Electrochemically Responsive Heterogeneous Catalysis for Controlling Reaction Kinetics

Abstract

We report a method to control reaction kinetics using electrochemically responsive heterogeneous catalysis (ERHC). An ERHC system should possess a hybrid structure composed of an electron-conducting porous framework coated with redox-switchable catalysts. In contrast to other types of responsive catalysis, ERHC combines all the following desired characteristics for a catalysis control strategy: continuous variation of reaction rates as a function of the magnitude of external stimulus, easy integration into fixed-bed flow reactors, and precise spatial and temporal control of the catalyst activity. Herein we first demonstrate a facile approach to fabricating a model ERHC system that consists of carbon microfibers with conformal redox polymer coating. Second, using a Michael reaction whose kinetics depends on the redox state of the redox polymer catalyst, we show that use of different electrochemical potentials permits continuous adjustment of the reaction rates. The dependence of the reaction rate on the electrochemical potential generally agrees with the Nernstian prediction, with minor discrepancies due to the multilayer nature of the polymer film. Additionally, we show that the ERHC system can be employed to manipulate the shape of the reactant concentration-time profile in a batch reactor through applying customized potential-time programs. Furthermore, we perform COMSOL simulation for an ERHC-integrated flow reactor, demonstrating highly flexible manipulation of reactant concentrations as a function of both location and time.

Microwave-Assisted Oxidation of Electrospun Turbostratic Carbon Nanofibers for Tailoring Energy Storage Capabilities

“…This understanding, together with our in-depth examination of the electrochemical, electronic, and crystalline properties of turbostratic ECNFs, may provide valuable insights into structural optimization of other defect-rich graphitic systems [30][31][32][33][34] for a wide range of applications such as (electro)catalysis, electrochemical biosensing, controlled molecular packing, and band structure engineering. [1,2,[30][31][32][33][34][76][77][78] …”

Electrochemical Applications of Microphase‐Separated Block Copolymer Thin Films

“…[62] This study was the integration of prior reports for the same reaction regarding heterogeneous catalysis with Ag + -oxidized polyvinylferrocene-based BCP microdomains [106] and potential-controlled heterogeneous catalysis with polyvinylferrocene-modified carbon electrodes. [107] In this study, the authors employed goldsupported thin PS-b-PAEFc films comprising spherical or cylindrical PAEFc microdomains. The catalytic activity of the PAEFc microdomains could be reversibly tuned on the basis of their oxidation states by adjusting a potential applied to the underlying electrode.…”

Switchable Stimuli-Responsive Heterogeneous Catalysis

“…In this case, the external stimulus is able to change the nature of active sites (in most of the cases, oxidation state) at the catalyst surface rather than modifying its accessibility and it is used to regenerate them, conferring to the catalyst good recyclability and long-term activity. An example of the application of this strategy is the work of Mao et al [50], in which an electrochemical stimulus (i.e., applied potential) was used to continuously manipulate the number of activated catalytic sites of a catalytic system made of a porous carbon fiber electrode conformally coated with poly(vinylferrocene), which is used as catalyst for the Michael addition of methyl vinyl ketone and ethyl-2-oxycyclopentane carboxylate. Ferrocenium (i.e., the oxidized form of ferrocene) catalyzes this reaction as a Lewis acid, whereas ferrocene has no catalytic activity.…”

“…(a) Schematic illustration of the electrochemical control over the number of active sites on the surface of the porous carbon fiber electrode; (b) comparison between the electrochemically responsive heterogeneous catalyst (ERHC) and a "on/off" bimodal responsive catalyst for kinetic control. Reprinted with permission from ref [50]…”