Unprecedented Electrochemiluminescence of Luminol on a Doped Diamond Thin-Film Anode. Enhancement by Electrogenerated Superoxide Radical Anion

Electrochemiluminescence (ECL) of 0.01 M luminol in NaOH medium of pH 12.0 on a boron-doped diamond (BDD) thin-film anode was studied in the absence and presence of H2O2'. Here we show a new characteristic property of BDD allowing light emission in a wide potential range of 0.5-5.0 V vs AglAgCl, KCl(sat.), a behavior not observed for other anodes. Maximum ECL intensity was found at 2.2-2.8 V without H2O2, which became 63 times more intense after adding 0.05 M H2O2. The strong enhancement of ECL in the presence of H2O2 is attributed to the larger production of emitter 3-aminophthalate dianion, formed by selective nucleophilic attack of superoxide radical anion (O2(center dot-)) to the radical electrogenerated from one-electron oxidation of the monoanionic form of luminol. Linear sweep voltammetry showed that (OH)-O-center dot was not generated from OH- oxidation, whereas O2(center dot-) can be produced from HO2- oxidation. The performance of O2(center dot-) ECL was confirmed by p-benzoquinone quenching.