Performance studies of Pd–Pt and Pt–Pd–Au catalyst for electro-oxidation of glucose in direct glucose fuel cell

Platinum is employed as anode catalyst for low temperature electro-oxidation of glucose in direct glucose fuel cell (DGFC), but it suffers from poisoning by intermediate oxidation products. In the present investigation, palladium and gold precursors are added with platinum precursor to form low metal loading (∼15–20% by wt.) carbon supported catalyst by NaBH₄ reduction technique. The prepared PtPdAu/C (metal ratio 1:1:1) and PdPt/C (metal ratio 4:1) catalysts are tested in DGFC. The Physical characterization of electro-catalysts by scanning electron microscope, transmission electron microscope, energy dispersive X-ray, X-ray diffraction and thermo-gravimetric analysis confirms the formation of nano-sized metal particles on carbon substrate with two prominent homogeneous bi- or tri-metallic crystal phases for PtPdAu/C. The cyclic voltammetry studies carried out for glucose (0.05 M) oxidation in (0.5 M KOH) alkaline medium shows the metal catalysts can efficiently electro-oxidize glucose. The catalysts tested as anode in a batch type DGFC using commercial activated charcoal as cathode produced peak power density of 0.52 mW cm⁻² for both PdPt/C and PtPdAu/C in 0.3 M glucose in 1 M KOH solution.     

High platinum utilization in ultra-low Pt loaded PEM fuel cell cathodes prepared by electrospraying

Cathode electrodes for proton exchange membrane fuel cells (PEMFCs) with ultra-low platinum loadings as low as 0.012 mg_Ptcm⁻² have been prepared by the electrospray method. The electrosprayed layers have nanostructured fractal morphologies with dendrites formed by clusters (about 100 nm diameter) of a few single catalyst particles rendering a large exposure surface of the catalyst. Optimization of the control parameters affecting this morphology has allowed us to overcome the state of the art for efficient electrodes prepared by electrospraying. Thus, using these cathodes in membrane electrode assemblies (MEAs), a high platinum utilization in the range 8–10 kW g⁻¹ was obtained for the fuel cell operating at 40 °C and atmospheric pressure. Moreover, a platinum utilization of 20 kW g⁻¹ was attained under more suitable operating conditions (70 °C and 3.4 bar over-pressure). These results substantially improve the performances achieved previously with other low platinum loading electrodes prepared by electrospraying.     

Performance enhancement of polymer electrolyte membrane fuel cell by PtCo3 nanoporous film as high mass-specific power density catalyst using laser deposition and processing

This study demonstrates the performance of polymer electrolyte membrane fuel cell (PEMFC) can be significantly enhanced with laser deposited and processed PtCo₃ nanoporous film as the catalyst layer. The PtCo₃ nanoporous film is fabricated by first depositing a thin film of stacked PtCo₃ nanoparticles on gas diffusion layer using pulsed laser deposition and then subjecting the film to scanning continuous-wave laser processing. The heating by the scanning laser beam increases electrochemical surface area substantially, which could be ascribed to formation of Pt skin on each nanoparticle via Pt surface segregation. Furthermore, the durability of the catalyst under accelerated degradation test is greatly enhanced, which may be attributed to inhibition of Co leaching by the Pt skin and strengthening of the contacts between nanoparticles caused by concomitant sintering effect. Application of such catalyst to the cathode of a PEMFC exhibits a 2.4-fold increase in current density with respect to that without laser processing, raising the cathode mass-specific power density to 8.79 kW g⁻¹ with 1 atm oxygen and 12.0 kW g⁻¹ with 1.5 atm oxygen.     

Investigation of tungsten carbide supported Pd or Pt as anode catalysts for PEM fuel cells

In this contribution, we present results of electrochemical characterization of prepared tungsten carbide supported palladium and platinum and Vulcan XC-72 supported palladium. These catalysts were employed as anode catalysts in PEMFC and results are compared to commercial platinum catalyst. Platinum seems to be irreplaceable as a proton exchange membrane fuel cell (PEMFC) catalyst for both the anode and the cathode, yet the high price and limited natural resources are holding back the commercialization of the PEMFCs. Tungsten carbide is recognized as promising catalyst support having the best conductivity among interstitial carbides. Higher natural resources and significantly lower price make palladium good candidate for replacement of the platinum catalyst. The presented results show that all prepared catalysts are very active for the hydrogen oxidation reaction. Linear sweep voltammetry curves of Pd/C and Pd/WC show existence of peaks at 0.07 V vs. RHE, which is assigned to absorbed hydrogen. H₂|Pd/WC|Nafion117|Pt/C|O₂ fuel cell has almost the same efficiency and similar power output as commercial platinum catalyst.     

Performance optimization of ultra-low platinum loading membrane electrode assembly prepared by electrostatic spraying

To improve the utilization of platinum and reduce the manufacturing cost of proton exchange membrane fuel cell (PEMFC), the electrostatic spraying was used to prepare the cathode catalyst layer of membrane electrode assembly (MEA) with platinum loading varying from 0.1 to 0.01 mg cm^?2. The performance of fuel cell was tested and analyzed by electrochemical impedance and polarization curve. Our results show that the platinum carbon (Pt/C) particles deposited by electrostatic spraying were well dispersed and the microporous structure of catalyst layer (CL) were relatively uniform. Replacing the CCS type MEA (catalyst coated on gas diffusion layer substrate) with the CCM type MEA (catalyst coated on proton exchange membrane) can reduce its electrochemical impedance and improve the power density of fuel cell. Compared to the Pt/C catalyst with a platinum mass fraction of 60%, a lower platinum-carbon ratio catalyst is more conducive to the uniform dispersion of catalyst particles and efficient utilization of platinum in the preparation of MEA with ultra-low platinum loading. However, their difference in peak power density decreases with the increase of platinum loading. Besides, increasing the back pressure can improve the performance of fuel cell, when the back pressure increased to 0.15 Mpa and the feeding gases were set as H₂/O₂, the peak power density of 0.56 W cm^?2 was obtained by the MEA with cathode platinum loading of 0.01 mg cm^?2, which is corresponding to the cathode platinum utilization of 56 kW·g_Pt^?1_cathode.     

Development of gas diffusion electrodes for low relative humidity proton exchange membrane fuel cells

A series of polyaniline nanofibers (PANFs) were synthesized and incorporated into gas diffusion electrodes (GDE) of proton exchange membrane fuel cells (PEMFC) to improve their performances at low relative humidity (RH) conditions. Three different placements to incorporate the PANFs in the anodes include (1) placing a PANFs layer between catalyst layer (CL) and membrane, (2) coating the CL with PANFs and catalyst mixed slurry, and (3) placing a PANFs layer between the CL and gas diffusion layer (GDL). Fuel cell performance data indicates that the last method is superior to the others and is adopted as incorporation method thereafter. Extensive studies on single cell performances have been conducted to compare the membrane electrode assemblies with and without the incorporation of PANFs in both anode and cathode. Polarization curves show the incorporation of H₂SO₄-doped PANFs is highly effective in improving the hydrophilic characteristic of the electrodes and thus can promote the PEMFC performance at low RH conditions. For example, with a lowering of reactant RH from 100 to 70%, the electrode with H₂SO₄-doped PANFs layer exhibits an increase in power density from 0.57 to 0.7 W cm⁻². On the other hand, a traditional carbon-supported platinum electrode exhibits a decline of performance from 0.73 to 0.55 W cm⁻².     

Durability studies on performance degradation of Pt/C catalysts of proton exchange membrane fuel cell

In the present paper, a proton exchange membrane fuel cell (PEMFC) using 20 wt.% Pt/C as anode and cathode catalysts, and ambient air at cathode was operated at a current density of 160 mA cm⁻² for 2250 h. The measurement results showed that electrochemically active specific areas (S_EAS) of both electrode catalysts calculated from CV curves after test evidently decreased. The decay rate of S_EAS of anode catalyst was much lower than that of cathode one. X-ray diffraction (XRD), energy dispersive analysis of X-ray (EDAX), and X-ray photoelectron spectrometry (XPS) were employed to characterize the anode and cathode catalysts before and after the life test. The XRD results showed that their crystal structures were perfect, the particle size of new Pt/C catalyst was about 2.5 nm, however, the particle sizes of anode and cathode ones markedly increased, and were about 4.9 nm and 6.8 nm, respectively, after the life test. Furthermore, the size of cathode catalyst was much bigger than that of anode one after test. The Pt element was also found in Nafion^® film as shown in EDAX result. The XPS results presented that the content of Pt oxidation states in cathode was much more than that in anode, and the corrosion of carbon support in cathode was also more severe than that in anode after the life test. The experimental results indicated that the increase of particle size of Pt/C catalyst was illustrated with the dissolution/redeposition mechanism. The degradation of cathode catalyst for oxygen electroreduction was one of the main factors affecting on the performance decay of PEMFC.     

Characterization and single cell testing of Pt/C electrodes prepared by electrodeposition

Electrodes for proton exchange membrane fuel cells (PEMFC) have been prepared by the electrodeposition method. For this task, the electrodeposition of platinum is carried out on a carbon black substrate impregnated with an ionomer, proton conducting, medium. Before electrodeposition, the substrate is submitted to an activation process to increase the hydrophilic character of the surface to a few microns depth.Electrodeposition of platinum takes place inside the generated surface hydrophilic layer, resulting in a continuous phase covering totally or partially carbon substrate grains. Cross sectional images show a decay profile of platinum towards the interior of the substrate, reflecting a deposition process limited by diffusion of PtCl₆²⁻ through the porous substrate. Electrodes with different platinum loads have been prepared, and membrane electrode assemblies (MEA) have been mounted with the electrodeposited electrodes as cathode and other standard components (commercial anode and Nafion^R 117 membrane). The electrochemically active surface area determined from hydrogen underpotential deposition charge, is lower on the electrodeposited electrodes than on standard electrodes. However, single cell testing shows higher mass specific activity on electrodeposited cathodes with low and intermediate Pt load (below 0.05 mg Pt cm⁻²).     

Performance of membrane electrode assemblies using PdPt alloy as anode catalysts in polymer electrolyte membrane fuel cell

Pd-based nanoparticles, such as 40 wt.% carbon-supported Pd₅₀Pt₅₀, Pd₇₅Pt₂₅, Pd₉₀Pt₁₀ and Pd₉₅Pt₅, for anode electrocatalyst on polymer electrolyte membrane fuel cells (PEMFCs) were synthesized by the borohydride reduction method. PdPt metal particles with a narrow size distribution were dispersed uniformly on a carbon support. The membrane electrode assembly (MEA) with Pd₉₅Pt₅/C as the anode catalyst exhibited comparable single-cell performance to that of commercial Pt/C at 0.7 V. Although the Pt loading of the anode with Pd₉₅Pt₅/C was as low as 0.02 mg cm⁻², the specific power (power to mass of Pt in the MEA) of Pd₉₅Pt₅/C was higher than that of Pt/C at 0.7 V. Furthermore, the single-cell performance with Pd₅₀Pt₅₀/C and Pd₇₅Pt₂₅/C as the anode catalyst at 0.4 V was approximately 95% that of the MEA with the Pt/C catalyst. This indicated that a Pd-based catalyst that has an extremely small amount of Pt (only 5 or 50 at.%) can be replaced as an anode electrocatalyst in PEMFC.     

Ionomer content in the catalyst layer of polymer electrolyte membrane fuel cell (PEMFC): Effects on diffusion and performance

The percolating paths of the carbons and electrolytes in a cathode catalyst layer (CCL) could be successfully visualized in three-dimensions in order to investigate both the electronic and ionic connectivity by modeling a three-dimensional (3-D), meso-scale CCL of a polymer electrolyte membrane fuel cell (PEMFC). The effective Knudsen diffusion coefficients could also be obtained by computing pore tortuosity values. Electrochemical simulation studies were carried out by feeding air at 70 °C. Low platinum (Pt) loading (0.1 mg cm⁻²) catalysts with ionomer contents ranging from 14 to 50% were studied. The performance of a PEMFC electrode was affected by the ionomer content which is optimal at about 33%. In this case, both electronic and ionic connectivity produced the broadest active surface area of the Pt catalyst. The polarization drop tendency was in good agreement with the experiment, and this percolation study could successfully explain the existence of an optimum amount of ionomer.     

Optimization of ionomer-free ultra-low loading Pt catalyst for anode/cathode of PEMFC via magnetron sputtering

In this study, thin-film Pt catalysts with ultra-low metal loadings (ranging from 1 to 200 μg cm⁻²) were prepared by magnetron sputtering onto various carbon-based substrates. Performance of these catalysts acting as anode, cathode, or both electrodes in a proton exchange membrane fuel cell (PEMFC) was investigated in H₂/O₂ and H₂/air mode. As base substrates we used standard microporous layers comprising carbon nanoparticles with polytetrafluoroethylene (PTFE) or fluorinated ethylene propylene (FEP) supported on a gas diffusion layer. Some substrates were further modified by magnetron sputtering of carbon in N₂ atmosphere (leading to CN_x) followed by simultaneous plasma etching and cerium oxide deposition. The CN_x structure exhibits higher resistance to electrochemical etching as compared to pure carbon as was determined by mass spectrometry analysis of PEMFC exhaust at different cell potentials for both sides of PEMFC. The role of platinum content and membrane thickness was investigated with the above four different combinations of ionomer-free carbon-based substrates. The results were compared with a series of benchmark electrodes made from commercially available state-of-the-art Pt/C catalysts. It was demonstrated that the platinum utilization in PEMFC with magnetron sputtered thin-film Pt electrodes can be up to 2 orders of magnitude higher than with the standard Pt/C catalysts while keeping the similar power efficiency and long-term stability.     

High performance membrane electrode assembly with ultra-low platinum loading prepared by a novel multi catalyst layer technique

An ultra-low platinum loading membrane electrode assembly (MEA) with a novel double catalyst layer (DCL) structure was prepared by using two layers of platinum catalysts with different loadings. The inner layer consisted of a high loading platinum catalyst and high Nafion content for keeping good platinum utilization efficiency and the outer layer contained a low loading platinum catalyst with low Nafion content for obtaining a proper thickness thereby enhancing mass transfer in the catalyst layers. Polarization characteristics of MEAs with novel DCL, conventional DCL and single catalyst layer (SCL) were evaluated in a H₂–air single cell system. The results show that the performance of the novel DCL MEA is improved substantially, particularly at high current densities. Although the platinum loadings of the anode and cathode are as low as 0.04 and 0.12 mg cm⁻² respectively, the current density of the novel DCL MEA still reached 0.73 A cm⁻² at a working voltage of 0.65 V, comparable to that of the SCL MEA. In addition, the maximum power density of the novel DCL MEA reached 0.66 W cm⁻² at 1.3 A cm⁻² and 0.51 V, 11.9% higher than that of the SCL MEA, indicative of improved mass transfer for the novel MEA. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) tests revealed that the novel DCL MEA possesses an efficient electrochemical active layer and good platinum utilization efficiency.     

Effects of Pt/C, Pd/C and PdPt/C anode catalysts on the performance and stability of air breathing direct formic acid fuel cells

Pt/C, Pd/C and PdPt/C catalysts are potential anodic candidates for electro-oxidation of formic acid. In this work we designed a miniature air breathing direct formic acid fuel cell, in which gold plated printed circuit boards are used as end plates and current collectors, and evaluated the effects of anode catalysts on open circuit voltage, power density and long-term discharging stability of the cell. It was found that the cell performance was strongly anode catalyst dependent. Pd/C demonstrated good catalytic activity but poor stability. A maximum power density of 25.1 mW cm⁻² was achieved when 5.0 M HCOOH was fed as electrolyte. Pt/C and PdPt/C showed poor activity but good stability, and the cell can discharge for about 10 h at 0.45 V (Pt/C anode) and 15 h at 0.3 V (PdPt/C) at 20 mA.     

Performance of a direct methanol alkaline membrane fuel cell

A study of a direct methanol fuel cell (DMFC) operating with hydroxide ion conducting membranes is reported. Evaluation of the fuel cell was performed using membrane electrode assemblies incorporating carbon-supported platinum/ruthenium anode and platinum cathode catalysts and ADP alkaline membranes. Catalyst loadings used were 1 mg cm⁻² Pt for both anode and cathode. The effect of temperature, oxidant (air or oxygen) and methanol concentration on cell performance is reported. The cell achieved a power density of 16 mW cm⁻², at 60 °C using oxygen. The performance under near ambient conditions with air gave a peak power density of approximately 6 mW cm⁻².     

Development of a carbon paper-supported Pd catalyst for PEMFC application

An oxygen diffusion cathode for a PEMFC has been prepared by directly depositing the catalyst (pure Pd) on a carbon paper support containing 5% of PTFE through an electroless deposition method. A very low-Pd loading of 0.04 mg_Pd cm⁻² and a higher one, containing 0.22 mg_Pd cm⁻², were obtained. Two different experimental approaches were used to evaluate their catalytic activity towards the oxygen reduction reaction. The overall results revealed that the prepared catalysts exhibit a high catalytic activity, but a low efficiency on the catalyst utilization.     

The effect of electrode parameters on the performance of anion exchange polymer membrane fuel cells

An investigation of several electrode parameters on performance of an alkaline membrane fuel cell is described. The studied parameters were: ionomer content, anode and cathode catalyst layer thickness, electrode aminating agent and membrane thickness.It was found that an optimum ionomer content depended on a balance between the OH⁻ ion/water mobility and the oxygen solubility/diffusivity through it and which varied with temperature. Thick catalyst layers were necessary for the anode as thin anode catalyst layers suffered from flooding. 40%Pt/C provided the best thickness (with loading of 0.4 mg_Pt cm⁻²) for cathodes operating with air.An aminated low density poly(ethylene-co-vinyl benzyl chloride) (LDPE-VBC) membrane was shown to be a good membrane for an alkaline membrane fuel cell, giving conductivities up to 0.13 S cm⁻¹ at 80 °C. A Membrane Electrode Assembly (MEA) utilizing this membrane with fully hydrated thickness of 57 μm produced good peak power density, at a high potential of 500 mV, of 337 mW cm⁻² with air (1 bar gauge) at 60 °C.     

High activity of Au-Cu/C electrocatalyst as anodic catalyst for direct borohydride-hydrogen peroxide fuel cell

Carbon supported Au-Cu bimetallic nanoparticles are prepared by a modified NaBH₄ reduction method in aqueous solution at room temperature. The electrocatalytic activities of the Au-Cu/C catalysts are investigated by cyclic voltammetry, chronoamperometry, chronopotentiometry and fuel cell experiments. It has been found that the Au-Cu/C catalysts have much higher catalytic activity for the direct oxidation of BH₄⁻ than Au/C catalyst. Especially, the Au₆₇Cu₃₃/C catalyst presents the highest catalytic activity for BH₄⁻ electrooxidation among all as-prepared catalysts, and the DBHFC using Au₆₇Cu₃₃/C anode catalyst and Au/C cathode catalyst shows the maximum power density of 51.8 mW cm⁻² at 69.5 mA cm⁻² and 20 °C.     

Effects of Pt loading in the anode on the durability of a membrane–electrode assembly for polymer electrolyte membrane fuel cells during startup/shutdown cycling

A polymer electrolyte membrane fuel cell (PEMFC) stack of a fuel cell vehicle (FCV) is inevitably exposed to reverse current conditions, which are formed by the oxygen reduction reaction (ORR) induced at the anode with a hydrogen/air boundary during startup/shutdown processes. With an increase in the reverse current, the degradation rate of the cathode that experiences a highly corrosive condition (locally high potential) increases. In this work, the anode Pt loading is decreased from 0.4 to 0.1 mg cm⁻² to decrease the reverse current. The decrease in the anode Pt loading is found to decrease the hydrogen oxidation rates (HOR) during normal operation, but this loading decrease barely affected the cell performance. However, a decrease in the anode Pt loading can significantly decrease the reverse current, leading to a diminished cathode degradation rate during startup/shutdown cycling. It is revealed by slow decreases in the cell performance (i–V curves) and electrochemical active surface area (EAS), and a slow increase in the charge-transfer resistance (R_ct), which can be attributed to corrosion of the carbon support and dissolution/migration/agglomeration of the platinum catalyst.     

Platinum decorated aligned carbon nanotubes: Electrocatalyst for improved performance of proton exchange membrane fuel cells

This study aims to improve the performance of proton exchange membrane fuel cells (PEMFCs) using carbon nanotubes as scaffolds to support nanocatalyst for power generation over prolonged time periods, compared to the current designs. The carbon nanotubes are prepared using chemical vapor deposition and decorated by platinum nanoparticles (Pt-NPs) using an amphiphilic approach. The PEMFC devices are then constructed using these aligned carbon nanotubes (ACNTs) decorated with Pt-NPs as the cathode. The electrochemical analyses of the PEMFC devices indicate the maximum power density reaches to 860 mW cm⁻² and current density reaches 3200 mA cm⁻² at 0.2 V, respectively, when O₂ is introduced into cathode. Importantly, the Pt usage was decreased to less than 0.2 mg cm⁻², determined by X-ray energy dispersive spectroscopy and X-ray photoelectron spectroscopy as complimentary tools. Electron microscopic analyses are employed to understand the morphology of Pt-ACNT catalyst (with diameter of 4-15 nm and length from 8 to 20 μm), which affects PEMFC performance and durability. The Pt-ACNT arrays exhibit unique alignment, which allows for rapid gas diffusion and chemisorption on the catalyst surfaces.     

The effects of ionomer content on PEM water electrolyser membrane electrode assembly performance

In this study, the effects of Nafion^® ionomer content in membrane electrode assemblies (MEAs) of polymer electrolyte membrane (PEM) water electrolyser were discussed. The MEAs were prepared with a catalyst coated membrane (CCM) method. The catalysts inks with Nafion ionomer could form uniform coatings deposited on the membrane surfaces. SEM and area EDX mapping demonstrated that anode catalyst coating was uniformly distributed, with a microporous structure. The contents of Nafion ionomer were optimized to 25% for the anode and 20% for cathode. A current density of 1 A cm⁻² was achieved at terminal voltage 1.586 V at 80 °C in a PEMWE single cell, with Nafion 117, Pt/C as cathode, and Ru_0.7Ir_0.3O₂ as anode.