The second point on the purity of the employed chemicals is arguably even more important as it concerns the foundation on what is experimentally measured. While not the prime focus of this work, we will briefly discuss the five different cations we have examined and why two of them have not been included despite being studied by other groups. In our case, and we believe that to be true in other laboratories, judging whether an electrolyte is sufficiently pure is somewhat subjective. Signs of purity are stable CVs and HOR/HER activities over an extended time, preferably for at least one hour. In the case of lithium and sodium, we used 99.995% (solid) and 99.9999% (solution) specified pure chemicals (always trace metal basis). We consumed multiple batches of these chemicals in our study and mostly obtained very stable CVs and high HER/HOR activities, except for two batches of LiOH and one batch of NaOH. In the case of KOH we found the specified 99.99% (solid) purity was insufficient for two out of three batches but had a good experience with the 99.995 % (solid) specified purity. We investigated one 99.99% specified batch further and believe to have found the reason why the purity of alkali metal hydroxides is so critical: After the Pt electrode was cycled in 0.1 M solution of KOH, we found metallic lead (Fig. ), but also zinc and copper on its surface via XPS. Removing these contaminants requires thorough polishing. We then performed the same test in our high purity NaOH and found again a strong lead signal (not shown). We quickly realized that this lead stemmed from the counter electrode (which was not cleaned after the KOH measurements). This was then cleaned extensively by cycling in acid. After an extensive hand-polishing of the electrode, only a miniscule amount of lead was found after cycling the electrode in NaOH again. When repeated in KOH (not shown), the lead signal returned. In the case of rubidium hydroxide (99.9% solution), nothing close to a proper CV could be obtained. Lastly, we found that the HOR/HER activity in cesium hydroxide (99.995 %, solid) is close to that of the other three alkali metals, but some features of the CV were different, and the HOR/HER activity deteriorated in subsequent measurements, therefore we excluded it from this study. The general challenge of measuring the HOR/HER in alkaline is the very negative potentials encountered on the SHE scale. Together with the substantial convective transport to the platinum surface in an RDE setup, any transition metal will be rapidly reduced and likely form a surface alloy with platinum, making it harder to remove by potential cycling. We think therefore, that every study, including this one to a minimal extent, suffers from the influence of impurities. We have also studied our electrolytes in ICP-OES, in which they exceeded the purities expected from their specifications. Historically, identifying trace metals was done through electrochemical means, e.g. the mercury drop electrode, suggesting that accurately probing the HOR/HER is on the limit of how pure chemicals can be commercially obtained. A good practice would be to conduct an XPS survey after each electrochemical measurement, which is nevertheless challenging for most laboratories.