M. Odén

The wurtzite phase of TiAlN has been known to form in industrial grade coatings with high Al content; yet, a significant knowledge gap exists regarding its behavior at high temperatures and the impact of defects on its properties. Specifically, its response to high temperatures and the implications of defects on its characteristics are poorly understood. Here, the high-temperature decomposition of nitrogen-deficient epitaxial wurtzite Ti1−xAlxNy (x = 0.79–0.98, y = 0.82–0.86) films prepared by reactive magnetron sputtering was investigated using x-ray diffractometry and high-resolution scanning transmission electron microscopy. The results show that wurtzite Ti1−xAlxNy decomposes by forming intermediary MAX phases, which then segregate into pure c-TiN and w-AlN phases after high-temperature annealing and intermetallic TiAl nanoprecipitates. The semicoherent interfaces between the wurtzite phase and the precipitates cause age hardening of approximately 4−6 GPa, which remains even after annealing at 1200 °C. These findings provide insight into how nitrogen vacancies can influence the decomposition and mechanical properties of wurtzite TiAlN.

Electrocatalysis enables the industrial transition to sustainable production of chemicals using abundant precursors and electricity from renewable sources. De‐centralized production of hydrogen peroxide (H 2 O 2 ) from water and oxygen of air is highly desirable for daily life and industry. We report an effective electrochemical refinery (e‐refinery) for H 2 O 2 by means of electrocatalysis‐controlled comproportionation reaction (), feeding pure water and oxygen only. Mesoporous nickel (II) oxide (NiO) was used as electrocatalyst for oxygen evolution reaction (OER), producing oxygen at the anode. Conducting polymer poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) drove the oxygen reduction reaction (ORR), forming H 2 O 2 on the cathode. The reactions were evaluated in both half‐cell and device configurations. The performance of the H 2 O 2 e‐refinery, assembled on anion‐exchange solid electrolyte and fed with pure water, was limited by the unbalanced ionic transport. Optimization of the operation conditions allowed a conversion efficiency of 80%.