Introducing Dichromate (Cr2O72-), an Oxidant with 100x the Current Density of O2 at 1/70th Its Solubility, and Other High-Power Oxidants for Redox Flow Batteries and Fuel Cells

While electrochemical fuels sample the range of the elements, from BH₄^– to NH₃ and Li to Zn, exploration of oxidants usually starts and ends with O₂, a low-power oxidant with solubility <1 mM.  In the studies presented, oxidants with solubilities up to 7,000 mM are characterized and demonstrated to produce current densities 100 times greater than O₂ at just 100 mM.  Alternative oxidants used in redox flow batteries (VO₂⁺, Ce⁴⁺) and fuel cells (H₂O₂, MnO₄^–) are compared against the unorthodox oxidants ClO^–, S₂O₈^2–, IO₃^–, CrO₄^2–, and Cr₂O₇^2–.  It is shown that Cr₂O₇^2– produces among the highest current densities of all oxidants studied, at a diverse array of catalyst materials, and does so without the familiar drawbacks of precipitation and bubble-producing decomposition of MnO₄^– and H₂O₂, respectively.  Cr₂O₇^2–'s high n (number of e^– transferred per molecule), D (diffusion coefficient) and C^max (maximum concentration) offer a route to achieving order-of-magnitude increases in the current and power densities of redox flow batteries currently using VO₂⁺ or Ce⁴⁺, which have low values for all three parameters.