Performance characterization of direct formic acid fuel cell using porous carbon-supported palladium anode catalysts

Palladium particles supported on porous carbon of 20 and 50 nm pore diameters were prepared and applied to the direct formic acid fuel cell (DFAFC). Four different anode catalysts with Pd loading of 30 and 50 wt% were synthesized by using impregnation method and the cell performance was investigated with changing experimental variables such as anode catalyst loading, formic acid concentration, operating temperature and oxidation gas. The BET surface areas of 20 nm, 30 wt% and 20 nm, 50 wt% Pd/porous carbon anode catalysts were 135 and 90 m²/g, respectively. The electro-oxidation of formic acid was examined in terms of cell power density. Based on the same amount of palladium loading with 1.2 or 2 mg/cm², the porous carbon-supported palladium catalysts showed higher cell performance than unsupported palladium catalysts. The 20 nm, 50 wt% Pd/porous carbon anode catalyst generated the highest maximum power density of 75.8 mW/cm² at 25 °C. Also, the Pd/porous carbon anode catalyst showed less deactivation at the high formic acid concentrations. When the formic acid concentration was increased from 3 to 9 M, the maximum power density was decreased from 75.8 to 40.7 mW/cm² at 25 °C. Due to the high activity of Pd/porous carbon catalyst, the cell operating temperature has less effect on DFAFC performance.     

Effect of temperature, oxidant and catalyst loading on the performance of direct formic acid fuel cell

We investigated the effect of temperature, oxidant and catalyst loading on the performance of direct formic acid fuel cell (DFAFC). When oxidant was changed from air to oxygen, the power density was increased to 17.3 mW/ cm² at 25 ‡C. The power density of DFAFC operated with oxygen showed a maximum value of 40.04 mW/cm² with the temperature rise from room temperature to 70 °C. The highest power density of DFAFC using air was observed for Pt-Ru black catalyst with loading of 8 mgPt/cm² at room temperature. At 70 ‡C; however, the performance of catalyst with the loading of 4 mgPt/cm² was higher than that of 8 mgPt/cm². The DFAFC, operated with oxygen and catalyst of 4 mgPt/cm² loading, showed the best performance at all temperature range. The enhancement of cell performance with an increase of catalyst loading is believed to come from an increase of catalyst active sites. However, operated at higher temperature or with oxygen, the cell with higher catalyst loading showed lower performance than expected. It is speculated that the thick catalyst layer inhibits the proton transport.     

Preparation of Pt-Pd catalysts for direct formic acid fuel cell and their characteristics

Pt-Pd catalysts were prepared by using the spontaneous deposition method and their characteristics were analyzed in a direct formic acid fuel cell (DFAFC). Effects of calcination temperature and atmosphere on the cell performance were investigated. The calcination temperatures were 300, 400 and 500 °C and the calcination atmospheres were air and nitrogen. The fuel cell with the catalyst calcined at 400 °C showed the best cell performance of 58.8 mW/cm². The effect of calcination atmosphere on the overall performance of fuel cell was negligible. The fuel cell with catalyst calcined at air atmosphere showed high open circuit potential (OCP) of 0.812 V. Also the effects of anode and cathode catalyst loadings on the DFAFC performance using Pt-Pd (1: 1) catalyst were investigated to optimize the catalyst loading. The catalyst loading had a significant effect on the fuel cell performance. Especially, the fuel cell with anode catalyst loading of 4 mg/cm² and cathode catalyst loading of 5 mg/cm² showed the best power density of 64.7 mW/cm² at current density of 200 mA/cm². This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Evaluation of direct formic acid fuel cells with catalyst layers coated by electrospray

We investigated cell performance and performed phenomenological analyses of direct formic acid fuel cells (DFAFCs) incorporating anode (palladium) and cathode (platinum) catalysts prepared using a new electrospray coating technique. To optimize the design of the DFAFC, we examined the cell performance by the Pd catalyst loading and formic acid feed rate. Of Pd catalyst loaded samples, 3 mg/cm² sample showed the highest electrical performance with formic acid feed rate of 5 ml/min. This behavior was caused by discrepancies in the mass transfer limitation. When the feed rate was greater than 10 mL/min, however, the 7 mg/cm² sample provided the highest electrical performance, which was attributed to enhanced electrooxidation reactions. For comparison of the effect of the catalyst coating method on the cell performance of DFAFC, polarization curves of the DFAFC incorporating catalysts prepared using a conventional airspray coating method were also measured. As a result of the comparison, the electrospray coatingused DFAFC showed better cell performance. Based on these results, the cell performance of the DFAFCs was optimized when the catalysts using the electrospray catalyst coating were employed, the amount of Pd loaded on the anode electrode was 3 mg/cm² (Pd thickness: ∼6 μm), and the formic acid feed rate was 10 mL/min.     

Effects of iron-tetrasulfophthalocyanine on the catalytic activities of Pt/C,PtRu/C,and Pd/C catalysts in a multi-anode direct formic acid fuel cell

This paper reports a systematic study of the effects of a promoter, iron-tetrasulfophthalocyanine (FeTSPc), on the catalytic activities of carbon supported Pt, PtRu, and Pd catalysts (Pt/C, PtRu/C, and Pd/C) for formic acid oxidation. A multi-anode direct formic acid fuel cell (DFAFC) was used to compare the effects on each catalyst of adding FeTSPc to the fuel stream. The FeTSPc significantly enhanced the activity of the Pt/C catalyst, but had little effect on the PtRu/C catalyst. The activity of the Pd/C catalyst was inhibited by the FeTSPc. A FeTSPc modified Pt/C was also evaluated in a conventional 5 cm² DFAFC.     

Direct Formic Acid Fuel Cells with 600 mA cm–2 at 0.4 V and 22 °C

A demonstration of direct formic acid fuel cells (DFAFCs) generating very high power density at ambient temperature is reported. In particular, the performance of the Pd black as an anode catalyst for DFAFCs with different formic acid feed concentrations at different operating temperatures has been evaluated. The Pd black based DFAFCs with dry air and zero backpressure can generate a maximum power density of 248 and 271 mW cm^–2 at 22 °C and 30 °C respectively. The open cell potential is 0.90 V. These results show that DFAFCs are potentially excellent alternative power sources for small portable electronic devices.     

Screening of PdM and PtM catalysts in a multi-anode direct formic acid fuel cell

Direct formic acid fuel cells (DFAFC) currently employ either Pt-based or Pd-based anode catalysts for oxidation of formic acid. However, improvements are needed in either the activity of Pt-based catalysts or the stability of Pd-based catalysts. In this study, a number of carbon-supported Pt-based and Pd-based catalysts, were prepared by co-depositing PdM (M = Bi, Mo, or V) on Vulcan^® XC-72 carbon black, or depositing another metal (Pb or Sn) on a Pt/C catalyst. These catalysts were systematically evaluated and compared with commercial Pd/C, PtRu/C, and Pt/C catalysts in a multi-anode DFAFC. The PtPb/C and PtSn/C catalysts were found to show significantly higher activities than the commercial Pt/C catalyst, while the PdBi/C provided higher stability than the commercial Pd/C catalyst.     

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.     

Passive micro tubular direct formic acid fuel cells (DFAFCs) with chemically assembled Pd anode nano-catalysts on polymer electrolytes

Wet-chemical assembling process has been developed for the formation of the anode electrocatalyst layers of a micro tubular direct formic acid fuel cell. By using this method, a porous layer of Pd nano-catalyst was bonded onto the inner surface of a tubular polymer electrolyte membrane by chemical reduction of Pd complex impregnated in the membrane. The performance characteristics as a function of parameters such as catalyst loading amount of Pd or the cell temperature were evaluated by using a half-cell testing method. The micro tubular DFAFC with a 2.5 mg-Pd cm⁻² anode and 6 mg-Pt cm⁻² cathode fabricated by wholly wet-chemical assembling process exhibited a peak power density over 4 mW cm⁻² under passive and air breathing conditions at ambient temperature and pressure.     

A Fuel‐Flexible Alkaline Direct Liquid Fuel Cell

We constructed a fuel‐flexible fuel cell consisting of an alkaline anion exchange membrane, palladium anode, and platinum cathode. When an alcohol fuel was used with potassium hydroxide added to the fuel stream and oxygen was the oxidant, the following maximum power densities were achieved at 60 °C: ethanol (128 mW cm⁻²), 1‐propanol (101 mW cm⁻²), 2‐propanol (40 mW cm⁻²), ethylene glycol (117 mW cm⁻²), glycerol (78 mW cm⁻²), and propylene glycol (75 mW cm⁻²). We also observed a maximum power density of 302 mW cm⁻² when potassium formate was used as the fuel under the same conditions. However, when potassium hydroxide was removed from the fuel stream, the maximum power density with ethanol decreased to 9 mW cm⁻² (using oxygen as oxidant), while with formate it only decreased to 120 mW cm⁻² (using air as the oxidant). Variations in the performance of each fuel are discussed. This fuel‐flexible fuel cell configuration is promising for a number of alcohol fuels. It is especially promising with potassium formate, since it does not require hydroxide added to the fuel stream for efficient operation.     

Tungsten and nickel tungsten carbides as anode electrocatalysts

Tungsten and nickel tungsten carbides were evaluated as the anode catalysts of a polymer electrolyte fuel cell (PEFC). These catalysts were prepared by the temperature-programmed carburization of tungsten and nickel tungsten oxides from 573 to 873-1073 K in a stream of 20% CH₄/H₂ and kept at temperature for 3 h. The 30% tungsten and nickel tungsten carbides mixed with Ketjen carbon (KC) were evaluated by cyclic voltammetry and linear sweep voltammetry using a rotating disk electrode and electrocatalytic activity (I-V performance) using a single cell. The W1023/KC catalyst achieved a power density of 6.4 mW/cm² (current density: 15.2 mA/cm²) which corresponded to 5.7% of that achieved by a commercial 20% Pt/C catalyst in a single cell (20% Pt/C: 111.7 mW/cm²) using our setup. From the XRD data, α-W₂C together with a small amount of WC was active during the anodic oxidation. The maximum power density of the 30 wt% 873 K-carburized NiW/KC was 8.2 mW/cm² at the current density of 19.0 mA/cm² which was 7.3% of the 20 wt% Pt/C.     

A Study on Process Parameters of Direct Ethanol Fuel Cell

Ethanol is one of the promising future fuels of Direct Alcohol Fuel Cells (DAFC). The electro‐oxidation of ethanol fuel on anode made of carbon‐supported Pt‐Ru electrode catalysts was carried out in a lab scale direct ethanol fuel cell (DEFC). Cathode used was Pt‐black high surface area. The membrane electrode assembly (MEA) was prepared by sandwiching the solid polymer electrolyte membrane, prepared from Nafion^® (SE‐5112, DuPont USA) dispersion, between the anode and cathode. The DEFC was fabricated using the MEA and tested at different catalyst loadings at the electrodes, temperatures and ethanol concentrations. The maximum power density of DEFC for optimized value of ethanol concentration, catalyst loading and temperature were determined. The maximum open circuit voltage (OCV) of 0.815 V, short circuit current density (SCCD) of 27.90 mA/cm² and power density of 10.30 mW/cm² were obtained for anode (Pt‐Ru/C) and cathode (Pt‐black) loading of 1 mg/cm² at a temperature of 90°C anode and 60°C cathode for 2M ethanol.     

Palladium-based electrodes: A way to reduce platinum content in polymer electrolyte membrane fuel cells

To decrease the Pt content, a polymer electrolyte membrane fuel cell (PEMFC) was formed using a carbon supported Pd₉₆Pt₄ catalyst as the anode material, and a carbon supported Pd₄₉Pt₄₇Co₄ catalyst as the cathode material. The as-obtained Pd-based PEMFC with an overall Pd:Pt:Co atomic composition of electrodes (anode + cathode) = 72:26:2 exhibited a performance not too far from that of the fuel cell with the conventional 100% Pt electrodes. With a Pt content of 35 wt% of that of the cell with full Pt electrodes, at a current density of 1 A cm⁻² the performance loss of the cell with the Pd-based catalysts was only 11%, with 6% ascribed to the anode catalyst and 5% to the cathode catalyst. The maximum power density of the Pd-based cell was 76% of that of the cell with Pt catalysts.     

Highly effective anode structure in a direct formic acid fuel cell

We report the mass transport characteristics of formic acid and performance enhancement in a direct formic acid fuel cell in terms of the property of anode components. The effect of hydrophobicity of anode diffusion media as well as catalyst layer was investigated applying different cell temperature and fuel concentration. The operation over 80 °C and concentrated formic acid is of great advantage to the enhancement of catalytic activity and better water management. On the other hand, the conductivity of formic acid decreases by means of the formation of more complex chains of formic acid and the fuel cell resistance increases by membrane dehydration effect due to the hygroscopic property of formic acid, resulting in overall decrease of cell performance and long-term stability. Optimizing operating conditions, the use of 60% PtRu/C with only 1 mg/cm² on plain carbon paper can be one of the good choice to achieve both sustainable power performance and higher utilization of anode catalysts keeping cell resistance.     

Performance of the Direct Methanol Carbonate Fuel Cell Using Anion Exchange Materials and Non‐Noble Metal Cathode Catalyst

A direct methanol fuel cell using a mixture of O₂ and CO₂ at the cathode was evaluated using anion exchange materials and cathode catalysts of Pt and a non‐Pt catalyst. The MEA based on non‐noble metal catalyst Acta 4020 showed superior performance than Pt/C based MEA in terms of open circuit potential and power density in carbonate environment. The fuel cell performance was improved by applying anion exchange ionomer in the catalyst layer. A maximum power density of 4.5 mW cm^–2 was achieved at 50 °C using 6.0 M methanol and 2.0 M K₂CO₃.     

Enhancement of CO Tolerance on Electrodeposited Pt Anode for Micro‐PEM Fuel Cells

Electrodeposited and sprayed Pt anode catalysts were electrochemically characterised by CO stripping voltammetry as well as their activity to CO tolerance in micro‐PEMFCs was demonstrated using polarisation measurements. While the onset and peak potentials of CO oxidation on the sprayed Pt/C varied with the CO coverage, these were lower (∼50 mV) with the electrodeposited Pt anode. This difference is attributed to the varying properties of the Pt–OH on either rough or smooth surface mainly created from different sizes of Pt particles. In fuel cell performance test, the electrodeposited Pt anode showed maximum power density of 360 mW cm^–2 and it was markedly (∼110 mW cm^–2) higher than the sprayed Pt/C anode. The enhanced activity of the electrodeposited Pt anode is also reflected by the fact that the entire amount of adsorbed CO becomes almost desorbed during the first three polarisation scans, while with the Pt/C anode at least five cycles are required.     

Pore‐forming technology and performance of MEA for direct methanol fuel cells

BACKGROUND: The commercialization of DMFCs is seriously restricted by its relatively low power density. Lots of work has been concentrated on catalysts with high activity, the optimization of flow path design, development of new kinds of proton exchange membrane and modification of Nafion membrane. Meanwhile, very few reports have involved the structure optimization of the membrane electrode assembly (MEA). To improve the performance of direct methanol fuel cells (DMFCs), the catalyst layer (CL) structures of anode and cathode were optimized by utilizing ammonium carbonate as pore forming agent. RESULTS: The polarization curves showed that in catalyst slurry the optimal content of ammonium carbonate was 50 wt%, and the DMFC performance was enhanced from 75.65 mW cm^?2 to 167.42 mW cm^?2 at 55 °C and 0.2 MPa O₂. Electrochemical impedance spectroscopy and electrochemical active surface area (EASA) testing revealed that the improved performance of optimized MEAs could be mainly attributed to the increasing EASA and the enhanced mass transfer rate of CLs. But poor methanol crossover limited the performance enhancement of MEAs with porous anodes. CONCLUSION: With regard to improving cell performance, this pore‐forming technology is better applied to the cathode catalyst layer to improve its structure rather than the anode catalyst layer. © 2012 Society of Chemical Industry     

Effect of pre-calcined ceramic powders at different temperatures on Ni-YSZ anode-supported SOFC cell/stack by low pressure injection molding

Recently, powder injection molding (PIM) has been exploited in the field of solid oxide fuel cells (SOFCs), especially for fabricating anode supports. The current study employs low pressure injection molding (LPIM) to manufacture near net shape, porous, tubular NiO-yttria stabilized zirconia (YSZ) anode supports for anode-supported SOFCs. The study investigates the effects of pre-calcining temperature of the ceramic powder on the microstructure, porosity and electrochemical performance of the cells in detail. Archimedes tests reveal that the porosity of an unreduced NiO-YSZ anode with 900 °C pre-calcined powder reaches a high of 25.9%, approaching the optimal value of 26%. Meanwhile, the anode prepared under this condition possesses more porous and homogeneous microstructures. At 800 °C, with humidified hydrogen as fuel and ambient air as the oxidant, the single cell with 900 °C pre-calcined powder delivers a maximum power density of 671 mW cm⁻² while the cell with raw powder, 555 mW cm⁻², and the cell with 1000 °C pre-calcined powder, 648 mW cm⁻². A four-cell stack is assembled by connecting four single cells in series. The stack could provide a maximum output power of 4.6 W and an open circuit voltage of 3.2 V when fuelled with humidified hydrogen at 800 °C.     

ZrC–C and ZrO2–C as Novel Supports of Pd Catalysts for Formic Acid Electrooxidation

The Pd/ZrC–C and Pd/ZrO₂–C catalysts with zirconium compounds ZrC or ZrO₂ and carbon hybrids as novel supports for direct formic acid fuel cell (DFAFC) have been synthesized by microwave‐assisted polyol process. The Pd/ZrC–C and Pd/ZrO₂–C catalysts have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), energy dispersive analysis of X‐ray (EDAX), transmission electron microscopy (TEM), and electrochemical measurements. The physical characteristics present that the zirconium compounds ZrC and ZrO₂ may promote the dispersion of Pd nanoparticles. The results of electrochemical tests show that the activity and stability of Pd/ZrC–C and Pd/ZrO₂–C catalysts show higher than that of Pd/C catalyst for formic acid electrooxidation due to anti‐corrosion property of zirconium compounds ZrC, ZrO₂, and metal–support interaction between Pd nanoparticles and ZrC, ZrO₂. The Pd/ZrC–C catalyst displays the best performance among the three catalysts. The peak current density of formic acid electrooxidation on Pd/ZrC–C electrode is nearly 1.63 times of that on Pd/C. The optimal mass ratio of ZrC to XC‐72 carbon is 1:1 in Pd/ZrC–C catalyst with narrower particle size distribution and better dispersion on surface of the mixture support, which exhibits the best activity and stability for formic acid electrooxidation among all the samples.     

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.