Overpotential

About: Overpotential is a research topic. Over the lifetime, 16474 publications have been published within this topic receiving 616632 citations.

Mechanism and activity of photocatalytic oxygen evolution on titania anatase in aqueous surroundings.

Abstract: Due to its high overpotential and low efficiency, the conversion of water to O2 using solar energy remains a bottleneck for photocatalytic water splitting. Here the microscopic mechanisms of the oxygen evolution reaction (OER) on differently structured anatase surfaces in aqueous surroundings, namely, (101), (001), and (102), are determined and compared systematically by combining first-principles density functional theory calculations and a parallel periodic continuum solvation model. We show that OER involves the sequential removal of protons from surface oxidative species, forming surface peroxo and superoxo intermediates. The initiating step, the first proton removal, dictates the high overpotential. Only at an overpotential of 0.7 V (1.93 V vs SHE) does this rate-controlling step become surmountable at room temperature: the free energy change of the step is 0.69, 0.63, and 0.61 eV for (101), (102), and (001) surfaces, respectively. We therefore conclude that (i) OER is not sensitive to the local surf...

The Electrochemistry of Ni Pattern Anodes Used as Solid Oxide Fuel Cell Model Electrodes

Abstract: Ni pattern electrodes with well-defined triple phase boundary (TPB) lengths were prepared in order to investigate the reaction mechanisms at solid oxide fuel cell (SOFC) anodes The anode microstructures were stable during thermal treatment and electrochemical measurements Electrochemical impedance spectroscopy was used to study the influence of the overpotential of the gas atmosphere, of the temperature, and of the pattern geometry on the electrochemical behavior of SOFC anodes It is found that the reaction kinetics are dominated by one main process This process is thermally activated with an activation of energy of E A = 088 ± 004 eV At overpotentials higher than 300 mV, a second process becomes relevant The partial pressure of water in the fuel gas atmosphere has a catalytic effect on the anode performance, whereas variations of the patrial pressure of hydrogen in the fuel gas atmosphere have no significant influence on the electrode behavior A model was established in order to explain the catalytic effect of water The direct proportionality between the relaxation frequency and the TPB length suggests a TPB limitation of the anode kinetics

Electrode kinetics of Cu–SiO2-based resistive switching cells: Overcoming the voltage-time dilemma of electrochemical metallization memories

Abstract: The kinetics of the switching process in Cu–SiO2-based electrochemical metallization memory cells was investigated as a function of the switching voltage and the SiO2 film thickness. We observe an exponential dependence of the switching rate on the switching voltage and no significant thickness dependence in the range from 5to20nm SiO2. We conclude from our data that the cathodic electrodeposition represents the rate-limiting step of the switching kinetics. The voltage-time dilemma seems to be overcome by the exponential dependence of the switching rate in combination with a threshold voltage presumably originating from a nucleation overpotential.