Enhanced electrochemical performance of modified thin carbon electrodes for all-vanadium redox flow batteries

We report the unique electrochemical properties of nitrogen-containing carbon nanostructures (N-CP) grown on commercial carbon paper (CP), used as electrocatalysts in all-vanadium redox flow batteries (VRFBs). The focus is on the anode, where mitigation of the hydrogen evolution reaction and loss in redox kinetics due to cycling is considered as a challenge. The growth of bamboo-like carbon nanostructures is achieved through a catalytic chemical vapor deposition (CVD) process with a very small geometric loading of Fe (from FeCl3) as the catalyst. Anhydrous acetonitrile, used as a nitrogen/carbon precursor, is fed to the electrode sample at 900 °C for 3 hours in a stream of H2-Ar (carrier gas). The three-electrode-cell study shows enhanced kinetics and durability of the electrode for V3+/V2+ redox reactions; N-CP shows a significant suppression of the peak potential separation (ΔE ∼ 80 mV), indicating faster kinetics compared to conventional CP (ΔE ∼ 160 mV). In addition, the subscale cell performance shows good durability (about 5% and 15% loss in energy efficiency in N-CP and CP, respectively) after 50 charge-discharge cycles. The improved durability of the N-CP electrode is attributed to the presence of nitrogen-carbon nanostructures, increased active area, and improved sp2 carbon content. Such findings can contribute to the development of large scale high performance VRFB systems.