Catalytic cascade reactions. From fundamentals of nanozymes to applications based on gas-diffusion electrodes

ended

Nanoparticles with etched substrate channels are proposed as a simplified enzyme mimic, nanozymes, for electrocatalysis providing concave catalytically active sites together with the local modulation of electrolyte composition. This concept will be extended to bimetallic core-shell structures with etched channels to provide locally confined catalyst surfaces with varying selectivity. The first catalytic reaction at the channel entrance selectively generates a product, which is further converted in a follow-up reaction catalysed at the core material at the bottom of the channel. The endeavour to locally assemble catalysts with different properties in nano-confined reaction volumes to actualise cascade reaction pathways will be extended to layered nanoparticle structures. Together with an anisotropic provision of a gaseous reactant through a hydrophobic/hydrophilic phase boundary of specifically designed gas diffusion electrodes multi-step catalytic cascade reactions become feasible. The development and extensive evaluation of multi-catalyst gas-diffusion electrodes using operando electrochemistry/spectroscopy and nano-electrochemical tools as well as multi flow-through electrolysers will provide the fundamental knowledge concerning the relative location of different catalyst particles, which synergistically perform chemical cascade reaction with high selectivity and at high current densities. These gas-diffusion electrodes will be integrated in novel electrolyser concepts targeting CO2 recycling at high current density in alkaline solution under suppression of H2 competition with previously unprecedented selectivity for the formation of higher hydrocarbons envisioning contributions to a closed carbon cycle economy and a substantial decrease of CO2 emission. Additionally, a novel tree-type rotating electrolyser design is proposed for the removal of hazardous gaseous pollutants from air e.g. at street crossings in cities as exemplified by NOx reduction to N2 or NH3.