Iron chelates as low-cost and effective electrocatalyst for oxygen reduction reaction in microbial fuel cells

Iron-chelated electrocatalysts for the oxygen reduction reaction (ORR) in a microbial fuel cell (MFC) were prepared from sodium ferric ethylenediamine-N,N′-bis(2-hydroxyphenylacetic acid) (FeE), sodium ferric diethylene triamine pentaacetic acid (FeD) supported on carbon Vulcan XC-72R carbon black and multi-walled carbon nanotubes (CNTs). Catalyst morphology was investigated by TEM; and the total surfaces areas as well as the pore volumes of catalysts were examined by nitrogen physisorption characterization. The catalytic activity of the iron based catalysts towards ORR was studied by cyclic voltammetry, showing the higher electrochemical activity of FeE in comparison with FeD and the superior performance of catalysts supported on CNT rather than on Vulcan XC-72R carbon black. FeE/CNT was used as cathodic catalyst in a microbial fuel cell (MFC) using domestic wastewater as fuel. The maximum current density and power density recorded are 110 (mA m⁻²) and 127 ± 0.9 (mW m⁻²), respectively. These values are comparable with those obtained using platinum on carbon Vulcan (0.13 mA m⁻² and 226 ± 0.2 mW m⁻²), demonstrating that these catalysts can be used as substitutes for commercial Pt/C.     

Effect of the Pt precursor on the morphology and catalytic performance of Pt-impregnated on Pd/C for the oxygen reduction reaction in polymer electrolyte fuel cells

We describe how the morphology and electrocatalytic activity of Pt-Pd with low levels of Pt are dependent on the type of Pt precursor that is used for the impregnation on to Pd/C. When a Pt precursor with a negative charge (H₂PtCl₆) is used in the preparation medium (Pt-Pd/C-H), its electrostatic interaction with the carbon surface results in some Pt nanoparticles being deposited on the carbon separately from the Pd surface. Due to the absence of such an electrostatic interaction with the Pt(NH₃)₄Cl₂ precursor, more selective deposition of Pt can be achieved on the Pd surface (Pt-Pd/C-N). Depending on the morphology, different electrocatalytic performance in oxygen reduction reaction would be observed. Compared to Pt-Pd/C-H, Pt-Pd/C-N shows 180% (half-cell at 0.9 V) and 160% (unit-cell at 0.8 V) enhanced performance, which is comparable to that on Pt/C. It is believed that the interaction between the Pt and the Pd substrate is more extensive in Pt-Pd/C-N than in Pt-Pd/C-H, and this is responsible for the large difference in the catalytic performances between these two catalysts.     

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

Performance of microbial fuel cells (MFCs) with carbon supported nickel phthalocyanine (NiPc)MnO_x composite (MFC-1) and nickel phthalocyanine (MFC-2) incorporated cathode was compared with a control MFC with non-catalysed carbon felt as cathode (MFC-3) and MFC-4 having Pt on cathode (as benchmark reference control). MFC-1 exhibited power density of 8.02 Wm^?3, which was four folds higher than control MFC-3 (2.08 Wm^?3) and 1.14 times higher than MFC-2 (6.97 Wm^?3). Coulombic efficiency of 30.3% obtained in MFC-1 was almost double of that obtained for control MFC-3 and it was 5.4% lesser as compared to MFC-4 (35.7%). Linear sweep voltammetry study of cathodes revealed that NiPc-MnO_x could enhance the electrocatalytic activity of oxygen reduction reaction (ORR) in comparison to control cathode. However, the power recovery from MFC-1 was noted little lower than what obtained from MFC-4 (10.58 Wm^?3), however the cost normalized power was two times higher than Pt catalyst on cathode. Thus, NiPc-MnO_x based catalyst developed in this study has potential to enhance ORR in cathodes of MFCs in order to harvest more power.     

Comparative study on the performance of pyrolyzed and plasma-treated iron(II) phthalocyanine-based catalysts for oxygen reduction in pH neutral electrolyte solutions

The performance of pyrolyzed and plasma-treated non-precious catalysts for the oxygen reduction is discussed in the light of their application in microbial fuel cells. An Ar-radio frequency (RF) plasma treatment is applied to enhance the electrochemical activity of iron(II) phthalocyanine (FePc)-based catalysts. The electrochemical properties of the catalysts are analyzed by galvanodynamic linear sweep voltammetry and chronoamperometric experiments. Surface elemental analysis of the catalysts is examined by means of X-ray photoelectron spectroscopy (XPS). The influence of plasma power and treatment time on the elemental surface concentration and performance of the catalysts is investigated. The electrochemical activity, expressed in terms of the current density at 0 V vs. Ag/AgCl, is up to 40% higher for the plasma-treated samples than for pyrolyzed ones. It is found that optimal treatment time was 30 min and optimal plasma power was 150 W for the best electroactivity of FePc-based catalysts. From the results of XPS data, it is revealed that Ar-plasma treatment of the catalysts leads to an increase in the oxygen and nitrogen concentration on the catalysts surface. A correlation is found between the activity and surface concentration of oxygen and nitrogen on the catalysts’ surface.     

The fabrication of silane modified graphene oxide supported Ni–Co bimetallic electrocatalysts: A catalytic system for superior oxygen reduction in microbial fuel cells

Microbial fuel cells (MFCs) exploit the ability of microorganisms to generate clean energy from organic pollutants in wastewater. However, the poor cathode performance and the use of the expensive rare metal platinum as a catalyst limit their application and scalability. In this study, we have synthesised a Ni–Co/GO nanocomposite and applied it as a potential cathode catalyst to single-chamber MFCs. To improve the performance of a Ni–Co-based hybrid nanocomposite, the support of graphene oxide (GO) is covalently modified with γ-amino propyl tri-ethoxy silane (APTES) through a silane modification reaction. The physical and chemical properties of the synthesised materials are characterised with Fourier transform infrared (FTIR), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) techniques. A microscopic study has shown that metal nanoparticles are distributed uniformly on the MGO matrix. The electrocatalytic activity of the synthesised hybrid nanocatalysts is analysed for oxygen reduction reaction (ORR). A cyclic voltammetry experiment has shown that the Ni–Co/MGO catalyst exhibits a higher reduction peak current value and a higher positive onset potential than the Ni–Co/GO catalyst and Pt/C catalyst, indicating an enhanced ORR activity of the Ni–Co/MGO catalyst. Ni–Co/MGO also exhibits the highest initial current of 0.116 mA in the chronoamperometry test, which decreases to 0.049 mA after 16000 s. The electrochemical results demonstrate that the synthesised Ni–Co/MGO catalyst has a higher electrocatalytic activity and higher stability than the state-of-the-art Pt/C catalyst. More importantly, a MFC with Ni–Co/MGO as a cathode catalyst shows the maximum power density of 1003.18 mWm⁻², which is much higher than in the case of the Ni–Co/GO catalyst (889.6 mWm⁻²) and approximately 2.1 times higher than that of the state-of-the-art Pt/C (483.48 mWm⁻²). Consequently, the Ni–Co/MGO nanocomposite also shows the highest open circuit voltage of 0.857 V among the other studied catalysts. Moreover, the Ni–Co/MGO catalyst has a lower biofouling level than a commercial 10 wt% Pt/C catalyst, which shows that the synthesised cathode catalyst is superior in terms of stability, overall performance and usage. These results suggest that the newly developed Ni–Co/MGO catalyst can be applied as a potential substitute for the Pt/C cathode catalyst for the practical application of MFCs.     

Kinetics and electrocatalytic activity of IrCo/C catalysts for oxygen reduction reaction in PEMFC

The purpose of this study is to develop a novel binary Iridium-Cobalt/C catalyst as a suitable substitute for platinum/C applied in proton exchange membrane fuel cells (PEMFCs). The carbon-supported IrCo catalysts were successfully synthesized using IrCl₃ and C₄H₆CoO₄ as the Ir and Co precursors respectively, in ethylene glycol (EG) refluxing at 120 °C. The nanostructured catalysts were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscope (TEM). Homogeneous catalyst particles supported on carbon showed a size of proximately 2 nm. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were conducted for the characterization of the catalyst performances. With a cathodic loading of 0.4 mg_Ir cm⁻², 20%Ir-30%Co/C achieved a maximum power density of 501.6 mW cm⁻² at 0.418 V, with a 50 cm² H₂/O₂ single cell. Although such a performance is about 26% lower than commercial Pt/C catalyst, it is still helpful in terms of Pt replacement and cost reduction.     

Non-Pt catalyst as oxygen reduction reaction in microbial fuel cells: A review

Oxygen Reduction Reactions (ORR) are one of the main factors of major potential loss in low temperature fuel cells, such as microbial fuel cells and proton exchange membrane fuel cells. Various studies in the past decade have focused on determining a method to reduce the over potential of ORR and to replace the conventional costly Pt catalyst in both types of fuel cells. This review outlines important classes of abiotic catalysts and biocatalysts as electrochemical oxygen reduction reaction catalysts in microbial fuel cells. It was shown that manganese oxide and metal macrocycle compounds are good candidates for Pt catalyst replacements due to their high catalytic activity. Moreover, nitrogen doped nanocarbon material and electroconductive polymers are proven to have electrocatalytic activity, but further optimization is required if they are to replace Pt catalysts. A more interesting alternative is the use of bacteria as a biocatalyst in biocathodes, where the ORR is facilitated by bacterial metabolism within the biofilm formed on the cathode. More fundamental work is needed to understand the factors affecting the performance of the biocathode in order to improve the performance of the microbial fuel cells.     

Porous Co3O4 decorated nitrogen-doped graphene electrocatalysts for efficient bioelectricity generation in MFCs

High-performance, low-cost, and robust oxygen reduction reaction (ORR) catalysts have played a very crucial role in the development of microbial fuel cells (MFCs). Herein, A novel in-situ Co₃O₄ nanoparticles (NPs) modified nitrogen-doped graphene with three-dimensional porous structure (3D GN-Co₃O₄) has been successfully synthesized and employed as an efficient ORR catalyst in MFCs. Benefiting from 3D porous architecture feature, highly intrinsic conductivity and synergistic effect between nitrogen-doped graphene and Co₃O₄ NPs, the 3D GN-Co₃O₄ as a cathode catalyst in alkaline condition realizes significantly enhanced electrochemical performance and outstanding cycling stability. Furthermore, the self-assembly of MFCs based on the 3D GN-Co₃O₄ cathode offers a high power density of 578 ± 10 mW m^?2, which is even comparable to the commercial Pt/C.     

Alkaline metal doped strontium cobalt ferrite perovskites as cathodes for intermediate-temperature solid oxide fuel cells

Perovskite oxides Sr_0.9K_0.1Fe_xCo_1-xO_3-δ (SKFCx, x = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) are investigated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) on Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte. The cubic phase of the SKFCx oxides is demonstrated by x-ray diffraction. The SKFCx cathode shows good compatibility with the SDC electrolyte up to 900 °C. Among the investigated compositions, SKFC0.1 displays the highest electrical conductivity of 443–146 S·cm^?1 from 350 °C to 800 °C in flow air. The area specific resistances (ASRs) of the SKFCx (x = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) cathodes are 0.047, 0.058, 0.066, 0.101, 0.155 and 0.175 Ω cm² at 650 °C in air on an SDC electrolyte. Among the five tested cathodes, SKFC0.1 exhibits the lowest area specific resistances between 550 °C and 750 °C, when tested on its symmetric cell configuration of cathode|SDC|cathode. The thermally stabilized cubic perovskite structure of the SKFC0.1 powder is demonstrated by high-temperature XRD. The average linear thermal expansion coefficient α_L of SKFC0.1 is 18.9$\times$10^?6 K^?1. A peak power density of 1643 mW·cm^?2 is achieved on SKFC0.1|SDC|Ni-SDC anode supported fuel cell at 650 °C. These features, and excellent electrocatalytic activity and good stability, indicate the potential of alkaline metal doped strontium cobalt ferrite perovskites are promising cathode materials for IT-SOFCs.     

An innovative membrane-electrode assembly for efficient and durable polymer electrolyte membrane fuel cell operations

An innovative membrane-electrode assembly, based on a polyoxometalate (POM)-modified low-Pt loading cathode and a sulphated titania (S-TiO₂)-doped Nafion membrane, is evaluated in a polymer electrolyte membrane fuel cell. The modification of fuel cell cathode with Cs₃HPMo₁₁VO₄₀ polyoxometalate is performed to enhance particles dispersion and increase active area, allowing low Pt loading while maintaining performance. The POM's high surface acidity favors kinetics of oxygen reduction reaction. The mesoporous features of POM allow the embedding of Pt inside the micro-mesopores, avoiding the Pt aggregation during fuel cell operation and delaying the aging process, with consequent increase of lifetime. On the other hands, commercial Nafion is modified with superacidic sulphated titanium oxide nanoparticles, allowing operation at low relative humidity and controlled polarization of the MEA. Further MEAs, formed by unmodified Nafion membrane and the POM-based cathode, as well as sulphated titanium-added Nafion and commercial Pt-based electrodes, are used as terms of comparison. The cell performances are studied by polarization curves, electrochemical impedance spectroscopy, Tafel plot analysis and high frequency resistance measurements. The dependence of cell performances on relative humidity is also studied. The catalytic and transport properties are improved using the coupled system, despite the reduced Pt loading, thanks to rich proton environment provided by cathode and membrane.     

A-site Ba-deficiency layered perovskite EuBa1−xCo2O6−δ cathodes for intermediate-temperature solid oxide fuel cells: Electrochemical properties and oxygen reduction reaction kinetics

A-site Ba-deficiency layered perovskite oxides, EuBa_1?xCo₂O_6?δ (EB_1?xCO, x = 0.02 and 0.04), have been synthesized by a citric acid-ethylene diamine tetraacetic acid complexation sol-gel method, and evaluated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Room temperature powder X-ray diffraction patterns indicate that the EB_1?xCO oxides crystallize in an orthorhombic symmetry with space group Pmmm. Among all of components, EB_0.98CO exhibits a good chemical compatibility with Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte, as evidenced by phase analysis of mixed EB_0.98CO-CGO after calcining at 950 °C for 12 h in air. Thermal expansion analysis gives an average thermal expansion coefficient of 16.7 × 10^?6 K^?1 for EB_0.98CO. Thermogravimetric measurement confirms the high oxygen nonstoichiometric characteristic of EB_0.98CO at elevated temperatures. The electrical conductivity values of EB_0.98CO exceed 300 S cm^?1 in the temperature range of 100–750 °C. When tested as cathode in IT-SOFCs, the polarization resistance of 0.107 Ω cm² and the overpotential of 10 mV at current density of 77 mA cm^?2 are achieved in the EB_0.98CO cathode at 700 °C in air. The EB_0.98CO cathode-based anode-supported single cell delivers the maximum power density of 505 mW cm^?2 at 700 °C. Finally the rate-limiting steps for oxygen reduction reaction at the EB_0.98CO cathode interface are determined to be the charge transfer reaction and gas-phase diffusion process.     

Nitrogen-doped carbon nanotubes with high activity for oxygen reduction in alkaline media

Nitrogen-doped carbon nanotubes (NCNTs) were prepared using a floating catalyst chemical vapour deposition method. The multiwalled NCNT contains 8.4 at% nitrogen and has a dimension of 100 nm in the diameter and 10-20 nm in the wall thickness. The catalytic activity and durability of the NCNTs towards oxygen reduction reaction (ORR) were evaluated by cyclic voltammetry (CV) and rotating ring-disk electrode (RRDE) techniques in KOH solution. In addition, the effects of KOH concentration on several ORR performance indicators of the NCNT catalyst, such as the number of electrons transferred, the diffusion-limiting current density, the onset and half-wave potentials, were also examined in electrolytes of various KOH concentrations, ranging from 0.1 to 12 M. Experimental results show that NCNTs exhibited comparable activity for ORR in alkaline electrolyte as compared with commercially available Pt/C catalyst, and much higher activity than commercial Ag/C catalysts. In addition, the NCNTs showed good stability from the potential cycling test, and the concentration of KOH had significant impact on the ORR performance indicators of the NCNT catalysts.