MOF-derived W/Zr bimetallic oxides@Carbon for comprehensively remedying melamine foam electrode defects in vanadium redox flow batteries

Due to a series of defects such as low conductivity, poor catalytic activity and unfavorable long-term cycling stability, the comprehensive modification and usage improvement of carbonized melamine foam remain a significant challenge. Here, introducing W site into Zr-UiO-66 framework is proposed to construct W/Zr bimetallic oxides@carbon melamine foam electrode, which exhibits larger specific surface area, higher conductivity and catalytic activity than the pristine MF electrode. Benefiting from the ordered arrangement of W, Zr sites in the MOF precursor, the catalyst has an extremely catalytic activity and ultra-high binding performance of W/Zr bimetallic oxide particles with MF substrate. The electrode W/ZrBO@C-1000 possesses improved specific surface areas, hydrophilicity, higher electrochemical reactivity and reversibility compared to the pristine CMF-1000 electrode, as confirmed by material and electrochemical characterizations. The corresponding VRFB is able to achieved an energy efficiency of 82.43% at 200 mA cm−2, and displays a desirable long-term stability over 500 consecutive charge–discharge cycles. Density function theory further clarifies the underlying catalysis mechanism of bimetallic oxides for vanadium redox reactions. The strategy of introducing bimetallic oxides basing on MOF precursors improves the performance of melamine foam electrodes, which is expected to be a solution to remedy defects and broaden its usage range in other flow batteries.