A simple electrochemical process for submonolayer deposition of ultrathin catalytic Ir films is demonstrated. This method enables effective utilization of one of nature's rarest elements while different substrates facilitate the exploration of promising bimetallic catalysts for a sustainable hydrogen economy. Semi-coherent Ir films were deposited on Au, Pt and Ni substrates using K₃IrCl₆–Na₂SO₄–H₂SO₄ electrolytes operated between 40 °C and 70 °C. However, the deposition reaction is quenched at the onset of H₂ production where adsorbed H blocks the reduction of IrCl_6−xH₂O_x^x−3 to Ir. The electrode can be reactivated for further deposition by pulsing the potential to more positive values where adsorbed H is oxidized. The electrocatalytic activity of ultrathin Ir and Pt films, and combinations thereof, were examined as function of the number of self-terminating deposition pulses. The ultrathin films match or exceed the best reported activity metrics for hydrogen oxidation in alkaline media and oxygen evolution in acid.