Octahedral PtNi/C catalysts have demonstrated superior catalytic performance in oxygen reduction reaction (ORR) over commercial Pt/C with rotating disk electrode (RDE). However, it is not trivial to translate such promising results to real-world membrane-electrode assembly (MEA). In this work, we have synthesized octahedral PtNi/C catalysts using poly(diallyldimethylammonium chloride) (PDDA) as a capping agent and investigated their performance from RDE to MEA. In RDE, mass activity and specific activity of the optimized octahedral PtNi/C catalyst for oxygen reduction reaction (ORR) are nearly 19 and 28 times high of the state-of-the-art commercial Pt/C, respectively. At MEA level, the octahedral PtNi/C catalyst exhibits excellent power generation performance and durability paired with commercial Pt/C anode. Its cell voltage at 1, 000 mA·cm⁻² reaches 0.712 V, and maximum power density is 881.6 mW·cm⁻² and its performance attenuation is also less, around 11.8% and 7% under galvanostatic condition of 1, 000 mA·cm⁻² for 100 h. Such results are investiaged by thermodynamic analysis and fundametal performance modeling, which indicate the single cell performance can be further improved by reducing the size of PtNi/C catalyst agglomerates. Such encouraging results have demonstrated the feasibility to convey the superior performance of octahedral PtNi/C from RDE to MEA.