Spindle-Like MOF Derived TiO₂@NC-NCNTs Composite with Modulating Defect Site and Graphitization Nanoconfined Pt NPs as Superior Bifunctional Fuel Cell Electrocatalysts

The modulating degree of defect and graphitization carbon coupled metal oxide composite is extremely important because these materials have been applied in various fatal fields, especially in energy storage/conversion and catalysis. Herein, we reported the in situ formation of long defect-rich nitrogen-doped carbon nanotubes (NCNTs) coupled with a porous TiO2@NC composite (TiO2@NC-NCNTs) derived from spindle type bimetallic (Ti/Co) MOF microrods. Thanks to the rational composition and unique structure, the as-prepared Pt/TiO2@NC-NCNTs-7 can be used as a bifunctional fuel cell electrocatalyst. For MOR, the optimized catalyst exhibits superior mass activity of 577 mA mg(Pt)(-1) (in acidic medium) and 3100 mA mg(Pt)(-1) (in alkaline medium), which is 2.02 and 4.08 times superior than the commercial Pt/C catalyst, and shows excellent CO tolerance and better cyclic stability. This state-of-the-art nanocatalyst also exhibits a more positive onset potential (1.01 V) and upper limiting current density (5.03 mA cm(-2)) than commercial Pt/C (0.96 V and 4.75 mA cm(-2)) toward oxygen reduction reaction. The optimized degree of defect and graphitization in N-doped carbon (including NC and NCNTs) of the nanocatalyst not only provides large amounts of active sites to Pt NP deposition but also is positive for the charge transfer improvement of the overall nanocatalyst. The strong-coupled Pt-NCNTs(NC)-TiO2 can further boost the catalytic activity and CO-tolerance. This work not only opens a new approach to develop a novel carbon/metal oxide composite with the desired morphology and properties but also provides new insights into the design and construction of state-of-the-art nanomaterials for fuel cells, water splitting, and photocatalysis.