UiO-66-NO2 as an Oxygen "Pump" for Enhancing Oxygen Reduction Reaction Performance

In this work, UiO-66-based metal-organic frameworks are investigated as an oxygen reduction reaction (ORR) catalyst for the first time. UiO-66-NO2 is solvothermally grown on the surface of cobalt phthalocyanine-anchored carbon nanotube (CoCNT) surface, serving as an oxygen "pump" to accelerate the oxygen reduction reaction (ORR). The UiO-66-NO2-attached CoCNT (UiO-66-NO2@CoCNT) exhibits superior electrochemical catalytic properties, exceeding the state-of-the-art commercial 20% Pt/C catalyst with more positive half-wave potential (15 mV difference, at 1600 rpm), better stability (no significant degradation for UiO-66-NO2@CoCNT vs 19% degradation for 20% Pt/C after 25 000 s), and higher methanol tolerance. When assembled in a flexible zinc-air battery, the UiO-66-NO2@CoCNT remains a competitive alternative to commercial 20% Pt/C catalyst with comparable power density and excellent flexibility, suggesting its potential in wearable electronic devices. The outstanding performance of UiO-66-NO2@CoCNT composite is closely related to the synergetic effect among the three components: CNT as a conductive backbone, cobalt phthalocyanines as the oxygen reduction catalytic active site, and UiO-66-NO2 as an ideal oxygen adsorption pump (the oxygen diffusion rate is 4.8 times that of 20% Pt/C and 17.7 times that of CoCNT). The synergy between the three components facilitates oxygen adsorption, transfer of adsorbed oxygen molecules, oxygen reduction, and electron conduction.