Introducing Dichromate (Cr2O7 2-), 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

Abstract

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.