Grading Electrodes Research Articles

Continuous Graded Catalyst Layers for PEM Fuel Cells with Improved Humidity Range Tolerance

Abstract Grading electrodes is a promising approach to reduce ohmic and mass transport-related voltage losses in proton exchange membrane fuel cells. In graded electrodes, the ionomer and/or catalyst are spatially non-uniformly distributed to optimize performance over a wide operating range. In this study, through-plane ionomer gradients were fabricated with a simple wet-layer deposition technique that can readily be adapted in a roll-to-roll process. The presence of ionomer gradients was verified using scanning transmission electron microscopy and the profiles were found to be continuous despite using only two coating steps. Single cell tests revealed that the gradients outperform conventional electrodes and maintain the optimal performance for different relative humidities. These improvements were traced back to enhanced mass transport and protonic conduction properties identified by detailed electrochemical analysis. This manufacturing approach for electrodes offers an accessible toolbox to produce versatile and specialized multi-layered catalyst layers for different applications.

Electrical Performance Analysis of Grading Electrodes After Scaling in Converter Valves

It is necessary to take out the electrode when detecting the scaling degree of the conventional grading electrode. The steps are cumbersome and there are safety risks. In this paper, through the analysis of the equivalent circuit model before and after the scaling of the grading electrode on the cooling water manifold in the converter valve, the loop resistance model suitable for the positive and negative potential sides is obtained. The constant voltage DC source is used as the driving voltage of the circuit, and the leakage current of the circuit is measured under different temperatures and conductivity conditions of the internal cooling water. The degree of scaling of the grading electrode is determined by analyzing the leakage current. The leakage current in the non-scaling state of the grading electrode and the leakage current in the scaling failure state of the grading electrode are taken as the reference values. It is concluded that when the leakage current of the measurement circuit decreases to 68 % - 80 % of the leakage current in the non-scaling state of the grading electrode, the grading electrode can be considered to fail.

Principle and simulation of a high voltage bushing for a repetitive electron accelerator

A cylindrical graded bushing for the electron gun of the ASTRA-M pulsed repetitive accelerator was developed and simulated. In previous tests of the cylindrical graded bushing, primary reasons of electrical breakdown and degradation of dielectric elements were determined. Computational software was used to analyze the electric fields and simulate processes in the voltage grading system of the cylindrical bushing. This enabled proper modification and correction to the insulator structure for known problems. The new bushing has a conical structure instead of cylindrical one. The voltage graduation system uses nonsymmetrical voltage dividing for equal potential distribution along the grading electrodes. The grading electrodes provide shielding of organic dielectric surfaces from accelerated electrons and ultraviolet irradiation. Transmitted energy losses of up to 10% have been estimated in the nonsymmetrical voltage divider of conical bushing by simulating of high voltage pulse of 600 kV amplitude and 400 ns duration.

Inside Cover: Behavior of Highly Diluted Electrolytes in Strong Electric Fields-Prevention of Alumina Deposition on Grading Electrodes in HVDC Transmission Modules by CO2-induced pH-Control (Chem. Eur. J. 38/2014)

Inside Cover: Behavior of Highly Diluted Electrolytes in Strong Electric Fields-Prevention of Alumina Deposition on Grading Electrodes in HVDC Transmission Modules by CO₂-induced pH-Control (Chem. Eur. J. 38/2014)

Behavior of highly diluted electrolytes in strong electric fields-prevention of alumina deposition on grading electrodes in HVDC transmission modules by CO2-induced pH-control.

Alumina deposition on platinum grading electrodes in high voltage direct current (HVDC) transmission modules is an unsolved problem that has been around for more than three decades. This is due to the unavoidable corrosion of aluminum heat sinks that causes severe damage to electrical power plants and losses in the range of a million Euro range per day in power outage. Simple experiments in a representative HV test setup showed that aluminates at concentrations even below 10(-8) mol L(-1) can deposit on anodes through neutralization by protons produced in de-ionized water (κ≤0.15 μS cm(-1)) at 20-35 kV (8 mA) per electrode. In this otherwise electrolyte-poor aqueous environment, the depositions are formed three orders of magnitude below the critical precipitation concentration at pH 7! In the presence of an inert electrolyte such as TMAT (tetramethylammonium-p-toluenesulfonate), at a concentration level just above that of the total dissolved aluminum, no deposition was observed. Deposition can be also prevented by doping with CO2 gas at a concentration level that is magnitudes lower than that of the dissolved aluminum. From an overview of aqueous aluminum chemistry, the mystery of the alumina deposition process and its inhibition by CO2 is experimentally resolved and fully explained by field accumulation and repulsion models in synergism with acid-base equilibria. The extraordinary size of the alumina depositions is accounted for in terms of proton tunneling through "hydrated" alumina, which is supported by quantum chemical calculations. As a consequence, pulse-purging with pure CO2 gas is presented as a technical solution to prevent the deposition of alumina.

Direct Energy Conversion Beam Dump for a 1.6-Mev Neutral Beam for the International Thermonuclear Experimental Reactor

A beam direct converter of the Kyoto type, which uses magnetic separation of the D[sup +] and D[sup [minus]] leaving the neutralizer, is adapted to a Lawrence Berkeley Laboratory concept of a neutral-beam injector for the International Thermonuclear Experimental Reactor, which used electrostatic separation of the D[sup +] and D[sup [minus]]. Among the advantages of a direct converter over an ordinary beam dump for the residual D[sup +] and D[sup [minus]] beam leaving the neutralizer is that the power density on the beam dump is reduced by a large factor, making heat removal easier. Further, [open quotes]soft landing[close quotes] virtually eliminates deuterium-deuterium neutron production on the dump electrodes, a particular advantage in the development stage. In addition, the total power consumed is less. This paper addresses the technological obstacle to feasibility, which is holding the large voltage (+1.6 and -1.6 MV for a 1.6-MeV neutral beam). The electrode system in the present design uses 15 grading electrodes around each 1.6 MV collector with 100 kV between them. Each grading electrode is subdivided into two. The total stored energy is 260 J (4 J per electrode) and an average of 10 kV/cm on the insulators. The calculated efficiency is 92%. 13more » refs., 10 figs.« less

High-Voltage D-C Transmission: General Background and Present Technical Status

The keys to practical application of high-voltage (HV) direct current for power transmission are the rectifier and inverter, which supply the high voltage required for terminals of the d-c line. The grid-controlled mercury-arc tube with grading electrodes has proved to be a suitable valve in such converters. Special features and characteristics of HV converters and of the terminal stations are mentioned, and projects in operation and under construction are specified. Future fields of application are discussed.

Operating Mechanisms of Grading Electrodes in Mercury-Arc Rectifier

Operating Mechanisms of Grading Electrodes in Mercury-Arc Rectifier