Rediscovering Cr₂O₇^2–, an Oxidant with Unrivaled Power and Energy Density, for Affordable, Next-Generation Energy Storage and Conversion

In the search for electrochemical energy storage systems with higher energy and power at reduced cost, alternative oxidants are rarely explored. Here we revisit the oxidant dichromate (Cr 2 O 7 2– ), once used in primary batteries for telegraphs, and carry out the first assessment of its suitability for fuel cells and flow batteries. We show that Cr 2 O 7 2– delivers 100 times the maximum current density from O 2 at just 1/70th of Cr 2 O 7 2– ’s 7.1 M solubility and yields the same voltage at carbon as O 2 does at Pt. Furthermore, we show that Cr 2 O 7 2– produces current densities that are higher than those of virtually all liquid-phase oxidants considered for energy storage. While the use of some high-power oxidants (e.g., H 2 O 2, MnO 4 – ) is impractical due to deleterious side reactions, Cr 2 O 7 2– reduction proceeds unhindered, enabling its use at high current densities. With these promising properties and an exceptionally low materials cost, Cr 2 O 7 2– likely provides a path to affordable energy storage.