Spherical carbon catalysts as scalable fixed-bed electrode in flow electrosynthesis

The shift towards economically friendly feedstocks and the electrification of chemical synthesis reactions gained much attention in the recent years. To remain competitive with conventional processes, continuous improvement of reactor concepts is imperative. This study introduces a novel flow-cell design for electrosynthesis reactions, using spherical polymer-based carbon-supported copper catalysts as a three-dimensional fixed-bed cathode and allowing an easy exchange of the catalyst as being common in heterogeneous organic synthesis. The work reveals the cell type’s promising potential for synthesis reactions in combination with insight in limitations and optimization approaches (e.g. pressure loss, electrode’s Ohmic resistance). The reduction of 5-hydroxymethylfurfural (HMF) to 2,5-di(hydroxymethyl)furan (DHMF) served as electrochemical test reaction. The electrolysis proved that only the carbon-supported copper catalyst fixed-bed electrode facilitates the combination of high HMF conversion (89.6 ± 10.7 %) and DHMF selectivity (84.0 ± 13.3 %), outperforming a conventional sheet electrode tested at the same conditions (X = 33.6 ± 6.6 %, S = 19.9 ± 9.3 %). The pressure loss as well as the electrode resistance could be decreased to minimum values of 0.1 ± 0.01 bar and 0.9 ± 0.8 Ω by the use of carbon spheres with a diameter of 0.5 mm, while electrolysis results were not significantly affected. Finally, a first step of a scale-up process was demonstrated with the expansion of the fixed-bed by doubling its width, resulting in a doubling of the productivity, while maintaining the high product selectivity (85.1 ± 3.5 %) at high degrees of conversion (80.5 ± 9.7 %). • Spherical carbon-based catalysts form excelled fixed bed electrodes. • Fixed bed concept achieves superior yield compared to flat sheet electrode. • Fixed bed electrode concept volume-based scale was proven. • Knowhow of heterogeneous catalyst design can be leveraged in electrode tuning.