Electro-oxidation of Cyclohexanol on a Copper Electrode Modified by Copper-dimethylglyoxime Complex Formed by Electrochemical Synthesis

Abstract

Copper-dimethylglyoxime complex (CuDMG) modified Copper electrode (Cu/CuDMG) showed a catalytic activity towards cyclohexanol oxidation in NaOH solution. The modified electrode prepared by the dimethylglyoxime anodic deposition on Cu electrode in the solution contained 0.20 M NH4Cl + NH4OH (pH 9.50) and 1 × 10 -4 M dimethylglyoxime. The modified electrode conditioned by potential recycling in a potential range of -900 ~ 900 mV vs. Ag/AgCl by cyclic voltammetry in alkaline medium (1 M NaOH). The results show that the CuDMG film on the electrode behaves as an efficient catalyst for the electro-oxidation of cyclohexanol in alkaline medium via Cu (III) species formed on the electrode.

The Role of Carbon on Copper–Carbon Composites for the Electrooxidation of Alcohols in an Alkaline Medium

“…Moreover, the anodic peaks a1 and a2 are shifted to more positive potentials of about −310 and 130 mV, respectively. Similar electrochemical behavior has been reported for the electrooxidation of methanol and cyclohexanol at copper electrodes in alkaline conditions [15][16][17]. Concerning a relative distribution of surface functional groups, the C 1s core-level spectra of the studied samples revealed differences in the chemistry of the carbon matrix.…”

“…Moreover, the anodic peaks a1 and a2 are shifted to more positive potentials of about −310 and 130 mV, respectively. Similar electrochemical behavior has been reported for the electrooxidation of methanol and cyclohexanol at copper electrodes in alkaline conditions [15][16][17]. Adsorption of unsaturated alcohols likely takes place on copper species of low valence state and it is further oxidized via the participation of Cu(III) species at a high potential (peak a3) parallel to CuOOH formation from Cu(II).…”

“…Considering the complexity of the electrooxidation-reduction reaction mechanisms of the copper species, we first explored the electrochemical response of a copper rod in 0.1 M NaOH by means of cyclic voltammetry (Figure 1). The voltammograms showed a pattern of well-defined anodic and cathodic peaks corresponding to copper-based electrogenerated redox species, widely reported in the literature [6,12,15,16]. Briefly, Reaction (1) describes the oxidation of Cu(0) to Cu(I) redox species as denoted by peaks a1/c1.…”

“…Particular emphasis is placed on the use of copper due to its rich redox chemistry, with multiple reductive and oxidative reactions catalyzed by different copper complexes and oxides obtained as a function of applied electric potential; i.e., the reduction of Cu(II) species to either Cu(I) or Cu(0) species, and then the oxidation to Cu(II) or Cu(III), which in some cases are redox species with limited solubility in alkaline media [6][7][8][9][10]. Several works have shown copper-based electrodes as active catalysts in multiple processes such as electroanalysis and sensors [11][12][13][14], electrooxidation of small organic molecules [15,16], fuel cells [14,17], organic electrosynthesis [18], water oxidation [19,20] and hydrogen evolution [20,21]. Besides, polycrystalline copper electrodes and Cu(0) nanoparticles, and even copper alloys-based electrodes, have exhibited high performance for hydrocarbon and alcohol synthesis directly from CO 2 electroreduction [22][23][24][25][26], as they are the reaction mechanisms strongly sensitive to a local pH value, electrolyte concentration, particle size, electrode composition and surface structure [27][28][29].…”