Structural transformation doubly triggered by hydrothermal temperature and reaction time in 3D mixed transition metal oxide: Great enhancement of pore size distribution and specific surface area

The three-dimensional (3D) nanostructured binary metal oxides have a massive prospect in energy-related applications owing to their outstanding electrochemical performance and stability. 3D hierarchical tremella-like nickel cobaltite (NiCo₂O₄) has been successfully synthesized by a hydrothermal method coupled with an annealing treatment process. The effects of temperature and reaction time in hydrothermal process on crystal structure, morphology, particles size, surface area and pore size distribution were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller analysis (BET) and Barrett-Joyner-Halenda (BJH) analysis. The results showed that 3D hierarchical nanoporous structures composed of interconnected thin nanoflakes with thickness of about 20 nm began to form when the mixture was heated for 6 h at 180 °C with considerably high specific surface area of 169.61 m²/g. On the other hand, the highest surface area (203.21 m²/g) and narrowest pore size distribution (9.13 nm) are achieved by the sample heated at a temperature of 160 °C for 12 h. These findings indicated that temperature and reaction time parameters in hydrothermal process play a major role in producing different quality and altered morphological structures of NiCo₂O₄ powders which later will affect the electrochemical performance of fuel cell.