Selectivity by the Clock: Programming Reactivity with Alternating Current Frequency

Electrochemical reactions are inherently programmable through the applied potential. However, conventional direct current (DC) electrolysis provides only limited control over reaction selectivity because it generates a static redox environment in which substrates and intermediates remain continuously exposed to either oxidizing or reducing conditions. As a result, reactive intermediates often undergo undesired overoxidation, overreduction, or competing side reactions. Alternating current (AC) electrolysis overcomes these limitations by periodically reversing electrode potential polarity, creating a dynamic redox environment in which oxidation and reduction can be regulated in the time domain. In addition to potential, AC electrolysis introduces frequency as a new experimental parameter for controlling reaction pathways. In this Account, we highlight our group's recent efforts to understand how AC frequency controls reaction selectivity. We show that AC frequency serves as a kinetic synchronization parameter, matching electrochemical time scales to the rates of key chemical steps. By controlling the duration that reactive intermediates experience oxidizing or reducing environments, AC electrolysis enables selective access to reaction pathways that are difficult or impossible to achieve under conventional DC conditions. Using representative examples, we illustrate several mechanistic modes through which AC frequency governs reaction outcomes. First, we demonstrate that frequency-controlled modulation of the redox environment can distinguish between one- and two-electron oxidation pathways of amines, enabling the selective generation of α-amino radicals while suppressing the formation of iminium ions. This principle was further extended to electrochemical hydrogen isotope exchange, in which AC frequency synchronizes proton transfer and hydrogen atom transfer to achieve efficient, site-selective isotope incorporation. Second, we show that AC frequency can synchronize with homogeneous catalytic cycles. In a Ni-catalyzed C-N cross-coupling reaction, the optimal frequency arises from matching the AC waveform to the formation rate of a key Ni(II) catalytic resting state. Third, we demonstrate that AC electrolysis can dynamically maintain catalytically active electrode structures and alter chemical speciation in heterogeneous electrocatalysis. In an industrial Ag-catalyzed dehalogenation process, AC electrolysis continuously regenerates a defect-rich Ag catalyst while suppressing chlorine-mediated decomposition pathways, leading to dramatically improved long term selectivity and catalyst stability. We further describe our efforts to establish finite-element modeling approaches for AC electrolysis. Using the AC-enabled partial reduction of (hetero)arenes as a model system, we show how electrochemical kinetics extracted from cyclic voltammetry can be integrated with finite-element simulations to reproduce experimental selectivity trends and identify the kinetic criteria required for selective partial reduction. These studies demonstrate that quantitative modeling can provide mechanistic insight and guide reaction design. Collectively, these examples reveal a unifying principle: AC electrolysis enables control of chemical reactivity by synchronizing electrochemical inputs with the intrinsic time scales of key selectivity determining chemical/electrochemical processes. Although significant challenges remain in developing predictive models for complex reactions, we envision that continued advances in electroanalytical methods, mechanistic studies, and computational modeling will transform AC electrolysis from an empirical optimization tool into a general strategy for programming reaction selectivity through temporal control of the electrochemical environment.