Nitrogen-Doped Tungsten Carbide-Modified Graphite Felt as a Bifunctional Electrocatalyst for an All-Vanadium Redox Flow Battery
Anteneh Wodaje Bayeh, Daniel Manaye Kabtamu, Yun-Ting Ou, Ning‐Yih Hsu, Hung‐Hsien Ku, Yaoming Wang, Tai‐Chin Chiang, Hsin‐Chih Huang, Chen‐Hao Wang
Abstract
To enhance the electrochemical capability of graphite felt (GF) electrodes in vanadium redox flow batteries (VRFBs), we prepare nitrogen-doped tungsten carbide nanowires (N-WC NWs), which are grown on the GF surface via a two-step route. In the first step, we use a hydrothermal process using tungstic acid (H2WO4) as a precursor, and the WO3 NWs are deposited on the GF surface. Subsequently, the grown WO3 NWs are simultaneously carbonized and N-doped using melamine as the source of nitrogen and carbon. Compared to pristine GF, the prepared N-WC NWs-GF electrode exhibits an apparent electrocatalytic effect on the VO2+/VO2+ and V3+/V2+ redox reaction. The presence of a negatively charged density on the nitrogen atom encourages the vanadium ions’ absorption. The nanowire structure exposes more active sites for the vanadium ions’ redox reactions. Hence, the prepared N-WC NWs-GF electrode demonstrates the optimal electrochemical activity with energy and voltage efficiencies of 74.8% and 78.9%, respectively, which are much greater than those of the 59.8% and 63.2% attained from pristine GF at 100 mA cm–2. Moreover, the N-WC NWs-GF presented good stability and durability in acidic electrolyte during long-term operations for 100 cycles at a higher current density of 100 mA cm–2.