Identifying the Active Site in Nitrogen-Doped Graphene for the VO²⁺/VO₂⁺Redox Reaction

Abstract

Nitrogen-doped graphene sheets (NGS), synthesized by annealing graphite oxide (GO) with urea at 700-1050 °C, were studied as positive electrodes in a vanadium redox flow battery. The NGS, in particular annealed at 900 °C, exhibited excellent catalytic performance in terms of electron transfer (ET) resistance (4.74 ± 0.51 and 7.27 ± 0.42 Ω for the anodic process and cathodic process, respectively) and reversibility (ΔE = 100 mV, Ipa/Ipc = 1.38 at a scan rate of 50 mV s(-1)). Detailed research confirms that not the nitrogen doping level but the nitrogen type in the graphene sheets determines the catalytic activity. Among four types of nitrogen species doped into the graphene lattice including pyridinic-N, pyrrolic-N, quaternary nitrogen, and oxidic-N, quaternary nitrogen is verified as a catalytic active center for the [VO](2+)/[VO2](+) couple reaction. A mechanism is proposed to explain the electrocatalytic performance of NGS for the [VO](2+)/[VO2](+) couple reaction. The possible formation of a N-V transitional bonding state, which facilitates the ET between the outer electrode and reactant ions, is a key step for its high catalytic activity.

Graphene modifications in polylactic acid nanocomposites: a review

“…Then, upon cooling, the solid graphene is readily collected. Jin et al [131], prepared nitrogen-doped graphene sheets (NGS) by annealing graphite oxide with urea under an Ar atmosphere for 3 h in a tubular furnace at 700-11,050°C. The NGS is studied as positive electrode in vanadium redox flow battery.…”

High-power positive electrode based on synergistic effect of N- and WO3 -decorated carbon felt for vanadium redox flow batteries

“…Therefore, apart from the amount of oxygen functional groups (C=O, C-OH) on the surface, other features related to the electrode activity, such as wettability and adsorption of vanadium onto surface electrode become also decisive. It is worth mentioning that the formation of Carbon-Nitrogen-Vanadium intermediate especially via quaternary and/or oxidic nitrogen groups [4] is a key step for the enhancement of the electrocatalytic activity [2,3], facilitating the electron transfer in the electrode/electrolyte interface M A N U S C R I P T…”

Properties of mesoporous carbon modified carbon felt for anode of all-vanadium redox flow battery

“…The improvement was attributed to improved surface wetting as a result of surface nitrogen functional groups, reduced activation energy resulting from bulk (quaternary) nitrogen doping for V-O bond formation, and improved electronic conductivity also associated with nitrogen doping of the bulk carbon. Jin et al [19] further confirmed the importance of quaternary nitrogen, demonstrating that it was the most likely active reaction site because other surface localized nitrogen species (pyridinic-N and pyrrolic-N) would become inactive through protonation of their lone electron pairs.…”

“…Carbon fiber based materials (CFBM) such as carbon felts (CFs) [14][15][16][17], and papers [18] meet many of these requirements, along with being robust, relatively inexpensive, and easily manufactured, and thus they have gained considerable research and commercial attention. However, these prospective carbon materials suffer from relatively poor electrochemical activities leading to poor reaction kinetics and reversibility, particularly for positive electrodes [19]. Many efforts have been undertaken to remedy these aforementioned shortcomings, with several strategies being pursued to enhance and modify the surface area and surface chemistry.…”