A novel single electrode supported direct methanol fuel cell

In this paper a single electrode supported direct methanol fuel cell (DMFC) is fabricated and tested. The novel architecture combines the elimination of the polymer electrolyte membrane (PEM) and the integration of the anode and cathode into one component. The thin film fabrication involves a sequential deposition of an anode catalyst layer, a cellulose acetate electronic insulating layer and a cathode catalyst layer onto a single carbon fibre paper substrate. The single electrode supported DMFC has a total thickness of 3.88 × 10^?2 cm and showed a 104% improvement in volumetric specific power density over a two electrode DMFC configuration under passive conditions at ambient temperature and pressure (1 atm, 25 °C).     

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).     

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.     

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).     

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 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.     

Power generation using an activated carbon and metal mesh cathode in a microbial fuel cell

An inexpensive activated carbon (AC) air cathode was developed as an alternative to a platinum-catalyzed electrode for oxygen reduction in a microbial fuel cell (MFC). AC was cold-pressed with a polytetrafluoroethylene (PTFE) binder to form the cathode around a Ni mesh current collector. This cathode construction avoided the need for carbon cloth or a metal catalyst, and produced a cathode with high activity for oxygen reduction at typical MFC current densities. Tests with the AC cathode produced a maximum power density of 1220 mW/m² (normalized to cathode projected surface area; 36 W/m³ based on liquid volume) compared to 1060 mW/m² obtained by Pt catalyzed carbon cloth cathode. The Coulombic efficiency ranged from 15% to 55%. These findings show that AC is a cost-effective material for achieving useful rates of oxygen reduction in air cathode MFCs.     

Electrochemical performance of a novel CoTETA/C catalyst for the oxygen reduction reaction

In this communication, we report a novel CoTETA/C catalyst for the oxygen reduction reaction (ORR) which was prepared from a carbon-supported cobalt triethylenetetramine chelate, followed by heat treatment in an inert atmosphere. Electrochemical performances were measured using rotating disk electrode (RDE) technique and a PEM fuel cell test station. For a H₂–O₂ fuel cell system, the maximum output power density reached 162 mW cm^?2 at 25 °C with non-humidified reaction gases. We found a nanometallic face-centered cubic (fcc) α-Co phase embedded in the graphitic carbon after pyrolysis, based on X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) measurements. These results indicated that CoTETA/C is a promising catalyst for the ORR.     

Oxygen reduction at the silver/hydroxide-exchange membrane interface

A solid-state cell is used to study the electrocatalysis of oxygen reduction at the silver/hydroxide-exchange membrane interface. The catalyst/membrane interface exhibits improved performance in comparison to a catalyst/aqueous sodium hydroxide interface. Surprisingly, the half-wave potential for oxygen reduction is shown to shift 185 mV higher at the silver/hydroxide-exchange membrane interface than for the silver/aqueous hydroxide solution interface, and the exchange current density is significantly higher at 1.02 × 10⁻⁶ A m⁻². On a cost per performance basis, silver electrocatalysts in a hydroxide-exchange membrane fuel cell may provide better performance than platinum in a proton-exchange membrane fuel cell.     

Energy-efficient chlorine production by gas-phase HCl electrolysis with oxygen depolarized cathode

For the first time, gas-phase electrolysis of HCl to chlorine was conducted in a fuel cell type reactor with an oxygen depolarized cathode. Very low cell voltages below − 1 V at industrially relevant current densities of 4 kA m^− 2 were obtained. Compared to technical HCl electrolysis processes, this leads to a reduction in electrical energy demand of approximately 30%. The temperature and the relative humidity (rH) of the cathode inlet gas were identified as key parameters controlling the overall performance of the system.     

Platinum nanoparticles supported on nitrobenzene-functionalised graphene nanosheets as electrocatalysts for oxygen reduction reaction in alkaline media

A systematic study on the electrocatalytic properties of Pt nanoparticles supported on nitrobenzene-modified graphene (Pt-NB/G) as catalyst for oxygen reduction reaction (ORR) in alkaline solution was performed. Graphene nanosheets were spontaneously grafted with nitrophenyl groups using 4-nitrobenzenediazonium salt. The electrocatalytic activity towards the ORR and stability of the prepared catalysts in 0.1 M KOH solution have been studied and compared with that of the commercial Pt/C catalyst. The results obtained show that the NB-modified graphene nanosheets can be good Pt catalyst support with high stability and excellent electrocatalytic properties. The specific activity of Pt-NB/G for O₂ reduction was 0.184 mA cm⁻², which is very close to that obtained for commercial 20 wt% Pt/C catalyst (0.214 mA cm⁻²) at 0.9 V vs. RHE. The Pt-NB/G hybrid material promotes a four-electron reduction of oxygen and can be used as a promising cathode catalyst in alkaline fuel cells.     

Intrinsically microporous polymer slows down fuel cell catalyst corrosion

The limited stability of fuel cell cathode catalysts causes a significant loss of operational cell voltage with commercial Pt-based catalysts, which hinders the wider commercialization of fuel cell technologies. We demonstrate beneficial effects of a highly rigid and porous polymer of intrinsic microporosity (PIM-EA-TB with BET surface area 1027 m² g^− 1) in accelerated catalyst corrosion experiments. Porous films of PIM-EA-TB offer an effective protective matrix for the prevention of Pt/C catalyst corrosion without impeding flux of reagents. The results of electrochemical cycling tests show that the PIM-EA-TB protected Pt/C (denoted here as PIM@Pt/C) exhibit a significantly enhanced durability as compared to a conventional Pt/C catalyst.     

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.     

Distribution profile of hydrogen and oxygen permeating in polymer electrolyte membrane measured by mixed potential

We have succeeded to measure distribution profiles of hydrogen and oxygen permeating in polymer electrolyte membrane (PEM), the information of which contribute to clarify the Pt deposition mechanism inside the PEM during fuel cell operation. Seven platinum probes were inserted into the PEM to monitor the mixed potential determined by the ratio of O₂ to H₂ diffused from the cathode and the anode, respectively. It was found that an equivalent location L_A(eq) of a large potential jump from ca. 0 V to 0.8 V (vs. RHE) shifted to the cathode side with decreasing oxygen partial pressure in the oxidant gas. The values of L_A(eq) accord well with those calculated from the permeabilities of H₂ and O₂ in the PEM. It was suggested that Pt ions dissolved and diffused from the cathode catalysts were dominantly reduced by H₂ at L_A(eq), forming so-called “Pt band”.     

Performance enhancement of phosphoric acid-based proton exchange membrane fuel cells by using ammonium trifluoromethanesulfonate

In a fuel cell system where concentrated phosphoric acid (PA) is used as a proton conducting medium, the use of PA causes some undesirable effects on oxygen reduction reaction (ORR) at Pt catalyst. Ammonium trifluoromethanesulfonate (ATFMS) is introduced as a cathode additive to increase the local oxygen concentration near the Pt catalyst. A cathode with the optimum composition of ATFMS shows a higher single cell performance than that without the additive when a single cell based on a PA-doped polymer membrane is operated at 150 °C. The enhanced ORR activity and oxygen solubility with the incorporation of ATFMS are proved with rotating disk electrode (RDE) and Pt microelectrode experiments. Single cell performance for longer than 600 h without decay in operating voltage could support the stability of the additive.     

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.     

Improved performance of anode with iron/sulfur-modified graphite in microbial fuel cell

The paper reports the operation of a new-design microbial fuel cell using compost leachate as a substrate, oxygen/electrodeposited MnO_x cathode and a new-anode concept with graphite modified by an iron/sulfur solid chemical catalyst which almost eliminates the starting delay time and gives very high current and power densities, I ~ 25 A m^− 3 at P_max ~ 12 W m^− 3 or I ~ 3.8 A m^− 2 at P_max ~ 1.8 W m^− 2.     

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.     

Ultra-low platinum loading high-performance PEMFCs using buckypaper-supported electrodes

The microstructure of the catalyst layer in proton exchange membrane fuel cells (PEMFCs) greatly influences catalyst (Pt) utilization and cell performance. We demonstrated a functionally graded catalyst layer based on a double-layered carbon nanotube/nanofiber film- (buckypaper) supported Pt composite catalyst to approach an idealized microstructure. The gradient distribution of Pt, electrolyte and porosity along the thickness effectively depresses the transport resistance of proton and gas. A rated power of 0.88 W/cm² at 0.65 V was achieved at 80 °C with a low Pt loading of 0.11 mg/cm² resulting in a relatively high Pt utilization of 0.18g_Pt/kW. The accelerated degradation test of catalyst support showed a good durability of buckypaper support because of the high graphitization degree of carbon nanofibers.     

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.