Highly Efficient Hydrogen and Electricity Production Combined with Degradation of Organics Based on a Novel Solar Water-Energy Nexus System.

A novel unassisted solar water-energy nexus system (SWENS) comprised of a monolithic photoanode, which was assembled by attaching a silicon cell (SC) at the reverse side of a high-activity hyaline antimony-doped TiO2 nanorod array (Sb/TNR), and a Pt-black/Pt cathode was proposed for effective electricity and hydrogen production accompanying water treatment. The Sb/TNR with vertically arranged nanorods on a F-doped SnO2 substrate, using a simple hydrothermal method, showed an excellently enhanced and stable photo-to-current density of ∼1.77 mA cm-2 (0.6 V vs Ag/AgCl), which is ∼181% that of the undoped sample because antimony doping enhanced the charge-transfer property and charge-carrier density of Sb/TNR. The SWENS showed a removal ratio of nearly 100% for 2-chlorophenol after 4 h of operation under AM 1.5 illumination and achieved an average H2 production rate of 31.4 μmol h-1 cm-2, an excellent electricity output with an open-circuit voltage of ∼2.16 V, a short-circuit current of ∼1857 μA cm-2, and a maximum power output of ∼967 μW cm-2, which is ∼10.8 times higher than the power density of the reported state-of-the-art photocatalytic fuel cell (PFC). This outstanding capability is due to the synergistic effect of the monolithic photoanode, in which the prepositive Sb/TNR generates abundant electrons and holes using short-wavelength photons, and the SC provides much higher potential than traditional PFCs to drive the electrons being transported to the cathode by absorbing the transmission of longer wavelength photons. The results also revealed that the SWENS showed remarkably stability in long-term application and is effective in clean energy production while degrading various refractory organics. This work proposed a new effective way to develop a composite water-energy nexus technology for simultaneous clean energy generation and water treatment.