Hydrogen Bonding-Capillary Synergy Enabled Nanoliamond/Graphene Aerogels toward High-Rate Supercapacitors

The enhancement of volumetric energy/power density in carbon-based supercapacitors is critical for space-constrained applications such as miniaturized electronics, wearable devices, and electric vehicles. Although reduced graphene oxide aerogels have emerged as promising electrode materials due to their high surface area, excellent conductivity, and tunable porosity, conventional synthesis methods face challenges in simultaneously achieving high density and porous architecture. In this study, we innovatively developed dense yet porous oxygen-functionalized nanodiamond/reduced graphene oxide (rGO@OND) composite aerogels using a one-pot hydrothermal method combined with capillary-force-induced densification. The rigid sp3-carbon framework of ONDs acts as nanoscale pillars, effectively preventing graphene restacking. Meanwhile, their unique sp3-core/graphitic-shell structure significantly reduces intersheet contact resistance. Scanning electrochemical microscopy (SECM) measurements revealed a remarkable enhancement in ionic diffusion coefficient from 1.81 × 10–3 cm2 s–1 for pure rGO to 1.13 × 10–2 cm2 s–1 for the rGO@OND-air24. The optimized rGO@OND-air24 electrode demonstrated exceptional volumetric capacitance (25.1 F cm–3 at 0.1 A cm–3 and 19.9 F cm–3 at 1.0 A cm–3). Symmetric supercapacitors assembled with rGO@OND-air24 achieved breakthrough performance metrics: a volumetric capacitance of 10.12 F cm–3, an energy density of 1.406 W h cm–3, and nearly 100% capacitance retention and Coulombic efficiency after 25,000 cycles. This work establishes a novel capillary-force densification strategy that opens new avenues for designing high-density energy storage systems tailored for specific application scenarios.