Performance of direct methanol fuel cells prepared by hot-pressed MEA and catalyst-coated membrane (CCM)

In Situ-Grown Ultrathin Catalyst Layers for Improving both Proton Exchange Membrane Fuel Cell and Anion Exchange Membrane Fuel Cell Performances

The mass transport and ion conductivity in the catalyst layer are important for fuel cell performances. Here, we report an in situ-grown ultrathin catalyst layer (UTCL) to reduce the oxygen mass transport and a surface ionomer-coated gas diffusion layer method to reduce the ion conducting resistance. A significantly reduced catalyst layer thickness (ca. 1 μm) is achieved, and coupled with the ionomer introduction method, the ultrathin catalyst layer is in good contact with the membrane, resulting in high ion conductivity and high Pt utilization. This ultrathin catalyst layer is suitable for both proton exchange membrane fuel cells and anion exchange membrane fuel cells, giving peak power densities of 2.24 and 1.11 W cm-2, respectively, which represent an increase of more than 30% compared with the membrane electrode assembly (MEA) fabricated by using traditional Pt/C power catalysts. Electrochemical impedance spectra and limiting current tests demonstrate the reduced charge transfer, mass transfer, and ohmic resistances in the ultrathin catalyst layer membrane electrode assembly, resulting in the promoted fuel cell performances.

Self-Standing, Ultrasonic Spray-Deposited Membranes for Fuel Cells

The polymer electrolyte membrane and its contact with electrodes has a significant effect on the performance of fuel and electrolysis cells but the choice of commercially available membranes is limited. In this study, membranes for direct methanol fuel cells (DMFCs) were made by ultrasonic spray deposition from commercial Nafion solution; the effect of the drying temperature and presence of high boiling solvents on the membrane properties was then analyzed. When choosing suitable conditions, membranes with similar conductivity, water uptake, and higher crystallinity than comparable commercial membranes can be obtained. These show similar or superior performance in DMFC operation compared to commercial Nafion 115. Furthermore, they exhibit low permeability for hydrogen, which makes them attractive for electrolysis or hydrogen fuel cells. The findings from our work will allow for the adjustment of membrane properties to the specific requirements of fuel cells or water electrolysis, as well as the inclusion of additional functional components for composite membranes.

Electrooxidation of 2-propanol on the mixture of nanoparticles of Pt and RuO2 supported on Ti

A thermal process was employed to prepare a catalyst consisting of a mixture of metallic-Pt and rutile RuO2 nanocrystals. This catalyst was used for the electrooxidation of 2-propanol in an alkaline solution. The effect of the catalyst composition on its microstructure, surface properties and catalytic activity was examined. With increasing the RuO2 content, the catalytic activity increases, reaches its maximum and then decreases. The catalytic effect is a result of the bifunctional mechanism of the mixture of Pt and RuO2 nanocrystals. The RuOHad particles are formed on Ru atoms of the RuO2 nanocrystals at potentials more negative than on Pt atoms. These oxy-species facilitate the dehydrogenation, breaking of C–C bonds and oxidation of both 2-propanol and its intermediates, adsorbed on assemblies of adjacent Pt atoms.

A Robust Composite Proton Exchange Membrane of Sulfonated Poly (Fluorenyl Ether Ketone) with an Electrospun Polyimide Mat for Direct Methanol Fuel Cells Application

As a key component of direct methanol fuel cells, proton exchange membranes with suitable thickness and robust mechanical properties have attracted increasing attention. On the one hand, a thinner membrane gives a lower internal resistance, which contributes highly to the overall electrochemical performance of the cell, on the other hand, strong mechanical strength is required for the application of proton exchange membranes. In this work, a sulfonated poly (fluorenyl ether ketone) (SPFEK)-impregnated polyimide nanofiber mat composite membrane (PI@SPFEK) was fabricated. The new composite membrane with a thickness of about 55 μm exhibited a tensile strength of 35.1 MPa in a hydrated state, which is about 65.8% higher than that of the pristine SPFEK membrane. The antioxidant stability test in Fenton’s reagent shows that the reinforced membrane affords better oxidation stability than does the pristine SPFEK membrane. Furthermore, the morphology, proton conductivity, methanol permeability, and fuel cell performance were carefully evaluated and discussed.

Novel electrocatalysts for borohydride fuel cells: enhanced power generation by optimizing anodic core–shell nanoparticles on reduced graphene oxide

C_Ni–S_Pd exhibits an excellent performance and rGO is a superior support compared with Vulcan and MWCNTs.

Efficient Design for a High-Energy and High-Power Capability Hybrid Electric Power Device with Enhanced Electrochemical Interfaces

Fabrication of novel electrode architectures with tailored electrochemical interfaces (EI) is an effective strategy for enhancing charge and mass transport processes within electrochemical devices. Here, we design and fabricate a well-hybrid electrode based on the coupling of polyaniline (PANI) nanowires and Pt-based electrocatalysts to manufacture a hybrid electric power device (HEPD) combining the advantages of supercapacitors and fuel cells. Because of the boosted charge transfer between PANI nanowires and Pt-based materials via enhanced EIs, the HEPD assembled with hybrid electrodes shows remarkable performance with a peak power density of 222 mW cm^-2, a specific power of 3810 W kg^-1, and a specific energy of 2100 Wh kg^-1, normalized to the mass of membrane electrode assemblies. The in situ Raman spectra and extended electrochemical studies demonstrate the intrinsic mechanism of charge transfer processes within hybrid electrodes, shedding light on the alternative progress of electrochemical energy conversion systems and storage devices.

Preparation method of Ni@Pt/C nanocatalyst affects the performance of direct borohydride-hydrogen peroxide fuel cell: Improved power density and increased catalytic oxidation of borohydride

The Ni@Pt/C electrocatalysts were synthesized using two different methods: with sodium dodecyl sulfate (SDS) and without SDS. The metal loading in synthesized nanocatalysts was 20wt% and the molar ratio of Ni: Pt was 1:1. The structural characterizations of Ni@Pt/C electrocatalysts were investigated by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM). The electrocatalytic activity of Ni@Pt/C electrocatalysts toward BH₄^- oxidation in alkaline medium was studied by means of cyclic voltammetry (CV), chronopotentiometry (CP), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results showed that Ni@Pt/C electrocatalyst synthesized without SDS has superior catalytic activity toward borohydride oxidation (22016.92Ag_Pt^-1) in comparison with a catalyst prepared in the presence of SDS (17766.15Ag_Pt^-1) in NaBH₄ 0.1M at 25°C. The Membrane Electrode Assembly (MEA) used in fuel cell set-up was fabricated with catalyst-coated membrane (CCM) technique. The effect of Ni@Pt/C catalysts prepared with two methods as anode catalyst on the performance of direct borohydride-hydrogen peroxide fuel cell was studied. The maximum power density was obtained using Ni@Pt/C catalyst synthesized without SDS at 60°C, 1M NaBH₄ and 2M H₂O₂ (133.38mWcm^-2).

Ni@M (M = Pt, Pd and Ru) core@shell nanoparticles on a Vulcan XC-72R support with superior catalytic activity toward borohydride oxidation: electrochemical and fuel cell studies

Ni@Pd/C has excellent catalytic activity and power density for borohydride oxidation in comparison with Ni@Pt/C and Ni@Ru/C.

Emerging methanol-tolerant AlN nanowire oxygen reduction electrocatalyst for alkaline direct methanol fuel cell

Replacing precious and nondurable Pt catalysts with cheap materials is a key issue for commercialization of fuel cells. In the case of oxygen reduction reaction (ORR) catalysts for direct methanol fuel cell (DMFC), the methanol tolerance is also an important concern. Here, we develop AlN nanowires with diameters of about 100–150 nm and the length up to 1 mm through crystal growth method. We find it is electrochemically stable in methanol-contained alkaline electrolyte. This novel material exhibits pronounced electrocatalytic activity with exchange current density of about 6.52 × 10⁻⁸ A/cm². The single cell assembled with AlN nanowire cathodic electrode achieves a power density of 18.9 mW cm⁻². After being maintained at 100 mA cm⁻² for 48 h, the AlN nanowire-based single cell keeps 92.1% of the initial performance, which is in comparison with 54.5% for that assembled with Pt/C cathode. This discovery reveals a new type of metal nitride ORR catalyst that can be cheaply produced from crystal growth method.

Development of cesium phosphotungstate salt and chitosan composite membrane for direct methanol fuel cells

A novel composite membrane has been developed by doping cesium phosphotungstate salt (CsxH3-xPW12O40 (0≤x≤3), Csx-PTA) into chitosan (CTS/Csx-PTA) for application in direct methanol fuel cells (DMFCs). Uniform distribution of Csx-PTA nanoparticles has been achieved in the chitosan matrix. The proton conductivity of the composite membrane is significantly affected by the Csx-PTA content in the composite membrane as well as the Cs substitution in PTA. The highest proton conductivity for the CTS/Csx-PTA membranes was obtained with x=2 and Cs2-PTA content of 5 wt%. The value is 6×10(-3) S cm(-1) and 1.75×10(-2) S cm(-1) at 298 K and 353 K, respectively. The methanol permeability of CTS/Cs2-PTA membrane is about 5.6×10(-7), 90% lower than that of Nafion-212 membrane. The highest selectivity factor (φ) was obtained on CTS/Cs2-PTA-5 wt% composite membrane, 1.1×10(4)/Scm(-3)s. The present study indicates the promising potential of CTS/Csx-PTA composite membrane as alternative proton exchange membranes in direct methanol fuel cells.

On the Use of Potential Denaturing Agents for Ethanol in Direct Ethanol Fuel Cells

Acidic or alkaline direct ethanol fuel cells (DEFCs) can be a sustainable alternative for power generation if they are fuelled with bio-ethanol. However, in order to keep the fuel cheap, ethanol has to be exempted from tax on spirits by denaturing. In this investigation the potential denaturing agents fusel oil, tert-butyl ethyl ether, and Bitrex were tested with regard to their compatibility with fuel cells. Experiments were carried out both in sulphuric acid and potassium hydroxide solution. Beside, basic electrochemical tests, differential electrochemical mass spectrometry (DEMS) and fuel cell tests were conducted. It was found that fusel oil is not suitable as denaturing agent for DEFC. However, tert-butyl ethyl ether does not seem to hinder the ethanol conversion as much. Finally, a mixture of tert-butyl ethyl ether and Bitrex can be proposed as promising candidate as denaturing agent for use in acidic and alkaline DEFC.