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

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 degrees 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 mu A 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 photoelectrochemical activity shows an optimal H2 formation of 270 mu mol with a release rate of 8.1 mu mol h-1 (mg catalyst)-1 under visible illumination (LED lamp: 3 x 13 W, 1.65 x 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.