P-Type Cobalt Phosphide Composites (CoP–Co<sub>2</sub>P) Decorated on Titanium Oxide for Enhanced Noble-Metal-Free Photocatalytic H<sub>2</sub> Evolution Activity
Rong Liang, Yanwen Wang, Chao Qin, Xuehua Chen, Zhizhen Ye, Liping Zhu
Abstract
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–Co2P) nanomaterials were synthesized by phosphating the solvothermally prepared Co(OH)2 nanoflowers at a low temperature (300 °C). Then, we combined the phosphides with commercial TiO2 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 TiO2 at the optimal weight percentage (nominal 0.5%) exhibited the highest photocatalytic hydrogen rate of approximately 824.5 μmol g–1 h–1 under simulated sunlight irradiation, which was nearly equal to 160 times that of bare TiO2 and 1.7 times that of single CoP-modified TiO2. The CoPx/TiO2 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.