Water electrolysis to produce hydrogen fuel is one of the most important processes to optimize on the way to sustainable energy provision schemes. Its efficiency in both alkaline and acidic media is drastically limited by the sluggish kinetics of the oxygen evolution reaction (OER) taking place at the anode side of modern electrolyzers. Numerous electrocatalysts have been proposed recently to increase the activity of the anodes; most of them are transition metal oxides and perovskite materials. However, the activities reported in the literature for these electrodes are in the majority of cases measured at low overpotentials, low or moderate current densities (often 10–50 mA cm^–2), relatively diluted electrolytes (e.g., 0.1 M KOH), and room temperatures. However, commercial electrolyzers operate at current densities that are at least 1 order of magnitude larger, elevated temperatures, and significantly higher pHs. To enable new generation of electrocatalysts, it is important to evaluate their intrinsic activities under industrially relevant conditions. This is not a trivial task, neither in industry nor in research laboratories, particularly due to (i) formation of a nonconducting gas phase in the vicinity of the electrode under such conditions, (ii) limitations due to mass transfer and uncompensated resistances, and (iii) problems in determination of the real electroactive electrode surface area. In this work, with the use of microelectrodes, we evaluate intrinsic OER catalytic activities of several state-of-the-art nickel-, cobalt- and nickel/iron-oxide/hydroxide thin films at different temperatures (up to 80 °C), in 5.4 M KOH and at current densities up to several A cm^–2. Additionally, Ni-modified Pt electrocatalysts for the hydrogen evolution reaction were also tested under similar conditions and compared with pure Pt electrodes.