Hydrogen production under visible illumination on NiFe0.8Mn1.2O4 synthesized by sol–gel processing

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Chinese explanation / 中文解读

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Original abstract

The spinel NiFe0.8Mn1.2O4 synthesized by sol–gel processing was successfully exploited for the hydrogen evolution reaction (HER) under visible light. XRD studies indicated that the oxide crystallizes in a spinel structure with a crystallite size of 51 nm, smaller than that observed by transmission electron microscopy (TEM, 465 nm), indicating an agglomeration process. p-type conduction is indicated by a positive thermoelectric power (S300K = +134 µV K−1), with an activation energy of 290 meV. The direct band gap (Eg = 1.10 eV), arising from the lifting of degeneracy of the 3d orbital in (Fe, Mn)O6 octahedra, was obtained from the diffuse reflectance, ideal for the exploitation of the visible solar spectrum. The correlated physical and electrochemical properties predict the feasibility of NiFe0.8Mn1.2O4 for HER from an energy diagram. The “Capacitance –Potential” characteristics yield a hole concentration (NA) of 2.8 × 1015 cm-3 and a flat band potential (Efb) of −30 mVSCE. The cathodic conduction band (−0.84 VSCE) is ideally positioned relative to the H2O/H2 couple (~ −0.48 VSCE), facilitating HER upon visible light irradiation. The optimization of NiFe0.8Mn1.2O4 dose, pH and S2O32- concentration has been undertaken, giving a maximum HER volume of 73 µmol with an evolution rate of 8.1 µmol g−1 min−1.

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