Dual-layer LDH on graphene foam: a hydrophobic base and hydrophilic cap for power boost

Hydrovoltaic power generation in porous conductors is often limited by the trade-off between strong wetting for ion activation and low internal resistance for efficient charge extraction. In this study, we engineered a dual-layer MgAl-layered double hydroxide (LDH) architecture on exfoliated graphene sheets (EGs) wrapped around melamine foam to enhance both interfacial charge separation and charge transport. Hydrophilic LDH strongly adsorbs onto oxygenated EG functionalities (-OH/-COOH), inducing flower-like growth that conformally covers the graphene network and blocks the EG-EG junctions, thereby increasing the electrical resistance. By contrast, the dual-layer design with a hydrophobic LDH base preserved continuous conductive pathways in the EG framework while limiting direct water contact at the bottom interface, reinforcing streaming-potential-driven ion-electron coupling under saline droplet activation. Moreover, the hydrophilic LDH cap amplified the output through its strong water uptake and ion adsorption capabilities, which intensified interfacial hydration. Multiscale microscopy and wetting/chemical analyses corroborated the distinct interfacial morphologies and biphilic contrast. Consequently, the dual-layer LDH/EG foam delivers a markedly boosted output, achieving currents up to ∼30 µA with pronounced power enhancement compared with both fully hydrophilic overcoated and LDH-free counterparts.