Cuprous complexes and dioxygen. Part 11. Concomitant one‐ and two‐electron reduction of O₂ by the Cu ion

Abstract

The autoxidation of Cu' in aqueous MeCN has been studied using a Clark oxygen electrode in the presence and absence of Cu". The reaction is inhibited by Cur' in the pH range of 0.5 to 5.0, reaching a lower limiting value at the highest concentrations. The reaction order changes from 1 to 2 with respect to Cu' under the influence of Cu2+ ion. Detailed kinetics analysis of a total of 275 measurements has shown that an unstable primary adduct Cu0; decomposes to give '0; or H02, depending on pH, and also reacts directly with a second Cu+ ion, avoiding one-electron reduction of O2 by this path. Reaction of H 0 2 is faster with Cu' than with Cu" by a factor of 20, and single-electron transfer within CuOl to Cu2+ and '0; predominates over reaction with a second copper ion for [Cu',,,] < 2 .M in the absence of Cu2+. The most likely value for the reaction of '07 with Cu'is 5.3 . lo8 M-IsC', but even this high rate constant is at the limit of significance. All secondary reactions following the initial formation of CuOz are shown to be very fast, a fact that should be properly considered in the discussion of mechanisms of copper-catalyzed oxidations and oxygenations.

Accessing copper oxidation states of dissolved negative electrode current collectors in lithium ion batteries

“…The stabilization of both dissolved copper species was conducted with complexing agents in order to enable the investigation of both species via CE. Therefore, Cu + was complexed with Cu + ‐selective NC to prevent the oxidation in contact with air, the favored disproportionation reaction to Cu 0 and Cu 2+ and the precipitation of Cu 2 O at neutral or alkaline pH [33,39–45]. Furthermore, the sample preparation was performed under a counter flow of argon to avoid oxidation of non‐stabilized Cu + by ambient O 2 (Supporting Information).…”

“…Previous complexation of Cu + with NC to an orange colored [Cu(NC) 2 ] + ‐complex successfully prevented the loss of Cu + . Therefore, a NC/ACN solution (100 mM NC) was applied since the coordination of ACN to Cu + provides additionally stability of this species during sample preparation [42–45]. However, the formation of the more stable Cu + ‐NC complex was not interfered by ACN.…”

“…Since the sample preparation was performed under argon atmosphere, oxidation of Cu + by ambient molecular oxygen can be excluded. Therefore, the formation of Cu 2+ can be attributed to the disproportionation reaction of non‐stabilized Cu + in the electrolyte to Cu 2+ and Cu 0 [44]. In contrast to the spontaneous precipitation of copper particles in aqueous solutions in presence of EDTA, no precipitated copper was observed in the electrolyte.…”

“…Proposed dissolution mechanisms of Cu + and Cu 2+ from negative electrode current collector: Acidic dissolution of the passivating oxide layer or possible oxidative corrosion of copper in case of contamination with O 2 (italic letters) [58]. Subsequently, the dissolved Cu + undergo a further disproportionation reaction to Cu 0 and Cu 2+ or could be oxidized by O 2 to Cu 2+ (italic letters) [39,44,45]. …”

“…The copper dissolution can be associated with the formation of acidic electrolyte decomposition products, e.g., HF and subsequent dissolution of the passivating oxide layer (mainly Cu 2 O) of the current collector [33,58,59]. Since Cu 2 O tends to dissolve more easily in presence of HF in comparison to CuO, continuous dissolution of particularly Cu + and subsequent disproportionation of Cu + to Cu 0 and Cu 2+ can be proposed for these conducted experiments [44, 58]. As a consequence, Cu 2+ was detected as the main copper species in the electrolyte.…”