Role of Seawater Ions in Forming an Effective Interface between Photocatalyst/Cocatalyst

Photocatalytic (PC) hydrogen production from water splitting is a promising route to fulfill the current energy demand in a sustainable manner. For photocatalysis to become industrially viable, seawater should be used as an ideal solvent. Until now, a variety of semiconductor photocatalysts have been exploited for seawater splitting; however, there has been a lack of a well-established catalytic system for seawater splitting, as seawater ions have an uncertain effect on water splitting. Recently, ionized carbon nitride PC has been shown to substantially enhance water splitting in the presence of ions; however, the underlying manner by which the ions promote PC has still not been fully understood. Presented here is a systematic evaluation of an ionized low-cost carbon nitride-based semiconductor for seawater splitting. A detailed study has been done using this salt-type semiconductor in the presence of a variety of ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl^-, SO₄^2-), and their role has been probed in modulating the photocatalytic activity. Multiple measurements have provided insight as to how the presence of cations aid advantageously in forming an effective in situ interface between catalyst/cocatalyst for improved electron transfer. Previously, these ions were purported to change the hole quenching ability only of the photocatalyst, whereas here it has been shown that the change in the electron transfer ability of the photocatalyst to cocatalyst appears to be the cause for augmented PC. This improved interfacial electron transfer has been used to rationalize the 8-fold enhancement in the photocatalytic rate in the presence of simulated seawater compared to deionized water and provides the impetus for the use of ionized carbon nitride structures for sustainable PC splitting of seawater.