Synthesis and physical properties of the CuFe2−xMnxO4 (0 ≤ x ≤ 2) solid solution

• The CuFe2−xMnxO4 (0 ≤ x ≤ 2) solid solutions have been prepared by solid state reaction.
• CuFe2−xMnxO4 system exhibits p-type conductivity with indirect transition band gaps.
• The charge transport occurs either between Fe2+/Fe3+ or Mn2+/Mn3+ ions in B-sites.
• CuFe1.6Mn0.4O4 demonstrates the best quantum conversion efficiency {η∗(H2) = 1.59}.

The CuFe2−xMnxO4 (0 ≤ x ≤ 2) solid solutions have been prepared by direct solid state reaction and the dependence of optical, electrical and electrochemical properties on the composition has been investigated. All samples exhibited the formation of a unique cubic phase irrespective of the composition with crystallite sizes on the order of 44 nm. Mn is localized in both octahedral and tetrahedral sites, and forms Mn3+–O2− complexes. The CuFe2−xMnxO4 system exhibits a p-type conductivity with indirect transition band gaps that decrease from 1.54 to 1.28 eV. Charge transport occurs either between Fe2+/Fe3+ or Mn2+/Mn3+ ions in B-sites according to the x value, and the conduction mechanism is controlled by small polaron hopping with a thermal activation of the mobility (μ), which is in the order of ∼10−5 cm2 V−1s−1 and does not depend on x. The conduction bands are particularly affected by the Mn introduction and the potentials can shift by as much as 0.5 eV. Finally, the CuFe2−xMnxO4 system was used as a bulk electrode in a photoelectrochemical cell and as a microphotoelectrode for H2-production. CuFe1.6Mn0.4O4 demonstrates the best quantum conversion efficiency in terms of electricity (η = 0.21) and H2-production (η∗ = 1.59).