EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The ever-increasing energy consumption by human societies leads to the unprecedented need for green and renewable fuels. Hydrogen is a suitable alternative, however still today the most cost-effective source remains from fossil fuels. Photocatalysis, is a promising strategy to generate hydrogen from renewable sources, such as water and sunlight. However, the efficiencies are not yet enough to cover the world energy demand. One approach for enhanced performance is heterogeneous photocatalysis., as it used the advantage of a material with enhanced light absorption and another with improved catalytic sites, the so-called co-catalyst.
Among various studies, transition metal based molecular metal sulfides, such as MoS$_2$, has shown excellent co-catalytic properties due to its stability and active sites for electrochemical H$_2$ production. Polythiomolybdate, such as (NH$_4$)$_2$[Mo$_3$S$_1$$_3$] clusters deposited on graphite paper (GP) and highly oriented pyrolytic graphite (HOPG), revealed an increased hydrogen generation efficiency due to the exposed sulfur ligands (apical, bridging, and terminal sulfur). Furthermore, it has been investigated that terminal and bridging sulfur in [Mo$_3$S$_1$$_3$]$^2$$^-$ clusters could actively participate in electrochemical HER, however, their potential as cocatalyst for photocatalytic HER has not yet been investigated.
In this study, we synthesize novel [Mo$_3$S$_1$$_3$]$^2$$^-$/TiO$_2$ composites having different weight percentages of [Mo$_3$S$_1$$_3$]$^2$$^-$ and investigate their HER activities in heterogeneous photocatalysis. XRD and XPS analyses confirmed the cluster deposition onto titania support. TXRF measurements show the exact loading of the clusters. Thermal treatment of the composites at different temperatures (200°C, 300°C, 400°C, and 500°C) under N$_2$ and air show the loss of apical, bridging, and terminal sulfur successively. The photocatalytic HER performances of these thermally treated composites have significantly changed as the heat treatment temperature increased. To investigate the changes in the composites during thermal treatment in situ XPS and in situ DRIFTS have been performed.