Improved performance of anode with iron/sulfur-modified graphite in microbial fuel cell

The paper reports the operation of a new-design microbial fuel cell using compost leachate as a substrate, oxygen/electrodeposited MnO_x cathode and a new-anode concept with graphite modified by an iron/sulfur solid chemical catalyst which almost eliminates the starting delay time and gives very high current and power densities, I ~ 25 A m^− 3 at P_max ~ 12 W m^− 3 or I ~ 3.8 A m^− 2 at P_max ~ 1.8 W m^− 2.     

Poly(vinyl alcohol) separators improve the coulombic efficiency of activated carbon cathodes in microbial fuel cells

High-performance microbial fuel cell (MFC) air cathodes were constructed using a combination of inexpensive materials for the oxygen reduction cathode catalyst and the electrode separator. A poly(vinyl alcohol) (PVA)-based electrode separator enabled high coulombic efficiencies (CEs) in MFCs with activated carbon (AC) cathodes without significantly decreasing power output. MFCs with AC cathodes and PVA separators had CEs (43%–89%) about twice those of AC cathodes lacking a separator (17%–55%) or cathodes made with platinum supported on carbon catalyst (Pt/C) and carbon cloth (CE of 20%–50%). Similar maximum power densities were observed for AC-cathode MFCs with (840 ± 42 mW/m²) or without (860 ± 10 mW/m²) the PVA separator after 18 cycles (36 days). Compared to MFCs with Pt-based cathodes, the cost of the AC-based cathodes with PVA separators was substantially reduced. These results demonstrated that AC-based cathodes with PVA separators are an inexpensive alternative to expensive Pt-based cathodes for construction of larger-scale MFC reactors.     

Power generation using an activated carbon and metal mesh cathode in a microbial fuel cell

An inexpensive activated carbon (AC) air cathode was developed as an alternative to a platinum-catalyzed electrode for oxygen reduction in a microbial fuel cell (MFC). AC was cold-pressed with a polytetrafluoroethylene (PTFE) binder to form the cathode around a Ni mesh current collector. This cathode construction avoided the need for carbon cloth or a metal catalyst, and produced a cathode with high activity for oxygen reduction at typical MFC current densities. Tests with the AC cathode produced a maximum power density of 1220 mW/m² (normalized to cathode projected surface area; 36 W/m³ based on liquid volume) compared to 1060 mW/m² obtained by Pt catalyzed carbon cloth cathode. The Coulombic efficiency ranged from 15% to 55%. These findings show that AC is a cost-effective material for achieving useful rates of oxygen reduction in air cathode MFCs.     

Asymmetric electrochemical capacitor microdevice designed with vanadium nitride and nickel oxide thin film electrodes

Vanadium nitride thin film has been coupled with electrodeposited nickel oxide in order to design an electrochemical capacitor microdevice. VN has been used as negative electrode while NiO was used as the positive one in 1 M KOH electrolyte. VN exhibits a pseudo-capacitive behavior while NiO shows a faradaic behavior. This asymmetric microdevice has been operated between 0.5 and up to 1.8 V in aqueous based electrolyte (1 M KOH). Long term cycling ability (10,000 charge/discharge cycles) has been demonstrated with interesting energy (1.0 μW h cm^− 2) and power (40 mW cm^− 2) densities.     

Infiltrated Sr2Fe1.5Mo0.5O6/La0.9Sr0.1Ga0.8Mg0.2O3 electrodes towards high performance symmetrical solid oxide fuel cells fabricated by an ultra-fast and time-saving procedure

Herein, the Sr₂Fe_1.5Mo_0.5O₆ (SFM) precursor solution is infiltrated into a tri-layered “porous La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ (LSGM)/dense LSGM/porous LSGM” skeleton to form both SFM/LSGM symmetrical fuel cells and functional fuel cells by adopting an ultra-fast and time-saving procedure. The heating/cooling rate when fabricating is fixed at 200 °C/min. Thanks to the unique cell structure with high thermal shock resistance and matched thermal expansion coefficients (TEC) between SFM and LSGM, no SFM/LSGM interfacial detachment is detected. The polarization resistances (Rp) of SFM/LSGM composite cathode and anode at 650 °C are 0.27 Ω·cm² and 0.235 Ω·cm², respectively. These values are even smaller than those of the cells fabricated with traditional method. From scanning electron microscope (SEM), a more homogenous distribution of SFM is identified in the ultra-fast fabricated SFM/LSGM composite, therefore leading to the enhanced performance. This study also strengthens the evidence that SFM can be used as high performance symmetrical electrode material both running in H₂ and CH₄. When using H₂ as fuel, the maximum power density of “SFM-LSGM/LSGM/LSGM-SFM” functional fuel cell at 700 °C is 880 mW cm^− 2. By using CH₄ as fuel, the maximum power densities at 850 and 900 °C are 146 and 306 mW cm^− 2, respectively.     

Platinum-macrocycle co-catalyst for electro-oxidation of formic acid

In this work, a new promoter, tetrasulfophthalocyanine (FeTSPc), one kind of environmental friendly material, was found to be very effective in both inhibiting self-poisoning and improving the intrinsic catalysis activity, consequently enhancing the electro-oxidation current during the electro-oxidation of formic acid. The cyclic voltammograms test showed that the formic acid oxidation peak current density has been increased about 10 times compared with that of the Pt electrode without FeTSPc. The electrochemical double potential step chronoamperometry measurements revealed that the apparent activity energy decreases from 20.64 kJ mol⁻¹ to 17.38 kJ mol⁻¹ after Pt electrode promoted by FeTSPc. The promoting effect of FeTSPc may be owed to the specific structure and abundant electrons of FeTSPc resulting in both the steric hindrance of the formation of poisoning species (CO) and intrinsic kinetic enhancement. In the single cell test, the performance of DFAFC increased from 80 mW cm⁻² mg⁻¹ (Pt) to 130 mW cm⁻² mg⁻¹ after the anode electrode adsorbed FeTSPc.     

A direct borohydride–peroxide fuel cell using a Pd/Ir alloy coated microfibrous carbon cathode

A direct borohydride fuel cell with a Pd/Ir catalysed microfibrous carbon cathode and a gold-catalysed microporous carbon cloth anode is reported. The fuel and oxidant were NaBH₄ and H₂O₂, at concentrations within the range of 0.1–2.0 mol dm⁻³ and 0.05–0.45 mol dm⁻³, respectively. Different combinations of these reactants were examined at 10, 25 and 42 °C. At constant current density between 0 and 113 mA cm⁻², the Pd/Ir coated microfibrous carbon electrode proved more active for the reduction of peroxide ion than a platinised-carbon one. The maximum power density achieved was 78 mW cm⁻² at a current density of 71 mA cm⁻² and a cell voltage of 1.09 V.     

High performance miniature glucose/O2 fuel cell based on porous silicon anion exchange membrane

Mesoporous silicon membranes are functionalized with ammonium groups and evaluated as high efficient anion exchange membrane in a miniaturized alkaline glucose fuel cell setup. N-Trimethoxysilylpropyl-N,N,N-trimethylammonium chloride is grafted onto the pore walls of porous silicon resulting in the anionic conductivity enhancement. The functionalization process is followed by FTIR spectroscopy where the optimized parameter could be determined. The ionic conductivity is measured using impedance spectroscopy and gives 5.6 mS cm^− 1. These modified mesoporous silicon membranes are integrated in a specially designed miniature alkaline (pH 13) glucose/air fuel cell prototype using a conventional platinum-carbon anode and a cobalt phthalocyanine-carbon nanotube cathode. The enhanced anion conductivity of these membranes leads to peak power densities of 7 ± 0.12 mW cm^− 2 at “air breathing” conditions at room temperature.     

Enhancement of the performances of a single concentric glucose/O2 biofuel cell by combination of bilirubin oxidase/Nafion cathode and Au–Pt anode

This work deals with a novel preparation method of bilirubin oxidase/2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid electrode. The enzyme and its mediator were adsorbed on carbon Vulcan XC-72R before their immobilization into a Nafion^® matrix. Promising results were obtained when this biocathode was associated with Au₇₀Pt₃₀ nanoparticles as anode in a single concentric glucose/O₂ biofuel cell (BFC). The latter BFC delivered at 37 °C a power density of 90 μW cm^?2 for a cell voltage of 0.4 V in phosphate buffer (pH 7.4) containing 0.01 M glucose. Moreover, the electrical performances were increased with the concentration of glucose by generating up to 190 μW cm^?2 for a cell voltage of 0.52 V when the concentration of the renewable fuel reached 0.7 M.     

Gelatin-functionalized carbon nanotubes for the bioelectrochemistry of hemoglobin

In this paper, we compared the use of gelatin-functionalized carbon nanotubes (CNTs) as substrates for Hemoglobin (Hb) immobilization and as electrodes for electrochemical reduction of the absorbed Hb. The non-covalently gelatin-functionalized CNTs possessed an improved solubility in aqueous solution and may have an enhanced biocompatibility with Hb. The characteristics of Hb/gelatin-CNTs composite films were studied by using UV–vis spectroscopy, FTIR spectroscopy and electrochemical methods. The immobilized Hb showed a couple of quasi-reversible redox peaks with a formal potential of −0.35 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffer solution (PBS). The surface concentration of electroactive Hb immobilized on gelatin-CNT/GC electrode was about 4.34 × 10⁻¹⁰ mol cm⁻².     

A cobalt-free electrode material La0.5Sr0.5Fe0.8Cu0.2O3 − δ for symmetrical solid oxide fuel cells

Cobalt-free perovskite oxide La_0.5Sr_0.5Fe_0.8Cu_0.2O_3 − δ (LSFC) was applied as both anode and cathode for symmetrical solid oxide fuel cells (SSOFCs). The LSFC shows a reversible transition between a cubic perovskite phase in air and a mixture of SrFeLaO₄, a K₂NiF₄-type layered perovskite oxide, metallic Cu and LaFeO₃ in reducing atmosphere at elevated temperature. The average thermal expansion coefficient of LSFC in air is 17.7 × 10^− 6 K^− 1 at 25 °C to 900 °C. By adopting LSFC as initial electrodes to fabricate electrolyte supported SSOFCs, the cells generate maximum power output of 1054, 795 and 577 mW cm^− 2 with humidified H₂ fuel (~ 3% H₂O) and 895, 721 and 482 mW cm^− 2 with humidified syngas fuel (H₂:CO = 1:1) at 900, 850 and 800 °C, respectively. Moreover, the cell with humidified H₂ fuel demonstrates a reasonable stability at 800 °C under 0.7 V for 100 h.     

Preparation process for improving cathode electrode structure in direct methanol fuel cell

The cathode electrode structure of the direct methanol fuel cell (DMFC) was improved by a novel catalyst ink preparation method. Regulation of the solvent polarity in the cathode catalyst ink caused increases in the electrochemical active surface (EAS) for the oxygen reduction reaction (ORR) as well as decreases in the methanol crossover effect. In a two-step preparation, agglomerates consisting of catalyst and Nafion ionomers were decreased in size, and polar groups in the ionomers formed organized networks in the cathode catalyst layer. Despite Pt catalysts in the cathode being only 0.5 mg cm^? 2, the maximum power density of the improved membrane electrode assembly (MEA) was 120 mW cm^? 2, at 3 M methanol, which was much larger than that of traditional MEA (67 mW cm^? 2).     

Simultaneous determination of acetaminophen,dopamine and ascorbic acid using a PbS nanoparticles Schiff base-modified carbon paste electrode

A highly sensitive method was investigated for the simultaneous determination of acetaminophen (AC), dopamine (DA), and ascorbic acid (AA) using a PbS nanoparticles Schiff base-modified carbon paste electrode (PSNSB/CPE). Differential pulse voltammetry peak currents of AC, DA and AA increased linearly with their concentrations within the ranges of 3.30 × 10⁻⁸–1.58 × 10⁻⁴ M, 5.0 × 10⁻⁸–1.2 × 10⁻⁴ M and 2.50 × 10⁻⁶–1.05 × 10⁻³ M, respectively, and the detection limits for AC, DA and AA were 5.36 × 10⁻⁹, 2.45 × 10⁻⁹ and 1.86 × 10⁻⁸ M, respectively. The peak potentials recorded in a phosphate buffer solution (PBS) of pH 4.6 were 0.672, 0.390, and 0.168 V (vs Ag/AgCl) for AC, DA and AA, respectively. The modified electrode was used for the determination of AC, DA, and AA simultaneously in real and synthetic samples.     

Electrochemical properties of liquid electrolyte added quasi-solid state TiO2 dye-sensitized solar cells

In this study a process has been introduced to replace traditional liquid or solid electrolyte coatings on dye-sensitized photoelectrode in solar cells. This process has more efficient diffusion of electrolyte, hence higher sensitivity. Better interfacial contact between polymer electrolyte and TiO₂ photoelectrode had improved electrochemical response and ionic conductivity of cell. Conductivity of this electrode was 9.33 × 10⁻³ S cm⁻¹ (at room temperature), which is much higher than the using traditional process for addition of electrolytes. It has 0.68 V open-circuit voltage and 3.19 mA cm⁻² short-circuit current density. Energy conversion efficiency of this cell was about 37% higher than the cell developed with traditional processes under constant light intensity (45 mW cm⁻²).     

Applications of ultrasonics in food science - novel control of fat crystallization and structuring

Low power (< 10 W m^− 2) ultrasound spectroscopy has been used for many years for the characterisation of food colloids with respect to particle size distribution, adiabatic compressibility, particle solvation and dissolution, crystal nucleation and solid content. Whilst high power (> 1 kW m^− 2) ultrasound methods are well-known to impact on fat crystallization and structuring, they have many drawbacks, causing off-flavours through product oxidation and a metallic taste probably associated with sonotrode wear. Furthermore, process development with power ultrasound is hit and miss, applications being largely empirical and poorly understood. We have recently shown that well-controlled crystal nucleation can be obtained using low power, quasi-continuous ultrasound and acoustical pressure fields, opening up a new field of application in food processing for ultrasonics.     

Selective oxidation of ethanol to acetic acid in highly efficient polymer electrolyte membrane-direct ethanol fuel cells

The selective conversion of ethanol into potassium acetate with concomitant production of electrical energy has been achieved in both passive and active direct fuel cells containing platinum-free electrodes and an anion-exchange polymer membrane. The power densities supplied by the passive systems at r.t. can be as high as 55 mW cm^?2, while the active systems can deliver up to 170 mW cm^?2 at 80 °C. Such high values have never been reported for direct ethanol fuel cells with whatsoever electrocatalyst in either alkaline or acidic media.     

Electroreduction of O2 at a mediated Melanocarpus albomyces laccase cathode in a physiological buffer

We report on oxygen reduction in a physiological buffer solution (0.05 M phosphate buffer containing dissolved O₂, 0.1 M NaCl, pH 7.4, 37 °C) by Melanocarpus albomyces laccase, co-immobilized with [Os(2,2’-bipyridine)₂(polyvinylimidazole)₁₀Cl]^+/2+ as a mediator, on glassy carbon electrodes. Such oxygen cathodes yielded current densities of 3.8 mA cm⁻² at 0.2 V vs. Ag/AgCl, the largest current density reported to date for a mediated laccase cathode in physiological buffer solutions, showing promise for development of biocatalytic fuel cell prototypes.     

Development of micro-tubular SOFCs with an improved performance via nano-Ag impregnation for intermediate temperature operation

Micro-tubular solid-oxide fuel cell consisting of a 10-μm thick (ZrO₂)_0.89(Sc₂O₃)_0.1(CeO₂)_0.01 (ScSZ) electrolyte on a support NiO/(ScSZ) anode (1.8 mm diameter, 200 μm wall thickness) with a Ce_0.8Gd_0.2O_1.9 (GDC) buffer-layer and a La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF)/GDC functional cathode has been developed for intermediate temperature operation. The functional cathode was in situ formed by impregnating the well-dispersed nano-Ag particles into the porous LSCF/GDC layer using a citrate method. The cells yielded maximum power densities of 1.06 W cm⁻² (1.43 A cm⁻², 0.74 V), 0.98 W cm⁻² (1.78 A cm⁻², 0.55 V) and 0.49 W cm⁻² (1.44 A cm⁻², 0.34 V), at 650, 600 and 550 °C, respectively.     

Buffer standards for the physiological pH of N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine (TRICINE) from T = (278.15 to 328.15) K

The pH values of two buffer solutions without NaCl and seven buffer solutions with added NaCl, having ionic strengths (I = 0.16 mol · kg⁻¹) similar to those of physiological fluids, have been evaluated at 12 temperatures from T = (278.15 to 328.15) K by way of the extended form of the Debye–Hückel equation of the Bates–Guggenheim convention. The residual liquid junction potentials (δE_j) between the buffer solutions of TRICINE and saturated KCl solution of the calomel electrode at T = (298.15 and 310.15) K have been estimated by measurement with a flowing junction cell. For the buffer solutions with the molality of TRICINE(m₁) = 0.06 mol · kg⁻¹, NaTRICINE(m₂) = 0.02 mol · kg⁻¹, and NaCl(m₃) = 0.14 mol · kg⁻¹, the pH values at T = 310.15 K obtained from the extended Debye–Hückel equation and the inclusion of the liquid junction correction are 7.342 and 7.342, respectively. These are in excellent agreement. The zwitterionic buffer TRICINE is recommended as a secondary pH standard in the region for clinical application.     

A novel MEA architecture for improving the performance of a DMFC

Direct methanol fuel cell (DMFC) consisting of a double-catalytic layered membrane electrode assembly (MEA) provide higher performance than that with the traditional MEA. This novel structured MEA includes a hydrophilic inner catalyst layer and a traditional electrode with an outer catalyst layer, which was made using both catalyst coated membrane (CCM) and gas diffusion electrode (GDE) methods. The inner catalyst was PtRu black on anode and Pt black on cathode. The outer catalyst was carbon supported Pt–Ru/Pt on anode and cathode, respectively. Thus in the double-catalytic layered electrodes three gradients were formed: catalyst concentration gradient, hydrophilicity gradient and porosity gradient, resulting in good mass transfer, proton and electron conducting and low methanol crossover. The peak density of DMFC with such MEA was 19 mW cm⁻², operated at 2 M CH₃OH, 2 atm oxygen at room temperature, which was much higher than DMFC with traditional MEA.