Pt decorated free-standing TiO<inf>2</inf> nanotube arrays: Highly active and durable electrocatalyst for oxygen reduction and methanol oxidation reactions

Free standing TiO2 nanotubes (TiO2-NT) have been synthesized by anodization method and Platinum (Pt) nanoparticles deposited uniformly over TiO2 nanotubes (Pt/TiO2-NT) by chemical impregnation method. Hard X-ray Photoelectron Spectroscopy (HAXPES) and photoluminescence (PL) studies revealed the oxygen defects on the surface of TiO2-NT. The electrochemical performance of Pt/TiO2-NT has been compared with TiO2 nanoparticles supported Pt (Pt/TiO2-NP) and commercial carbon supported Pt (Pt/C). This Pt/TiO2-NT exhibit enhanced electro catalytic activity for both oxygen reduction as well as methanol oxidation reaction (ORR and MOR). The onset potential for ORR shows a considerable shift of 50 mV towards higher side and exhibited 12% increase in specific activity compared with state-of-art Pt/C electrocatalyst. Pt/TiO2-NT also displayed strikingly better mass activity, which is 17-fold higher than that of Pt/C and 3.4-fold more than that of Pt/TiO2-NP. The Accelerated Durability Test (ADT) (durability of catalyst after 10000 cycles) showed that Pt/TiO2-NT retained higher electrochemical surface area compared to other samples: 12% reduction from the initial value for Pt/TiO2-NT; 40% reduction for Pt/TiO2-NP and 76% for Pt/C. Pt/TiO2-NT exhibited long term stability towards ORR compare to both Pt/TiO2-NP and Pt/C. The anode oxidation capability of Pt/TiO2-NT has been tested and it showed enhanced electro catalytic activity for MOR compared to both Pt/TiO2-NP and Pt/C electrocatalysts in terms of activity and COpoisoning tolerance. The enhanced performance by Pt/TiO2-NT can be imputed to the increased oxygen defects as deciphered from HAXPES, favoring the interface charge transfer between Pt and TiO2-NT. These results together demonstrate Pt/TiO2-NT a candidate catalytic material for cathode as well as anode catalysts in polymer-electrolyte membrane fuel cells (PEMFCs).