2,929 research outputs found
Ionic conductivity of an extruded Nafion 1100 EW series of membranes
No full textThe proton conductivity of a series of extruded Nafion membranes @of equivalent weight ~EW! of 1100 and nominal dry thickness of 51, 89, 127, and 178 mm# has been studied. Measurements were made in 1 M H2SO4 at 298 K using a four-electrode, dc technique. The membrane area resistance increases with thickness, as expected, from 0.07 to 0.16 V cm2 for Nafion 112 and Nafion 117, respectively. However, in contrast to the published literature, after correcting for the membrane thickness, the conductivity of the membranes decreases with decreasing membrane thickness. For example, values of 0.083 and 0.16 S cm21 were obtained for Nafion 112 and 117 membranes, respectively. In situ current-interrupt measurements in a proton exchange membrane fuel cell confirmed the relatively poor conductivity of the membrane electrode assemblies ~MEAs! based on the thinner membranes. While a high contact resistance to the electrodes may have contributed to the in situ MEA resistance, water balance measurements over the MEA showed that the high resistance was not due to a low water content or to an uneven water distribution in the MEAs. The implications of the findings for the understanding of the membrane properties are discussed
Letter from Ralph H. Cameron to Carl Hayden
No full textLetter from Ralph H. Cameron asking to speak to Carl Hayden concerning a matter relevant to the bill granting National Park status to the Grand Canyon
Letter from Carl Hayden to Ralph H. Cameron
No full textLetter from Carl Hayden to Ralph H. Cameron responding favorably to a request to meet in regards to the bill granting National Park status to the Grand Canyon
Modelling and simulation of the degradation of perfluorinated ion-exchange membranes in PEM fuel cells
No full textA polymer-electrolyte membrane fuel cell model that incorporates chemical degradation in perlfluorinated sulfonic acid membranes is developed. The model is based on conservation principles and includes a detailed description of the transport phenomena. A degradation sub-model describes the formation of hydrogen peroxide \/\it via\/ distinct mechanisms in the cathode and anode, together with the subsequent formation of radicals \/\it via\/ Fenton reactions involving metal-ion impurities. The radicals participate in the decomposition of reactive end groups to form carboxylic acid, hydrogen fluoride and CO_2. Degradation proceeds through unzipping of the polymer backbone and cleavage of the side chains. Simulations are presented and the numerical code is shown to be extremely time efficient. Known trends with respect to operating conditions are qualitatively captured and the exhibited behaviour is shown to be robust to changes in the rate constants. The feasibility of a chemical degradation mechanism based on peroxide and radical formation is discussed
Letter from Ralph H. Cameron to Carl Hayden
No full textLetter from Ralph H. Cameron to Carl Hayden thanking him for forwarding Senate Bill No. 390 with the report of March 31st, 1918, and expressing interest in their upcoming meeting in Washington
Letter from Ralph H. Cameron to Carl Hayden
No full textLetter from Ralph H. Cameron to Carl Hayden requesting a delay on the introduction of the Grand Canyon bill until he can meet with himself and Senator Ashurst in Washington
Native drama entitled The panting patriot of the pattern parliament, or The palmy parient of the peerless prodigies : in five acts / by the author.
No full textAttributed to Ralph Delaney. Refer to Morris Miller's Australian literature 1795-1938, p. 377.; Electronic reproduction. Canberra, A.C.T. : National Library of Australia, 2013.; ANL's copy lacks cover and is slightly damaged.Panting patriot of the pattern parliament.Palmy parient of the peerless prodigies
The reduction of l-cystine hydrochloride at lead using static and rotating disc electrodes
No full textThe reduction of the disulphide, l-cystine hydrochloride to the l-cysteine hydrochloride thiol, in 0.1 mol dm?3 HCl at 298 K, has been studied at pre-treated, circular, 0.50 cm2 lead disc electrodes using steady state linear sweep voltammetry, non-steady state voltammetry and controlled potential coulometry. The diffusion coefficient for l-cystine hydrochloride was approximately 4.8 × 10?10 m2 s?1 from the three techniques. Reduction of the disulphide was irreversible and hydrogen evolution occurred as a competitive reaction at approximately ?1.35 V vs. SCE. Analysis of the mixed control kinetics, using a Koutecky–Levich approach, allowed the relative roles of charge transfer and mass transport to be resolved. Anomalously high Tafel slopes, of typically ?183 mV, were observed due to disulphide adsorption. The charge transfer kinetics are consistent with the first electron gain being rate determining while reaction orders are +1 with respect to both the disulphide and proton concentrations. The mechanism of l-cystine hydrochloride reduction has been critically discussed
The reduction of l-cystine in hydrochloric acid at mercury drop electrodes
No full textThe reduction of L-cystine in 0.1 mol dm3 HCl at 298 K has been studied at mercury electrodes. Dropping mercury electrode (DME), static mercury drop electrode (SMDE) and hanging mercury drop electrode (HMDE) modes were used with normal, sampled d.c. and differential pulse polarographic detection. The charge transfer kinetics for the irreversible reduction of L-cystine were complicated by reactant and product adsorption, by the formation of cysteinate complexes between mercury and the product thiol as well as by formation of Hg2Cl2. High Tafel slopes of 182 mV per decade were observed with a cathodic transfer coefficient of 0.32. The diffusion coefficient of L-cystine was found to be 5.3 · 10-10 m2 s-1 in 0.1 mol dm-3 HCl and 4.2 · 10-10 m2 s-1 in 2.0 mol dm-3 HCl at 298 K. The
mechanism of L-cystine reduction at mercury has been discussed and the effects of pH and reactant concentration have been quantified
Recent trends and developments in polymer electrolyte membrane fuel cell modelling
No full textModelling and simulation are well-established tools for investigating the physical processes inside a polymer electrolyte membrane (PEM) fuel cell. The early literature paid great attention to steady-state transport phenomena in the main components, which continues to be a focus of ongoing activities. There is, on the other hand, a growing interest in modelling other aspects of fuel cell operation, such as transient performance and degradation phenomena. There has also been a growth in the number of molecular and pore-level studies of transport phenomena in fuel cell components, enabled by developments in simulation techniques and enhancements in computer hardware. Such approaches are capable of representing important small-scale phenomena more faithfully than traditional macroscopic models. This review summarises recent activity in PEM fuel cell modelling, with a focus on detailed physical models, and considers its potential significance. An industrial perspective is also provided, highlighting the current use of modelling in the test and design cycles, and outlining future requirements.<br/
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