Feasibility of ultra-low Pt loading electrodes for high temperature proton exchange membrane fuel cells based in phosphoric acid-doped membrane

Factors as the Pt/C ratio of the catalyst, the binder content of the electrode and the catalyst deposition method were studied within the scope of ultra-low Pt loading electrodes for high temperature proton exchange membrane fuel cells (HT-PEMFCs). The Pt/C ratio of the catalyst allowed to tune the thickness of the catalytic layer and so to minimize the detrimental effect of the phosphoric acid flooding. A membrane electrode assembly (MEA) with 0.05 mg_Ptcm⁻² at anode and 0.1 mg_Ptcm⁻² at cathode (0.150 mg_Ptcm⁻² in total) attained a peak power density of 346 mW cm⁻². It was proven that including a binder in the catalytic layer of ultra-low Pt loading electrodes lowers its performance. Electrospraying-based MEAs with ultra-low Pt loaded electrodes (0.1 mg_Ptcm⁻²) rendered the best (peak power density of 400 mW cm⁻²) compared to conventional methods (spraying or ultrasonic spraying) but with the penalty of a low catalyst deposition rate.     

Highly fluorinated comb-shaped copolymer as proton exchange membranes (PEMs): Fuel cell performance

The fuel cell performance (DMFC and H₂/air) of highly fluorinated comb-shaped copolymer is reported. The initial performance of membrane electrode assemblies (MEAs) fabricated from comb-shaped copolymer containing a side-chain weight fraction of 22% are compared with those derived from Nafion and sulfonated polysulfone (BPSH-35) under DMFC conditions. The low water uptake of comb copolymer enabled an increase in proton exchange site concentrations in the hydrated polymer, which is a desirable membrane property for DMFC application. The comb-shaped copolymer architecture induces phase separated morphology between the hydrophobic fluoroaromatic backbone and the polysulfonic acid side chains. The initial performance of the MEAs using BPSH-35 and Comb 22 copolymer were comparable and higher than that of the Nafion MEA at all methanol concentrations. For example, the power density of the MEA using Comb 22 copolymer at 350 mA cm⁻² and 0.5 M methanol was 145 mW cm⁻², whereas the power densities of MEAs using BPSH-35 were 136 mW cm⁻². The power density of the MEA using Comb 22 copolymer at 350 mA cm⁻² and 2.0 M methanol was 144.5 mW cm⁻², whereas the power densities of MEAs using BPSH-35 were 143 mW cm⁻².     

Study on the membrane electrode assembly fabrication with carbon supported cobalt triethylenetetramine as cathode catalyst for proton exchange membrane fuel cell

An improved fabrication technique for conventional hot-pressed membrane electrode assemblies (MEAs) with carbon supported cobalt triethylenetetramine (CoTETA/C) as the cathode catalyst is investigated. The V-I results of PEM single cell tests show that addition of glycol to the cathode catalyst ink leads to significantly higher electrochemical performance and power density than the single cell prepared by the traditional method. SEM analysis shows that the MEAs prepared by the conventional hot-pressed method have cracks between the cathode catalyst layer and Nafion membrane, and the contact problem between cathode catalyst layer and Nafion membrane is greatly suppressed by addition of glycol to the cathode catalyst ink. Current density-voltage curve and impedance studies illuminate that the MEAs prepared by adding glycol to the cathode catalyst ink have a higher electrochemical surface area, lower cell ohmic resistance, and lower charge transfer resistance. The effects of CoTETA/C loading, Nafion content, and Pt loading are also studied. By optimizing the preparation parameters of the MEA, the as-fabricated cell with a Pt loading of 0.15 mg cm⁻² delivers a maximum power density of 181.1 mW cm⁻², and a power density of 126.2 mW cm⁻² at a voltage of 0.4 V.     

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.     

Ultra-low Pt loading for proton exchange membrane fuel cells by catalyst coating technique with ultrasonic spray coating machine

This paper reports use of an ultrasonic spray for producing ultra-low Pt load membrane electrode assemblies (MEAs) with the catalyst coated membrane (CCM) fabrication technique. Anode Pt loading optimization and rough cathode Pt loading were investigated in the first stage of this research. Accurate cathode Pt coating with catalyst ink using the ultrasonic spray method was investigated in the second stage. It was found that 0.272 mg_Pt/cm² showed the best observed performance for a 33 wt% Nafion CCM when it was ultrasonically spray coated with SGL 24BC, a Sigracet manufactured gas diffusion layer (GDL). Two different loadings (0.232 and 0.155 mg_Pt/cm²) exposed to 600 mA/cm² showed cathode power mass densities of 1.69 and 2.36 W/mg_Pt, respectively. This paper presents impressive cathode mass power density and high fuel cell performance using air as the oxidant and operated at ambient pressure.     

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.     

Parametric investigation of a high-yield decal technique to fabricate membrane electrode assemblies for direct methanol fuel cells

This study comprehensively investigates various technical aspects of a roll-press-based decal process that is used to fabricate membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs). Decal transfer yield, flexibility of processing conditions and electrochemical performance of MEAs are taken into account for monitoring the productiveness of the current method. A complete transfer of both electrodes is achieved even under a pressure as low as 1.0 MPa, which is 8–35 times lower than that of conventional decal processes. This method permits use of a H⁺-form Nafion membrane in a wide press temperature domain ranging from 140 to 180 °C without the occurrence of degradation problems that are generally encountered in the conventional decal processes. The effective hot-pressing time is successfully shortened to only 2–5 s, which is far less than those of the conventional decal processes (3–10 min). The structure of cathode catalyst layer is optimized by regulating the ionomer amount. The decal MEA prepared under optimal conditions delivers a peak power density of 115 mW cm⁻² at 60 °C, which is substantially high in a DMFC operation. Superior throughput and flexibility of processing conditions over a wide range make the current method appropriate for use in the mass-production of MEAs.     

Optimum compositions of membrane electrode assemblies (MEAs) for direct dimethyl ether fuel cell

We investigated the effects of the compositions of catalyst layers and diffusion layers on performances of the membrane electrode assemblies (MEAs) for direct dimethyl ether fuel cell. The performances of the MEAs with different thicknesses of Nafion membranes were compared in this work. The optimal compositions in the anode are: 20 wt% Nafion content and 3.6 mg cm⁻² Pt loading in the catalyst layer, and 30 wt% PTFE content and 1 mg cm⁻² carbon black loading in the diffusion layer. In the cathode, MEA with 20 wt% Nafion content in the catalyst layer and 30 wt% PTFE content in the diffusion layer presented the optimal performance. The MEA with Nafion 115 membrane displayed the highest maximum power density of 46 mW cm⁻² among the three MEAs with different Nafion membranes. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance improvement by a glue-functioned Nafion layer coating on gas diffusion electrodes in PEM fuel cells

To reduce the performance difference of membrane electrode assembles (MEAs) between catalyst coated membrane (CCM) and gas diffusion electrode (GDE) methods, this study presents a novel structure of a glue-functioned Nafion layer coating on the catalyst layer of GDEs to enhance performance. The process of hot pressing is omitted from the membrane electrode assembly (MEA) fabrication in this study. In exploring the effect of the glue-functioned Nafion layer, five MEAs are compared, including one made by the CCM method and four by the GDE method. Loadings of 0, 0.1, 0.3 and 0.5 mg cm⁻² of glue-functioned Nafion layer are coated on the surface of the catalyst layer at room temperature with a condensed Nafion solution (20 wt%). The performance of the 0.3 mg cm⁻² Nafion layer coating improves 55% compared with that without an extra Nafion layer for the peak power density, and the performance difference reduces from 61.2% to 39.4% when compared with the one using the CCM method. However, the performance of the 0.5 mg cm⁻² Nafion layer coating is almost the same as without the Nafion layer. This indicates that increased Nafion cannot guarantee higher performance.     

Water-alcohol dispersible and self-cross-linkable sulfonated poly(ether ether ketone): Application as ionomer for direct methanol fuel cell catalyst layer

A sulfonated poly(ether ether ketone) containing hydroxyl groups (HO-SPEEK) has been synthesized for investigation as the ionomer in cathode of direct methanol fuel cells. Na salt-formed HO-SPEEK shows excellent solubility in some aqueous solutions of monohydric alcohol and can be successfully self-cross-linked in-situ during the hot-pressing process of membrane-electrode assembly (MEA) fabrication. The resulted cross-linked HO-SPEEK displays improved stability and mechanical strength. MEA incorporating the HO-SPEEK as both membrane and ionomer shows excellent peak power density of 29.0 mW cm⁻² at 25 °C with 4 M methanol, which is comparable to the Nafion reference MEA (31.8 mW cm⁻²) and 2.9-fold higher than that of the MEA prepared from catalyst ink that contained dimethyl sulfoxide (10.3 mW cm⁻²). Thanks to the avoidance of high-boiling point solvent, the resulted HO-SPEEK-based cathode is loosened with many large pores for reactant gas and product transportation. These results demonstrate that water-alcohol dispersible and cross-linkable sulfonated hydrocarbons hold technological promise as ionomer for electrode.     

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.     

Performance enhancement of membrane electrode assemblies with plasma etched polymer electrolyte membrane in PEM fuel cell

In this work, a surface modified Nafion 212 membrane was fabricated by plasma etching in order to enhance the performance of a membrane electrode assembly (MEA) in a polymer electrolyte membrane fuel cell. Single-cell performance of MEA at 0.7 V was increased by about 19% with membrane that was etched for 10 min compared to that with untreated Nafion 212 membrane. The MEA with membrane etched for 20 min exhibited a current density of 1700 mA cm⁻² at 0.35 V, which was 8% higher than that of MEA with untreated membrane (1580 mA cm⁻²). The performances of MEAs containing etched membranes were affected by complex factors such as the thickness and surface morphology of the membrane related to etching time. The structural changes and electrochemical properties of the MEAs with etched membranes were characterized by field emission scanning electron microscopy, Fourier transform-infrared spectrometry, electrochemical impedance spectroscopy, and cyclic voltammetry.     

Effects of hot pressing conditions on the performances of MEAs for direct methanol fuel cells

The effects of hot pressing conditions (hot pressing temperature, pressure and time) on the performances of membrane electrode assemblies for direct methanol fuel cells were investigated. The performances of membrane electrode assemblies (MEAs) were characterized by the polarization curves and electrochemical impedance spectra (EIS). The surface morphologies of the electrodes were observed by scanning electron microscopy (SEM). The compression ratios of electrodes were determined by testing the thicknesses of the anodes and the cathodes before and after the hot pressing process. The MEA which was hot pressed at 135 °C under 80 kg cm⁻² for 90 s, showed the highest power density of 46.0 mW cm⁻² at 80 °C and ambient pressure. As the hot pressing temperature, pressure and time increased, the compression ratios of the anodes and cathodes increased, and the activating time required for MEA to reach optimum performance increased, too. The cell resistances of the MEAs hot pressed at higher hot pressing temperature (135 °C) and pressure (120 kg cm⁻²), or for longer time (90 s), decreased because of the good contact between the membrane and electrodes. The MEAs that were hot pressed under higher temperature (135 °C) and higher pressure (120 kg cm⁻²) benefited for long-time cell operating.     

Improving cell performance and alleviating performance degradation by constructing a novel structure of membrane electrode assembly (MEA) of DMFCs

The conventional electrodes of direct methanol fuel cells (DMFCs) usually encounter a problem that the catalysts sink into the diffusion layer after a period of operation, causing a lowered catalyst utilization and degraded cell performance. Aiming to alleviate this problem, in this work a novel anode electrode structure is proposed, in which a microporous layer containing Nafion polymer is added between the catalyst layer and the microporous layer with PTFE. The presence of the Nafion-contained layer can expand the three-phase interface region of the electrochemical reactions and improve the utilization of the catalyst. The single cell test showed that the peak power densities of the novel membrane electrode assembly (MEA) fed with 0.5 M and 2 M methanol solutions reached 38.35 mW cm⁻² and 101.82 mW cm⁻², which increased by 100.42% and 15.27% compared with those of conventional single microporous layer. Electrochemical impedance spectroscopy (EIS) measurements indicated the charge transfer resistance of the conventional MEA structure was increased by 303.78%, while the new one was decreased by 47.91% after continuously operating for 48 h. The anode electrochemical active surface area (ECSA) values of the novel MEA and the conventional MEA were 52.6 m² g^-1 and 44.3 m² g^-1. These experimental results showed that the performance of the double microporous layer MEA was higher than that of the conventional MEA. This new microporous layer structure is promising to be used in fuel cells to improve cell performance and alleviate performance degradation after long-term operating.     

Surfactant-assisted synthesis of platinum nanoparticle catalysts for proton exchange membrane fuel cells

High-performance platinum nanoparticle catalysts (Pt–NPCs) remain the most widespread applied electrocatalysts for oxygen reduction reaction (ORR). Here, cetyltrimethylammonium bromide (CTAB), a surface-controlling agent, is introduced to modulate the microstructure and size of Pt nanoparticles (NPs) via a microwave-assisted heating process. The Pt-NPC assisted by 5 wt% CTAB exhibits the highest mass activity (MA) of 0.072 A mg_Pt^?1 and specific activity (SA) of 0.077 mA cm^?2, higher than those of commercial Pt/C (0.023 A mg_Pt^?1 and 0.035 mA cm^?2). Transmission electron microscopy (TEM) results indicate that Pt NPs are uniformly dispersed onto carbon supports with an average size of 2.39 nm. When applied in membrane electrode assembly (MEA), it exhibits the highest power density of 1.142 W cm^?2, which is about 1.24 times larger than that of commercial Pt/C.     

Redistribution of phosphoric acid in membrane electrode assemblies for high-temperature polymer electrolyte fuel cells

We demonstrate that the performance of a high-temperature polymer electrolyte fuel cell with a phosphoric acid-based electrolyte is almost independent of the way of introducing the acid into the membrane electrode assembly (MEA). The same power densities were obtained with different MEAs in which the poly(2,5-benzimidazole) membrane was either pre-doped or not and in which either one or two catalyst layers were impregnated with H₃PO₄. Chemical analysis after shut down revealed that in all these MEAs the phosphoric acid distribution between the membrane and the electrodes was nearly the same. An MEA with acid impregnation via the electrodes was started up rapidly from room temperature, delivered a power density of 120 mW cm⁻² at 600 mV (H₂/air, 160 °C, ambient pressure) after only 11 min and was operated for 1000 h (degradation rate: 0.06 mV/h). Based on the analysis of the H₃PO₄ content in the MEA components, reflections on the kinetics of the redistribution of phosphoric acid within the MEA are provided.     

A novel self-humidifying membrane electrode assembly with water transfer region for proton exchange membrane fuel cells

A novel self-humidifying membrane electrode assembly (MEA) with the active electrode region surrounded by a unactive “water transfer region (WTR)” was proposed to achieve effective water management and high performance for proton exchange membrane fuel cells (PEMFCs). By this configuration, excess water in the cathode was transferred to anode through Nafion membrane to humidify hydrogen. Polarization curves and power curves of conventional and the self-humidifying MEAs were compared. The self-humidifying MEA showed power density of 85 mW cm⁻² at 0.5 V, which is two times higher than that of a conventional MEA with cathode open. The effects of anode hydrogen flow rates on the performance of the self-humidifying MEA were investigated and its best performance was obtained at a flow rate of 40 ml min⁻¹. Its performance was the best when the environmental temperature was 40 °C. The performance of the self-humidifying MEA was slightly affected by environmental humidity. The area of WTR was optimized, and feasible area ratio of the self-humidifying MEA was 28%.     

Fabrication and evaluation of a passive alkaline membrane micro direct methanol fuel cell

A passive silicon microfabricated direct methanol fuel cell employing a polymer anion exchange membrane has been identified as a promising integrable power supply for portable devices in the MEMS field. In this work the fabrication steps of the different components: silicon current collectors and membrane-electrode assembly (MEA), as well as the mounting approach and performance evaluation for the whole passive alkaline micro air-breathing direct methanol fuel cell (μADMFC) are shown. This system, with a small active area of 0.25 cm², was tested near of the real application conditions with totally passive fueling and at room temperature. Different MEA configurations and methanol and KOH concentrations were compared. Best performance was observed for the MEA with a previously sprayed catalytic layer on carbon cloth instead of the MEAs with the catalytic layer deposited directly onto the alkaline membrane. A maximum power density of 2.2 mW cm⁻² was achieved for 15 μL of 1 M methanol + 4 M KOH fuel solution.     

Suppressing methanol crossover with a deposited quaternary Pt-based catalyst on the Nafion surface

A Pt₄₉–Ru₃₅–Ir₆–Os₁₀ alloy layer is deposited on the Nafion membrane surface using the impregnation-reduction (IR) method to mitigate methanol crossover. The methanol crossover in a membrane electrode assembly (MEA) with a deposited Pt–Ru–Ir–Os layer is compared with a MEA without any layer on the proton exchange membrane (PEM). The deposited Pt₄₉–Ru₃₅–Ir₆–Os₁₀ layer functions like a catalytically active layer, a methanol barrier, and an electrode all at the same time. This layer yields up to a 30% suppression of methanol crossover and a 15% improvement in fuel cell voltage performance (@170 mA cm⁻²) at 80 °C. The porous metal alloy layer with a high surface area of the Pt–Ru layer suppresses methanol crossover by the catalytic activity of the deposited layer. The presence of the solid Pt₄₉–Ru₃₅–Ir₆–Os₁₀ layer on the Nafion membrane surface reduces the proton conductivity of the PEM (from 10.75 to 4.22 mS cm⁻¹), and degrades the output of the cell voltage performance (from 0.350 to 0.335 V at 90 mA cm⁻² of current density) at 60 °C, even though methanol crossover is reduced (from 6928 ppm to 4415 ppm (CO₂ concentration at cathode exhaust is proportional to methanol crossover)).     

Sputtered Pt loadings of membrane electrode assemblies in proton exchange membrane fuel cells

The fabrication of electrodes use in proton exchange membrane fuel cells (PEMFCs) by Pt sputter deposition has great potential to increase Pt utilization and reduce Pt loading without loss of cell performance. A radio frequency (RF) magnetron sputter deposition process (RF power = 100 W and argon pressure = 10^?3 Torr) was adopted to prepare Pt catalyst layers of PEMFC electrodes. The effects of cathode Pt and Nafion loadings on membrane electrode assembly (MEA)/cell performance were investigated using cell polarization, cyclic voltammetry, AC impedance, and microstructure analysis. Among the tested MEAs with various cathode Pt loadings (0.02–0.4 mg cm^?2), the one with 0.1 mg‐Pt cm^?2 (grain size = 3.90 nm, mainly Pt(111)) exhibited the best cell performance (320 and 285 mW cm^?2 at 0.44 and 0.60 V, respectively), which was similar to or better than those of some commercial nonsputtered/sputtered electrodes with the same or higher Pt loadings. The electrode Pt utilization efficiency increased as the Pt loading decreased. A Pt loading of greater than or lower than 0.1 mg cm^?2 yielded a lower electrode electrochemical active surface (EAS) area but a higher charge transfer and diffusion resistance. Nafion impregnation (0.1 to 0.3 mg cm^?2) into the sputtered Pt layer (Pt = 0.1 mg cm^?2) noticeably increased the EAS area, consistent with the decrease of the capacitance of the electrode double layer, but did not improve MEA/cell performance, mainly because of the increase in the kinetic and mass transfer resistances associated with oxygen reduction on the cathode. Copyright © 2011 John Wiley & Sons, Ltd.