The energy crisis and environmental challenges have accelerated the development of new energy sources and energy storage devices, highlighting the importance of research on Ni(OH) ₂ , a widely used active material in energy storage systems. At present, research on Ni(OH) ₂ mainly focuses on the preparation of α-Ni(OH) ₂ and improvements in its structural stability. To obtain α-Ni(OH) ₂ with enhanced durability, this work attempts to directly prepare Al–Mn co-substituted α-Ni(OH) ₂ through an one-step electrodeposition method. The results indicate that Mn ²⁺ may influence the local pH at the cathode−catholyte interface via the formation of coordination complexes with OH ^– , thereby affecting the co-deposition of Al ³⁺ . Samples exhibiting a Mn fraction similar to the initial electrolyte and an Al fraction about 2.5−time as that in the initial electrolyte ratio can be produced using MnCl ₂ –AlCl ₃ –NiCl ₂ solutions as both anolyte and catholyte. Additionally, samples with a Mn ratio of about one-tenth of the original electrolyte and an Al ratio comparable to the initial value can be achieved by alternately using MnCl ₂ –AlCl ₃ –NiCl ₂ and AlCl ₃ –NiCl ₂ solutions as the anolyte and catholyte. The phase characteristics of the electrodeposited Al−Mn co-substituted α-Ni(OH) ₂ remained after 30 days of immersion in 6 M KOH, and their alkaline stability surpassed that of samples prepared by chemical precipitation.

Quench–polish–quench (QPQ) of 40Cr steel was performed to improve its tribological properties and corrosion resistance, thereby enhancing the service performance of components such as gears and bearings. The 40Cr steel was treated by QPQ at 580 °C and 620 °C for 90 or 120 min. Optical microscopy (OM, Sunny Group, Ningbo, China), scanning electron microscopy (SEM, Hitachi, Tokyo, Japan), and X-ray diffraction (XRD Rigaku Corporation, Tokyo, Japan) were used to characterise the microstructure and phase constitution. Ball-on-disk tribometry, electrochemical tests, and salt spray tests in 3.5 wt.% NaCl evaluated surface performance. At 580 °C, a composite structure of Fe₃O₄ and ε-Fe₂₋₃N formed on the surface. When the temperature rose to 620 °C, ε-Fe_2–3N gradually transformed into γ′-Fe₄N. Within the scope of this study, the diffusion layer depth exhibits an approximately linear relationship with increasing processing temperature and holding time, and the surface hardness is 67–112% higher than that of the untreated sample. After QPQ treatment, the wear mechanism changed from adhesive wear to abrasive wear. However, under the treatment conditions of 620 °C × 120 min, brittle surface spalling increased roughness, thereby increasing the coefficient of friction. As treatment time increases, nitrogen atoms continue to diffuse outward as Fe₂N transforms to the γ′ phase. This increases the composite layer’s porosity and decreases its corrosion resistance. The best corrosion resistance was observed at 580 °C for 120 min, with a corrosion potential of −0.4325 V, corrosion current density of 1.80 × 10⁻⁶ A·cm⁻², and polarisation resistance of 24,500 Ω. Corrosion performance depends on overall surface integrity. Porosity morphology strongly influences this property. For 40Cr steel, the results show that surface properties are primarily determined by the quality of the compound layer’s microstructure. Specifically, density, phase-composition stability, and defect control are more important than the commonly held view of layer thickness.