Self-assembled TiO2 Nanopore-Confined Growth of Pd NPs on Pristine Graphene for Superior Electrocatalytic Performance toward Formic Acid Oxidation

Nanoporous cocatalysts can guide the growth of catalysts with promoted activity, but it is extremely challenging to identify, synthesize, and integrate them to fabricate supported nanoelectrocatalysts with high performance. An ultrathin, uniform layer of nanoporous TiO2 has been self-assembled on pristine graphene to mediate Pd growth. Ultrasmall, uniform, and highly dispersed Pd nanoparticles (NPs) have been selectively grown in TiO2 nanopores due to nanopore-enhanced adsorption of PdCl42- and in situ nucleation of Pd seeds. The obtained graphene-supported TiO2-nanopore-confined Pd NPs show remarkably improved formic acid oxidation reaction (FAOR) catalytic performance compared to Pd NPs grown on graphene and on nonporous-TiO2-modified graphene and commercial Pd/C. The activity is among the highest reported for Pd-based catalysts. The superior performance is ascribed to the ultrasmall and highly dispersed Pd NPs embedded in graphene-supported nanoporous TiO2, which create an ultrahigh electrochemically active surface area, and the large interface area between TiO2 and intimately grown Pd NPs, which significantly enhances intrinsic catalytic activity via the bifunctional mechanism. This work not only develops a strategy to fabricate graphene-supported Pd NPs with cocatalysts effectively integrated for achieving excellent catalytic performance but also sheds light on the mechanisms of nanopore-confined growth of Pd NPs and nanopore-enhanced promotion of FAOR catalysis.