Continuous and conformal thin TiO2-coating on carbon support makes Pd nanoparticles highly efficient and durable electrocatalyst

Abstract

Improving the activity and durability of Pd or Pt nanoparticle (NP) electrocatalyst is an urgent issue for the widespread use of fuel cells. In order to achieve high catalytic activity, incorporation of metal oxides into electrocatalysts has been pursued, mainly for the purpose of enabling strong metal-support interaction (SMSI) between the NPs and metal oxides. In this study, we demonstrate a novel method to coat TiO2 on carbon nanotubes (CNTs) through sonochemical reaction of TiO(acac)2 (acac = acetyl acetate) in dimethyl sulfoxide (DMSO). The TiO2-coated CNT (TC(S)) is characterized by a continuous conformal TiO2-coating with the thickness of ∼1.5 nm throughout without any exposed CNT surface. The same reaction in ethylene glycol (EG) or N, N-dimethylformamide (DMF) also produced TCs (TC(E) and TC(F), respectively), but without the conformity and/or continuity seen in TC(S). Formation of Pd NPs on TC by a second sonochemical reaction in EG results in Pd/TC electrocatalysts with significantly increased activity and durability for formic acid oxidation reaction (FAOR) from the reference Pd NPs on CNT. Pd/TC(S) shows the highest activity and durability, surpassing all in the literature data. The enhanced FAOR activity of Pd/TC(S) can be attributed to the SMSI effect from the interface between Pd NPs and TiO2-coating plus the bifunctional mechanism of TiO2. The increased durability can be explained as the result of protecting CNT against the corrosion from CNT-Pd contact.