Publications Internationales

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Author: search.filters.author.Trari, M.Subject: search.filters.subject.Hydrogen

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    Semiconducting and electrochemical properties of the spinel FeCo2O4 synthetized by co-precipitation. Application to H2 production under visible light
    (Elsevier, 2023) Bouakaz, H.; Abbas, Moussa; Benallal, S.; Brahimi, R.; Trari, M.
    FeCo2O4 elaborated by co-precipitation was characterized photo-electrochemically for the first time in order to assess its performance for the hydrogen production. The X-ray diffraction revealed a single phase crystallizing in the spinel structure with a lattice constant of 8.1075 Å and a crystallite size of 35 nm. The UV–Visible diffuse reflectance of the black product exhibits an absorption above 650 nm and a direct optical transition at 1.53 eV was determined, assigned to the crystal field splitting of Co3+: 3d orbital hexa-coordinated. The transport properties indicated semi-conducting properties of FeCo2O4, the positive thermo-power (S300k = 666 μV K−1) demonstrated that holes are majority charge carriers. The Electrochemical Impedance Spectroscopy (EIS) realized in Na2SO4 (0.1 M) electrolyte showed two semicircles at high and intermediate frequencies, characteristic of the charge transfer and grain boundaries respectively. The first diameter (1249 Ω cm2) decreases under visible light down to 742 Ω cm2, thus supporting the semiconducting behavior and no inhibiting effect is observed due to the appearance of the photo-effect. The inverse of the square of the capacitance as a function of the potential (C−2 – E) exhibits a line, negatively slopped, characteristic of p-type behavior with a hole concentration of 21.9 × 1020 cm−3. The conduction band (−0.76 VSCE), made up of Co3+: 3d orbital is more cathodic than the H2-level leading to a spontaneous H2 evolution under visible irradiation (29 mW cm−2) with a liberation rate of 0.58 μmol H2/h−1/g. FeCo2O4 an showed excellent chemical stability after its reuse for the H2 production, as evidenced by X-ray diffraction
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    Photoelectrochemical characterization of nano-crednerite AgMnO2 synthesized by Auto-Ignition : a novel Pphotocatalyst for H2 evolution
    (Springer, 2022) Koriche, N.; Brahimi, R.; Bellal, B.; Trari, M.
    AgMnO2 nanocrystallites (31 nm) were prepared by sol-gel auto-ignition at 400°C in air. The crednerite characterized by X-ray diffraction (XRD) showed a single phase, crystallizing in a monoclinic unit cell (SG: C2/m). The refinement was made by isotypy with CuMnO2. The oxide is a narrow band-gap semiconductor with an indirect transition at 1.43 eV. The electrical conduction occurs predominantly by small polaron hopping between mixed valences Ag2+/+ in the (a, b) planes with an activation energy of 0.35 eV. The density of holes (NA = 2 × 1015 cm–3) and their mobility (μh = 0.8 × 10–4 m–2 V–1 s–1) indicate a conduction being thermally activated. The oxygen insertion in the layered crystal lattice induces p-type conductivity, a fact confirmed by the electrochemical measurements. The flat band potential (Efb = –0.04 V) indicates a cationic character of both valence and conduction bands deriving mostly from Ag+ 4d-orbital. The electrochemical impedance spectroscopy shows the predominance of the bulk contribution followed by diffusion of O2– species. The energetic band diagram of AgMnO2 established from the photoelectrochemical study, predicts a spontaneous hydrogen formation; a rate evolution of 39 µmol g–1 min–1 and a power conversion of 0.37% were obtained under visible light irradiation (27 mW cm–2)
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