Heteropolyacid-Mediated Self-Assembly of Heteropolyacid-Modified Pristine Graphene Supported Pd Nanoflowers for Superior Catalytic Performance toward Formic Acid Oxidation

The in situ growth of Pd nanoflowers on pristine graphene is achieved using phosphomolybdic acid (HPMo) to mediate self-assembly. The HPMo serves simultaneously as a linker, stabilizer, and structure-directing agent, and the nanoflowers are formed by kinetically controlled growth. When the resulting material, Pd nanoflowers on HPMo-modified graphene (HPMo-G) support, is used to catalyze the formic acid oxidation reaction (FAOR), much higher catalytic activity and durability are found than with HPMo-G supported Pd nanospheres, graphene supported Pd nanoparticles, and commercial Pd/C catalysts. The catalytic activity for Pd nanoflowers on HPMo-G is also among the highest reported for Pd-based catalysts. The superior electrocatalytic performance is attributed to the unique nanoflower shape, a promotion by the HPMo mediator, and the excellent support properties of pristine graphene. The use of HPMo to mediate self-assembly of metals on graphene can be extended to fabricate other hybrid nanostructures promising broad applicability.