Synthesis and characterization of Pt/CuBi2O4. Application to photocatalytic H2 evolution under visible light

Abstract

The platinized spinel Pt/CuBi2O4 (Pt/CBO) is successfully employed as catalyst for the H2 formation under visible irradiation for the first time. CBO is synthetized by sol gel route from nitrates precursors and calcined at 800 °C. The X-Ray Diffractometry (XRD), X-Ray photoelectron spectroscopy (XPS), UV–Visible diffuse reflectance, Raman spectroscopy and Scanning Electron Microscopy (SEM/EDX) were used for the physical characterization. CBO crystallizes in a tetragonal symmetry (Space Group: P4/ncc). The spinel is p-type semiconductor with a narrow optical gap (1.51 eV) with a transition directly permitted. The reduction of adsorbed H2O molecules to gaseous H2 at ∼ -0.5 VAg/Agcl is evidenced by cyclic voltammetry. The latter is determined from the capacitance measurement in KOH (0.1 M) solution where the spinel exhibits a chemical stability with an exchange current of 50 µA cm−2. The conduction band deriving from the Bi3+: 6p, (3.59 eV/Vacuum / −1.15 VAg/Agcl) is energetically localized above the H2O level (∼-0.7 VAg/Agcl), leading to the feasibility of CBO for the H2 release. The photo-electrochemical activity shows an optimal H2 formation of 270 µmol with a release rate of 8.1 µmol h−1 (mg catalyst)−1 under visible illumination (LED lamp: 3 × 13 W, 1.65 × 1019 photons s−1) in KOH electrolyte (0.1 M) using I− as reducing agent. Pt-islands deposited under UV light improves significantly the photocatalysis (61 %) due to its low overvoltage (∼70 mV) with a quantum yield of 0.91 %, compared to CBO alone.