Structural, physical, electrocatalytic, and energy storage properties of hydrothermal Y ₂ CoMnO ₆ microrods/nanorods

Abstract This work presents a two‐step hydrothermal method for preparing Y 2 CoMnO 6 microrods/nanorods (YCMO MRs/NRs) with tunable aspect ratios by adjusting hydrothermal temperature, pH value, and postannealing conditions. At pH values above 13, YCMO forms rod‐like structures, and both hydrothermal temperature and time significantly influence rod sizes. The YCMO MRs (210°C, 24 h) have a diameter of 920 nm and a length of 4.90 µm, while the YCMO NRs (180°C, 16 h) have a diameter of 450 nm and a length of 3.95 µm. X‐ray diffraction data reveal both MRs and NRs mainly adopt a monoclinic structure ( P 2 1 / n space group), while NRs have a smaller unit cell due to the suppressed grain growth at lower temperatures. X‐ray photoelectron spectroscopy (XPS) confirms dual oxidation states for Mn and Co ions. The YCMO MRs exhibit a relaxor‐like dielectric behavior due to the dipolar effects associated with the charge carrier hopping between the Co 2+ /Mn 4+ pair. Ferromagnetic behavior was observed in the YCMO MRs at 5 K with saturation magnetization ( M S ) of 3.21 µ B /f.u. and coercive field ( H C ) of 9.80 kOe as well as magnetic Curie temperature ( T C ) of 83 K, while NRs have higher M S of 3.75 µ B /f.u. and larger H C of 18.0 kOe due to interface effects. Optical absorption spectra reveal the semiconductor bandgaps of 1.64 eV and 1.68 eV for YCMO MRs/NRs, respectively. Electrochemical tests reveal that the YCMO NRs have better oxygen evolution reaction (OER) performance with an overpotential of 510 mV @ 1 mA/cm 2 and a lower Tafel slope of 107 mV/dec as well as the specific capacitance of 93.78 F/g @ 1 A/g (twice that of the YCMO MRs), and the maximum energy density of 3.26 Wh/kg at 250 W/kg (1.6 times larger than that of the YCMO MRs). Furthermore, the specific capacitance retention of the YCMO NRs was achieved 81.2% after the first 1000 cycles and 68.5% after 5000 cycles at a current density of 10 A/g. No degradation was observed in the galvanostatic charge–discharge (GCD) cycle patterns for the first five and last five cycles, demonstrating the high cyclic stability of the YCMO NRs. These findings suggest that the YCMO NRs are promising candidates for electrocatalytic and energy storage applications.