Photocatalytic water splitting in the gap between plasmonic gold nanoclusters

Plasmon-mediated photocatalytic water splitting holds promise for efficient solar energy harvesting. Experimental studies have shown that “hot spots” in an assembly of plasmonic nanoclusters, which is the real case for practical applications, are beneficial for photocatalysis, but the interactions between different nanoclusters are difficult to observe by experimental techniques. Theoretical studies, however, have employed the model with a water molecule adsorbed on a single plasmonic metal nanocluster. Here, we employed the representative model of a water molecule placed in the gap between two gold nanoclusters and computationally investigated the effects of the configurations of plasmonic nanoclusters on plasmon-mediated water splitting. Results show that the hot electron transfer mode can be tuned by the plasmonic configurations. Compared to the configuration with only one gold nanocluster, more significant contribution of direct charge transfer was observed for the configuration with two gold nanoclusters, which is attributed to a stronger field enhancement; as a result, the water splitting rate was also enhanced. Results also demonstrate a charge transfer chain from one gold nanocluster to the water molecule and then to the other gold nanocluster, which is tunable by the distances between the water molecule and the gold nanoclusters. This charge transfer chain significantly affected the amount of hot electrons accumulated on the water molecule. Caused by this, the configuration where the water molecule was placed right at the center of the two gold nanoclusters, i.e., the configuration corresponding to the strongest field enhancement, was surprisingly not the most favorable one for the reaction.