Nickel(II) hydroxide is a well-known material for the oxygen evolution reaction (OER) in alkaline media, particularly when iron is incorporated into its lattice. Moderate heat treatment of nickel(II) hydroxide (≤700 °C) leads to the formation of nickel(II) oxide (nano)particles, which exhibit reduced OER activity the higher the heat treatment temperature was. In this work, we report that heat treatment of nickel(II) hydroxide in air at even higher temperatures (60 min at 900 °C) results in an oxide material with high OER activity superior to that of the nickel(II) hydroxide. Similarly, the stability of the nickel(II) oxide under electrochemical conditions is increased compared to nickel(II) hydroxide. Electrochemical in situ Raman measurements show the formation of surface nickel oxy-hydroxides (NiOOH) at positive potentials and are significantly affected by the initial heat treatment. From XPS, Raman, and XRD results, it is concluded that a Ni 3+ -enriched phase, possibly a higher-valent mixed nickel oxide, is present at the surface of the nickel(II) oxide sample treated at 900 °C resulting in an increased OER activity compared to NiOOH. This basic understanding of high-temperature-treated nickel oxide may contribute to resolving the present stability issues of OER electrocatalysts and may help to leverage alkaline electrolysis as important key technology for a renewable energy supply.

Many text books and publications do not focus on the necessity of chain tilting in crystalline lamellae of oligomers and polymers, a fundamental aspect of their crystallization already discussed by Flory. Herein we investigate the chain tilt of ethylene oxide oligomers (EOs) containing various midchain defects by WAXS, SAXS and solid state 13C MAS NMR spectroscopy. At low temperatures, one out of the two EO chains of EO9-meta-EO9 and EO11-TR-EO11 containing a 1,3-disubstituted benzene or a 1,4-disubstituted 1,2,3-triazole defect in central position of the oligomer chain forms crystals and the other EO chain as well as the defect remain in the amorphous phase. The aromatic midchain defect of these two oligomers can be incorporated into the crystalline lamella upon heating below T m. Then, the adjoining amorphous EO chain crosses from the lamellae to the amorphous regions at an angle ξ, which is preordained by the substitution pattern of the aromatic defect, revealing that the chain tilt angle ranges between 36° ≤ ϕ ≤ 60°.