(Invited) Tuning Matrix Solvation for Adjusting the Formal Potential of Redox-Active Centers

The redox transformation of small molecules such as H 2 and CO 2 by means of molecular catalysts is of central importance for the conversion of renewable energy. Outer coordination sphere design currently drives the development of such catalysts toward enzyme-like performances. The redox potential of the catalyst is among the key features defining its properties in order to achieve high current densities at low overvoltage. The use of salts from the Hofmeister series in electrolytes provides a new way of adjusting the formal potential of redox systems embedded in polymeric matrices without directly manipulating the chemical structure. Based on viologen moieties serving as model redox active species, we demonstrate that the difference in hydration of chaotropic and kosmotropic anions has an effect on the net solvation of positively charged redox polymers and impact their redox potential. To systematically understand the effect of the counterions on the redox potential shift, electrochemical and spectroscopic analyses of free-diffusing viologens in solution were compared with structure-analog viologen-modified polymer films. Ultimately, the modulation of the solvent induced matrix interactions may be translated as a general lever to control catalyst properties such as electron and proton mobility, substrate binding or product release in analogy to the mode of function of active site of redox enzymes.