Structural Characterization of Cu[sub 2]O After the Evolution of H[sub 2] under Visible Light Irradiation

Abstract

Photocatalysis of Cu 2 O powder was investigated to evaluate its ability for the stoichiometric decomposition of water into O 2 and H 2 . Although thus far it has been indicated that Cu 2 O can function as a photocatalyst for the overall water splitting, H 2 evolution was found to take place solely while there was no generation of O 2 . Moreover, the evolution rate of H 2 gradually decreased during prolonged irradiation, and consequently, the evolution of H 2 ceased. From the structural analyses of deactivated Cu 2 O, it appeared that the H 2 evolution originates in the self-oxidation of Cu 2 O to CuO. © 2008 The Electrochemical Society. ͓DOI: 10.1149/1.3054330͔ All rights reserved.Manuscript submitted October 16, 2008; revised manuscript received November 28, 2008. Published December 23, 2008 It has been reported that cuprous oxide ͑Cu 2 O͒ shows mechanocatalysis for the overall splitting of water into H 2 and O 2 ͑in the dark͒. 1 Cu 2 O powder is also a photocatalyst working under visible light irradiation; 2,3 however, the instance of the photocatalytic water splitting is unknown, although the edges of the conduction band and the valence band of Cu 2 O may be available for the water reactions to form H 2 and O 2 ͑Scheme 1͒. 4 According to photoelectrochemical studies on Cu 2 O, a few problems associated with water splitting have been indicated as follows: ͑i͒ when employing Cu 2 O as a photocathode, it often underwent reductive transformation, resulting in the formation of metallic Cu ͑Cu 0 ͒, because of the low activity of Cu 2 O for the reduction of water into H 2 , 4,5 and ͑ii͒ in a twoelectrode electrochemical cell system comprising a Cu 2 O photocathode and a Pt anode without bias, there was no confirmation of O 2 from water ͑at the Pt counter electrode͒, which may imply that the holes photogenerated at Cu 2 O ͑valence band͒ are not capable of water oxidation into O 2 . 6 In the present study, we examined the photocatalysis of Cu 2 O powder for overall water splitting. It was found that Cu 2 O induces the evolution of H 2 , particularly through an irreversible structural change in Cu 2 O to form CuO ͑i.e., selfoxidation͒. The details of this process are described in the following section. ExperimentalCu 2 O powder was prepared by the reduction of Cu 2+ ion in the presence of sodium thiosulfate. Ten cubic centimeters of 1.0 mol dm −3 CuSO 4 ·9H 2 O ͑Kanto Chemical͒ aqueous solution was dropped into 100 cm 3 of 1.0 mol Na 2 S 2 O 3 aqueous solution, and subsequently, the mixture solution was dropped into 200 cm 3 of 1 mol dm −3 NaOH solution at 80°C. The resulting reddish-brown precipitate ͑Cu 2 O͒ was separated by filtration and washed with deionized water; the precipitate was dried at 40°C under Ar atmosphere.X-ray powder diffraction ͑XRD͒ patterns were measured using a Shimadzu XD-610 diffractometer with Cu K␣ radiation ͑0.154 nm͒. Transmission electron microscope ͑TEM͒ observation was conducted using a Hitachi H-8000 TEM ͑accelerating voltage: 200 kV͒ in order to obtain sample images and electron diffr...

Pompon Dahlia‐like Cu2O/rGO Nanostructures for Visible Light Photocatalytic H2 Production and 4‐Chlorophenol Degradation

“…Interfacing the Cu 2 O semiconductor with rGO nanosheets to form a heterojunction almost doubles the specific activity, consistent with greater visible light absorption. [42] Hydrogen production over the hierarchical Cu 2 O was superior to that of non-porous (13 μmol.g À 1 .h À 1 ) [43] and Cu 2 O nanoparticles (10 μmol.g À 1 .h À 1 ) [7] of comparable size, and the AQE higher than reported for Pt-decorated 500 nm Cu 2 O nanocubes (AQE = 1.2 %), [41b] 375 nm hierarchical Cu 2 O nanocubes (AQE = 1.2 %), [44] and Pt-free 300-500 nm Cu 2 O powder (AQE = 0.3 %) [7] and 150 nm Cu 2 O nanostructures on a silicon wafer (AQE in water = 0.3 %) under visible light, [45] demonstrating advantageous photophysical properties of our Pompom Dahlia-like aggregates. Hydrogen production over various Cu 2 O photocatalysts is summarised in Table S3.…”

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi2O4 nanocrystals

“…Cuprous oxide itself is unstable under cathodic and anodic bias, 12,13 and the hope is to achieve greater stability in mixed metal oxides. 14,15 Many of these p-type oxides, incl.…”

TiO2/Cu2O Core/Ultrathin Shell Nanorods as Efficient and Stable Photocatalysts for Water Reduction

“…[1][2][3][4][5] Protection of electrodeposited Cu 2 Ophotocathodes with oxide thin overlayers has been examined as an approach for its application in photoelectrochemical water reduction. Hydrogen produced by photocatalytic water splitting over semiconductors by the direct use of sunlight offers aclean and renewable chemical fuel.…”