The blue arrow represents the transformation from homogeneous electrocatalysis to the more sustainable heterogeneous electrocatalysis. Examples of electrocatalytic reactions given in the blue box are inspired by refs. 10 , 11 , 72 . In nitroxide-catalysed alcohol oxidation, solution-based molecular electrocatalysts constituted the first generation, and electrode-bound film-electrocatalysts form the second generation 34 . The yellow arrow represents the transition from solution-electrochemical EPR to film-electrochemical EPR, with examples of cells and working electrodes (WEs) used throughout recent decades as listed in ref. 3 . The text size reflects the representation of the concept or topic in the literature. The dates given refer to the following representative publications: 1959 73 , 1960 74 , 1966 75 , 2019a 76 , 2019b 19 and 2020 36 .
