Synthesis of five-twined platinum decahedra is currently a great challenge. Reported herein is a solution synthesis of ultrafine decahedral platinum crystals (average size 5.9 nm) mediated by graphite nanosheets together with poly (dimethyl diallyi ammonium chloride). The graphite nanosheets play a critical role in the formation of Pt decahedra. The obtained Pt decahedral crystals provide a valuable platform for the fundamental study of facet-dependent activity of platinum. The hybrid of Pt decahedral crystal decorated graphite nanosheets shows outstanding activity and durability for the oxidation of formic acid. The hybrid possesses a remarkable current density of 4.3 mA cm(-2), which is 2 times that of state-of-the-art Pt/C catalyst. The superior catalytic performance is well correlated with the unique structures of decahedral Pt crystals. The synthesis protocol disclosed in this study would pave a new route to fabricate high-performance electrocatalysts for fuel cells. (C) 2016 Elsevier Inc. All rights reserved.