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Oxidation induced irredeemable magnetic loss is of key concern in the high temperature applications of Sm2Co17-type permanent magnets. Herein, the atomic-scale oxidation mechanism of a Sm2Co17 magnet is unveiled using aberration-corrected transmission electron microscopy. Heating at 500 °C in air, the oxidation scale growth and energy product reduction of the magnets undergo a two-stage process. Due to the formation of a transition oxidation zone between the internal oxidation zone (IOZ) and matrix, the stage-I (t 1 1 ¯ 1} pyramidal planes act as the preferential oxygen diffusion pathways at the magnet side and top surfaces, respectively. This results in the non-uniform oxidation, i.e., the oxidation scale at the cylindrical sides of the magnet is 1.4–2 times thicker than that at the top. Oxygen penetration along basal or pyramidal planes firstly induces the oxidation of 1:3R Z-plates and Cu depletion from the 1:5H boundaries in the magnet. Then the 1:5H and 2:17R phases are decomposed into Sm, CoFe and Cu metal lamellae, which finally evolve into the IOZ with nano-oxides, oxygen-enriched CoFe and Cu particles inside. This work sheds light on the atomic-scale oxidation behavior of Sm2Co17-type magnets.

Layered alkali metal oxides have been emerged as an alternative group of low-cost and promising electrocatalysts in water oxidation. The distinct layered configuration may offer some interesting possibilities to tune the intrinsic activity by regulating the intralayer edge-shared CoO6 octahedra and the CoO2 interlayer spacing/strain. In this work, electrochemical desodiation tuning method is explored on intralayer Ag, Cu, Ce-doped Na0.7CoO2 for highly active OER catalysts. It is demonstrated that the ΔGOH* value in the volcano plot is optimized by proper desodiation. Meanwhile, the lattice strain introduced along with the desodiated process modulates the ΔGOH*, according to first principle calculations. It shows that ∼0.157 % compressive strain in the CoO2 layers and ∼1% tensile strain between CoO2 layers are introduced in the desodiated Ag doped Na0.7CoO2. Among these catalysts, the desodiated Ag-Na0.7CoO2 sample exhibits an optimal RuO2-beyond water oxidation (OER) activity with the lowest overpotential of 236 mV@10 mA/cm2, the smallest Tafel slope of 48 mV/dec and the highest mass current density of 227.8 A/g. This work provides an interesting avenues to optimize existing layered materials with inter/intralayer modifications for highly efficient water oxidation electrolysis.