Flexible Carbon Sponge Electrodes for All Vanadium Redox Flow Batteries

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.