power densities of 2068 ± 32 mW m−2, 1736 ± 49 mW m−2 and 1441 ± 45 mW m−2, respectively. By analyzing the content and bonding configuration of nitrogen, sulfur, iron, cobalt and nickel, it is further verified that pyridinic nitrogen and graphitic nitrogen can reduce the charge transfer resistance, and iron–nitrogen (Fe–N) bonding and cobalt–nitrogen (Co–N) bonding are considered to be active sites which are beneficial to enhance oxygen reduction activity, while nickel–nitrogen (Ni–N) bonding is insensitive to oxygen reduction activity. Consequently, Fe-NSC is an effective catalyst for oxygen reduction reaction in MFC.

Improved performance of microbial fuel cell by using conductive ink printed cathode containing Co3O4 or Fe3O4

Microbial fuel cell (MFC) technology has been widely experimented nowadays, as it is a promising clean energy technology, which can harvest bioelectricity while simultaneously treating wastewater. Platinum (Pt), a precious transition metal, has long been regarded as a superior catalyst material for oxygen reduction reaction (ORR) at the cathode of the MFCs, however the high cost associated with it clutch it back for field scale applications. In this study, Co3O4 or Fe3O4 was blended with synthetically prepared conductive ink to act as microporous layer to explore its efficacy as an ORR catalyst. Applicability of these catalysts on cathode was investigated in dual chambered aqueous cathode MFCs and the performance was compared with MFC without any cathode catalyst, MFC with only conductive ink and another MFC with Pt as benchmark ORR catalyst. X-Ray diffraction, Fourier transform infrared spectra, Raman and field emission scanning electron microscope analysis were done to characterize the prepared catalysts. Cathode containing Co3O4 with conductive ink demonstrated higher reduction current (- 30 mA) than cathode having Pt and conductive ink with Fe3O4 (- 9 mA each) during cyclic voltammetry analysis. MFCs having cathodes printed with conductive ink containing Co3O4 and Fe3O4 exhibited a maximum volumetric power density of 6.62 W m−3 and 5.06 W m−3, respectively, which were much higher than the one without any catalyst (2.95 W m−3). Similarly, coulombic efficiency (CE) of 22.3%, 17.1% and 11.2% was observed in MFCs having cathode with conductive ink containing Co3O4 or Fe3O4 and without any catalysts, respectively. Moreover, more than 90% chemical oxygen demand removal efficiency was observed for MFCs having cathode with conductive ink containing Co3O4 or Fe3O4. Importantly, the performance obtained from MFC with conductive ink blended Co3O4 was found superior compared to MFC having Pt as cathode catalyst, where later produced power density of 6.13 W m−3 and CE of 21.1%. Hence, it can be concluded that Co3O4 can be used as an alternative to expensive platinum for efficient ORR in MFCs to make this technology effective for field scale application.

Bimetallic metal-organic frameworks derived cobalt nanoparticles embedded in nitrogen-doped carbon nanotube nanopolyhedra as advanced electrocatalyst for high-performance of activated carbon air-cathode microbial fuel cell

A new type of nitrogen-doped carbon nanotube embedded cobalt nanoparticles nanopolyhedra (Co-NCNTNP) electrocatalyst synthesized via pyrolysis bimetallic metal-organic frameworks was investigated to modify the activated carbon air-cathode microbial fuel cell (MFC). X-ray diffraction and transmission electron microscope characterization confirmed the combination of nitrogen-doped carbon nanotube and transition metal element in Co-NCNTNP. Rotating disk electrode measurement revealed the oxygen reduction reaction (ORR) of as-prepared Co-NCNTNP was mainly proceeded via a four-electron pathway like Pt/C. When fabricated into activated carbon cathode, the optimized MFC reached the maximum power density of 2252 ± 46 mW m−2, which was 154% higher than that of control. Moreover, the resistance including total resistance and charge transfer resistance of modified cathode significantly decreased comparing to the control, which was beneficial to better MFC performance. Therefore, all attracting properties suggested that noble-metal-free and high-efficiency Co-NCNTNP could be considered as a Pt-alternative electrocatalyst for ORR in MFC.

Novel multi walled carbon nanotube based nitrogen impregnated Co and Fe cathode catalysts for improved microbial fuel cell performance

For application in a microbial fuel cell (MFC), transition metal and nitrogen co-doped nanocarbon catalysts were synthesised by pyrolysis of multi-walled carbon nanotubes (MWCNTs) in the presence of iron- or cobalt chloride and nitrogen source. For the physicochemical characterisation of the catalysts, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) was used. The results obtained by rotating disk electrode (RDE) method showed an extraordinary electrocatalytic activity of these catalysts towards oxygen reduction reaction (ORR) in neutral media, which was also confirmed by the MFC results. The Co-N-CNT and Fe-N-CNT cathode catalysts exhibited maximum power density of 5.1 W m−3 and 6 W m−3, respectively. Higher ORR activity and improved electric output in the MFC could be attributed to the formation of the active nitrogen-metal centers. All findings suggest that these materials can be used as potential cathode catalysts for ORR in MFC to replace expensive noble-metal based materials.

Cobalt and nitrogen-doped carbon catalysts for enhanced oxygen reduction and power production in microbial fuel cells

Cathodic oxygen reduction reaction (ORR) is essential for the performance of microbial fuel cell (MFC). Cobalt and nitrogen-doped carbon (CoNC) was synthesized to catalyze ORR in MFCs. CoNC prepared at 900°C (CoNC-900) exhibited a remarkable catalytic activity (4.3% smaller compared with state-of-the-art Pt/C for reduction current density), predominant four-electron reaction with electron transfer number as high as 3.96, and excellent stability (5.5% lesser after 10 000 cycles for reduction current density). The maximum power density of the CoNC-900 MFC was 13.3% higher than that of Pt/C MFC. Long term operation tests showed that CoNC-900 MFC was very stable. The unprecedented performance of CoNC for ORR was attributable to the highly microporous structure and the cobalt coordinated by pyridinic nitrogen. This work demonstrates that CoNC is a very promising catalyst toward ORR in MFCs.

Fouling resistant nitrogen doped carbon powder with amino-tri-methylene-phosphate cathode for microbial fuel cell

Long term stable performance of a microbial fuel cell (MFC) is difficult to achieve because of scale formation on cathode. Nitrogen doped carbon powder (NDCP) was used as cathode along with amino-tri-methylene-phosphate (ATMP) as an anti-scaling agent in a MFC. Maximum power density of 66 mW/m2 obtained in the MFC using NDCP as cathode, was 2.2 times higher than that obtained with simple carbon powder. High electroactive surface area and meso-porous structure of the NDCP improved electrochemical performance of the MFC having NDCP cathode. After 40 days of operation, the maximum power density decreased by only 12.5% in the MFC using NDCP and having ATMP in its cathode as compared to a 55.6% decrease in the MFC using only carbon powder in cathode due to fouling. Ultrathin shell structure of NDCP catalyst molecules, as evident from transmission electron microscopy (TEM) images, ensured high catalyst performance providing good electron transfer for enhancing oxygen reduction reaction (ORR). Less deposition of calcite molecules on cathode surface, illustrated via X-ray diffraction (XRD) after 40 days of operation, clearly reveals high anti-fouling property of ATMP as a cathode material. ATMP being a commercial anti-scaling agent has inherent chelation properties to stop chemical fouling and thus helped in demonstrating stable long term performance of cathode in the MFCs. NDCP along with ATMP could be used for fabrication of a cost effective fouling resistant cathode for long term use by increasing ORR in MFCs to achieve stable power generation by minimizing scale formation on cathode and effective wastewater treatment simultaneously.Graphical abstract

Carbon-supported binary transition metal chalcogenide used as cathode catalyst for oxygen reduction in microbial fuel cell

This study investigates the application of carbon-supported inverse spinel binary transition metal chalcogenide as the catalyst for oxygen reduction reaction (ORR) in air-cathode microbial fuel cell (MFC). The obtained maximum power density (MPD) is 2000 ± 59 mW m−2, 2.25 times as high as the bare activated carbon (AC) (888 ± 56 mW m−2). Total resistance of the modified MFC was decreased evidently, and the kinetics activity toward ORR was promoted significantly and rotating disk electrode results show that catalyst electrocatalytic activity for ORR through four-electron reaction pathway. X-ray photoelectron spectroscopy and Brunauer–Emmett–Teller results indicate that NiCo2S4/AC contains more octahedral catalytic active sites of Co3+ and micropores than NiCo2O4/AC. S atom is successfully incorporated into AC and shows more benefit than oxygen atom. All findings suggest that the synthetic composite can be a potential cathode catalyst for ORR in MFC.

Graphene-Based Electrocatalysts to Boost Electrocatalytic Reduction of Oxygen in Bioelectrochemical Systems

Microbial fuel cells (MFCs) can be considered as an efficient and flexible platform for integrated waste treatment and energy recovery [1]. The extensive research work devoted to this technology over the past decade demonstrates the promising outlook of MFCs, but practical application is still limited by the high costs associated to the materials used for device assembly, such as cathode materials which accounts for over 50% of the overall MFC capital cost. The sluggish kinetics of oxygen reduction reaction (ORR) has led to the use of expensive catalysts, such as platinum, which is not suitable to be applied to sustainable technologies. Hence, a great variety of materials have been developed for MFC cathodes, including nitrogen-doped activated carbons and non platinum group metal catalysts. Such materials allow achieving ORR rate comparable to Pt, the morphology and structure of the catalysts playing an important role on the efficiency and durability of ORR active sites [2,3]. The development of new carbon nanostructures with highly tunable morphology and structure has led to the use of graphene for several applications, including as component for MFC cathodes [4,5]. However, challenges, such as complexity in synthesis and costs, still limit the applicability of graphene as cathode component of MFCs. Therefore, a facile and efficient approach to develop graphene based catalysts can be considered a promising direction to achieve sustainable wastewater treatment and bioenergy production by BESs. In this work, we report a facile method for large-scale preparation of ORR catalysts based on graphene oxide (GO) obtained by electrochemical oxidation of graphite in aqueous solutions of inorganic salts. We developed different strategies to include nitrogen functionalities in GO structure, including post treatments based on annealing with ammonia gas and one-step nitrogen-doping of GO. By combining the use of atomic force microscopy with electrochemical and spectroscopic techniques, we correlated the different morphology and surface chemistry of GO with catalytic activity towards ORR. Differences in catalytic activity obtained by supporting iron on GO surface were also elucidated, investigating the nature of ORR active sites. The applicability of GO-based materials as ORR cathodes of MFCs was evaluated by assembling single chamber air-cathodes MFCs operating with sodium acetate in phosphate buffer solution. Coulombic efficiency, polarization and power density curves, and voltage generation cycles over time were acquired. The body of results demonstrated the potential ability of GO electrocatalysts to substitute platinum for ORR in MFCs. Acknowledgements. The present work was carried out with the support of the “European Union's Horizon 2020 research and innovation programme” (under H2020-FTIPilot-2015-1, Grant Agreement n. 720367-GREENERNET), the University of Rome Tor Vergata (under the Research Call “Consolidate the Foundations”, project name: BEST WATER), and CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil. References. [1] A. Rinaldi, B. Mecheri, V. Garavaglia, S. Licoccia, P. Di Nardo, E.Traversa. Energ. Environ. Sci., 1 (2008) 417-429. [2] C. Santoro, A. Serov, L. Stariha, M. Kodali, J. Gordon, S. Babanova, O. Bretschger, K. Artyushkova, P. Atanassov, Energ. Environ. Sci. 9 (2016) 2346-2353. [3] A. Iannaci, B. Mecheri, A. D'Epifanio, M. J. Lázaro Elorri, S. Licoccia. Int J Hydrogen Energ. 41 (2016) 19637-19644. [4] H. Yuan, Z. He. Nanoscale 7 (2015) 7022-7029. [5] K. Parvez, S. Yang, Y. Hernandez, A. Winter, A. Turchanin, X. Feng, K. Müllen. ACS Nano. 6 (2012) 9541-9550.

High-Performance Carbon Aerogel Air Cathodes for Microbial Fuel Cells.

Microbial fuel cells (MFCs) can generate electricity from the oxidation of organic substrates using anodic exoelectrogenic bacteria and have great potential for harvesting electric energy from wastewater. Improving oxygen reduction reaction (ORR) performance at a neutral pH is needed for efficient energy production. Here we show a nitrogen doped (≈4 wt%) ionothermal carbon aerogel (NDC) with a high surface area, large pore volume, and hierarchical porosity, with good electrocatalytic properties for ORR in MFCs. The MFCs using NDC air cathodes achieved a high maximum power density of 2300 mW m-2 , which was 1.7 times higher than the most commonly used Pt/C air cathodes and also higher than most state-of-the-art ORR catalyst air cathodes. Rotating disk electrode measurements verified the superior electrocatalytic activity of NDC with an efficient four-electron transfer pathway (n=3.9). These findings highlight NDC as a better-performing and cost-efficient catalyst compared with Pt/C, making it highly viable for MFC applications.

Iron-Based Electrocatalysts Supported on Nanostructured Carbon to Enhance Oxygen Reduction in Microbial Fuel Cells

Sustainable waste management and energy supply can find a concrete answer in the technology of microbial fuel cells (MFCs). One of the major barriers to the widespread diffusion of this technology is the high cost of materials, among which the platinum-based cathode accounts for about 50 % of the total cell cost. Although platinum is a highly effective oxygen reducing catalyst, its activity is decreased by a variety of poisoning substances present in wastewater [1]. Latest development on nanostructured carbon for energy storage and conversion has brought to light carbon nanofibers (CNF), carbon nanotubes (CNT) and activated carbon (AC) as good candidates to replace costly Pt. These materials have high surface area and conductivity, and nitrogen doping has been demonstrated to be an effective approach to modulate their electronic properties [2]. Moreover, recent advances on non platinum group metal (NPGM) catalysts demonstrated the possibility to replace Pt with earth-abundant elements, such as Mn, Fe, Co, and Cu [3]. Among all, iron based catalysts supported on carbon have being used at cathodes of MFCs, active sites arising from Fe/N/C coordination. Aim of this study is to evaluate and compare catalytic activity towards oxygen reduction reaction (ORR) of catalysts based on iron phthalocyanine (FePc) supported over different carbon substrates with physical and morphological differences. Commercial carbon black, carbon nanotubes, and black pearls were used as catalyst support. Furthermore, the use of different advanced nanostructured carbon materials, such as carbon nanofibers and carbon xerogels was also investigated, owing to their porous structure and surface properties which can be tailored according to catalytic requirements [4, 5]. To facilitate catalyst dispersion and obtain effective ORR active sites, the supports were modified by a two-step treatment with nitric acid and ammonia gas. The treatment allowed introducing oxygen and nitrogen functionalities on the carbon surface while maintaining an extensively developed porous structure, as demonstrated by elemental analysis, BET, and X-ray photoelectron spectroscopy (XPS). Electrocatalysts derived from iron phthalocyanine (FePc) and the different carbon supports were prepared and their electrochemical activity towards ORR was assessed by cyclic voltammetry and rotating disk voltammetry experiments. The electrochemical results demonstrated that the prepared electrocatalysts are all active towards ORR at neutral pH; the higher the density of pyridinic nitrogen on the sample surface, the greater is the performance, as indicated by XPS. The applicability of FePc-based materials as ORR cathodes of MFCs was evaluated by assemblying FePc cathodes in single chamber air-catodes MFCs operating with sodium acetate in phosphate buffer solution, which coulombic efficiency, polarization and power density curves, and voltage generation cycles over time were acquired. The body of results demonstrated the potential ability of FePc-electrocatalysts to substitute platinum for ORR in MFCs.

Iron/Polyindole-based Electrocatalysts to Enhance Oxygen Reduction in Microbial Fuel Cells

Electrocatalysts derived from polyindole (PID) and iron phthalocyanine (FePc) on carbon nanotubes (CNTs)/carbon Vulcan (C) have been synthesized and used as cathodes in Microbial Fuel Cells (MFCs). The morphology characterization performed by scanning electron microscopy (SEM) indicated a good dispersion of polyindole and FePc on carbon surface for all samples.The electrochemical activity towards oxygen reduction reaction (ORR) has been assessed by cyclic voltammetry (CV), showing enhanced performance of CNTs-based composites in comparison with C-based composites. Rotating disk voltammetry experiments demonstrated that ORR at FePc/CNTs and FePc/PID/CNTs catalysts led to more positive half-wave potential values and higher kinetic current density values compared to that of reference Pt/C; the best ORR performance was displayed by FePc/PID/CNTs sample. In MFCs operating with sodium acetate in phosphate buffer solution, FePc/PID/CNTs cathode allows achieving a maximum power density of 799±41mWm−2 and a current density of 3480±83mAm−2 that are higher than those achieved with commercial Pt/C cathode (646±25mWm−2 and 3011±84mAm−2, respectively). The long-term MFC operation conducted for 700h indicates a stable performance of FePc/PID/CNTs cathode, demonstrating its potential ability to substitute platinum catalyst for ORR in MFCs.

Nickel oxide and carbon nanotube composite (NiO/CNT) as a novel cathode non-precious metal catalyst in microbial fuel cells

Comparing with the precious metal catalysts, non-precious metal catalysts were preferred to use in microbial fuel cells (MFCs) due to the low cost and high oxygen reduction reaction (ORR) efficiency. In this study, the transmission electron microscope and X-ray diffraction as well as Raman investigation revealed that the prepared nanoscale NiO was attached on the surface of CNT. Cyclic voltammogram and rotating ring-disk electrode tests showed that the NiO/CNT composite catalyst had an apparent oxygen reduction peak and 3.5 electron transfer pathway was acquired under oxygen atmosphere. The catalyst performance was highly dependent on the percentage of NiO in the CNT nanocomposites. When 77% NiO/CNT nano-sized composite was applied as cathode catalyst in membrane free single-chamber air cathode MFC, a maximum power density of 670 mW/m(2) and 0.772 V of OCV was obtained. Moreover, the MFC with pure NiO (control) could not achieve more than 0.1 V. All findings suggested that NiO/CNT could be a potential cathode catalyst for ORR in MFCs.

Polyelectrolyte-single wall carbon nanotube composite as an effective cathode catalyst for air-cathode microbial fuel cells.

Polyelectrolyte-single wall carbon nanotube (SCNT) composites are prepared by a solution-based method and used as metal-free cathode catalysts for oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). In this study, two types of polyelectrolytes, polydiallyldimethylammonium chloride (PDDA) and poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea] (PEPU) are applied to decorate the SCNTs and the resulting catalysts exhibit remarkable catalytic ability toward ORR in MFC applications. The enhanced catalytic ability could be attributed to the positively charged quaternary ammonium sites of polyelectrolytes, which increase the oxygen affinity of SCNTs and reduce activation energy in the oxygen reduction process. It is also found that PEPU-SCNT composite-based MFCs show efficient performance with maximum power density of 270.1 mW m(-2), comparable to MFCs with the benchmark Pt/C catalyst (375.3 mW m(-2)), while PDDA-SCNT composite-based MFCs produce 188.9 mW m(-2). These results indicate that PEPU-SCNT and PDDA-SCNT catalysts are promising candidates as metal-free cathode catalysts for ORR in MFCs and could facilitate MFC scaling up and commercialization.

A novel stainless steel mesh/cobalt oxide hybrid electrode for efficient catalysis of oxygen reduction in a microbial fuel cell

To explore efficient and cost-effective cathode material for microbial fuel cells (MFCs), the present study fabricates a new type of binder-free gas diffusion electrode made of cobalt oxide (Co3O4) micro-particles directly grown on stainless steel mesh (SSM) by using an ammonia-evaporation-induced method. In various electrochemical analyses and evaluations in batch-fed dual-chamber MFCs, the SSM/Co3O4 hybrid electrode demonstrates improved performances in terms of electrocatalytic activity, selectivity, durability and economics toward oxygen reduction reaction (ORR) in pH-neutral solution, in comparison with conventional carbon supported platinum catalyst. This study suggests a new strategy to fabricate a more effective electrode for ORR in MFCs, making it more technically and economically viable to produce electrical energy from organic materials for practical applications.