Advanced Nickel Oxide Composites Unlock Efficient Green Hydrogen and Energy Storage Solutions

Breakthrough Composite Materials for Sustainable Energy

Researchers have developed innovative nickel oxide composites that demonstrate exceptional performance in both electrochemical water splitting and energy storage applications. The carefully engineered NiO/g-C₃N₄ and NiO/rGO nanocomposites represent a significant advancement in multifunctional materials for renewable energy technologies. These hybrid materials combine the unique properties of nickel oxide with two-dimensional carbon-based structures to create synergistic effects that enhance both hydrogen evolution reaction (HER) efficiency and energy storage capacity., according to technology insights

Breakthrough Composite Materials for Sustainable Energy
Structural Characterization Reveals Composite Architecture
Optimized Porosity and Surface Area Enhance Performance
Surface Chemistry and Elemental Composition
Morphological Features and Crystalline Structure
Exceptional Hydrogen Evolution Reaction Performance
Promising Energy Storage Capabilities
Future Implications and Applications

Structural Characterization Reveals Composite Architecture

Powder X-ray diffraction analysis confirms the successful integration of nickel oxide with both graphitic carbon nitride (g-C₃N₄) and reduced graphene oxide (rGO). The NiO/g-C₃N₄ composite exhibits characteristic diffraction peaks at 27.1° and 12.9°, corresponding to the (002) and (100) crystal planes of g-C₃N₄, alongside prominent NiO peaks at 37.4°, 43.6°, 63.7°, and 76.7° representing the (111), (200), (220), and (311) planes of cubic nickel oxide. Meanwhile, the NiO/rGO composite shows a distinct peak at 26.3° corresponding to the (002) plane of reduced graphene oxide, with additional NiO peaks at 35.6°, 42.9°, and 60.0°.

Raman spectroscopy further validates the composite structures, revealing characteristic D and G bands for carbon materials and vibrational modes specific to nickel oxide. The presence of graphitic carbon nitride is confirmed by multiple bands between 706.7 cm⁻¹ and 1653.8 cm⁻¹, attributed to aromatic C-N heterocycles and s-triazine ring breathing modes. The NiO vibrational modes appear as distinct peaks at 482.2 cm⁻¹ and 995.2 cm⁻¹ in both composites., according to market trends

Optimized Porosity and Surface Area Enhance Performance

Brunauer-Emmett-Teller (BET) analysis reveals crucial differences in the porous structures of these materials. Nickel oxide powder alone demonstrates a substantial surface area of 137.9 m²/g with an average pore radius of 3.41 nm, indicating a mesoporous nature. The composite materials show type-IV isotherms with distinct hysteresis loops, characteristic of mesoporous materials.

The NiO/rGO composite outperforms its counterpart with a surface area of 52 m²/g and pore volume of 0.3856 cm³/g, compared to NiO/g-C₃N₄’s 46 m²/g surface area and 0.3423 cm³/g pore volume. This enhanced porous structure in NiO/rGO facilitates better adsorption and diffusion processes, contributing to its superior electrochemical performance., as our earlier report, according to related coverage

Surface Chemistry and Elemental Composition

X-ray photoelectron spectroscopy (XPS) provides detailed insight into the chemical states and elemental composition of both composites. For NiO/g-C₃N₄, the Ni 2p spectrum shows characteristic peaks at 854.2 eV (2p3/2) and 871.4 eV (2p1/2), confirming the presence of nickel oxide. The C 1s spectrum reveals multiple carbon species, including C-C, C-OH, C-O-C, -COOH, and C-N bonds, while the N 1s spectrum demonstrates successful incorporation of graphitic carbon nitride through C-N bonds., according to market developments

The NiO/rGO composite similarly confirms the presence of reduced graphene oxide through deconvoluted C 1s peaks at 284.8 eV (C-OH), 285.7 eV (C-C), 286.5 eV (C-O), and 288.7 eV (O-C-O). The oxygen species analysis shows peaks corresponding to C-O, Ni-O, C=O, and C-O-C functional groups, highlighting the complex surface chemistry that contributes to the material’s electrochemical activity.

Morphological Features and Crystalline Structure

Microscopic analysis reveals distinct morphological differences between the two composites. The NiO/g-C₃N₄ composite features nanoparticles of nickel oxide with approximately 21 nm particle size distributed on sheet-like g-C₃N₄ structures. In contrast, the NiO/rGO composite exhibits nanorod structures with lengths around 130 nm and diameters of 42 nm, interspersed with densely arranged rGO sheets.

High-resolution transmission electron microscopy (HRTEM) reveals fringe spacing values of 0.18 nm and 0.21 nm, consistent with d-spacing values obtained from XRD analysis. Selected area electron diffraction (SAED) patterns confirm the polycrystalline nature of both composites, showing diffraction rings corresponding to (100), (002), and (200) planes of both rGO and NiO components.

Exceptional Hydrogen Evolution Reaction Performance

The electrochemical performance for hydrogen evolution reaction demonstrates the practical utility of these composites. The NiO/g-C₃N₄ electrode achieves an impressively low overpotential of 73 mV at a current density of 10 mA/cm², significantly outperforming the NiO/rGO electrode’s 126 mV overpotential. This superior performance is attributed to the immediate contact between NiO and g-C₃N₄, which enhances electron transport and current response.

Tafel slope analysis provides further insight into the HER kinetics. The NiO/g-C₃N₄ catalyst shows a remarkably low Tafel slope of 34 mV/dec, compared to 89 mV/dec for NiO/rGO. This lower value indicates faster HER kinetics and suggests the material follows the Volmer-Tafel hydrogen formation mechanism. The excellent charge separation and active site effectiveness in NiO/g-C₃N₄ contribute to its superior catalytic efficiency, despite rGO’s inherently higher conductivity.

When compared to other reported catalysts, NiO/g-C₃N₄ demonstrates competitive performance, outperforming materials such as g-CN@NiO (83 mV/dec), CuO/g-CN (55 mV/dec), Co/g-CN (44.2 mV/dec), and Ni/NiO@rGO (63 mV/dec). Chronoamperometry studies confirm excellent stability, with no noticeable degradation in activity after 23 hours of continuous operation at 10 mA/cm².

Promising Energy Storage Capabilities

Beyond hydrogen production, both composites exhibit significant potential for energy storage applications. Cyclic voltammetry measurements between 0 and 0.6 V in 3M KOH electrolyte reveal pseudo-capacitive behavior characterized by redox reactions of Ni²⁺/Ni³⁺. The increasing redox potential with higher scan rates indicates surface-controlled processes, though some limitations from internal resistance and charge transfer kinetics are observed at elevated scan rates.

Galvanostatic charge-discharge measurements between 1 and 10 A/g current densities show non-linear curves characteristic of faradaic pseudo-capacitive behavior. The charge storage mechanism relies on quasi-reversible faradaic redox processes between nickel oxidation states at the electrode-electrolyte interface, where NiO particles undergo electrochemical transformation in the KOH electrolyte.

Future Implications and Applications

The development of these multifunctional nickel oxide composites represents a significant step toward integrated energy systems that can both produce clean hydrogen and store electrical energy efficiently. The superior performance of NiO/g-C₃N₄ in hydrogen evolution, combined with the enhanced porous structure of NiO/rGO, suggests potential for tailored material design based on specific application requirements.

These findings open new possibilities for developing cost-effective, efficient catalysts and energy storage materials that could accelerate the transition to renewable energy systems. The demonstrated stability and performance under alkaline conditions make these composites particularly promising for practical applications in electrolyzers and advanced battery systems.

The comprehensive characterization and performance evaluation of these nickel oxide composites provide valuable insights for materials scientists and engineers working toward sustainable energy solutions. The synergistic effects between nickel oxide and carbon-based materials demonstrate how careful material design can overcome individual component limitations to create superior multifunctional materials.