Water-floating nanostructured g-C3N4/SWCNT nanocomposite films enabling simultaneous thermoelectric power generation and photocatalytic hydrogen production

Sustainable energy harvesting from aquatic environments has typically relied on a single output, either thermoelectric generators (TEGs) driven by evaporative cooling or photocatalytic hydrogen production, failing to exploit the complex energy gradients at the air–water interface. Here, we report the first integration of thermoelectric and photocatalytic functions into a single water-floating platform, using a tailored nanocomposite of graphitic carbon nitride (g-C3N4) and single-walled carbon nanotubes (SWCNTs). The integration is synergistic: the SWCNT network provides an efficient charge-transport pathway that enhances photocatalytic activity while maintaining the heat-source-free temperature gradient required for TEG operation. The 7.5% g-C3N4/SWCNT film exhibited a peak power factor of 18.3 μW/(m·K 2 ), while the 100% device achieved a 5.1 mV output voltage under UV irradiation—a 38% improvement over pristine SWCNT-TEGs. The system also produced hydrogen and methane from water containing a sacrificial agent, establishing a new paradigm for multifunctional aquatic energy harvesters addressing the Water-Energy Nexus.