Flexible Carbon Sponge Electrodes for All Vanadium Redox Flow Batteries

Abstract In the present work, a flexible carbon sponge is experimentally characterized and proposed as an alternative electrode for advanced vanadium redox flow batteries. Such an electrode is prepared via directly carbonizing the commercially‐available and inexpensive melamine formaldehyde resin sponge in argon, to inherit the well‐defined and three‐dimensional bi‐continuous architecture of the melamine sponge with 99.6% porosity and 40 μm average pore size. By applying the carbon sponges as the electrodes, it is demonstrated that the vanadium flow battery at 200 mA cm −2 can yield an energy efficiency of 77.9%, significantly higher than that with commonly‐used graphite felt electrodes (72.9%). After a thermal treatment in air, the energy efficiency of carbon sponge can further be improved to 81.2% at mA cm −2 due to introduction of favorable oxygen containing functionalities. The operating stability with the carbon sponge is proven by a 200 cycling test with minor efficiency decay.