Monodisperse platinum particles of various diameters were grown from platinum seeds utilizing a stepwise addition of calculated amounts of platinum salt and ascorbic acid. Ascorbic acid, being a weak reducing agent, prevented new seed nucleation while fully reducing the platinum salt in solution. It was discovered that as the platinum seeds were grown into much larger particles they became more faceted; increasing their surface area-to-volume ratio. This new nanoparticle synthesis technique allows the creation of uniquely faceted platinum nanoparticles of controllable size that are ideal for catalysis.