Unprecedented Electrochemiluminescence of Luminol on a Boron-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 H 2 O 2 . Here we show a new characteristic property of BDD allowing light emission in a wide potential range of 0.5–5.0 V vs Ag|AgCl, KCl(sat.), a behavior not observed for other anodes. Maximum ECL intensity was found at 2.2–2.8 V without H 2 O 2, which became 63 times more intense after adding 0.05 M H 2 O 2 . The strong enhancement of ECL in the presence of H 2 O 2 is attributed to the larger production of emitter 3-aminophthalate dianion, formed by selective nucleophilic attack of superoxide radical anion (O 2 •– ) to the radical electrogenerated from one-electron oxidation of the monoanionic form of luminol. Linear sweep voltammetry showed that • OH was not generated from OH – oxidation, whereas O 2 •– can be produced from HO 2 – oxidation. The performance of O 2 •– in ECL was confirmed by p -benzoquinone quenching.