P-Type Cobalt Phosphide Composites (CoP-CoP) Decorated on Titanium Oxide for Enhanced Noble-Metal-Free Photocatalytic H Evolution Activity.

Nowadays, transition-metal phosphides have been reported to function well in photocatalytic water splitting and possess great potential to substitute traditional noble-metal cocatalysts in the future. Herein, p-type cobalt phosphide (CoP-CoP) nanomaterials were synthesized by phosphating the solvothermally prepared Co(OH) nanoflowers at a low temperature (300 °C). Then, we combined the phosphides with commercial TiO through facile mechanical mixing to fabricate a useful noble-metal-free photocatalyst. The phosphating time that had an influence on the composition of phosphides was tuned, and 3 h was an ideal condition after comparison. The cobalt phosphide-modified TiO at the optimal weight percentage (nominal 0.5%) exhibited the highest photocatalytic hydrogen rate of approximately 824.5 μmol g h under simulated sunlight irradiation, which was nearly equal to 160 times that of bare TiO and 1.7 times that of single CoP-modified TiO. The CoP/TiO heterojunction interfaces were studied using photoluminescence (PL), time-resolved PL, and photoelectrochemical methods, which revealed that the effective charge separation and transfer accelerated by the built-in electric field of p-n junction contributed significantly to the photocatalytic performance.