Enhanced activity of H₂O₂-treated copper(ii) oxide nanostructures for the electrochemical evolution of oxygen

Abstract

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 environmental-friendly process for producing H2 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 currents at 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 O2 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% IrOx/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 O2, 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 O2 evolution by the CuO nanostructures is thus attributed to not just its higher surface area, but also to the higher population of Cu III active sites on its surface.

Treating Copper(II) Oxide Nanoflowers with Hydrogen Peroxide: A Novel and Facile Strategy To Prepare High‐Performance Copper(II) Oxide Nanosheets with Exposed (1 1 0) Facets

“…Their results showed that the CuO straw leaves were formed by a crystal‐splitting growth process, and they exhibited much higher activity than the irregular sample for the degradation of rhodamine B under visible‐light irradiation, which was ascribed to the exposed (1 1 0) facets and high crystallinity. Handoko et al . synthesized nanostructured CuO, which was transformed from nanostructured Cu 2 O precursors by treatment with H 2 O 2 .…”

Electrospun Cu‐Deposited Flexible Fibers as an Efficient Oxygen Evolution Reaction Electrocatalyst

“…Cu/PVdF‐HFP fiber catalyst showed the best OER activity among the catalysts tested, suggesting the reaction energetics of Cu/PVdF‐HFP were optimal for OER. Based on the widely accepted reaction mechanism for OER (Figure ), it is likely that the slightly electron‐deficient Cu site formed on the Cu/PVdF‐HFP fiber could enhance the electrophilicity of the adsorbed O (O ad ), and hence promote the formation of OOH ad via nucleophilic attack from OH − within the electrolyte . It can also facilitate the subsequent deprotonation of OOH ad , through electron‐withdrawing inductive effects, to give molecular O 2 .…”

“…Based on the widely accepted reaction mechanism for OER ( Figure 5), [68][69] it is likely that the slightly electron-deficient Cu site formed on the Cu/ PVdF-HFP fiber could enhance the electrophilicity of the adsorbed O (O ad ), and hence promote the formation of OOH ad via nucleophilic attack from OH À within the electrolyte. [33] It can also facilitate the subsequent deprotonation of OOH ad , through electron-withdrawing inductive effects, to give molecular O 2 . [47] The trend in the shift observed in XPS follows the trend in the activity of the OER, further supporting our hypothesis.…”

Copper Containing Molecular Systems in Electrocatalytic Water Oxidation—Trends and Perspectives

“…Although the main topic of this review is the application of complexes majorly based on organic ligands either as molecular catalyst of OER or precursor remaining on the grounds of preferably in situ electrochemical methods, it has to be mentioned that several papers have been published on systems that have been fabricated from the corresponding pre-made inorganic components such Cu/CuO nanowires [106,107], CuO [107], annealed CuO [108], H 2 O 2 -treated CuO [109], or others. These examples were summarized by Naruta et al recently (see the ESI of their publication) [101], therefore we do not intend to duplicate their work.…”