Two-dimensional auxetic pentagonal materials as water splitting photocatalysts with excellent performances

Fantastic two-dimensional (2-D) materials have been used in various fields, especially in green energy fields, because of their unique structures and accompanied physical properties. Here, we theoretically propose a novel 2-D materials family namely penta-B2X (X = S, Se, Te) that can perfectly meet the needs of photocatalytic water splitting. The penta-B2S, penta-B2Se and penta-B2Te all belong to semiconductors with indirect bandgaps of 1.889 eV, 1.998 eV and 1.928 eV, respectively. More importantly, we note that the penta-B2X (X = S, Se, Te) family has high (up to similar to 10(5) cm(-1)) and anisotropic light absorption coefficients in the visible-ultraviolet region, and their band edge positions are able to nicely satisfy the redox potentials at pH = 7 without external adjustment. Besides, they have high and anisotropic carrier mobility (up to similar to 10(3) cm(2-) V-1 s(-1)) to ensure that the recombination of photogenerated carriers can be effectively reduced. Meanwhile, the penta-B2X (X = S, Se, Te) family possesses interesting in-plane negative Poisson's ratios (NPR) of - 0.141, - 0.117 and - 0.059, respectively. Thus, our results suggest that penta-B2X (X = S, Se, Te) can be used not only as promising water splitting photocatalysts with excellent performances but also for the design of funny nano electromechanical devices.