The shape and structure of electrocatalysts at the nanoscale level have a decisive effect on their activity and durability in low-temperature fuel cells. Herein, we report the discovery of unexpected structural phenomena in exotic nanostructures: the anomalous compressive strain and superior electron retention properties of highly porous Pt (HP-Pt) nanoparticles synthesized using a weakly interacting organic capping agent, tetradecyl trimethyl ammonium bromide. Even though the particle size of the HP-Pt nanoparticles was much larger than those of commercial electrocatalysts, bond length shortening occurred anomalously, and the downshifted d-band center eventually led to increased oxygen reduction reaction activity. This is because the HP-Pt nanoparticles had a highly porous urchin-like dendritic structure, interestingly in the single-crystalline phase, despite the large particle size. In addition, their electron retention properties were superior to those of commercial samples, which led to drastically enhanced stability against Pt dissolution at high potentials. (C) 2012 Elsevier Inc. All rights reserved.