Pulse electroplating technology has been applied in the preparation of Pt/C electrocatalysts for hydrogen fuel cell electrodes for decades. The major challenge remaining unsolved is the aggregation of Pt nanoparticles on the carbon support. This research reports a nanoparticle seeded pulse electroplating method for preparing Pt/C electrocatalysts used for oxygen reduction reaction (ORR). Pt or Pt alloy nanoparticles were pre-deposited onto a carbon support as nuclei, followed by Pt pulse electrodeposition. This new approach is able to overcome Pt particle aggregation issues and improve catalyst performance. The technology can also be used for the preparation of core/shell Pt/C electrodes when non-Pt or Pt alloy nanoparticles are used as seeding materials. Experimental results show that a Pt/C electrode with less than 0.1 mg/cm(2) Pt loading density, synthesized based on 3.0 nm Pt nanoparticle seeds, can achieve a higher ORR activity than a commercial electrode with 0.5 mg/cm(2) Pt loading. When Pt-Pd-Ru alloy nanoparticles of 2.0 nm average diameter were used as seeding nuclei the prepared Pt/C electrode showed higher ORR performance than the commercial electrode, further reduced Pt loading density. Atomic level STEM analyses showed that numerous free Pt atoms were surrounding Pt nanoparticles, serving as nuclei. The seeding atoms, along with nanoparticles, promote the even growth of Pt particles on carbon support during electroplating. This result is verified by SEM images which indicate that electroplated Pt particles on the carbon surface are uniformly distributed and each particle is loosely packed with Pt nanosized flakes. The flower-like structure, with higher surface areas, enhances mass transfer rates and leads tothigher ORR efficiencies. Although a commercial Pt/C electrode was used as a baseline catalyst for comparing prepared electrodes, this exploratory research was based on a rotational disk electrode. Fuel cell testing is needed to confirm the finding. Published by Elsevier B.V.