All the measurements were done using smooth polycrystalline Ni (Ni-poly) rotating disk electrodes (RDE). The Ni disk had a diameter of 3.2 mm and was inserted in a Teflon cylinder with a 10 mm diameter. The Ni disk was made of Ni rod (Goodfellow Cambridge Limited, England, 99.9 %). Before the modification with Rh, the disk was polished with alumina-based grinding paper, sonicated for 1 minute, washed in deionized water, subsequently in diluted HCl, and again in deionized water. Galvanic displacement was done by drop-casting 10 µL of 0.1 mol dm -3 RhCl3 (Sigma Aldrich) solution in 0.1 mol dm -3 HClO4 for a specified amount of time (up to 303 s). After the exchange, the electrode was rinsed in deionized water, then in 0.1 mol dm -3 KOH or 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. For the measurements of clean Ni-poly, the electrode was transferred to the electrochemical cell directly after the polishing. The roughness factor (RF) of such prepared Ni-poly electrodes amounts to 10±1, determined by double-layer capacitance measurements as described in .