Preparation of single-atom palladium catalysts with high photocatalytic hydrogen production performance by means of photochemical reactions conducted with frozen precursor solutions

The photocatalytic production of hydrogen via single-atom catalysts (SACs), in which photoactive metal species are isolated as single atoms on supports, has received increasing interest for the ecologically friendly and sustainable production of hydrogen due to the high catalytic activity, selectivity, stability, and complete utilization of active components in these catalysts. However, a truly facile means of fabricating SACs without the aggregation of the active atoms remains poorly developed. The present work addresses this issue by proposing the use of a novel photochemical reaction conducted in a frozen precursor solution to prepare SACs with active Pd atoms stabilized on graphene carbon nitride (g-C3N4) supports. The single Pd atoms are demonstrated to be fully isolated on the g-C3N4 supports, and the optimal Pd-C3N4 SAC with 0.3 wt% Pd (the ICP result is 0.2855 wt%) is shown to provide a much higher photocatalytic hydrogen production performance (8.736 mmol g(-1) h(-1)) than the non-frozen control group fabricated with an equivalent liquid precursor. Furthermore, computational methods are applied to explain how the proposed photochemical process stabilizes single-atom active sites and the chemical mechanisms responsible for the excellent photocatalytic hydrogen production performance of the SAC. These results demonstrate that the proposed fabrication method can be universally applied for the preparation of SACs.