Electrochemical performance and stability of thin film electrodes with metal oxides in polymer electrolyte fuel cells

Thin film electrodes are prepared by thermal evaporation of nanometer thick layers of metal oxide and platinum on a gas diffusion layer (GDL), in order to evaluate different metal oxides\u27 impact on the activity and stability of the platinum cathode catalyst in the polymer electrolyte fuel cell. Platinum deposited on tin, tantalum, titanium, tungsten and zirconium oxide is investigated and the morphology and chemistry of the catalysts are examined with scanning electron microscopy and X-ray photoelectron spectroscopy. Cyclic sweeps in oxygen and nitrogen are performed prior and after potential cycling degradation tests. Platinum seems to disperse better on the metal oxides than on the GDL and increased electrochemically active surface area (ECSA) of platinum is observed on tin, titanium and tungsten oxide. A thicker layer metal oxide results in a higher ECSA. Platinum deposited on tungsten performs better than sole platinum in the polarisation curves and displays higher Tafel slopes at higher current densities than all other samples. The stability does also seem to be improved by the addition of tungsten oxide, electrodes with 3 nm platinum on 3, 10 and 20 nm tungsten oxide, performs better than all other electrodes after the accelerated degradation tests. \ua9 2009 Elsevier Ltd

Hydrogen oxidation reaction on thin platinum electrodes in the polymer electrolyte fuel cell

A method for measuring the kinetics of the hydrogen oxidation reaction (HOR) in a fuel cell under enhanced mass transport conditions is presented. The measured limiting current density was roughly 1600 mA cm(Pt)(-2), corresponding to a rate constant of the forward reaction in the Tafel step of 0.14 mol m(-2) s(-1) at 80 degrees C and 90% RH. The exchange current density for the HOR was determined using the slope at low overvoltages and was found to be 770 mA cmp(Pt)(-2). The high values for the limiting and exchange current densities suggest that the Pt loading in the anode catalyst can be reduced further without imposing measurable voltage loss

The impact of iridium on the stability of platinum on carbon thin-film model electrodes

Increasing the stability and lifetime of the electrodes is one of the most important factors in order to realise a large scale use of polymer electrolyte membrane fuel cells (PEMFC). By using well-defined thin-film model electrodes, the stability of Pt and Pt on Ir were examined as cathode catalysts in a single cell PEMFC setup. The electrodes were fabricated by evaporating thin layers of Pt and Pt on Ir onto the microporous layer of a gas diffusion layer. The amount of Pt deposited was equivalent to 3 nm (about 6.3 mu g cm(-2)) and the amount of Ir was varied between 1.5 nm and 20 nm (between 3.4 mu g cm(-2) and 45.3 mu g cm(-2)). All samples with Ir showed an increased stability over samples with sole Pt during cyclic corrosion test between 0.6V and 1.2V vs. the reversible hydrogen electrode. For thin layers of Ir, the initial activity for the oxygen reduction reaction was equal to or superior to that of sole Pt but for thicker Ir films it was somewhat lower. Hydrogen underpotential deposition and CO stripping were used to estimate the electrochemical surface area during the experiments and physical characterisation using scanning electron microscopy and X-ray photoelectron spectroscopy were used to determine the structure of the samples. The results suggest that Ir can stabilise Pt in the cathode electrode. (C) 2013 Elsevier Ltd. All rights reserved

Membrane-less hydrogen bromine flow battery

In order for the widely discussed benefits of flow batteries for electrochemical energy storage to be applied at large scale, the cost of the electrochemical stack must come down substantially. One promising avenue for reducing stack cost is to increase the system power density while maintaining efficiency, enabling smaller stacks. Here we report on a membrane-less, hydrogen bromine laminar flow battery as a potential high power density solution. The membrane-less design enables power densities of 0.795 W cm$^{-2}$ at room temperature and atmospheric pressure, with a round-trip voltage efficiency of 92\% at 25\% of peak power. Theoretical solutions are also presented to guide the design of future laminar flow batteries. The high power density achieved by the hydrogen bromine laminar flow battery, along with the potential for rechargeable operation, will translate into smaller, inexpensive systems that could revolutionize the fields of large-scale energy storage and portable power systems

Mesoporous Nanostructured Nb-Doped Titanium Dioxide Microsphere Catalyst Supports for PEM Fuel Cell Electrodes

International audienc

Enabling direct H₂O₂ production through rational electrocatalyst design.

Future generations require more efficient and localized processes for energy conversion and chemical synthesis. The continuous on-site production of hydrogen peroxide would provide an attractive alternative to the present state-of-the-art, which is based on the complex anthraquinone process. The electrochemical reduction of oxygen to hydrogen peroxide is a particularly promising means of achieving this aim. However, it would require active, selective and stable materials to catalyse the reaction. Although progress has been made in this respect, further improvements through the development of new electrocatalysts are needed. Using density functional theory calculations, we identify Pt-Hg as a promising candidate. Electrochemical measurements on Pt-Hg nanoparticles show more than an order of magnitude improvement in mass activity, that is, Ag-1 precious metal, for H2O2 production, over the best performing catalysts in the literature