Spinel ferrite MFe2O4 (M = Ni, Co, or Cu) nanoparticles prepared by a proteic sol-gel route for oxygen evolution reaction

Fast and Facile Microwave Synthesis of Cubic CuFe2O4 Nanoparticles for Electrochemical CO2 Reduction

“…[32,33] Thus, the group of Khan first employed pure CuFe 2 O 4 for PEC CO 2 RR to methanol and then switched to a composite with graphene oxide, thereby increasing the Faradaic efficiency to 87%, reportedly due to better charge separation. [32,33] Improved activity -also for the conversion to methanol-could also be observed for a composite with TiO 2 , as reported by Hafeez et al [34] Common synthesis methods include co-precipitation, [29] solidstate reaction, [11,19] sol-gel synthesis, [31] combustion synthesis, [35] or solvothermal synthesis. [30,36] Methods requiring calcination temperatures of more than 300 °C yield tetragonal CuFe 2 O 4 , if cooled slowly, and cubic, if quenched rapidly from high temperatures.…”

“…Generally, three main methods are employed to determine the degree of inversion for spinel-type materials: Rietveld refinement of XRD data, Mössbauer spectroscopy, and XPS. [16,31] Since all three rely on mathematical fitting of experimental results and thus depend on the quality of the measurement data and the fitting parameters, a complementary determination with several methods is recommendable. We performed Rietveld refinement on the Cu and Ag-XRD patterns for CuFe 2 O 4 obtained under different conditions.…”

“…The high-resolution 2p-spectra for Cu can be fitted with two signals for the metal ion in octahedral and tetrahedral sites, respectively. [23,31,32,58,59] This fitting approach is based on an influence of the coordination environment on the ratios of multiplet splitting, [58][59][60] but neglects additional effects on multiplet splitting and is further complicated by the possible presence of Cu þ and/or Cu 0 . To some extent, the expected influence of Cu þ / Cu 0 can be derived from the Auger signal, which is highly similar for all CuFe 2 O 4 samples obtained at 175 °C for different reaction times and supports the predominant oxidation state of þII for copper, which is further apparent in the high shake-up intensity.…”

“…Additionally, CuFe 2 O 4 is an effective electrocatalyst for oxygen evolution, for which it showed a very low overpotential, even surpassing the performance of CoFe 2 O 4 and NiFe 2 O 4 . [ 31 ] CuFe 2 O 4 has also been used for the photoelectrochemical (PEC) CO 2 reduction reaction (CO 2 RR). [ 32,33 ] Thus, the group of Khan first employed pure CuFe 2 O 4 for PEC CO 2 RR to methanol and then switched to a composite with graphene oxide, thereby increasing the Faradaic efficiency to 87%, reportedly due to better charge separation.…”

“…Common synthesis methods include co‐precipitation, [ 29 ] solid‐state reaction, [ 11,19 ] sol–gel synthesis, [ 31 ] combustion synthesis, [ 35 ] or solvothermal synthesis. [ 30,36 ] Methods requiring calcination temperatures of more than 300 °C yield tetragonal CuFe 2 O 4 , if cooled slowly, and cubic, if quenched rapidly from high temperatures.…”