📄 Our Lab Paper

Surface Electroactive Sites of Tungstated Zirconia Catalysts for Vanadium Redox Flow Batteries

ACS Applied Materials & Interfaces 2024, 16, 7047–7056 (ACS Publications) | DOI: 10.1021/acsami.3c14633

Authors：Aknachew Mebreku Demeku, Daniel Manaye Kabtamu*, Guan-Cheng Chen, Yun-Ting Ou, Zih-Jhong Huang, Tai-Chin Chiang, Hsin-Chih Huang, and Chen-Hao Wang*

📄 Abstract

Surface electroactive sites for tungstate zirconia (WZ) were created by utilizing tungstate-immobilized UiO-66 as precursors via a double-solvent impregnation method under a mild calcination temperature. The WZ-22-650 catalyst, containing a moderate W content (22%), demonstrated a high density of surface electroactive sites. Proper heat treatment facilitated the binding of oligomeric tungsten clusters to stabilized tetragonal ZrO2, resulting in improved catalytic performance toward the VO2+/VO2+ redox couples compared to other tested samples. The substantial surface area, mesoporous structure, and establishment of new W-O-Zr bonds affirm the firm anchoring of WOx to ZrO2. This robust attachment enhances surface electroactive sites, elevating the electrochemical performance of vanadium redox flow batteries (VRFBs). Charge-discharge tests further demonstrate that the superior voltage efficiency (VE) and energy efficiency (EE) for VRFBs using the WZ-22-650 catalyst are 87.76 and 83.94% at 80 mA cm-2, which are 13.42% VE and 10.88% EE better than heat-treated graphite felt, respectively. Even at a higher current density of 160 mA cm-2, VRFBs utilizing the WZ-22-650 catalyst maintained considerable efficiency, recording VE and EE values of 76.76 and 74.86%, respectively. This facile synthesis method resulted in WZ catalysts displaying superior catalytic activity and excellent cyclability, offering a promising avenue for the development of metal-oxide-based catalysts.

🔬 Key Findings

MOF-precursor synthesis of WZ catalysts: Using tungstate-immobilized UiO-66 with double-solvent impregnation to anchor WOx onto ZrO2 via new W-O-Zr bonds.

WZ-22-650 (22% W) is the optimal composition with the highest surface electroactive site density and catalytic performance.

87.76% VE and 83.94% EE @ 80 mA/cm² — exceeding heat-treated graphite felt by 13.42% VE and 10.88% EE.

High-current durability: Maintained 76.76% VE and 74.86% EE even at 160 mA/cm².

Excellent cyclability: WZ-22-650 demonstrates superior catalytic activity and long-term cycling stability, offering a promising route for metal-oxide-based VRFB catalysts.

📊 Key Figures

Figure 1: Charge-discharge curves and efficiency comparison for WZ-22-650 catalyst.

Figure 2: Long-term cycling performance of WZ-22-650 catalyst in VRFB.