The Key Role of Solvation in Enhancing Electrochemical Promotion of Brønsted Acid Catalysis

Abstract Electrostatic polarization of catalyst-solution interfaces can modulate the rate of liquid-phase heterogeneous Brønsted acid catalysis by up to 5 orders of magnitude. Previous studies in acetonitrile establish that maximal rate-potential scaling emerges only at high ionic strength, indicating that rate promotion is sensitive to the interfacial electrostatic potential profile. Herein, we examine the role of the solvent on the electrolyte strength sensitivity of polarization-induced promotion of Brønsted acid catalysis. Using carbon paper with Brønsted acid functionalities, we measured 1-methylcyclopentanol dehydration rates in dimethyl carbonate, acetonitrile, and propylene carbonate, with electrolyte concentrations ranging from 1 to 600 mM. In acetonitrile and dimethyl carbonate, the alcohol dehydration rate-potential scaling is a function of ionic strength, implying that the proton traverses only a fraction of the electrostatic potential drop to form a surface-bound oxonium intermediate prior to the rate-limiting C–O bond cleavage. In contrast, in more polar propylene carbonate, the rate-potential scaling aligns well with the maximum dependence predicted for a single-charge process and is insensitive to electrolyte concentration down to 1 mM. This behavior is consistent with the proton traversing the entire electrostatic potential drop to form a freely solvated oxonium intermediate outside the electrochemical double layer. These findings highlight that enhanced solvation of protonated intermediates is essential for maximizing electrostatic promotion in Brønsted acid catalysis. Together, the kinetic data show that solvent selection modulates both the intrinsic reaction rate and sensitivity to catalyst potential, emphasizing the importance of understanding interfacial electrostatic effects in thermochemical reaction systems.