Fig. 6. (A) Mass normalized CO stripping curves of Pt/C (Johnson Matthey, 20 wt%) and single-crystalline dendritic Pt₃Cu and PtCuNi nanocubes in 0.5 M H₂SO₄ solution. (B) CV curves of PtCuNi dendritic cubes before and after 5000 cycles of oxygen reduction reaction (ORR) accelerated durability test (ADT). Only 2.7% activity loss was observed. (C) CV curves of Pt/C and dendritic Pt₃Cu nanocubes in methanol oxidation, revealing a 5.2-fold enhancement on mass activity. (D) ORR polarization curves of PtCuNi/C and commercial Pt/C recorded at a rotation rate of 1600 rpm. The half-wave potential of dendritic PtCuNi nanocubes shifted 37 mV to higher potential than Pt/C. (E) and (F) Specific activity and mass activity comparison for methanol oxidation (PtCu/C and commercial Pt/C) and oxygen reduction reaction (PtCuNi/C and commercial Pt/C), which are given as kinetic current densities normalized to the ECSA and the loading amount of Pt, respectively.51 The Pt loading was 4 μg for all the catalysts in methanol oxidation reaction test and were 2 and 4 μg for nanodendrites and commercial Pt/C in oxygen reduction reaction test, respectively.