Black phosphorus-based heterostructures for photocatalysis and photoelectrochemical water splitting

Semiconductor-based photocatalytic and photoelectrochemical (PEC) processes can convert solar energy into high-density chemical energy or for the treatment of environmental pollutants, which are ideal ways to deal with environmental and energy crises. The development of high-efficiency photocatalysts and photoelectrodes is the key to the in-depth development and practical application of the two technologies. Black phosphorus (BP) has excellent physicalcochemical properties such as adjustable band gap, high carrier mobility, large specific surface area and anisotropy, making it one of the most promising catalysts. BP-based heterostructure can not only realize the effective separation of photogenerated carriers but also improve the stability of BP, and is widely used in photocatalytic and PEC reactions. In this review, we first introduce the crystal structure, band structure, anisotropy, and preparation of BP with different dimensions (bulk, zero-dimension and two-dimension). Then, according to the transfer path of the photogenerated carriers and the components, the BP-based heterostructures are divided into type I heterojunction, type II heterojunction, Z-scheme heterojunction, S-scheme heterojunction, BP/carbon-based material heterostructure, BP/metal heterostructure and multi-component heterostructure. Highlighted are the diverse photocatalytic applications of BP-based heterostructure, such as water splitting and CO2 reduction, N2 fixation, pollutant degradation, photothermal and photodynamic therapy. Finally, some concluding views and opinions are stated on the challenges and opportunities faced by the further development of BP-based heterostructures in photocatalysis and PEC water splitting.