Energy Environ. Sci. http://doi.org/chdn (2018)

Energy and water represent two pillars for human life. Societies endeavour to obtain new energy sources and clean, fresh water. Rather than pursue each separately, scientists have recently tied together wastewater treatment and desalination, harvesting energy from waste to remove salt from seawater. However, a common wastewater treatment strategy, using the microbial fuel cell, employs pH- and salt-sensitive organisms.

Now, Kim et al. report an abiotic water–energy nexus that executes light-driven wastewater remediation, fuel production and seawater desalination. The researchers fabricated photoanodes, composed of hydrogen-treated titanium dioxide nanorods, to absorb UV-light and undergo photochemistry. This treatment improved the photoelectrochemical performance by increasing the material conductivity and the nanorods’ substrate-oxidation abilities. The nanorod electrodes could oxidize chloride, producing urea-decomposing radicals, and simultaneously produce hydrogen gas (H2) from the excess protons and electrons.

To test the solar water–energy nexus, the researchers built a three-chamber device, separating the anode and cathode compartments with a seawater-containing ion chamber between ion-selective membranes. The chloride diffused from the seawater to the anode and was consumed by nanorod photochemistry, while the sodium ions diffused into the cathode chamber to boost electrolyte conductivity and H2 evolution activity. Altogether, the photoelectrodes could completely remove urea within 12 hours, and 50% of seawater’s salt at an 80% Faradaic yield for H2 evolution.