Viable Route to Green Hydrogen: Sea Water Photocatalysis

Abstract

The photocatalytic (PC) hydrogen production from water splitting is a promising route to fulfill the current energy demand in an eco-friendly and sustainable manner. For photocatalysis to become industrially viable, seawater should be used. This solvent owes its salinity due to various ions (Na+, K+, Mg2+, Ca2+, Cl−, Br−, SO2 4−, and CO3 2−). To date, there are contradicting reports in the literature on the influence of these ions on the PC splitting of water. A variety of different neutral transition metal-oxide-based photocatalysts have been exploited. Although they might be effective in splitting deionized water, however, thus far, there has been a lack of a well-established route to effectively using any semi-conductor for seawater splitting. Presented here are the details of our work where an intriguing, ionized, low-cost semiconductor has been successfully evaluated for sea-water splitting. The structure consists of a modified carbon nitride such that it forms an ionized organic polymer-based system. A detailed study has been done using this salt-type semiconductor in the presence of various ions, and their role has been probed in modulating the photocatalytic activity. Photoelectrochemical measurements have provided insight as to how the presence of cations aids advantageously in forming an effective in-situ interface between catalyst/co-catalyst for improved charge transfer. This improved interfacial charge transfer rationalizes the 8-fold enhancement in the photocatalytic rate in the presence of simulated seawater compared to deionized water. It provides an impetus for using these carbon nitride structures for sustainable PC splitting of seawater.