The Swiss Army Knife of Electrodes—Pillar[6]arene-Modified Electrodes for Molecular Electrocatalysis over a Wide pH Range

Molecular catalysts can be immobilised on common electrode materials, including metal oxides, through various methods such as physi- or chemisorption. However, systems which are stable across a wide pH range are uncommon. Typically, each electrochemical transformation requires a specifically tailored system to ensure strong catalyst binding and high activity. In aqueous media, combating hydrolysis is crucial to enable catalysis under strongly acidic and basic conditions. One method to achieve this is the functionalisation of mesoporous indium tin oxide electrodes with the macrocyclic host molecule pillar[6]arene (PA[6]). These electrodes exhibit stability within a pH range of 2.4–10.8 and can be equipped with electrochemically active ruthenium complexes via host-guest interactions for various oxidation reactions. Benzyl alcohol oxidation is used as a model reaction in acidic media, while ammonia oxidation is performed to evaluate the system’s performance under basic conditions. PA[6]-modified electrodes show catalytic activity for both reactions when complexed with different guest molecules. Due to the stable binding of PA[6], they can be reused after degradation of the catalyst by a simple reabsorption procedure. Moreover, the system can be employed to perform successive reactions in electrolytes with varying pH, allowing the same electrode to be utilised in multiple different electrocatalytic reactions.