Binary pentagonal auxetic materials for photocatalysis and energy storage with outstanding performances.

Since the discovery of penta-graphene, two-dimensional (2-D) pentagonal-structured materials have been highly expected to have desirable performance because of their unique structures and accompanied physical properties. Hence, based on the first-principles calculations, we performed a systematical study on the structure, stability, mechanical and electronic properties, and potential applications on carbon-based pentagonal materials with binary compositions, namely, Penta-CnX6-n (n = 1, 2, 4, 5; X = B, N, Al, Si, P, Ga, Ge, As). We found that eleven out of thirty-two Penta-CnX6-n have good stability and can be further studied. Among them, two materials, namely, Penta-C4P2 and Penta-C5P are metallic, and others are indirect band gap semiconductors, whose band gaps calculated by the HSE06 functional are in the range of 1.37-6.43 eV, covering the infrared-visible-ultraviolet regions. Furthermore, we found that metallic Penta-CnX6-n can become promising anode materials for Na-ion batteries (NIBs) with high storage capacity, while some semiconducting Penta-CnX6-n can become excellent water splitting photocatalysts. In addition, Penta-C4P2 and Penta-C2Al4 were found to have obvious in-plane negative Poisson's ratio (NPR) of -0.083 and -0.077, respectively. More interestingly, we found that Penta-C2Al4 exhibits a peculiar in-plane half negative Poisson's ratio (H-NPR) with the fundamental mechanism clarified. These outstanding performances endow binary pentagonal materials with excellent application prospects.