Green and efficient electrolysis of seawater using carbon nanotube-based hybrid films

Producing hydrogen by splitting seawater using renewable energy is a promising way to obtain a clean energy carrier. However, neither direct electrolysis nor post-desalination electrolysis techniques work well due to the complex composition of seawater and the large amount of energy needed. We report a solar-driven continuous seawater electrolysis system (CSES) by which seawater could be first distilled into pure water and then electrolyzed to obtain green hydrogen. The CSES is based on a multi-functional single-wall carbon nanotube (SWCNT)-based hybrid film, which is composed of a partially oxidized SWCNT layer and a high-entropy alloy nanowires/SWCNT layer. The SWCNT-based hybrid film functions as both a solar-driven interfacial water evaporation membrane and a water-splitting electrode. A high seawater evaporation efficiency of 1.22 kg m⁻² h⁻¹ under 1 sun irradiation and a low overpotential of 119 mV and 220 mV for hydrogen evolution reaction along with 330 mV and 356 mV for OER at current densities of 100 and 300 mA cm⁻², respectively, are demonstrated. The CSES has a hydrogen productivity of 1.04 × 10⁴ L day⁻¹ m⁻² (under a constant current of ∼1.4 A) and works continuously for 100 h without any external energy consumption.