After analyzing alkaline water electrolysis reactions, we turn to HOR and ORR -the key reactions in fuel cell technologies. HOR was measured in H2-saturated 0.1 mol dm -3 at 10 mV s -1 , like in . As the measurements were not fully stationary, some (pseudo)capacitive contributions are visible due to the HUPD process. On the other hand, we wanted to avoid extensive Rh oxide formation, so we restricted voltammetric measurements to potentials beyond HUPD peaks (i.e., double-layer region) where the capacitive response is the lowest. HOR was measured for Rh-modified Ni-poly electrode upon 30 s of exchange, directly after the replacement (Figure , a) and after prolonged cycling to 1.2 V vs. RHE (allowed to rest at 0 V vs. RHE for 10 min after cycling, Figure ). In both cases, diffusion limitations are reached, which can be seen from the equidistant diffusion currents and the Levich plot (Figure ). However, in both cases diffusion currents are lower compared to the Pt-poly electrode and Pt/C-modified RDE from Ref. . Kinetic currents (jk) evaluated at 0.05 V vs. RHE point that jk for as-deposited Rh-modified electrode amounts 1.58 mA cm -2 , while after cycling it increases slightly to 1.75 mA cm -2 . Still, this is one order of magnitude lower compared to Pt-poly (RF = 20) where jk was found to be 17.7 mA cm -2 . We note that Ni-poly does not have HOR activity , thus, the observed activity is solely due to the Rh phase. Previously, Rh-Ni alloys have been tested for HOR activity , and it was found that Rh-Ni alloys display composition-dependent activity, while the most active composition is Ni89Rh11 . Interestingly, in that study as well diffusion-limiting currents commonly found for Pt electrodes were not reached on Rh-Ni alloy electrodes, and the diffusion currents we find here fall in the range of the ones reported in Ref. , where they have been measured under fully stationary conditions. Obviously, in contrast to HER, the HOR performance of Rh-modified electrodes is not as good and the electrodes perform not as well as platinum, despite tremendous activity improvements with respect to pure Ni-poly, which is not HOR active at all. Next, we study ORR on Rh-modified Ni-poly (Figure , a) and compare ORR performance to the Pt-poly electrode (RF = 20). Although in this work we have not prepared very smooth Ni-poly and its surface is rough, the RF is lower compared to the used Pt-poly benchmark where also small Pt particles are seen, being formed during the platinization (Figure , inset 3D SEM images). Higher RF of Pt-poly is also confirmed by a larger blank cyclic voltammogram compared to that of Rh-modified Ni-poly (Figure , a and d). In the case of Pt-poly, full diffusion limitations corresponding to the 4e -reduction of O2 are reached. Moreover, there is a relatively small hysteresis between anodic and cathodic scan which is approximately 35 mV wide at the half-wave potential. ORR onset potential for Pt-poly was found to be close to 1.0 V vs. RHE. On the other hand, Rh-modified Ni-poly shows lower ORR onset potential (0.86 V vs. RHE), and much wider hysteresis between anodic and cathodic scans, amounting to 104 mV at the half-wave potential. In the case of Pt-poly, we have previously discussed how the effects of potential scan rate affect the hysteresis and ascribed its width to the slow Pt-oxide reduction under different potentiodynamic conditions . Thus, when this knowledge is combined with the slow reduction of Rhoxide discussed before (see Figure , b), larger hysteresis width in the case of Rh-modified Ni-poly, compared to Pt-poly, can be ascribed to hardly reducible Rh-oxides being formed on the electrode surface. We note that the relatively high ORR activity of the Rh-modified Ni-poly electrode is primarily due to the presence of Rh as the Ni-poly electrode has very poor ORR activity which is largely affected by the state of the surface, that is, the presence of Ni-oxide species. Moreover, the oxidation of Ni-poly surface in alkaline media leads to reduced selectivity of O2 reduction and large amounts of peroxide formed . Here, on the contrary, using the Koutecky-Levich (K-L) analysis , we found that ORR on the Rh-modified Ni-poly surface follows the 4e -ORR path in the entire potential window where ORR was investigated (Figure ). On the other hand, using the K-L analysis we have found that kinetic ORR currents (jk) have finite values in the entire ORR potential window investigated, which were only a few times higher than limiting diffusion currents (jd). Thus, using the K-L equation: