Investigation of Carbon Supported Nanostructured PtAu Alloy as Electrocatalyst for Direct Borohydride Fuel Cell

Carbon supported bimetallic PtAu electrocatalysts for sodium borohydride electrooxidation are prepared by a modified citrate stabilized NaBH₄ reduction process at different pH and temperature values. The physical properties of the materials are characterized by X‐ray diffraction spectroscopy, energy dispersive spectrometry, X‐ray photoelectron spectroscopy and transmission electron microscopy. Nano sized electrocatalysts have narrow size distributions and are uniformly dispersed on the surface of carbon support. Electrochemical performances of catalysts for sodium borohydride electrooxidation are tested with 25 cm² single fuel cell. The highest performance is obtained at a peak power density of 161 mW cm⁻² with 20 wt. % PtAu/C catalyst of 7.03 nm. Impact of the fuel cell operation parameters including concentration of NaBH₄, flow rates of oxidant and fuel, and fuel cell operation temperature are investigated. The best operation parameters are obtained at 1 M NaBH₄ concentration, 3 cm³ min⁻¹ NaBH₄ flow rate, 0.2 dm³ min⁻¹ oxygen flow rate and 65 °C fuel cell temperature.     

A parametric study of a platinum ruthenium anode in a direct borohydride fuel cell

Data on the performance of a direct borohydride fuel cell (DBFC) equipped with an anion exchange membrane, a Pt–Ru/C anode and a Pt/C cathode are reported. The effect of oxidant (air or oxygen), borohydride and electrolyte concentrations, temperature and anode solution flow rate is described. The DBFC gives power densities of 200 and 145 mW cm⁻² using ambient oxygen and air cathodes respectively at medium temperatures (60 °C). The performance of the DBFC is very good at low temperatures (ca. 30 °C) using modest catalyst loadings of 1 mg cm⁻² for anode and cathode. Preliminary data indicate that the cell will be stable over significant operating times.     

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.     

Electrochemical oxidation of boron containing compounds on titanium carbide and its implications to direct fuel cells

Electrochemical oxidation of sodium borohydride (NaBH₄) and ammonia borane (NH₃BH₃) (AB) have been studied on titanium carbide electrode. The oxidation is followed by using cyclic voltammetry, chronoamperometry and polarization measurements. A fuel cell with TiC as anode and 40 wt% Pt/C as cathode is constructed and the polarization behaviour is studied with NaBH₄ as anodic fuel and hydrogen peroxide as catholyte. A maximum power density of 65 mW cm⁻² at a load current density of 83 mA cm⁻² is obtained at 343 K in the case of borhydride-based fuel cell and a value of 85 mW cm⁻² at 105 mA cm⁻² is obtained in the case of AB-based fuel cell at 353 K.     

A tubular microbial fuel cell

Cell potential and power performance for tubular microbial fuel cells utilising manure as fuel are reported. The microbial fuel cells do not use a mediator, catalysts or a proton exchange membrane. The cell design has been scaled up to a size of 1.8 m in length using electrodes of 0.4 m² in area. The cell does not require a strictly controlled anaerobic environment and has potential practical applications when adapted into the form of a helix allowing fuel to flow through it. The cell could be used for power generation in remote applications. The peak power density of the cell is over 3 μW cm ⁻² (30 mW m⁻²). The performance can be improved by a more effective design of the interface between the anode and cathode chambers.     

Photoelectrochemical reaction of biomass-related compounds in a biophotochemical cell comprising a nanoporous TiO<Subscript>2</Subscript> film photoanode and an O<Subscript>2</Subscript>-reducing cathode

Photoelectrochemical decomposition of bio-related compounds such as ammonia, formic acid, urea, alcohol, and glycine by a biophotochemical cell (BPCC) comprising a nanoporous TiO₂ film photoanode and an O₂-reducing cathode generating simultaneously electrical power was investigated. The bio-related compounds studied were all photodecomposed by the present BPCC when they were either liquid or soluble in water. It was shown that ethanol exhibits similar characteristics both under 1 atm O₂ and air as studied by cyclic voltammograms. Although the present BPCC utilizes only UV light, a solar simulator at AM 1.5G and 100 mW cm⁻² light intensity gave also moderate photocurrent–photovoltage (J–V) characteristics with about 2/5 of the short circuit photocurrent (J _sc) values (J _sc) of that under a Xe lamp irradiation at the intensity of 503 mW cm⁻². It was demonstrated that varieties of bio-related compounds can be used as a direct fuel simultaneously for photodecomposition and electrical power generation. The charge transport processes in the BPCC operation were analyzed using glycine by an alternating current impedance spectroscopy, showing that the charge transfer reactions on the photoanode and the cathode surfaces compose the major resistance for the cell performance.     

High Performance by Applying IrCo/C Nanoparticles as an Anode Catalyst for PEMFC

IrCo bimetallic anode catalysts for polymer electrolyte membrane fuel cell (PEMFC) have been synthesized with a modified ethylene glycol method. X‐ray diffraction, TEM, CV, and linear sweep voltammetry results show that after the modification of Co, Ir nanoparticles supported on carbon exhibit high activity for hydrogen oxidation reaction (HOR). The maximum power density of 610.5 mW cm^–2 of a 50 cm² single cell is achieved using 20%Ir–30%Co/C catalyst as the anode, with a loading of 0.2 mg_Ir cm^–2. It is suggested that IrCo/C proposed in this work may be used as anode catalyst of PEMFC.     

A 2<Superscript>7-3</Superscript> fractional factorial optimization of polybenzimidazole based membrane electrode assemblies for H<Subscript>2</Subscript>/O<Subscript>2</Subscript> fuel cells

We describe the usefulness of a statistical fractional factorial design to obtain consistent and reproducible behavior of a membrane-electrode-assembly (MEA) based on a phosphoric acid (PA) doped polybenzimidazole (PBI) membrane, which allows a H₂/O₂ fuel cell to operate above 150 °C. Different parameters involved during the MEA fabrication including the catalyst loading, amount of binder, processing conditions like temperature and compaction load and also the amount of carbon in the gas diffusion layers (GDL) have been systematically varied according to a 2^7-3 fractional factorial design and the data thus obtained have been analyzed using Yates’s algorithm. The mean effects estimated in this way suggest the crucial role played by carbon loading in the gas diffusion layer, hot compaction temperature and the binder to catalyst ratio in the catalyst layer for enabling continuous performance. These statistically designed electrodes provide a maximum current density and power density of 1,800 mA cm⁻² and 280 mW cm⁻², respectively, at 160 °C using hydrogen and oxygen under ambient pressure.     

In situ active chlorine generation for the treatment of dye-containing effluents

This study examined the possibility to remove colour causing-compounds from synthetic effluent by indirect electrochemical oxidation using iridium oxide anode electrodes. Using a high concentration of chloride ions (17.1 mM) and various current densities, it was possible to produce high concentration of active chlorine with a specific production rate of 2.8 mg min⁻¹ A⁻¹. The best performance for acid methyl violet 2B dye (MV2B) decomposition was obtained using Ti/IrO₂ anodes operated at a current density of 15 mA cm⁻² during 40 min of treatment in the presence of 3.42 mM of chloride ions. Under these conditions, more than 99% of MV2B was removed (with a reaction rate apparent constant of 0.20 min⁻¹), whereas COD and TOC removal were 51% and 75%, respectively. The electrolytic cell was then used for the degradation of three other synthetic dye solutions: Eosin yellowish (EOY), Trypan Blue (TRB), Acridine Orange (ACO). TRB was the most difficult dye to remove from solution with a value reaction rate constant of 0.12 min⁻¹, compared to 0.19 min⁻¹ and 0.24 min⁻¹ recorded for ACO and EOY dyes, respectively. More than 99% of these dyes were removed by electrochemical oxidation.     

In situ grown carbon nanotubes on carbon paper as integrated gas diffusion and catalyst layer for proton exchange membrane fuel cells

In situ grown carbon nanotubes (CNTs) on carbon paper as an integrated gas diffusion layer (GDL) and catalyst layer (CL) were developed for proton exchange membrane fuel cell (PEMFC) applications. The effect of their structure and morphology on cell performance was investigated under real PEMFC conditions. The in situ grown CNT layers on carbon paper showed a tunable structure under different growth processes. Scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) demonstrated that the CNT layers are able to provide extremely high surface area and porosity to serve as both the GDL and the CL simultaneously. This in situ grown CNT support layer can provide enhanced Pt utilization compared with the carbon black and free-standing CNT support layers. An optimum maximum power density of 670 mW cm⁻² was obtained from the CNT layer grown under 20 cm³ min⁻¹ C₂H₄ flow with 0.04 mg cm⁻² Pt sputter-deposited at the cathode. Furthermore, electrochemical impedance spectroscopy (EIS) results confirmed that the in situ grown CNT layer can provide both enhanced charge transfer and mass transport properties for the Pt/CNT-based electrode as an integrated GDL and CL, in comparison with previously reported Pt/CNT-based electrodes with a VXC72R-based GDL and a Pt/CNT-based CL. Therefore, this in situ grown CNT layer shows a great potential for the improvement of electrode structure and configuration for PEMFC applications.     

Performance improvement of a micro borohydride fuel cell operating at ambient conditions

In this study, aqueous borohydride solutions were employed to fuel a micro cell. Electrochemical performance of the micro borohydride fuel cell was tested at ambient conditions without any auxiliary facilities. Electrochemical impedance spectroscopy (EIS) analyses were performed to characterize the cell performance. Both anion and cation exchange membranes were tried to separate the fuel from the cathode. Membrane properties were found to be a decisive factor for cell performance. A maximum power density of 40 mW/cm² at room temperature was achieved when the Nafion NRE211 membrane was used. Hydrogen evolution at the anode side resulted from the competitive hydrolysis reaction influenced cell performance by obstructing transfer of the electrolyte. The cell also demonstrated promising performance even when an Ag cathode was used.     

Investigation of fuel and media flexible laminar flow-based fuel cells

We investigate the performance of air-breathing laminar flow-based fuel cells (LFFCs) operated with five different fuels (formic acid, methanol, ethanol, hydrazine, and sodium borohydride) in either acidic or alkaline media. The membraneless LFFC architecture enables interchangeable operation with different fuel and media combinations that are only limited by the actual anode catalyst used. Furthermore, operating under alkaline conditions significantly improves methanol and ethanol oxidation kinetics and stabilizes sodium borohydride. LFFCs operated with hydrazine and sodium borohydride as fuels exhibit power densities of 80 and 101 mW/cm², respectively. To optimize anode performance, particularly for ethanol electro-oxidation, we introduced a hydrogen cathode to the membraneless LFFC design which renders the cell an ideal platform for anode investigation. Here, we highlight two simple diagnostic methods, in situ single electrode studies and electrochemical impedance spectroscopy (EIS), for characterizing and optimizing the performance of a direct ethanol LFFC anode.     

Electrochemical hydrogen pump for recirculation of hydrogen in a fuel cell stack

The objective of this work is to evaluate the use of an electrochemical hydrogen pump for recirculation of hydrogen in a fuel cell stack. The hydrogen pump needed about 130 mV at 0.5 A cm⁻², primarily because of the cell resistance (0.18 Ω cm²). This voltage loss was higher than a fuel cell voltage gain resulting from hydrogen recirculation. However, if one pumping cell is used for 10 active cells this means 13 mV loss per cell (or about 2%) which may be an acceptable voltage penalty. A stack with hydrogen recirculation should operate with less voltage fluctuation and should need purging less often than a stack operating with a dead-end mode of hydrogen supply. An additional benefit of hydrogen purification may be achieved in the systems with a fuel processor where operation in a dead-end mode is not possible. Attention must be paid to water management when designing and operating a hydrogen pump within a fuel cell stack.     

硼氢化物催化水解制氢作为燃料电池氢源(英文)

Borohydrides present interesting options for the electrochemical power generation acting either as hydrogen source or anodic fuel for direct borohydride fuel cells(DBFC).In this work,Mg-Ni composite synthesized by mechanically alloying method,used as the catalyst for the hydrolysis of borohydride,has been investigated.Co-doping treatment has been carried out for the purpose of improving the hydrolysis rate further.The as-prepared and Co-doped Mg-Ni composites with low cost showed high catalytic activity to the hydrolysis of borohydride for hydrogen generation.After Co-doping,the hydrogen generation rate was around 280 ml·g-1·min-1.Borohydride would be a promising hydrogen source for fuel cells.     

From soil to lab: Utilization of clays as catalyst supports in hydrogen generation from sodium borohydride fuel

The stabilized aqueous solution of sodium borohydride NaBH₄ is a promising hydrogen fuel but the stored hydrogen has to be released with the help of a catalyst through hydrolysis. In the present study, we developed Co- and clay-based supported catalysts. Three raw clays were taken from soil in Lebanon. Once purified and annealed, they were used as supports. Two of them, mainly composed of kaolinite and illite respectively, showed to be promising owing to their attractive specific surface areas (58.0 and 67.1 m² g⁻¹) as well as the high reactivity of the corresponding 15 wt.% Co catalysts (i.e. NaBH₄ conversions of 100% and hydrogen generation rates up to ∼31 L(H₂) min⁻¹ g⁻¹(Co)). A kinetic study was also carried out. The main results are reported and discussed herein.     

Performance of fluidized bed electrode in a molten carbonate fuel cell anode

A fluidized bed electrode could lower concentration polarization and activation polarization because of its high mass and heat transfer coefficient. The polarization characteristics of the fluidized bed electrode are systematically investigated in a molten carbonate fuel cell anode with an O₂/CO₂/gold reference electrode. The results show that polarization performance of the anode is improved by selecting proper flow rates of H₂, O₂ and CO₂, choosing suitable nickel particle content together with appropriate O₂/CO₂ ratio, and increasing reaction temperature as well as the area of the current collector. Limiting current density of 115.56 mA·cm⁻² is achieved under optimum performance as follows: a cylindrically curved nickel plate current collector, nickel particle content of 7.89%, the reaction temperature of 923 K, H₂ flow rate of 275 mL·min⁻¹, O₂/CO₂ flow rate of 10/20 mL·min⁻¹ and O₂/CO₂ ratio of 1 : 2.     

Preparation of a crosslinked polyelectrolyte membrane for fuel cells with an allyl methacrylate based two‐step reaction

In this study, a proton‐exchange membrane for fuel cells was prepared via a two‐step reaction with an allyl methacrylate (AMA) as an asymmetric crosslinking agent. First, a linear‐chain polymer was synthesized, consisting of hydrophilic 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS), hydrophobic 2,2,2‐trifluoroethyl methacrylate (TFEMA), and AMA. Subsequently, we crosslinked the linear‐chain polymer by reacting the remaining allyl group during dry heating. The proton conductivity of the prepared membrane was 7 × 10^?2 S/cm at room temperature. The membrane was characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and atomic force microscopy. The polymer electrolyte membrane fuel cell (PEMFC) performance was evaluated for a membrane electrode assembly composed of the crosslinked AMPS–TFEMA–AMA/ fluoroalkyl graft polymer (FGP) membrane. As a result of a power‐generation test, a maximum power density of 174 mW/cm² at a current density of 400 mA/cm² was observed for a PEMFC single cell. Consequently, it was confirmed that the AMPS–TFEMA–AMA/FGP membrane for PEMFC could easily be prepared via a two‐step reaction at a low cost and that PEMFC exhibited a cell performance and that of cells with the Nafion membrane. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrochemical treatment of water containing chlorides under non-ideal flow conditions with BDD anodes

In this work a undivided parallel plate cell equipped with boron doped diamond (BDD) anode was tested as electrochemical reactor for disinfection of water. Two configurations were adopted: a single pass configuration (SPC) and a recirculated configuration (RC) in which also a reservoir was inserted in the hydraulic circuit. In both the experimental configurations the system worked in continuous mode with a flow rate ranging from 0.05 to 0.42 dm³ min⁻¹; in the RC the recirculating flow rate ranged from 0.45 to 6 dm³ min⁻¹. Thermostated (25 °C) galvanostatic electrolyses were carried out with aqueous solutions containing 100 mg dm⁻³ of chloride ions: values of current density from 2.5 to 5.0 mA cm⁻² were used. Steady state data revealed that active chlorine and chlorate ions were the main oxidation products. Particular attention was paid to the hydrodynamics both for SPC and RC: pulse-response curves were experimentally obtained with an inert tracer, and the behaviour of the system was interpreted by models based on a combination of ideal flow reactors, bypass flow elements, and dead zones. The hydrodynamic models were utilized to predict the outlet concentration of the electrolysis products. A good agreement between model predicted and experimental data was obtained for a wide range of experimental conditions. Preliminary disinfection tests were then performed using Escherichia coli as model microorganism. Results were discussed in terms of both disinfection efficiency and by-products formation.     

Increased generation of electricity in a microbial fuel cell using <Emphasis Type="Italic">Geobacter sulfurreducens</Emphasis>

The microbial fuel cell (MFC) has attracted research attention as a biotechnology capable of converting hydrocarbon into electricity production by using metal reducing bacteria as a biocatalyst. Electricity generation using a microbial fuel cell (MFC) was investigated with acetate as the fuel and Geobacter sulfurreducens as the biocatalyst on the anode electrode. Stable current production of 0.20–0.24 mA was obtained at 30–32 °C. The maximum power density of 418–470 mW/m², obtained at an external resistor of 1,000 Ω, was increased over 2-fold (from 418 to 866 mW/m²) as the Pt loading on the cathode electrode was increased from 0.5 to 3.0 mg Pt/cm². The optimal batch mode temperature was between 30 and 32 °C with a maximum power density of 418–470 mW/m². The optimal temperature and Pt loading for MFC were determined in this study. Our results demonstrate that the cathode reaction related through the Pt loading on the cathode electrode is a bottleneck for the MFC’s performance.     

Micro-tubular solid oxide fuel cells fabricated from hollow fibres

Recent literature is reviewed on a phase inversion process followed by sintering, used to fabricate ceramic hollow fibres (HFs) as precursors to micro-tubular solid oxide fuel cells (MT-SOFCs) with sub-millimetre inner diameters. These aimed to address the outstanding technological and economic issues that have delayed mass production of SOFCs, by increasing electrode surface areas per unit volume relative to planar structures, increasing power outputs per unit volume/mass, facilitating sealing at high temperatures, and decreasing fabrication costs per kW. Some recent experimental results are presented of the effects of temperature, hydrogen flow rate, thermal cycling and time of NiO reduction with H₂ on the subsequent performance of 25 mm long H₂|Ni–CGO|CGO|LSCF|air MT-SOFCs, incorporating cerium–gadolinium oxide (CGO) electrolyte, nickel anodes and lanthanum strontium cobalt ferrite–CGO (LSCF–CGO) cermet cathodes, designed to operate at 500–600 °C. Maximum power densities of 3–5.5 kW m⁻² were achieved as the temperature was increased from 550–600 °C. The co-extruded MT-SOFCs were resilient to three thermal cycles when heated to operating temperature in ca. 5 min. Their performance was intimately related to the reduction time, suggesting slow conversion of the NiO to Ni within the fabricated anodes. At constant cell voltage, mass transport limited current densities increased from ca. 11 to ca. 13.5 kA m⁻² as hydrogen flow rates were increased from 15 to 60 cm³ min⁻¹, though had residual NiO in the anode been fully reduced, current densities would have been significantly greater.