Hexagonal structured Zn(1−x)CdxO solid solution thin films: synthesis, characterization and applications in photoelectrochemical water splitting

Abstract

Hexagonal nanostructured zinc–cadmium oxide [Zn_(1−x)Cd_xO where x = 0.08, 0.15, and 0.17] solid solution thin films were deposited on FTO coated glass substrates from a common solution of zinc acetate and a newly developed polymeric cadmium precursor by an aerosol-assisted chemical vapour deposition (AACVD) technique. The polymeric cadmium precursor [Cd₃(TFA)₄(OAc)₂(THF)₄]_n (1) was synthesized by the reaction of cadmium(II)acetate dihydrate with triflouroacetic acid in THF solution and characterized by melting point, microanalysis, FTIR, ¹H-NMR, thermogravimetry (TG/DTG) and single crystal X-ray analysis. The deposited thin films were characterized by powder XRD, SEM, EDX and UV-visible spectrophotometry, and tested for photoelectrochemical (PEC) water splitting to hydrogen and oxygen. The effect of various thin film deposition parameters such as solvent type, temperature and electrolyte concentration on PEC properties has been investigated. The SEM analysis illustrated that the morphology of the films changes significantly with the change of the solvent. The films deposited from THF solution have a needle-like appearance scattered vertically on the FTO-coated glass substrate. An optical band gap of 2.40 eV has been estimated by UV-visible spectrophotometry. The current–voltage characterization proved that the nanocrystalline hexagonal structured Zn_0.83Cd_0.17O electrodes exhibit an n-type semiconducting behaviour and the photocurrent was found to be strongly dependent on the deposition solvent, deposition temperature and electrolyte concentration. The maximum photocurrent density of 0.23 mA cm⁻² at 0.55 V vs. Ag/AgCl/3 M KCl (∼1.23 V vs. RHE) was obtained for the Zn_0.83Cd_0.17O photoelectrode deposited at 500 °C for 45 min from 0.5 M solution of (1) and Zn(CH₃COO)₂·2H₂O in THF.