Template-Free Broccoli-Shaped Battery-Type Supercapacitor Electrodes Integrated with a 1D/2D Carbon Hybrid Matrix with 0D Calcium Molybdenum Nanospheres

The promise of calcium-molybdate-based electrodes for energy-storage applications is restricted by their low conductivity across a range of voltages and limited capacity. This study proposes a novel and simple strategy to address these challenges. In this study, we synthesized broccoli-shaped three-dimensional (3D) interconnected networks by integrating one-dimensional (1D) functionalized carbon nanofibers (f-CNFs) with two-dimensional (2D) reduced graphene oxide (r-GO) nanosheets to form a robust backbone, which effectively stabilized the assembly of spherical-shaped calcium-molybdate (CaMoO₄) nanosphere composites (CMCG) using a simple two-step hydrothermal method. Interestingly, air-annealing promoted a morphological transformation toward more spherical shapes, enabling clearer size determination, illustrating pseudocapacitive surface redox reactions including Ca²⁺ and MoO₄²⁻. The charge-storage properties of the CMCG composite exhibit dominant battery-type behavior with the existence of 1D/2D hybrid carbon networks due to its unique morphology with a highly porous nanostructure, increased voids and cavities, leading to faster diffusion that increases the accumulation/intercalation of charges at the electroactive sites, thereby contributing significantly to the overall capacitance. The specific capacity of the CMCG electrode was initially set to ∼617 C g⁻¹ (172 mAh g⁻¹) at 1 A g⁻¹; meanwhile, at 10 A g⁻¹, the specific capacity was decreased to ∼350 C g⁻¹ (97.23 mAh g⁻¹), with a remarkable 92% capacitance retention over 5000 cycles, and an ultrahigh energy density of ∼32.19 Wh kg⁻¹ and a power density ∼10 110 W kg⁻¹, which is, so far, the highest value reported for hybrid supercapacitors. Thus, the as-synthesized composite emerges as a promising candidate for next-generation energy storage, combining high electrochemical activity with cost-effective scalability.