Electrocatalytic activity of Nb-doped hexagonal WO₃ nanowire-modified graphite felt as a positive electrode for vanadium redox flow batteries

Abstract

In this paper, we report a facile hydrothermal method to synthesize low-cost, high-catalytic-activity, and stable niobiumdoped hexagonal tungsten trioxide nanowires (Nb-doped h-WO3 NWs); these NWs were employed as catalysts to improve the electrocatalytic activity of graphite felt (GF) electrodes for use as positive electrodes in an all-vanadium redox flow battery (VRFB). The effect of Nb doping and its composition on the electrochemical performance of GF electrodes for a VRFB was investigated. Cyclic voltammetry and electrochemical impedance spectroscopy results showed that Nb-doped h-WO3 NWs with a Nb/W atomic ratio of 0.03 exhibited the highest electrocatalytic activities for VO 2+ /VO2 + couples among all the tested electrodes. This observation was attributed to the optimal Nb-doping concentration producing moderate defect states, thereby creating structural disorders, such as oxygen vacancies, in WO3 and leading to the generation of more active sites for the VO 2+ /VO2 + redox reaction on the electrode. Moreover, in charge-discharge tests, a VRFB single cell using the Nb-doped h-WO3 NWs (Nb/W = 0.03) catalyst demonstrated an excellent energy efficiency of 78.10% with a current density of 80 mA cm −2 . This efficiency is much higher than that demonstrated by VRFB cells with untreated GF (67.12%) and heat-treated GF obtained through conventional method (72.01%). Furthermore, in the stability test of a VRFB single cell with the Nb-doped h-WO3 NWs (Nb/W = 0.03) catalyst, almost no decay of the cell was observed even after 30 cycles. This observation indicates the outstanding stability of the cell during the redox reaction of vanadium ions under highly acidic conditions.

Pt Nanoparticles Sensitized Ordered Mesoporous WO3 Semiconductor: Gas Sensing Performance and Mechanism Study

“…The peak positions of the first doublet are 35.8 and 37.9 eV, corresponding to W 6+ 4f 7/2 and 4f 5/2 , respectively. The peak positions of the second doublet are 35.10 and 37.20 eV, corresponding to W 5+ 4f 7/2 and 4f 5/2 , respectively . These results indicate that WO 3 /Pt‐0.5 materials contain both W 6+ and W 5+ states.…”

Electrocatalysis at Electrodes for Vanadium Redox Flow Batteries

“…4% as compared to 53.8% for the plain graphite felt. Niobium-doped WO 3 nanowires were prepared on graphite felt by a hydrothermal procedure for use as the positive electrode [419]. Highest activity in terms of reduced peak separation and increased peak currents in CV and reduced R ct in impedance measurements was found at a Nb/W ratio of 0.03.…”

One-step hydrothermal synthesis and characterization of Mg/Mo co-doped VO2 nanorods

“…These include thermolysis [6,14,27], sputtering [16,17], spray pyrolysis [28], ion implantation [29,30], chemical vapor deposition (CVD) [31,32], pulsed laser deposition (PLD) [33][34][35], sol-gel [27,36], and hydrothermal techniques [8,[37][38][39]. Among these, hydrothermal synthesis technique is environmentally friendly, cost-effective, flexible, does not need complicated setup and can be scaled up easily for mass production [8,37,38]. So far, many research works have been conducted using this method for the syntheses of undoped and doped VO 2 nanoparticles [8,38,39].…”