Diarylamine/diarylnitroxide cycle: quantum chemical and electrochemical estimation

Abstract

Possibility for diarylamine/diarylnitroxide cycling via electrochemical N–O bond formation/bond breaking processes was considered using quantum-chemical and electrochemical methods. It was shown that electrochemically reduced diarylnitroxides undergo fast N–O bond cleavage in the presence of oxophilic Li ions. The possible reaction scheme was suggested. In contrast, in the presence of Na+ salts, aminoxyl anions are stable and can be considered as possible anodic redox active material in energy storage systems utilizing Na+ ions migration. Direct oxygenation of diarylaminyl radicals with dioxygen yielding diarylnitroxide is not feasible; multiple competing routes involving the aromatic moiety are observed instead. The results obtained shed light on possibilities and limitations for functioning of nitroxide-based redox active electrode materials.

A PROXYL‐Type Norbornene Polymer for High‐Voltage Cathodes in Lithium Batteries

“…Diaryl nitroxide radicals currently give the highest redox potentials of over 4 V versus Li/Li + , although the long-term stability is not ideal. [20,21] Nitronyl nitroxide (3.5 V), [15] verdazyl (around 2.9 V), [22] and triphenylmethyl radicals (around 2.9 V) [23] would offer improved stability, but lower voltages. On the other hand, a nitroxide radical with a five-membered ring, tetramethylpyrrolidine 1-oxyl (PROXYL), and their derivatives are reported as chemically robust and to give higher potentials than TEMPO (≈3.7 V).…”