The first set of measurements relates to smooth Ni-poly rotating disk electrodes (RDE). The Ni disk had a diameter of 3 mm and was inserted in a Teflon cylinder with a 10 mm diameter. The disk was polished to mirror-finish using alumina powder and then sonicated for 1 minute, washed in deionized water, diluted HCl, and again in deionized water. Then it was transferred to the electrolytic cell, and HER measurements were done. Ni/Rh displacement experiments were done by immersing Ni-poly RDE into 0.1 mol dm -3 RhCl 3 solution in 0.1 mol dm -3 HClO 4 for a given amount of time (for the measurements with Ni-poly RDE up to 45 s). After the exchange, the electrode was rinsed in deionized water, 1 mol dm -3 KOH solution, covered with the droplet of the same solution, and quickly transferred into the electrochemical cell. The transfer to the cell typically took under 30 s.