Generating green hydrogen via nickel sulfide modified titania thin film photocatalysts

Abstract

The emerging field of photocatalysis is a promising technology to pave the way to a greener future: photocatalytic water splitting can be used to synthesize green hydrogen. For this purpose, we modified mesoporous thin films of the well-known photocatalyst titania with a nickel sulfide cocatalyst prepared from nickel xanthate single source precursors via solution processing. Scanning transmission electron microscopy images of a sample cross-section revealed homogeneously deposited NiS nanoparticles throughout the whole titania layer. UV-Vis spectroscopy showed an increased light absorption of the NiS-modified titania samples into the visible range up to 600 nm. The photocatalytic performance of the modified catalyst films was evaluated using hydrogen evolution experiments with methanol as sacrificial electron donor. During those experiments, we observed a partly reversible color change of the catalysts, which we relate to an activation-deactivation mechanism. With an optimal NiS loading of 2.2 w%, we achieved the highest hydrogen evolution rate, averaging 3.3 mmol h⁻¹ g⁻¹ over twenty hours under near-UV light at 365 nm. This corresponds to an efficiency almost 250 times higher than that of the pristine titania and reaching 55% of the hydrogen evolution rate of titania modified with a similar amount of platinum cocatalyst. The obtained rate, combined with the vast difference in cost of platinum and nickel, is a promising result to enable the production of green solar fuels.