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

Abstract

Nanoparticles of cubic CuFe2O4 are obtained in a fast microwave‐assisted hydrothermal synthesis. By adjusting the pH value and solvent ratio (ethylene glycol to water), phase purity and high crystallinity is achieved at very short reaction times of 1 min, or low temperatures of 120 °C, without the need for subsequent heat treatment steps. The influence of the synthesis time or temperature on material properties and performance in electrochemical CO2 reduction to CO are investigated. While particle size and crystallinity are not changed significantly with longer synthesis times at 175 °C, prolonged heating results in a decrease of the degree of inversion, which leads to a decrease in the CO2 reduction ability. The best performance is observed for CuFe2O4 with an intermediate degree of inversion of approx. 0.75, together with the largest crystallite size and micro‐strain, as revealed by Rietveld refinement. For CuFe2O4 synthesized under these conditions, a CO evolution rate of 0.2 μmol h−1 g−1 is obtained at a Faradaic efficiency of 20%. The CO to H2 ratio is 1:3, which makes it a promising candidate for a sustainable production of syngas.

Ni2FeS4as a highly efficient earth-abundant co-catalyst in photocatalytic hydrogen evolution

“…† These changes in a sample that had experienced prolonged heating times might be due to changes in the relative ratio of nickel, possibly together with changes in the degree of inversion, as was observed in other microwave assisted synthesis routes of spinel oxides. 71 Ni 2 FeS 4 is absorbing light strongly over the entire visible light range and into the near infrared (NIR) region, as also apparent by its black colour (Fig. S6 and S7 †).…”

“…These changes in a sample that had experienced prolonged heating times might be due to changes in the relative ratio of nickel, possibly together with changes in the degree of inversion, as was observed in other microwave assisted synthesis routes of spinel oxides. 71…”

“…A similar This journal is © The Royal Society of Chemistry 2023 loss of the more redox active and better microwave absorbing cation at the surface was observed in the synthesis of CuFe 2 O 4 , alongside cation migration of Cu 2+ . 71 Possibly, an extended irradiation with microwaves results in changes in the Ni coordination as well. Santos-Carballal et al suggested a normal spinel structure to be the thermodynamically more stable one, that is not formed in synthetic approaches due to kinetic reasons.…”

Medium‐ and High‐Entropy Spinel Ferrite Nanoparticles via Low‐Temperature Synthesis for the Oxygen Evolution Reaction

“…For Cu on the other hand, a partial reduction to Cu + and Cu 0 was observed, in agreement to literature observations of Cu being prone to reduction when alcohols are used as a solvent. [53,48] For Mn, the Mn 2p 3/2 spectra for (MnMg)Fe 2 O 4 and (MnZn)Fe 2 O 4 allow for a reasonably good fit with the multiplet parameters from Biesinger et al for MnO. [62] Small amounts of a reduced manganese species appear to be present in (MnZn)Fe 2 O 4 .…”

“…[23] The degree of inversion not only depends on the ionic radii of employed cations, the ligand field stabilization energy (LFSE) in tetrahedral and octahedral crystal field, respectively, but also to a large extend on the synthesis strategy. [48][49][50] While this introduces another parameter for tailoring the properties via the adjustment of the structure, it makes a prediction of entropic stabilization effects highly challenging.…”