Composite manganese oxide percolating networks as a suspension electrode for an asymmetric flow capacitor

In this study, we examine the use of a percolating network of metal oxide (MnO₂) as the active material in a suspension electrode as a way to increase the capacitance and energy density of an electrochemical flow capacitor. Amorphous manganese oxide was synthesized via a low-temperature hydrothermal approach and combined with carbon black to form composite flowable electrodes of different compositions. All suspension electrodes were tested in static configurations and consisted of an active solid material (MnO₂ or activated carbon) immersed in aqueous neutral electrolyte (1 M Na ₂SO₄). Increasing concentrations of carbon black led to better rate performance but at the cost of capacitance and viscosity. Furthermore, it was shown that an expanded voltage window of 1.6 V could be achieved when combining a composite MnO₂-carbon black (cathode) and an activated carbon suspension (anode) in a charge balanced asymmetric device. The expansion of the voltage window led to a significant increase in the energy density to ∼11 Wh kg^-1 at a power density of ∼50 W kg ^-1. These values are ∼3.5 times and ∼2 times better than a symmetric suspension electrode based on activated carbon.