Anodic Cu₂S and CuS nanorod and nanowall arrays: preparation, properties and application in CO₂ photoreduction

Abstract

Copper sulfide semiconductors made from earth-abundant elements have an optical absorption edge at ca. 1.2 eV, nearly ideal for solar energy harvesting. We report the growth and formation mechanism of vertically oriented arrays of copper sulfide nanostructures formed by electrochemical anodization. Key parameters that affect the morphology and phase of the nanostructures are type and strength of electrolyte, anodization voltage and duration. Cu₂S and CuS nanostructures were obtained on both copper foil and copper-coated flexible Kapton substrates, and depending on the anodization parameters, consisted of vertically oriented arrays of nanowalls, nanoleafs or rods with branched nanodendrites. The anodization parameters also controlled the phase and stoichiometry of the nanostructures. p-type conduction for Cu₂S nanostructures and n-type conduction for CuS nanostructures were revealed by admittance spectroscopy and Mott Schottky analysis. We also observed a weak, but nevertheless promising and previously unnoticed, photocatalytic action in copper sulfide nanorod and platelet arrays for the sunlight-driven conversion of CO₂ into CH₄. Under irradiation by AM 1.5G simulated sunlight at room temperature, a CH₄ production rate as high as 38 μmol m(-2) h(-1) was obtained using the copper sulfide nanostructure arrays as stand-alone photocatalysts for CO₂ photoreduction.

One-pot hydrothermal synthesis of CdS decorated CuS microflower-like structures for enhanced photocatalytic properties

“…In addition, the peak positions of Cu 2p for Cd-1-T4 are apparently shifted to much lower binding energy region, compared with those of Cd-0-T6 and Cd-1-T6, illustrating the formation of much more Cu + on the surface. These results are in well agreement with the observation of S 2p region and previous reports 30, 52 . The reason for the formation of Cu 2 S may be ascribed to the amount of thiourea and chloride ions from the addition of cadmium chloride in the precursor solution 45, 52–54 .

Figure 7XPS analysis of as-synthesized samples in the Cu 2p, Cd 3d and S 2p regions.

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“…These results are in well agreement with the observation of S 2p region and previous reports 30, 52 . The reason for the formation of Cu 2 S may be ascribed to the amount of thiourea and chloride ions from the addition of cadmium chloride in the precursor solution 45, 52–54 .

Figure 7XPS analysis of as-synthesized samples in the Cu 2p, Cd 3d and S 2p regions. ( a ) Samples prepared by changing the amount of Cd content with fixing thiourea, and ( b ) Samples obtained by modulating the contents of both Cd and thiourea.

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“…For the samples without CdCl 2 addition (Cd-0 and Cd-0-T6), only two main peaks located at 162.3 eV (S 2p3/2) and 163.5 eV (S 2p1/2) are observed which are assigned to S 2− , indicating the presence of metal sulfides (CuS) 4 . Another peak at around 161.5 eV appeared after the addition of CdCl 2 for the XPS spectra of S 2p region, confirming the formation of metal sulfides including Cu 2 S 29, 51, 52 . Moreover, the peak positions of Cu 2p1/2 at 951.9 eV and S 2p at 161.5 eV are slightly shifted to lower binding energy region with the increase of CdCl 2 content, indicating the existence of more Cu + on the surface in Cd-0.5, Cd-1, Cd-2, and Cd-4.…”

Graphene‐Like Multilayered CuS Nanosheets Assembled into Flower‐Like Microspheres and Their Electrocatalytic Oxygen Evolution Properties

“…For the peaks of 161.3 (S 2p 3/2 ) and 163.2 eV (S 2p 1/2 ) are characteristic of sulfide, which should be attributed to the S−S bond in graphene‐like multilayered structure of CuS . The peaks at 162.2 (S 2p 3/2 ) and 163.2 eV (S 2p 1/2 ) are indicative of CuS, and the peak of 168.5 eV can be ascribed to the sulfate species (e. g. CuSO 4 ) formed by the oxidation of CuS in air . These results indicated that the as‐prepared products are mainly composed of Cu 2+ and S 2− .…”

Anodic copper oxide nanowire and nanopore arrays with mixed phase content: synthesis, characterization and optical limiting response

“…In contrast with vacuum deposition processes-electrochemical anodization processes are scalable, the process instrumentation cost is low, and it is relatively simple to adjust anodization conditions in order to allow tuning of nanoscale morphology as well as the semiconducting and optical properties of the resulting semiconductors. Therefore, anodically formed copper-based nanostructures are attracting increased attention [2][3][4]. The use of copper oxide nanostructures is motivated by the Earth abundance and relatively low price of copper, coupled with the high performance potential of copper oxide for several leading edge applications; these include semiconductor catalysis, solar photovoltaics and biosensing [5][6][7][8][9].…”