RESUMEN
Nickel(II) diethyldithiocarbamate, NiII(dtc)2, is known to undergo a 2e- ligand-coupled electron transfer (LCET) oxidation to form [NiIV(dtc)3]+. However, the thermodynamics and kinetics of this 2e- process can be greatly affected by solvent coordination. For low coordinating solvents like acetonitrile and acetone, 2e- oxidation is observed via cyclic voltammetry (CV) at a single potential while stronger coordinating solvents like methanol, N,N-dimethylformamide, dimethyl sulfoxide, and pyridine exhibit a 1e- oxidation wave by formation of [NiIII(dtc)2(sol)x]+ intermediates. The decay of these complexes to eventually yield [NiIV(dtc)3]+ was monitored as a function of CV scan rate and temperature to extract rate constants and activation parameters. A thorough analysis of activation parameters revealed that ΔHapp⧧ generally increased with solvent coordination ability, suggesting solvent dissociation was a key factor in the rate limiting step. However, ΔSapp⧧ was found to be negative for all solvents, suggesting an associative mechanism in line with dimer formation with NiII(dtc)2 to facilitate ligand exchange. Density function theory calculations supported the competitive nature of dissociative and associative steps. Using these calculations, we propose two paths for decay of [NiIII(dtc)2(sol)x]+ species based on the coordination strength of the solvent. These studies point to the ability of solvents to either aid or hinder multielectron LCET reactions.
RESUMEN
The temperature dependency of the electrochemical analysis of acetyl ferrocene (AcFc) and iron(III) acetylacetonate ([Fe(acac)3 ]) has been investigated for non-aqueous redox flow batteries (NARFBs). AcFc and [Fe(acac)3 ] were utilized as catholyte and anolyte species, respectively, in an electrochemical cell with a cell voltage of 1.41â V and Coulombic efficiencies >99% for up to 50 total cycles at room temperature (RT, 25 °C). Experiments with a rotating ring disk electrode (RRDE) indicate that the diffusion coefficient reduces with decreasing temperature from 25 °C to 0 °C, yet the overall storage capacity was higher than that of an aqueous redox flow battery (ARFBs). The electrochemical kinetic rate constant (k0 ) of AcFc was found to be greater than that of [Fe(acac)3 ]. However, the value of k0 was not affected by the variable temperature. 1 H NMR investigations reveal that temperature change during battery trials did not occur in any structural modification. The obtained result demonstrates the suitability of this battery at low temperatures.