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

Electrochemical CO₂ reduction is a promising strategy for the sustainable synthesis of carbon-based chemicals or fuels such as CO, or CH₄.[1] Copper-based materials are of special interest due to their broad substrate scope. While copper itself is the first known metal catalyst able to directly yield CH₄, CO, methanol, or C₂₊ products such as ethanol can also be obtained, e.g. from oxide derived catalysts.[2][3] Another interesting copper oxide is the spinel CuFe₂O₄, due to its versatile electronic and magnetic properties. Those can be tuned <i>via</i> variations in the cation distribution between octahedral and tetrahedral sites.[4] Changes in the cation distribution, or degree of inversion, can additionally lead to a structural transformation between the cubic and tetragonal form, due to the strong Jahn-Teller effect of Cu²⁺. Both degree of inversion and structure are strongly dependant on the synthesis conditions.[4]<br/>In this contribution we introduce a fast microwave-assisted solvothermal synthesis of cubic CuFe₂O₄. Very short synthesis times of 1 min and low temperatures of 120 °C in ethylene-glycol/water mixtures could be realised, without a loss of phase-purity and no necessity for subsequent thermal treatment.[5] The degree of inversion was found to decrease with increasing synthesis time, whereas the particle size and crystallinity was almost independent of the synthesis conditions. The influence of the synthesis conditions – and thus material properties – on the activity in electrochemical CO₂ reduction to CO in 0.1 M KHCO₃ was investigated. The best activity was obtained for CuFe₂O₄ with an intermediate degree of inversion of approx. 0.75, together with a large crystallite size and micro-strain. Since hydrogen was produced as the only site-product, CuFe₂O₄ can be an interesting candidate for the production of syngas.<br/> <br/>References:<br/>[1] Q. Lu, F. Jiao, <i>Nano Energy</i> <b>2016</b>, <i>29</i>, 439<br/>[2] S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K. Nørskov, T. F. Jaramillo, I. Chorkendorff, <i>Chem. Rev</i>. <b>2019</b>, <i>119</i>, 7610<br/>[3] D. Raciti, C. Wang, <i>ACS Energy Lett.</i> <b>2018</b>, <i>3</i>, 1545<br/>[4] R. Zhang, Q. Yuan, R. Ma, X. Liu, C. Gao, M. Liu, C.-L. Jia, H. Wang, <i>RSC Adv.</i> <b>2017</b>, <i>7</i>, 21926<br/>[5] J. Zander, M. Weiss, R. Marschall, <i>Adv. Energy Sustainability Res.</i> <b>2023</b>, 2200184