A novel MEA architecture for improving the performance of a DMFC

Direct methanol fuel cell (DMFC) consisting of a double-catalytic layered membrane electrode assembly (MEA) provide higher performance than that with the traditional MEA. This novel structured MEA includes a hydrophilic inner catalyst layer and a traditional electrode with an outer catalyst layer, which was made using both catalyst coated membrane (CCM) and gas diffusion electrode (GDE) methods. The inner catalyst was PtRu black on anode and Pt black on cathode. The outer catalyst was carbon supported Pt–Ru/Pt on anode and cathode, respectively. Thus in the double-catalytic layered electrodes three gradients were formed: catalyst concentration gradient, hydrophilicity gradient and porosity gradient, resulting in good mass transfer, proton and electron conducting and low methanol crossover. The peak density of DMFC with such MEA was 19 mW cm⁻², operated at 2 M CH₃OH, 2 atm oxygen at room temperature, which was much higher than DMFC with traditional MEA.     

Preparation process for improving cathode electrode structure in direct methanol fuel cell

The cathode electrode structure of the direct methanol fuel cell (DMFC) was improved by a novel catalyst ink preparation method. Regulation of the solvent polarity in the cathode catalyst ink caused increases in the electrochemical active surface (EAS) for the oxygen reduction reaction (ORR) as well as decreases in the methanol crossover effect. In a two-step preparation, agglomerates consisting of catalyst and Nafion ionomers were decreased in size, and polar groups in the ionomers formed organized networks in the cathode catalyst layer. Despite Pt catalysts in the cathode being only 0.5 mg cm^? 2, the maximum power density of the improved membrane electrode assembly (MEA) was 120 mW cm^? 2, at 3 M methanol, which was much larger than that of traditional MEA (67 mW cm^? 2).     

Use of MEA technology in the synthesis of pharmaceutical compounds: The electrosynthesis of N-acetyl-l-cysteine

The electrosynthesis of N-acetyl-l-cysteine (NAC) from the electroreduction of N,N-diacetyl-l-cystine (NNDAC) using a Polymer Electrolyte Membrane Electrochemical Reactor (PEMER) has been carried out. The Membrane Electrode Assembly (MEA) was formed by a cathode with a catalyst layer made of Pb/C 20 wt% supported on Toray Paper and a catalyst loading of 0.5 mg Pb cm^?2. The anode was a 2 mg Pt cm^?2 gas diffusion anode fed with H₂. The main advantages of this process are: (1) the electrochemical reactor allows to carry out the electrosynthesis without supporting electrolyte, improving in this way the NAC purification and (2) a pronounced decrease of the electrosynthesis energy consumption due to both, the small internal resistance of the PEMER (electrode gap very small and electrolyte very conductive) and the choice of the H₂ oxidation as anodic reaction in stead of the oxygen evolution reaction from water oxidation. The large number of pharmaceutical applications of NAC, as well as the high versatility of the PEMER for electrosynthesis processes, makes interesting the use of MEAs for electroorganic synthesis.     

Development of MEMS-based direct methanol fuel cell with high power density using nanoimprint technology

Performance of MEMS-based DMFC is low, because graphite-based porous electrodes show poor compatibility with MEMS technology. Nanoimprint technology was adopted in this paper to prepare fine pattern on proton exchange membrane (PEM) in MEMS-based DMFC as a promising alternative to the graphite-based porous electrodes. Micro-convex with the diameter of about 600 nm and the height of 50–70 nm was prepared on Nafion^® 117 membrane by the nanoimprint at 130 °C using silicon mold. Thick Pt film (20 nm) was deposited as catalyst directly on the nanoimprinted Nafion^® 117 membrane. Then the Pt-coated PEM was sandwiched with micro-channeled silicon plates to form a micro-DMFC. With passively feeding of 1 M methanol solution and air at room temperature, the as-prepared cell had the open circuit voltage (OCV) of 0.74 V and the maximum power density of 0.20 mW/cm². The measured OCV was higher than those (0.1–0.3 V) of the state-of-the-art MEMS-based DMFC with planar electrode and pure Pt catalyst.     

The effect of different valency cations on DMFC performance

An in situ study of the effects of Na⁺, Mg²⁺ and Cr³⁺ on direct methanol fuel cell (DMFC) performance is reported. The result showed that dramatic decrease of the cell voltage was mainly ascribed to the increase of the cathode overpotential. Meanwhile, the different contamination effects by introducing Na⁺, Mg²⁺ and Cr³⁺ to the anode and the cathode were compared. When the same molar concentration of different cations was added to the anode feed, the contamination effect on the cell performance followed the order of Na⁺ > Mg²⁺ > Cr³⁺. Owing to the fast transfer speed and the low affinity to the sulfonic acid groups in the ionomer phase, the low-valent cations may cause much more proton losses than the high-valent cations in the cathode catalyst layer (CCL) within the same time. So the low-valent cations led to the higher cathode overpotential than the high-valent cations. When the same molar concentration of cations was directly added to the CCL, the contamination effects on the cell voltage showed an opposite trend which is Na⁺ < Mg²⁺ < Cr³⁺. This is presumably because a high-valent cation can exchange more protons than a low-valent cation in the CCL.     

Cost-effective solid oxide fuel cell prepared by single step co-press-firing process with lithiated NiO cathode

A cost-effective cell fabrication process was developed for intermediate temperature solid oxide fuel cells (IT-SOFCs). Co-doped ceria Ce_0.8Gd_0.05Y_0.15O_1.9 (GYDC) was synthesized by carbonate co-precipitation method. Lithiated NiO was prepared by glycine-nitrate combustion method and adopted as cathode material for IT-SOFCs. Single cell was fabricated by one-step dry-pressing and co-firing anode, anode functional layer (AFL), electrolyte and cathode together at 1200 °C for 4 h. The cell presented decent performance and an overall electrode polarization resistance of 0.54 Ω cm² has been achieved at 600 °C. These results demonstrate the possibility of using lithiated NiO as cathode material for ceria-based IT-SOFCs and the development of affordable fuel cell devices is encouraged.     

A completely spray-coated membrane electrode assembly

We present a proton exchange membrane fuel cell (PEMFC) manufacturing route, in which a thin layer of polymer electrolyte solution is spray-coated on top of gas diffusion electrodes (GDEs) to work as a proton exchange membrane. Without the need for a pre-made membrane foil, this allows inexpensive, fast, large-scale fabrication of membrane-electrode assemblies (MEAs), with a spray-coater comprising the sole manufacturing device. In this work, a catalyst layer and a membrane layer are consecutively sprayed onto a fibrous gas diffusion layer with applied microporous layer as substrate. A fuel cell is then assembled by stacking anode and cathode half-cells with the membrane layers facing each other. The resultant fuel cell with a low catalyst loading of 0.1 mg Pt/cm² on each anode and cathode side is tested with pure H₂ and O₂ supply at 80 °C cell temperature and 92% relative humidity at atmospheric pressure. The obtained peak power density is 1.29 W/cm² at a current density of 3.25 A/cm². By comparison, a lower peak power density of 0.93 W/cm² at 2.2 A/cm² is found for a Nafion NR211 catalyst coated membrane (CCM) reference, although equally thick membrane layers (approx. 25 μm), and identical catalyst layers and gas diffusion media were used. The superior performance of the fuel cell with spray-coated membrane can be explained by a decreased low frequency (mass transport) resistance, especially at high current densities, as determined by electrochemical impedance spectroscopy.     

A novel single phase cathode material for a proton-conducting SOFC

A novel single phase BaCe_0.5Bi_0.5O_3 ? δ (BCB) was employed as a cathode material for a proton-conducting solid oxide fuel cell (SOFC). The single cell, consisting of a BaZr_0.1Ce_0.7Y_0.2O_3 ? δ (BZCY7)-NiO anode substrate, a BZCY7 anode functional layer, a BZCY7 electrolyte membrane and a BCB cathode layer, was assembled and tested from 600 to 700 °C with humidified hydrogen (～3% H₂O) as the fuel and the static air as the oxidant. An open-circuit potential of 0.96 V and a maximum power density of 321 mW cm^?2 were obtained for the single cell. A relatively low interfacial polarization resistance of 0.28Ω cm² at 700 °C indicated that the BCB was a promising cathode material for proton-conducting SOFCs.     

Methane-fueled SOFC with traditional nickel-based anode by applying Ni/Al2O3 as a dual-functional layer

Novel γ-Al₂O₃ supported nickel (Ni/Al₂O₃) catalyst was developed as a functional layer for Ni–ScSZ cermet anode operating on methane fuel. Catalytic tests demonstrated Ni/Al₂O₃ had high and comparable activity to Ru–CeO₂ and much higher activity than the Ni–ScSZ cermet anode for partial oxidation, steam and CO₂ reforming of methane to syngas between 750 and 850 °C. By adopting Ni/Al₂O₃ as a catalyst layer, the fuel cell demonstrated a peak power density of 382 mW cm^?2 at 850 °C, more than two times that without the catalyst layer. The Ni/Al₂O₃ also functioned as a diffusion barrier layer to reduce the methane concentration within the anode; consequently, the operation stability was also greatly improved without coke deposition.     

High capacity and excellent cyclability of vanadium (IV) oxide in lithium battery applications

A VO₂ · 0.43H₂O powder with a flaky particle morphology was synthesized via a hydrothermal reduction method. It was characterized by scanning electron microscopy, electron energy loss spectroscopy, and thermogravimetric analysis. As an electrode material for rechargeable lithium batteries, it was used both as a cathode versus lithium anode and as an anode versus LiCoO₂, LiFePO₄ or LiNi_0.5Mn_1.5O₄ cathode. The VO₂ · 0.43H₂O electrode exhibits an extraordinary superiority with high capacity (160 mAh g^?1), high energy efficiency (95%), excellent cyclability (142.5 mAh g^?1 after 500 cycles) and rate capability (100 mAh g^?1 at 10 C-rate).     

MEA with double-layered catalyst cathode to mitigate methanol crossover in DMFC

Methanol permeation is one of the key problems for direct methanol fuel cell (DMFC) applications. It is necessary to change the structure of the cathode of membrane electrode assembly (MEA). Therefore, a novel MEA with double-layered catalyst cathode was prepared in this paper. The double-layered catalyst consists of PtRu black as inner catalyst layer and Pt black as outer catalyst layer. The inner catalyst layer is prepared for oxidation of the methanol permeated from anode. The results indicate that this double-layered catalyst reduced the effects of methanol crossover and assimilated mixed potential losses. The performance of MEA with double-layered catalyst cathode was 52.2 mW cm⁻², which was a remarkable improvement compared with the performance of MEA with traditional cathode. The key factor responsible for the improved performance is the optimization of the electrode structure.     

Poly(vinyl alcohol) separators improve the coulombic efficiency of activated carbon cathodes in microbial fuel cells

High-performance microbial fuel cell (MFC) air cathodes were constructed using a combination of inexpensive materials for the oxygen reduction cathode catalyst and the electrode separator. A poly(vinyl alcohol) (PVA)-based electrode separator enabled high coulombic efficiencies (CEs) in MFCs with activated carbon (AC) cathodes without significantly decreasing power output. MFCs with AC cathodes and PVA separators had CEs (43%–89%) about twice those of AC cathodes lacking a separator (17%–55%) or cathodes made with platinum supported on carbon catalyst (Pt/C) and carbon cloth (CE of 20%–50%). Similar maximum power densities were observed for AC-cathode MFCs with (840 ± 42 mW/m²) or without (860 ± 10 mW/m²) the PVA separator after 18 cycles (36 days). Compared to MFCs with Pt-based cathodes, the cost of the AC-based cathodes with PVA separators was substantially reduced. These results demonstrated that AC-based cathodes with PVA separators are an inexpensive alternative to expensive Pt-based cathodes for construction of larger-scale MFC reactors.     

Fabrication and characterization of large-size electrolyte/anode bilayer structures for low-temperature solid oxide fuel cell stack based on gadolinia-doped ceria electrolyte

Preliminary progress is reported in this communication in building a planar anode-supported low-temperature solid oxide fuel cell (SOFC) stack based on gadolinia-doped ceria (GDC) electrolyte, i.e. fabrication and characterization of a Ø80 planar bilayer structure composed of GDC electrolyte film and Ni–GDC anode substrate. The anode substrates were prepared from mixtures of NiO, GDC, and carbon black by die-pressing. After pre-firing to remove the carbon black, the anode substrates were deposited with a GDC layer using a spray coating technique. The green bilayers of anode substrate and electrolyte film were then co-sintered at 1500 °C for 3 h. Through proper control of the sintering process, bilayer structures with excellent flatness were achieved after co-sintering. Scanning electron microscopy (SEM) observation indicated that the electrolyte film was about 22 μm in thickness, highly dense, crack-free, and well-bonded to the anode substrate. Small disks which were cut out from the Ø80 bilayer structure were electrochemically examined in a single button-cell mode incorporating a (LaSr)(CoFe)O₃–GDC composite cathode. With humidified hydrogen as the fuel and air as the oxidant, the cell demonstrated an open-circuit voltage of 0.884 V and a maximum power density of 562 mW/cm² at 600 °C. The results imply that high-quality anode-supported electrolyte/anode bilayer structures were successfully fabricated. Based on them, planar anode-supported SOFC stacks will be assembled in the future.     

Impact of reforming catalyst on the anodic polarisation resistance in single-chamber SOFC fed by methane

This paper emphasises the electrochemical and catalytic properties of a Ni–10% GDC (10% gadolinium-doped ceria) cermet anode of a single-chamber solid oxide fuel cell (SC-SOFC). Innovative coupling of electrochemical impedance spectroscopy with gas chromatography measurements was carried out to characterise the anode material using an operando approach. The experiments were conducted in a symmetric anode/electrolyte/anode cell prepared by slurry coating resulting in 100 μm-thick anode layers. The electrochemical performance was assessed using a two-electrode arrangement between 400 °C and 650 °C, in a methane-rich atmosphere containing CH₄, O₂ and H₂O in a 14:2:6 volumetric ratio. The insertion of a Pt–CeO₂ based catalyst with high specific surface area inside the cermet layer was found to promote hydrogen production from the Water Gas Shift reaction and consequently to improve the electrochemical performances. Indeed, a promising polarisation resistance value of 12 Ω cm² was achieved at 600 °C with a catalytic loading of only 15 wt.%.     

Low Pt content Pt–Ru–Ir–Sn quaternary catalysts for anodic methanol oxidation in DMFC

In this communication we report our research work on low Pt content Pt–Ru–Ir–Sn quaternary catalysts for use in DMFC anodes. The carbon-supported quaternary metal alloy catalyst was synthesized according to the solution reduction method and was deposited onto a carbon fiber paper or a carbon aerogel nanofoam to form the anode for direct methanol fuel cells. The Pt loading of the electrode is 0.1 mg/cm². The testing results from a three-electrode electrochemical cell show that the simultaneous use of higher Ir (25–35 wt.%) and Sn (10 wt.%) content gives satisfactory stability and higher activity for methanol oxidation than the commercially available E-TEK anode (80%[0.5Pt 0.5Ru]/C on carbon cloth). Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscope (SEM), and Bruner–Emmett–Teller method (BET) measurements were carried out to characterize the composition, structure, morphology, and surface area of the developed catalysts.     

Fabrication by Co-extrusion and electrochemical characterization of micro-tubular hollow fibre solid oxide fuel cells

A phase inversion process was used to co-extrude cerium–gadolinium oxide (Ce_0.9Gd_0.1O_1.95)/NiO–CGO dual-layer hollow fibres (HF), which were then sintered to form, respectively, the electrolyte and high porosity anode precursor of a solid oxide fuel cell (SOFC) with anode inner diameter of 0.8 mm. Graded CGO–lanthanum strontium cobalt ferrite (La_0.6Sr_0.4Fe_0.8Co_0.2O₃) cathode layers were then painted onto the CGO electrolyte to form a micro-tubular HF-SOFC. With a carefully designed anode current collector, this produced maximum power densities of 1186–5864 W m^? 2 at 450–570 °C. High magnification imaging analysis revealed large three-phase boundary regions within the anode, a dense electrolyte layer and clearly highlighted the multiple CGO–LSCF cermet and pure LSCF cathode layers. The performance of the HF-SOFC with a twenty millimetre active length showed no degradation after four thermal cycles between 300 °C and 570 °C.     

Surface modified Pt/C as a methanol tolerant oxygen reduction catalyst for direct methanol fuel cells

A new procedure has been successfully developed by which PtN_x/C is synthesized to enhance methanol tolerance while maintaining a high catalytic activity for the oxygen-reduction reaction (ORR). The nitrogen-modified Pt surface, which is prepared using a chelating agent followed by heat treatment, exhibits considerable selectivity toward the ORR in the presence of methanol. The high methanol tolerance could be attributed to the suppression of methanol adsorption resulting from the modification of the Pt surface with nitrogen. A direct methanol fuel-cell (DMFC) test showed that a power density of up to 120 m W cm⁻² was generated when PtN_x/C was used as the cathode catalyst (1 mg cm⁻²) in 6 M methanol and oxygen at 70 °C.     

Fabrication of a large area cathode-supported thin electrolyte film for solid oxide fuel cells via tape casting and co-sintering techniques

A large area cathode-supported electrolyte film, comprising porous (La_0.8Sr_0.2)_0.95MnO₃ (LSM95) cathode substrate, LSM95/Zr_0.89Sc_0.1Ce_0.01O_2?x (SSZ) cathode active layer, and SSZ electrolyte, has been successfully fabricated by tape casting and co-sintering techniques. The interface reaction between cathode and electrolyte was inhibited by using A-site deficient LSM. A dense enough SSZ thin film with a thickness of ～26 μm was obtained at 1250 °C. By using Pt as anode, the obtained single cell reached the maximum power density of 0.54 W cm^?2 at 800 °C in O₂/humidified H₂, with open circuit voltage (OCV) value of 1.08 V.     

Micro-tubular solid oxide fuel cells fabricated by phase-inversion method

A novel structured micro-tubular solid oxide fuel cell (MT-SOFC) has been fabricated by combining a phase-inversion, dip-coating and high temperature co-sintering process with impregnation of the electrode catalyst into a porous electrode matrix. The asymmetric porous anode made by phase-inversion is divided into two different layers, a thick fuel delivery layer with large finger-like pores and a thin function layer with small finger-like pores. The MT-SOFC demonstrates maximum power densities of 0.44, 0.54, 0.65 and 0.78 W/cm² at 650, 700, 750 and 800 °C, respectively with H₂–15%H₂O as fuel and ambient air as oxidant. Combining the power output with the quick start-up behavior, novel structured MT-SOFC offers a potential solution for rapid start-up high performance power devices.     

Iodinated carbon materials for oxygen reduction reaction in proton exchange membrane fuel cell. Scalable synthesis and electrochemical performances

Doped graphene-based cathode catalysts are considered as promising competitors for ORR, but their power density has been low compared to Pt-based cathodes, mainly due to poor mass-transport properties. A new electrocatalyst for PEMFCs, an iodine doped grahene was prepared, characterized, and tested and the results are presented in this paper. We report a hybrid derived electrocatalyst with increased electrochemical active area and enhanced mass-transport properties. The electrochemical performances of several configurations were tested and compared with a typical Pt/C cathode configuration. As a standalone catalyst, the iodine doped graphene gives a performance with 60% lower than if it is placed between gas diffusion layer and catalyst layer. If it is included as microporous layer, the electrochemical performances of the fuel cell are with 15% bigger in terms of power density than the typical fuel cell with the same Pt/C loading, proving the beneficial effect of the iodine doped graphene for the fuel cell in the ohmic and mass transfer region. Moreover, the hybrid cathode manufactured by commercial Pt/C together with the material with best proprieties, is tested in a H₂-Air fuel cell and a power density of 0.55 W cm⁻² at 0.52 V was obtained, which is superior to that of a commercial Pt-based cathode tested under identical conditions (0.46 W cm⁻²).