Mediatorless Carbohydrate/Oxygen Biofuel Cells with Improved Cellobiose Dehydrogenase Based Bioanode

Direct electron transfer (DET) between cellobiose dehydrogenase from Humicola insolens ascomycete (HiCDH) and gold nanoparticles (AuNPs) was achieved by modifying AuNPs with a novel, positively charged thiol N‐(6‐mercapto)hexylpyridinium (MHP). The DET enabled the use of the HiCDH enzyme as an anodic biocatalyst in the design of a mediatorless carbohydrate/oxygen enzymatic fuel cell (EFC). A biocathode of the EFC was based on bilirubin oxidase from Myrothecium verrucaria (MvBOx) directly immobilised on the surface of AuNPs. The following parameters of the EFC based on Au/AuNP/MHP/HiCDH bioanode and Au/AuNP/MvBOx biocathode were obtained in quiescent air saturated PBS, pH 7.4, containing: (i) 5 mM glucose‐open‐circuit voltage (OCV) of 0.65 ± 0.011 V and the maximal power density of 4.77 ± 1.34 μW cm⁻² at operating voltage of 0.50 V; or (ii) 10 mM lactose‐OCV of 0.67 ± 0.006 V and the maximal power density of 8.64 ± 1.91 μW cm⁻² at operating voltage of 0.50 V. The half‐life operation times of the EFC were estimated to be at least 13 and 44 h in air saturated PBS containing 5 mM glucose and 10 mM lactose, respectively. Among advantages of HiCDH/MvBOx FCs are (i) simplified construction, (ii) relatively high power output with glucose as biofuel, and (iii) the absence of the inhibition of the HiCDH based bioanode by lactose, when compared with the best previously reported CDH based bioanode.     

A Direct Electron Transfer‐Based Glucose/Oxygen Biofuel Cell Operating in Human Serum

We report on the fabrication and characterisation of the very first direct electron transfer‐based glucose/oxygen biofuel cell (BFC) operating in neutral glucose‐containing buffer and human serum. Corynascus thermophilus cellobiose dehydrogenase and Myrothecium verrucaria bilirubin oxidase were used as anodic and cathodic bioelements, respectively. The following characteristics of the mediator‐, separator‐ and membrane‐less, a priori, non‐toxic and simple miniature BFC, was obtained: an open‐circuit voltage of 0.62 and 0.58 V, a maximum power density of ca. 3 and 4 μW cm^–2 at 0.37 and 0.19 V of cell voltage, in phosphate buffer and human serum, respectively.     

A study on direct glucose and fructose alkaline fuel cell

Direct glucose fuel cell (DGFC) has huge potential as a power source in low power long term portable devices. Electro-oxidation of glucose and fructose on PtRu/C catalyst are studied using cyclic voltammetry in alkaline medium to study the reason for deactivation of glucose fuel cell. A simple direct glucose fuel cell with PtRu/C as anode and activated charcoal as cathode was constructed and operated to study the effect of different temperature and concentration of glucose and KOH. An open-circuit voltage (OCV) of 0.91 V is obtained using 0.3 M glucose in 1 M KOH solution. OCV increased with the increase in glucose concentration. The maximum peak power density of 1.38 mW cm⁻² is obtained using 0.2 M glucose in 1 M KOH at 30 °C and it decreases with further increase in glucose concentration and temperature. In order to determine the reason for decrease in performance of glucose fuel cell due to conversion of glucose to fructose, the fuel cell was operated using 0.2 M fructose in 1 M KOH. The peak power density delivered is 0.57 mW cm⁻². The DGFC is continuously operated for 260 h at constant load of 500 Ω produces final constant voltage of 0.21 V.     

Long‐Term Stability Studies of Anode‐Supported Microtubular Solid Oxide Fuel Cells

A long‐term stability study of an anode‐supported NiO/YSZ‐YSZ‐LSM/YSZ microtubular cell was performed, under low fuel utilization conditions, using pure humidified hydrogen as fuel at the anode side and air at the cathode side. A first galvanometric test was performed at 766 °C and 200 mA cm^–2, measuring a power output at 0.5 V of ∼250 mW cm^–2. During the test, some electrical contact breakdowns at the anode current collector caused sudden current shutdowns and start‐up events. In spite of this, the cell performance remains unchanged. After a period of 325 h, the cell temperature and the current density was raised to 873°C and 500 mA cm^–2, and the cell power output at 0.5 V was ∼600 mW cm^–2. Several partial reoxidation events due to disturbance in fuel supply occurred, but no apparent degradation was observed. On the contrary, a small increase in the cell output power of about 4%/1,000 h after 654 h under current load was obtained. The excellent cell aging behavior is discussed in connection to cell configuration. Finally, the experiment concluded when the cell suffered irreversible damage due to an accidental interruption of fuel supply, causing a full reoxidation of the anode support and cracking of the thin YSZ electrolyte.     

Evaluation of a Non‐sealed Solid Oxide Fuel Cell Stack with Cells Embedded in Plane Configuration

A non‐sealed solid oxide fuel cell stack with cells embedded in plane configuration was fabricated and operated successfully in a box‐like stainless‐steel chamber. For a two‐cell stack, it demonstrated an open circuit voltage (OCV) of 2.13 V and a maximum power output of 569 mW at the flow rate of 67 sccm CH₄ and 33 sccm O₂. A fuel utilization of 4.16% was obtained. The cell performance was dominated by two different mechanisms, the polarization of the cathode at low current and the concentration polarization of the anode at high current. Finally, a scaled‐up stack with six cells in series generated an OCV of 6.4 V and a maximum power output of 8.18 W.     

Study of a Single‐Chamber Solid Oxide Fuel Cell Microstack with V‐Shaped Congener‐Electrode‐Facing Configuration

Single‐chamber solid oxide fuel cell (SC‐SOFC) microstacks with V‐Shaped congener‐electrode‐facing configuration were fabricated and operated successfully in a box‐like stainless steel chamber. Two gas channels with small gas inlets were used to transport the fuel and oxygen to the anodes and cathodes, respectively. The temperature of an anode‐facing‐anode two‐cell stack was higher than that of a cathode‐facing‐cathode two‐cell stack during the test procedure. For a three‐cell stack, the cell in the middle region presented the highest power output. The open circuit voltage (OCV) and maximum power output of the three‐cell stack in a gas mixture of 100 sccm N₂, 120 sccm CH₄, and 80 sccm O₂ were 3.0 V and 413 mW, respectively.     

Two‐Stage Oxidation of Glucose by an Enzymatic Bioanode

The present study reports the design of a novel bioanode to deeply oxidize glucose in an enzymatic biofuel cell (EFC). This enzymatic glucose cell utilizes three co‐immobilized enzymes: NAD‐dependent glucose dehydrogenase (GDH), NAD(P)⁺‐dependent gluconate‐5‐dehydrogenase (Ga5DH), and diaphorase (DI). Glucose is oxidized to gluconate by NAD‐dependent GDH, gaining two electrons per glucose; the gluconate obtained as a by‐product is oxidized at the C5 carbon to 5‐keto‐gluconate by Ga5DH. Operation of our bioanode enabled the oxidation of glucose in two stages, resulting in the gain of four electrons. The three‐enzyme EFC provides a maximum power density of 10.51 ± 1.72 μW cm^–2, which is about 1.6 times higher than the maximum power density of an EFC using a bioanode based on the co‐immobilization of two enzymes (GDH and DI). Our results hold promise for increasing the current density of EFCs, and for application in glucose biosensor.     

Synthesis, characterization and application of platinum based bi-metallic catalysts for direct glucose alkaline fuel cell

In the context of development of direct glucose fuel cell (DGFC), low metal loading (ca. 15 wt.%) bi-metallic platinum–bismuth (PtBi/C) and platinum–gold (PtAu/C) catalysts are synthesized by immobilizing metal sols on carbon substrate (Vulcan XC 72R). Physical characterization of electro-catalysts, studied using TEM, SEM, EDX and XRD, reveals the formation of nano-sized metal particles on carbon substrate. The cyclic voltammetry and chronoamperometry of the prepared catalysts point out that PtAu/C is more active and stable than PtBi/C and commercial PtRu/C towards glucose electro-oxidation in alkaline medium. The catalysts are tested as anode in batch DGFC using activated charcoal as cathode in different glucose and electrolyte (KOH solution) concentrations at ambient temperature (30 °C). Open-circuit voltage of ∼0.9 V is obtained for PtAu/C and commercial PtRu/C and 0.8 V for PtBi/C anode in 0.2 M glucose and in 1 M KOH. However, the peak power density per unit metal loading or specific peak power density obtained is 1.6 mW cm⁻² mg⁻¹ for PtAu/C followed by PtBi/C (1.25 mW cm⁻² mg⁻¹) and commercial PtRu/C (1.13 mW cm⁻² mg⁻¹). For PtBi/C and PtRu/C, the cell performance increases up to 0.2 M glucose concentration and then decreases. However, for PtAu/C catalyst the cell performance increases up to 0.3 M glucose concentration and then decreases. A prominent transition zone is observed in which current density sharply decreases with the decrease in voltage (increase in overpotential) for PtBi/C and PtRu/C at 0.3 M glucose concentration, which is not observed in the case of PtAu/C. The transition zone for PtAu/C is insignificant and at higher glucose concentration (0.4 M) pointing out that PtAu/C is much stable catalyst than PtBi/C and commercial PtRu/C.     

Bioorganic materials as a fuel source for low-temperature direct-mode fuel cells

In this study a direct-mode fuel cell in which the fuel and electrolyte are mixed with each other is tested. An alkaline electrolyte is used. The aim was to develop a fuel cell which operates directly by mixing the fuel with the electrolyte. The target is to create a fuel cell with a capacity of a few mW cm⁻² with starch as a fuel source. Starch, glucose, and sorbitol were tested as fuels for the fuel cell. With the selected fuel cell type and with glucose as the fuel, a maximum current density of 8 mA cm⁻² with a voltage of 0.5 V was obtained.     

Freestanding Micro‐SOFCs with Electrodes Prepared by Electrostatic Spray Deposition

We report a freestanding micro solid oxide fuel cell with both the anode and cathode deposited using electrostatic spray deposition (ESD) technique. The cell is consisted of dense yittria‐stabilized zirconia (YSZ) electrolyte (100 nm thick), porous lanthanum strontium manganite (LSM)–YSZ cathode (∼3 μm thick), and porous NiO‐YSZ anode (∼3 μm thick). LSM‐YSZ and NiO‐YSZ composite powders were initially prepared by glycine nitrate process and super‐critical fluid processes, respectively, and both cathode and anode layers were deposited by the ESD. The resulting freestanding micro cell exhibited an open circuit voltage close to the theoretical value of 1.09 V, and a maximum power density of 41.3 mWcm^–2 at 640 °C.     

Design,Fabrication and Preliminary Study of a Mini Power Source with a Planar Six‐cell PEM Unitised Regenerative Fuel Cell Stack

A novel micro planar fuel cell power supplier, in which a six‐cell PEM unitised regenerative fuel cell (URFC) stack is used as the power generator, was designed and fabricated. Six membrane electrode assemblies were prepared and integrated on one piece of membrane by spraying catalyst slurry on both sides of the membrane. Each cell was made by sandwiching a membrane electrode assembly (MEA) between two graphite monopolar plates and six cell units were mechanically fixed in two organic glass endplates. When the stack was operated in an electrolysis mode, hydrogen was generated from the splitting of water and stored using a hydrogen storage alloy; conversely, when the stack was operated in fuel cell mode, hydrogen was supplied by the hydrogen storage alloy and oxygen was supplied from air by self‐breathing of the cathode. At room temperature and standard atmospheric pressure, the open‐circuit voltage (OCV) of the system reached 4.9 V, the system could be discharged at a constant current density of 20 mA cm^–2 for about 40 min, and the work voltage was ∼2.9 V. The system showed good stability for 10 charge–discharge cycles.     

Properties of the enzyme electrode fabricated with a film of polythiophene derivative and its application to a glucose fuel cell

A polymer electrode in the form of a thin film was prepared by electrochemical copolymerization of 3‐methylthiophene and thiophene‐3‐acetic acid. Glucose oxidase (GOx) was immobilized by covalent binding to the carboxyl groups on the electrode, and the GOx‐immobilized electrode (GOx‐electrode) was used as an anode in a glucose fuel cell. It was demonstrated by cyclic voltametry that in the presence of p‐benzoquinone (BQ), which was adopted as an electron mediator, the GOx‐electrode generated a significant glucose‐oxidation current depending on the concentrations of both glucose and BQ. A large surface area of the GOx‐electrode was considered to afford effective environment for the enzyme reaction and electron transfer. The fuel cell using the GOx‐electrode as an anode gave a power output of 42 μW/cm²‐anode at 30°C, when its anodic compartment contained 100 mM glucose and 10 mM BQ. The performance of the cell was influenced by the concentrations of glucose and BQ in the anodic compartment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A Visual Study of Bubble Formation in Microfluidic Fuel Cells

Two microfluidic fuel cells having microchannel widths of 1.0 mm (cell #1) and 0.5 mm (cell #2) with electrode spacing of 0.4 mm were tested at volumetric flow rates ranging from 0.1 to 1.0 ml min^–1. The concentration of hydrogen peroxide was tested at 0.1, 0.3, and 0.6 M. An additional microfluidic fuel cell (cell #3) having microchannel width of 0.5 mm and electrode spacing of 0.2 mm was also tested. Bubble formation under various tested conditions in different microchannels are presented. The open circuit voltage of the cells increased as reactant volumetric flow rate increased. Effect of electrode spacing on cell performance depends on the reactant concentration and volumetric flow rate. Also reported was the area‐specific internal resistance of the present cells and their fuel utilization corresponding to peak power density at a given flow rate with [H₂O₂] = 0.1 M. For cell #1, cell #2, and cell #3, respectively, the maximum power densities were 9, 40, and 16 mW cm^–2 at 1.0 ml min^–1 and 0.6 M, while the maximum power densities were 5, 11, and 15 mW cm^–2 at 1.0 ml min^–1 and 0.1 M.     

Experimental results on the direct electrochemical oxidation of methanol in PEM fuel cells

The cell performance of direct methanol fuel cells (DMFC) is 0.5 V at 0.5 A cm^–2 under high pressure oxygen operation (3 bar abs.) at 110 °C. However, high oxygen pressure operation at high temperatures is only useful in special market niches. Therefore, our work has now focused on air operation of a DMFC under low pressure (up to 1.5 bar abs.). At present, a power density of more than 100 mW cm^–2 can be achieved at 0.5 V on air operation at 110 °C. These measurements were carried out in single cells with an electrode area of 3 cm² and the air stoichiometry only amounted to 10. The effects of methanol concentration and temperature on the anode performance were studied by pseudo half cell measurements and the results are presented together with their impact on the cell voltage. A cell design with an electrode area of 550 cm², which is appropriate for assembling a DMFC stack, was tested. A three-celled stack based on this design revealed nearly the same power densities as in the small experimental cells at low air excess pressure and the voltage–current curves for the three cells were almost identical. At 110 °C a power output of 165 W at a stack voltage of 1.5 V can be obtained in the air mode.     

Triple-layer proton exchange membranes based on chitosan biopolymer with reduced methanol crossover for high-performance direct methanol fuel cells application

A novel triple-layer proton exchange membrane comprising two thin layers of structurally modified chitosan, as methanol barrier layers, both sides coated with Nafion^®105 is prepared and tested for high-performance direct methanol fuel cell applications. A tight adherence is detected between layers from SEM and EDX data for the cross-sectional area of the newly designed membrane, which are attributed to high affinity of opposite charged polyelectrolyte layers. Proton conductivity and methanol permeability measurements show improved transport properties for the multi-layer membrane compared to Nafion^®117 with approximately the same thickness. Moreover, direct methanol fuel cell tests reveal higher open circuit voltage, power density output, and overall fuel cell efficiency for the triple-layer membrane than Nafion^®117, especially at concentrated methanol solutions. A power output of 68.10 mW cm^?2 at 5 M methanol feed is supplied using multi-layer membrane, which is found to be about 72% more than that of for Nafion^®117. In addition, fuel cell efficiency for multi-layer membrane is measured about 19.55% and 18.45% at 1 and 5 M methanol concentrations, respectively. Owing to the ability to provide high power output, significantly reduced methanol crossover, ease of preparation and low cost, the triple-layer membrane under study could be considered as a promising polyelectrolyte for high-performance direct methanol fuel cell applications.     

A Novel Cell‐Array Design for Single Chamber SOFC Microstack

A novel design of single chamber solid oxide fuel cell (SC‐SOFC) microstack with cell‐array arrangement is fabricated and operated successfully in a methane–oxygen–nitrogen mixture. The small stack, consisting of five anode‐supported single cells connected in series, exhibits an open circuit voltage (OCV) of 4.74 V at the furnace temperature of 600 °C and a maximum power output of 420 mW (total active electrode area is 1.4 cm²) at the furnace temperature of 700 °C. A gas mixture of CH₄/O₂ = 1 leads to best performance and stability.     

An enzyme-based microfluidic biofuel cell using vitamin K3-mediated glucose oxidation

Viamin K₃-modified poly-l-lysine (PLL-VK₃) was synthesized and used as the electron transfer mediator during catalytic oxidation of NADH by diaphorase (Dp) at the anode of biofuel cell. PLL-VK₃ and Dp were co-immobilized on an electrode and then coated with NAD⁺-dependent glucose dehydrogenase (GDH). The resulting enzymatic bilayer (abbreviated PLL-VK₃/Dp/GDH) catalyzed glucose oxidation. Addition of carbon black (Ketjenblack, KB) into the bilayer enlarged the effective surface area of the electrode and consequentially increased the catalytic activity. An oxidation current of ca. 2 mA cm⁻² was observed when the electrochemical cell contained a stirred 30 mM glucose, 1.0 mM NAD⁺, pH 7.0 phosphate-buffered electrolyte solution. The performance of glucose/O₂ biofuel cells, constructed as fluidic chips with controllable fuel flow and containing a KB/PLL-VK₃/Dp/GDH-coated anode and an Ag/AgCl or a polydimethylsiloxane-coated Pt cathode, were evaluated. The open circuit voltage of the cell with the PDMS-coated Pt cathode was 0.55 V and its maximum power density was 32 μW cm⁻² at 0.29 V when a pH 7.0-buffered fuel containing 5.0 mM glucose and 1.0 mM NAD⁺ was introduced into the cell at a flow rate of 1.0 mL min⁻¹. The cell's output increased as the flow rate increased. During 18 h of continuous operation of the cell with a load of 100 kΩ, the output current density declined by ca. 50%, probably due to swelling of the enzyme bilayer.     

Production and characterization of cellobiose dehydrogenase from <Emphasis Type="Italic">Phanerochaete chrysosporium</Emphasis> KCCM 60256 and its application for an enzymatic fuel cell

The enzyme cellobiose dehydrogenase (CDH), with high ability of electron transport, has been widely used in enzymatic fuel cells or biosensors. In this study, the cellobiose dehydrogenase gene from Phanerochaete chrysosporium KCCM 60256 was amplified and expressed in the methylotrophic yeast Pichia pastoris X-33. The recombinant enzyme (PcCDH) was purified using a metal affinity chromatography under non-denaturing conditions. The purified enzyme was analyzed by SDS-PAGE, confirming a corresponding band about 100 kDa. The enzyme activity of this purified PcCDH was determined as 1,845U/L (65mg/L protein). The enzyme showed the maximum activity at pH 4.5 and high activity in broad ranges of temperature from 30°C to 60°C. Moreover, the application of PcCDH to enzymatic fuel cell (EFC) was demonstrated. Lactose was used as the substrate in the EFC system; anode and cathode were immobilized with PcCDH and laccase, respectively. The cell’s open circuit voltage and maximum power density of the EFC system were, respectively, determined as 0.435 V and 314 μW/cm² (at 0.247 V) with 10 mM lactose.     

Electrostatic Spray Deposition of Doped Ceria Films

Dense and thin electrolyte films are desirable for solid oxide fuel cells (SOFCs) because of their low gas leakage and low ohmic resistances. This work aims at the preparation of thin dense Gd‐doped ceria (CGO) electrolyte films using a cost‐effective deposition method in ambient atmosphere–electrostatic spray deposition (ESD). The deposition parameters such as deposition temperature, concentration and flow rate of precursor solution were changed systematically to examine their effects on film morphology and hence electrochemical performance. While the film morphology was examined by a scanning electron microscope, the electrochemical performance was revealed by measuring open circuit voltages (OCVs) of NiO‐CGO/CGO/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ (BSCF) cells in 500–700 °C with humidified hydrogen as fuel and air as oxidant. The results show that a CGO film of 25 μm thick obtained at a deposition temperature of 400 °C, a precursor solution flow rate of 6 ml h^–1 and a precursor concentration of 0.3 M was dense with very few isolated pores and the OCV of the associated cell was 0.915 V at 500 °C. This implies that the CGO film has negligible gas leakage and ESD is a promising method for preparing thin dense electrolyte films for SOFCs.     

液相进样直接甲醇燃料电池性能研究

报道了用研制的Pt-Ru/C催化剂, 采用特殊工艺制备了膜电极, 并组装了直接甲醇质子交换膜单电池系统。考察了电极扩散层制备方法、催化剂层中催化剂、Teflon-C以及Nafion液的用量等电极制备工艺条件以及空气作为氧化剂对单电池性能的影响。结果表明：采用刷涂法制备电极扩散层比喷涂法好,催化剂层中催化剂的优化含量为0.6mg·cm-2,Teflon-C、Nafion液的最佳用量分别为0.3 mg·cm-2、0.5 mg·cm-2。当工作温度为80℃时,输出电压为0.3V,氧气作为阴极气体的输出电流密度为36mA·cm-2;而空气作为阴极气体的输出电流密度为22.5mA·cm-2。膜电极有效面积为9cm2的的液相进样直接甲醇/氧气燃料电池三电池电堆的最大功率为0.285W,此时输出电压为0.7V,输出电流为0.407A;而液相进样直接甲醇/空气三电池电堆的输出电压为0.635V,输出电流为0.252A时,最大功率为0.160W。