Architecting Robust Oxygen-Deficient Hollow Sphere Double Perovskite Nd2CoMnO6 as a Unified Trifunctional (Oxygen Reduction Reaction/Oxygen Evolution Reaction/Hydrogen Evolution Reaction) Electrocatalytic Material

Hollow structures with intricate spherical structures and compositions have garnered significant attention due to their crucial relevance for electrocatalysis. Hollow spherical porous material Nd2CoMnO6 (NCMO-H) and its counterpart material Nd2CoMnO6 (NCMO-G) were synthesized. The hollow material was synthesized using a carbon sphere as a template via an incorporation method, followed by calcination in air to remove the template, whereas its counterpart material was synthesized using the sol–gel method. This simple and scalable synthesis method yielded a catalyst exhibiting superior structural, morphological, and electronic characteristics relative to its counterpart, as confirmed by X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), and UV–vis studies. The optimized NCMO-H exhibited direct and indirect band gaps of ∼3.01 eV and 3.07 eV, respectively, alongside improved trifunctional electrocatalytic activity, with onset potentials of 0.86 V for oxygen reduction reaction (ORR), 1.50 V for oxygen evolution reaction (OER), and –0.25 V for hydrogen evolution reaction (HER) versus reversible hydrogen electrode (RHE). Furthermore, the reduced overpotential, Tafel slope, and exceptional structural durability illustrate the superior catalytic kinetics and electrochemical performance. This approach reveals substantial promise for the development of highly efficient trifunctional materials aimed at clean-energy applications.