Heteromorphic-nanochannel actinomorphic structured nickel oxide/graphene in nanoceramic-based hydrogel for energy harvesting from humidity and piezoelectricity

Actinomorphic-structured nickel oxide (NiO)/graphene (Gr) nanoarchitectures embedded within a nanoceramic cobalt–zinc (Co–Zn) hydrogel matrix constitute an emerging class of hygroscopic nanomaterials for next-generation humidity gradient power generation (HGPG) platforms. These engineered hybrids exhibit exceptional hygroscopic uptake; however, their ability to sustain spatially non-equilibrated moisture profiles—crucial for continuous humidity-to-electricity transduction—is inherently constrained by unoptimized surface chemistry and structural anisotropy. Such deficiencies compromise the sequential ionization cascade required to establish persistent electrochemical potential gradients, thereby attenuating current and voltage outputs. Compounding these limitations, state-of-the-art HGPG devices frequently rely on intricate, resource-intensive fabrication routes, hindering industrial scalability and real-world deployment. To address these barriers, this study introduces a heteromorphic nanochannel framework wherein actinomorphic NiO/Gr (NG) assemblies are immobilized within a nanoceramic hydrogel matrix and subsequently functionalized via stearic acid (SA) surface treatment to engineer stable, self-sustaining moisture gradients. The NG composites were fabricated through a facile, low-energy sonicated solution immersion process, followed by doctor-blade deposition onto a cellulose substrate. Material optimization was carried out by varying the Gr contents (0.5 wt.%-2.0 wt.%), as well as by modifying SA content (i.e., 1 - 4 wt.%), immersion temperature (i.e., 30 °C, 60 °C, and 90 °C), and immersion duration (i.e., 2, 4, 6, and 8 hours) to enhance the hydrophilic properties through SA treatment. Further enhancement was achieved by incorporating hematite and applying a Co-Zn hydrogel layer, significantly improving the composite’s moisture absorption and charge generation from ambient humidity. The synthesized hygroscopic materials were comprehensively characterized. The HGPG device with 1.0 wt.% Gr loading (S-NG-1.0) demonstrated the highest humidity response, yielding an output voltage of 2.24 ± 0.03 mV, a current density of 0.2 ± 0.0 nA/cm2, and an output power of 0.50 ± 0.01 pW. Notably, the device maintained stable performance for over 400 days, indicating excellent long-term durability. Subsequently, an HGPG device incorporating SA-treated hematite/NiO/Gr composites with a Co-Zn hydrogel film exhibited improved output voltage of 11.5 ± 0.2 mV, a current density of 0.92 ± 0.02 nA/cm2, and an output power of 13.2 ± 0.2 pW. Moreover, the NG composite integrated with hematite and Co-Zn hydrogel also showed promise in piezoelectric nanogenerator (PENG) applications, achieving an average peak-to-peak output voltage (VPP) of 12 V. Finally, a hybrid HGPG-PENG device was successfully developed by integrating a waste-derived material with the composite film, producing a VPP of 13 V and a power density of 65 μW/cm2. This work delineates a scalable, material-agnostic strategy for engineering multifunctional hygroscopic–piezoelectric nanocomposites, elucidates the structure–property–performance relationships underpinning moisture-driven energy transduction, and validates their long-term operational resilience. The novel approach of integrating NG with hematite and Co-Zn hydrogel in HGPG and PENG devices highlights significant potential for the development of scalable and reliable energy harvesting technologies.