Physical properties of the solid solution CuFe2-xMnxO4 prepared by sol-gel route: Application to photocatalytic hydrogen production

[Display omitted] •The spinel CuFe2-xMnxO4, elaborated by sol gel route exhibits p-type behaviour with a conduction band (−1.11 V) above the H2 level.•The formation of the tetragonal phase with a well crystallization and a good stoichiometry was confirmed by both the X-Ray diffraction (XRD) and XPS analysis.•A Fill factor of 0.56 was obtained under a light power (E) of 40 mW cm−2 for CuFe0.4Mn1.6O4.•H2-evolution rate of 3.4 μmol min−1 g−1 was obtained on CuFe0.4Mn1.6O4 under a light flux of 2.09 × 1019 photons s−1. The solid solution CuFe2-xMnxO4 prepared by sol–gel method and annealed at 850 °C crystallizes in the spinel structure. The structural, optical and transport properties were systematically investigated. The formation of the tetragonal phase with a well crystallization and stoichiometry was confirmed by both the X-Ray diffraction (XRD) and XPS analysis. It has been found that the optical gap decreases with increasing the Mn-concentration. The electrical properties are characteristic of p-type behavior where the conductivity decreases with the Mn content, and is governed by the thermal emission over the inter-crystalline barrier. Moreover, the spinels possesses a mobility of ∼10−5 cm2 V−1 s−1. The fill factor (FF) was correlated to the diffusion length (L) which demonstrates the intrinsic character of the lifetime of the charges carriers. The capacitance measurement in Na2SO4 solution showed that the conduction band derives from Cu2+: 3d orbital, while the valence band has a limited character of copper. As application, the solid solution was successfully tested for the H2 formation under visible light using three holes scavenger namely S2−, SO32− and oxalic acid. The best photoactivity was found with oxalate in basic medium with an H2 evolution rate of 3.4 μmol min−1 g−1, due to its appropriate redox potential.