Mediated Fuel Cells: Soluble Redox Mediators and Their Applications to Electrochemical Reduction of O₂ and Oxidation of H₂, Alcohols, Biomass, and Complex Fuels

Abstract

Mediated fuel cells are electrochemical devices that produce power in a manner similar to that of conventional proton exchange membrane fuel cells (PEMFCs). They differ from PEMFCs in their use of redox mediators dissolved in liquid electrolyte to conduct oxidation of the fuel or reduction of the oxidant, typically O 2 , in bulk solution. The mediators transport electrons (and often protons) between the electrode and the catalysts or chemical reagents in solution. This strategy can help overcome many of the challenges associated with conventional fuel cells, including managing complex multiphase reactions (as in O 2 reduction) or the use of challenging or heterogeneous fuels, such as hydrocarbons, polyols, and biomass. Mediators are also commonly used in enzymatic fuel cells, where direct electron transfer from the electrode to the enzymatic active site can be slow. This review provides a comprehensive survey of historical and recent mediated fuel cell efforts, including applications using chemical and enzymatic catalysts.

Recent Advances in Asymmetric Catalytic Electrosynthesis

“…As redox mediators can allow for redox events to occur at lower potentials (in absolute numbers), this may also enable higher selectivities and functional group tolerance [15]. There is plenty of room for innovation in this field, not the least for reductive transformations, and inspiration for electrosynthetic applications is likely to be found in photoredox catalysis, as well as the proceedings of the organic battery community [124].…”

Analysis of the Electrochemical Response of Surface‐confined Bidirectional Molecular Electrocatalysts in the Presence of Intermolecular Interactions

“…where S is the electrode area. Equation 7, with boundary conditions (10)- (11), can be solved analytically. Thus, the following explicit solutions for the surface coverage of species Red and for the current can be obtained by following an easy procedure described in, [39]…”

“…Thus, it is possible to modulate specifically the interactions between the catalysts and the substrate [8–10] . Moreover, molecular species have generally low cost, well‐defined active sites and good chemical compatibility with different media [4,8, 10–11] . In the case of biomolecules, especially in the case of enzymes, a great number of strategies have been developed for them to act over the conversion of small molecules involved in the production of solar fuels as hydrogen or oxygen [12–14] …”

“…[8][9][10] Moreover, molecular species have generally low cost, well-defined active sites and good chemical compatibility with different media. [4,8,[10][11] In the case of biomolecules, especially in the case of enzymes, a great number of strategies have been developed for them to act over the conversion of small molecules involved in the production of solar fuels as hydrogen or oxygen. [12][13][14] Molecular and biomolecular electrocatalysts can play homogeneously in solution or heterogeneously by surface confinement by adsorption or grafting to a given electrode.…”

Lignocellulose, Cellulose and Lignin as Renewable Alternative Fuels for Direct Biomass Fuel Cells

“…[1,25,26] Zhao et al [1] focused overall on the progress of LCBfed MFCs, in particular sugar-fed MFCs, with a short part regarding photo fuel cells and FFCs, Ahmad et al [25] presented an overview on the performance of MFC fed with different type of soluble and insoluble commercial cellulose, with a comparison between cellulose-fed MFCs and starch-and chitin-fed MFCs. Finally, Anson and Stah [26] reported the use of LCB as the fuel of FFCs. Unlike previous reviews, which report the use of LCB as the fuel only for low temperature fuel cells, this Review deals with LCB-fed low-, intermediate-, and high-temperature DBFCs and compares their performance with that of IDFCs.…”