IEEE(CHAPTER9)(Electro chemical power sources)(345 380)

A series of experiments are conducted in order to investigate the performance of a proton exchange membrane (PEM) fuel cell using a commercially available polybenzimidazole (PBI)-based high temperature membrane. During the study a drastic degradation in performance is observed over time and a significant amount of solid material built-up is found in the flow field plate and the membrane-electrode assembly (MEA). The built-up material is examined by the use of a Scanning Electron Microscope (SEM). Further elemental analysis using Energy Dispersive X-ray Spectroscopy (EDS) finds that the built-up material contains large amount of phosphorus, thus relating it with the excess phosphoric acid found in the MEA. Additional experimental studies show that the built-up material is caused by the excess acid solution in the MEA, and when the excess phosphoric acid is removed from the MEA the fuel cell performance improves significantly and becomes very stable.

A DMFC model is developed to study the effects of cathode catalyst layer thickness. The distribution of methanol concentration in the cathode catalyst layer is considered. Modeling results agree well with experimental data for difference CCL thickness. Neglecting methanol contamination in the CCL significantly overpredicts fuel cell performance.

Solvents influence on crossover and capacity decay was studied for vanadium NARFBs. Nafion and low permeability Nafion/SiO 2 was evaluated in two solvent environments. A method to estimate species crossover was developed from self-discharge tests. 84/16 vol% AC/1,3 DO mixture improved capacity retention and efficiency. Crossover rate variation was due to membrane changes in the different solvents.

Current densities under the land and channel are separately measured in DMFCs. Current density is much higher under the land than that under the channel. The main reason for the higher current density is the much higher ECA under the land.

Practical Electro-Chemistry By BERTRAM BLOUNT /JJ F.I.C., Assoc.Inst.C.E CONSULTING CHEMIST TO THE CROWN AGENTS FOR THE COLONIES FULLY ILLUSTRATED SECOND EDITION REVISED AND BROUGHT UP TO DATE

Influences of feeding gas compositions on the performance of co-planar, single chamber solid oxide fuel cells (SC-SOFCs) are investigated with emphasis on the role of water vapor. The maximum open circuit voltage (OCV) and peak power density are obtained at a methane-to-oxygen ratio of 3.5 under the wet gas condition, and a stoichiometric ratio of 2.0 for methane partial oxidation under the dry gas condition. In addition to the partial oxidation of methane on the anode and electrocatalytic reactions, both steam reforming and methane combustion occur on the anode and cathode, respectively, in the presence of water vapor. Local volume expansion and a rise in temperature associated with these parasitic reactions intensify inter-mixing of the reactant and product gases by which the OCV and power density drastically deteriorate with decreasing anode-to-cathode gap distance, as confirmed by impedance analysis for the LSM-YSZ|YSZ|LSM-YSZ symmetrical cell.

Journal of Electrochemical Science and Engineering, 2012

Through this story an attempt has been made to present a chronology of electrochemical engineering-from its appearance as an individual science, via its growth throughout the five decades of its existence as an individual science, until today. The collaboration and linkage of electrochemical engineering with other disciplines has also been discussed in this essay. The role and duties of electrochemical engineering in the 21 st century have been touched upon to the extent that it was possible.

If app ia bte) UNC Chemistry Dept. Office of Naval Research (Code 413) 6c. ADDRESS (City. Slate and ZIP Code) 7b. ADDRESS (City. State and ZIP Code

An electrolysis-cell design for simultaneous electrochemical reduction of CO 2 and H 2 O to make syngas ͑CO + H 2 ͒ at room temperature ͑25°C͒ was developed, based on a technology very close to that of proton-exchange-membrane fuel cells ͑PEMFC͒, i.e., based on the use of gas-diffusion electrodes so as to achieve high current densities. While a configuration involving a proton-exchange membrane ͑Nafion͒ as electrolyte was shown to be unfavorable for CO 2 reduction, a modified configuration based on the insertion of a pH-buffer layer ͑aqueous KHCO 3 ͒ between the silver-based cathode catalyst layer and the Nafion membrane allows for a great enhancement of the cathode selectivity for CO 2 reduction to CO ͓ca. 30 mA/cm 2 at a potential of −1.7 to −1.75 V vs SCE ͑saturated-calomel reference electrode͔͒. A CO/H 2 ratio of 1/2, suitable for methanol synthesis, is obtained at a potential of ca. −2 V vs SCE and a total current density of ca. 80 mA/cm 2 . An issue that has been identified is the change in product selectivity upon long-term electrolysis. Results obtained with two other cell designs are also presented and compared.

Electrochemistry has undergone significant transformations in the last few decades. It is not now the province of academics interested only in measuring thermodynamic properties of solutions or of industrialists using electrolysis or manufacturing batteries, with a huge gulf between them. It has become clear that these two, apparently distinct subjects, and others, have a common ground and they have grown towards each other, particularly as a result of research into the rates of electrochemical processes. Such an evolution is due to a number of factors, but principally the possibility of carrying out reproducible, dynamic experiments under an ever-increasing variety of conditions with reliable and sensitive instrumentation. This has enabled many studies of a fundamental and applied nature to be carried out.