Effects of Intentionally Incorporated Metal Cations on the Oxygen Evolution Electrocatalytic Activity of Nickel (Oxy)hydroxide in Alkaline Media

Fe-doped Ni (oxy)­hydroxide, Ni­(Fe)­O x H y , is one of the most-active oxygen-evolution-reaction (OER) catalysts in alkaline conditions, while Fe-free NiO x H y is a poor OER catalyst. One approach to better understand the role of Fe, and enable the design of catalysts with higher activities, is to find other cations that behave similarly and compare the common chemical features between them. Here we evaluate the effects of La, Mn, Ce, and Ti incorporation on the OER activity and redox behavior of NiO x H y in rigorously Fe-free alkaline solution using cyclic voltammetry and electrochemical quartz-crystal microgravimetry. We use X-ray photoelectron spectroscopy and time-of-flight secondary-ion-mass spectrometry to confirm that measurements are free from relevant levels of trace Fe contamination. We find that only Ce leads to increased activity in NiO x H y (about a factor of 10 enhancement), but this effect is transient, likely due to phase separation. We further find no clear correlation between activity and the nominal Ni2+/3+ redox potential, suggesting that the “oxidizing” power of the Ni is not directly correlated with the OER activity. These findings suggest a uniqueness to Fe and are consistent with it being the active site in Ni­(Fe)­O x H y .