Crystal structure-controlled synthesis of NiMoO₄/NiO hierarchical microspheres for high-performance supercapacitors and photocatalysts

Global environmental challenges and energy crises have driven researchers to develop multifunctional and highly efficient nanomaterials. This study presents dual-functional NiMoO₄ (NMO)/NiO hierarchical microspheres that can serve as supercapacitors and photocatalysts prepared using a microwave-assisted hydrothermal method. The α- and β-phase contents of NMO can be regulated by controlling the post-annealing temperature and pH value of the precursor solution. The as-prepared NMO/NiO nanocomposites exhibited dual Faradaic redox reactions attributed to NMO and NiO, leading to remarkable supercapacitor performance. In addition, the constructed heterojunction between NMO and NiO also improved charge separation, leading to excellent photocatalytic capability. Based on the results, NMO with a higher β-phase content showed better supercapacitive and photocatalytic performance owing to its higher conductivity. The optimal NMO/NiO composite displayed a specific capacitance of 943 F g⁻¹ at 1 A/g and excellent cycling stability, with 83.1 % retention at 5 A/g after 4000 cycles. Additionally, it demonstrated an outstanding photocatalytic capability for the degradation of methylene blue (MB), achieving a rate constant of (0.0113 min⁻¹).