Measurements of the Steady‐State Activation Overpotential of Chlorine Evolving Electrodes

Abstract

Detailed measurements of interfacial concentration and concentration overpotential of chlorine evolving platinized platinum electrodes were performed in 4.9M NaC], at 25~ and 1 atm chlorine or 1 arm nitrogen in the cell. Based on these and electrode polarization measurements, steady-state activation overpotential curves were obtained. The applied method enabled for the first time in this field, development of true steady-state activation overpotential curves. Our findings indicated that 30-40 mV/decade slopes typically obtained in nitrogen atmosphere were essentially a sequence of quasi equilibria at the electrode interface. Also, micropolarization data obtained near the open circuit with chlorine atmosphere in the cell were found to be a concentration overpotential phenomenon. The true activation overpotential was found to become a significant part of the electrode polarization only after it exceeded several millivolts in chlorine saturated brine. In nitrogen saturated brine, where the open circuit was undefined, the activation overpotential became significant for polarizations that exceeded two decades of steady-state low current density polarization. In this case, the activation overpotential was observable as a departure from a 32 mV/decade slope. The obtained activation overpotential curves can be used as a base for developing kinetic parameters, however, a considerably greater emphasis than in the past must be given to the corresponding interfacial conditions. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-03-29 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-03-29 to IP

Organic Photoredox Catalysis

“…In an effort to improve the robustness of this class, other 9-mesityl acridiniums have been synthesized, bearing alkyl substituents on the acridinium ring system 319−321 as well as N-phenyl substitution to prevent dealkylation. 319 323 The alkyl C−H bond is thought to be cleaved by H atom abstraction with Cl•. The alkyl radical 71.14 is captured by O 2 to generate alkyl peroxyl radical 71.15, which is detected in the steady EPR spectrum, and the alcohol and ketone products are ultimately formed by disproportionation.…”

“…Although combined yields of 71.2 and 71.3 are low (9–18%), the authors report a turnover number (TON) of 7 based on the consumption of cyclohexane 71.4 , demonstrating the catalytic activity of Mes-Acr-Me + . As the cycloalkanes possess prohibitively high oxidation potentials, the proposed mechanism involves oxidation of Cl – to Cl • by Mes-Acr-Me + [ E 1/2 ( Cl•/Cl – ) = +1.15 V vs SCE] . The alkyl C–H bond is thought to be cleaved by H atom abstraction with Cl • .…”

Metal-free oxygenation of cyclohexane with oxygen catalyzed by 9-mesityl-10-methylacridinium and hydrogen chloride under visible light irradiation

“…The one-electron oxidation potential of the electron-transfer state of Acr + -Mes is 2.06 V vs. SCE in MeCN 12, more positive than that of Cl À (1.15 V vs. SCE). 16 The quenching of the electron-transfer state of Acr + -Mes is due to electron transfer oxidation of Cl À with Acr -Mes + to form Cl and Acr -Mes. On the other hand, electron-transfer reducing ability of the electron-transfer state of Acr + -Mes is enough to reduce O 2 to O 2…”

Mechanistic Insight into the Light-Triggered CuAAC Reaction: Does Any of the Photocatalyst Go?

“…For the evaluation of the reductive cycle involvement, we estimated the free energy associated with the oxidation of DABCO, Et 3 N, NaN 3 , and Cl – with redox potential values of +0.56, +0.96, +1.08, and +1.15 V (all vs SCE), , respectively, from 1 EY* and 3 EY* (eq ). The estimated Δ G et from the 1 EY* are Δ G et = −0.69 eV, Δ G et = −0.29 eV, Δ G et = −0.17 eV, and Δ G et = −0.1 eV for DABCO, Et 3 N, NaN 3 , and Cl – , respectively.…”