Enhanced activity of H2O2-treated copper(ii) oxide nanostructures for the electrochemical evolution of oxygenElectronic supplementary information (ESI) available: (1) Detailed characterisation of catalysts described in this manuscript, (2) online mass spectrometry data, (3) calculation of turnover frequencies, (4) surface area estimation, (5) stability assessments, (6) details of Raman measurements and peak assignments, and (7) synthesis and characterisation of CuIII-containing NaCuO2. See DOI:

• Main Authors: Handoko, Albertus D, Deng, Suzi, Deng, Yilin, Cheng, Andy Wing Fai, Chan, Kuang Wen, Tan, Hui Ru, Pan, Yanlin, Tok, Eng Soon, Sow, Chorng Haur, Yeo, Boon Siang
• Format: Article
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/c5cy00861a

The successful design and synthesis of earth-abundant and efficient catalysts for the oxygen evolution reaction (OER) will be a major step forward towards the use of electrochemical water splitting as an environmentally-friendly process for producing H 2 fuel. Due to their poor activity, copper-based materials have not been considered apt for catalysing OER. In this work, we demonstrate that unique copper( ii ) oxide nanostructures obtained via hydrothermal synthesis and subsequent hydrogen peroxide treatment exhibit unusually high and sustainable OER activity. In 0.1 M KOH electrolyte, the CuO nanostructures catalyse OER with current densities of 2.6-3.4 mA cm −2 at 1.75 V ( vs. RHE). The calculated turnover frequency (per Cu site) of ~2 × 10 −3 s −1 for O 2 production is markedly higher than that of high-surface area electrodeposited Cu metal nanoparticles by 40-68 times. The OER activity of the CuO nanostructures is also stable, approaching about half of 20% IrO x /Vulcan XC-72 after an hour-long OER. In situ Raman spectroscopy at OER-relevant potentials recorded compelling evidence that Cu III active species may be responsible for the unusual OER activity of the CuO nanostructures, as indicated by its signature vibration at 603 cm −1 . This hitherto unobserved peak is assigned, with the aid of the model compound NaCu III O 2 , to the Cu-O stretching vibration of Cu III oxide. This feature was not found on electrodeposited Cu metal, which exhibited correspondingly weaker OER activity. The enhanced catalysis of O 2 evolution by the CuO nanostructures is thus attributed to not just their higher surface area, but also the higher population of Cu III active sites on their surface. H 2 O 2 -treated CuO nanostructures show 40-68× higher OER activity than Cu nanoparticles.