Actinomorphic-structured nickel oxide/graphene composites treated with stearic acid on cellulose-based substrate for humidity-to-energy harvesting applications

Harnessing ambient humidity as a sustainable energy source offers a promising route toward clean energy generation. The development of hygroscopic materials is crucial in this context, as their structural and surface properties critically govern the formation of stable moisture gradients and enable efficient humidity-to-electricity conversion. However, inconsistencies in these properties have limited the long-term performance of existing materials. To address this, we report the development of heteromorphic-nanochannel, actinomorphic-structured nickel oxide/graphene (NiO/Gr) composites functionalized via stearic acid (SA) treatment on cellulose substrates. Synthesized using a facile sonicated solution immersion method with graphene loadings from 0.5 to 2.0 wt.%, the composites were optimized through SA treatment at varying parameters to optimize hydrophilicity. The S-N/G-1.0 sample, comprising 1.0 wt.% Gr and treated with 2.0 wt.% SA at 60 °C for 6 h, exhibited optimal wettability (contact angle: 65.3° ± 1.2°) and superior energy-harvesting performance, achieving output voltage of (2.24 ± 0.03) × 10 -3 V, current density of (1.79 ± 0.02) × 10 -10 A/cm 2 , and power output of (5.02 ± 0.13) × 10 -13 W. Notably, the device retained stable performance over 400 days. This research has contributed to enhancing the fundamental knowledge of the sustained humidity-to-energy conversion mechanism, paving the way for the development of reliable energy-harvesting nanomaterials. • Humidity-gradient power generation (HGPG) device was designed for energy harvesting • NiO/graphene (Gr) composites were employed for HGPG applications for the first time • Heteromorphic-nanochannel, actinomorphic-structured NiO/Gr (N/G) was fabricated • Stearic acid (SA) treatment enabled optimal hydrophilicity of the NiO/Gr composite • The device exhibited remarkable long-term operational stability over 400 days