Enhancement of photocatalytic activity of carbon nitride/black phosphorus/tungsten disulfide (CN/BP/WS2) heterojunctions via nickel doping in the hydrogen evolution reaction

The complementary properties of mesoporous graphitic carbon nitride (m-CN) and black phosphorus (BP) as non-metallic semiconductors offer many opportunities for the rational design of efficient photocatalysts for the photocatalytic hydrogen evolution reaction (HER). However, pristine m-CN and BP exhibit significant photo- induced charge carrier recombination rates and weak light absorption, resulting in a low photocatalytic HER activity. To overcome these problems and improve their photocatalytic HER activities, rational design of heterojunctions is one of the most efficient ways. Here, we present for the first time the ternary m-CN/BP/WS2 dual S-scheme heterojunctions, prepared by combining as-prepared m-CN/BP hybrids with tungsten disulfide (WS2). Encouragingly, the ternary m-CN/BP/WS2 heterojunction photocatalysts provided a HER rate of 3.74 mmol H2 g- 1 h- 1, which is 1.84 times higher than that of the m-CN/BP binary heterojunctions under simulated solar light illumination (>= 420 nm). In addition, the photocatalytic HER activity of the m-CN/BP/WS2 heterojunction was further enhanced by nickel (Ni) doping (m-CN/BP/WS2-Ni). The incorporation of Ni (3 wt%) into the optimized m-CN/BP/WS2 heterojunctions (20 wt% WS2) resulted in the best photocatalyst with a HER rate of 10.33 mmol H2 g- 1h- 1 and a solar to hydrogen (STH) efficiency of 3.33 %, which is 2.76 times higher than that of non-doped m-CN/BP/WS2 heterojunctions. Due to the dual S-scheme charge transfer mechanism and the incorporation of Ni as a co-catalyst, the sequential multistep charge migration led to the enhancement of the photocatalytic activity of the ternary m-CN/BP/WS2-Ni heterojunction photocatalyst, which can be attributed to the larger active sites, higher light absorption and more effective charge separation.