Modification Based on MoO₃ as Electrocatalysts for High Power Density Vanadium Redox Flow Batteries

Abstract

Molybdenum oxide MoO3 has been widely used in catalysts and electrochemical energy devices, but, to date, has not been investigated as an electrocatalyst in redox flow cells. In this study, MoO3 in the form of micro‐flakes was introduced onto carbon paper as an electrocatalyst and MoO42− as electrolyte additive for the vanadium redox couple reactions in the vanadium redox flow battery (VRFB). When the carbon paper was modified with MoO3 or MoO42− added to the electrolyte, the peak potential separations were measured as 171 and 203 mV for V2+/V3+ and 130 and 111 mV VO2+/VO2+ redox reactions, respectively, as compared with 306 and 144 mV for the bare pre‐treated carbon paper. A vanadium redox flow cell with MoO3‐CP electrodes exhibited a voltage efficiency of 85.4 % at 100 mA cm−2. The power density reached 200 mW cm−2 at a current density of 150 mA cm−2 when cycled within the voltage range of 0.6–1.7 V. These results indicate that MoO3‐based modification is a promising method for high power density VRFB applications.

A review of electrolyte additives and impurities in vanadium redox flow batteries

“…Mn 2 + , Te 4 + and In 3 + exhibited similar enhancement in the electroactivity but Pt, Pd and Au salts were found to catalyse the hydrogen evolution which will decrease the coulombic efficiency of the VRFBs. Recently, Cao et al reported that adding MoO 4 2 − into the electrolyte can achieve a similar improvement as that involving the modification of carbon paper electrodes with MoO 3 , leading to an increase in the cell voltage efficiency by more than 5% over the current density range 100-150 mA cm −2 [80] .…”

Electrocatalysis at Electrodes for Vanadium Redox Flow Batteries

“…Cao et al prepared MoO3 deposits on carbon paper and examined the activity of this electrode material for both the positive 2+ + 2 VO /VO and the negative V 2+ /V 3+ electrode reactions [421]; as an alternative approach, the effects of added [2][3][4] MoO in the electrolyte solutions was examined. Smaller peak potential separations were found.…”

Molybdenum-assisted reduction of VO2+ for low cost electrolytes of vanadium redox flow batteries

“…This was responsible for the improvement of voltage efficiency of the VRFB cell. In one study 57 , it was also shown that addition of 5 mM of Na2MoO4 directly to the electrolytes modified the surface of the electrodes during cycling and produced similar effects on VRFB cell performance as MoO3 deposited on electrodes. In our experiments, the deposition of molybdenum compounds after cycling was not observed, and the dissolved molybdenum appeared to slightly worsen the reversibility of redox couples, though not seriously.…”