Photocatalytic and Piezocatalytic Properties of h-NbP and h-NbN Monolayers for Green Hydrogen Production: Insight from Density Functional Theory Calculations
Devender Takhar, Balaji Birajdar, R. Ghosh
Abstract
Two-dimensional (2D) materials with intrinsic piezo- and ferro-electricity are highly prospective in designing novel catalysts for green hydrogen generation. This work systematically investigates the photocatalytic and piezocatalytic capabilities of buckled hexagonal (h-) NbP and NbN ferroelectric monolayers utilizing hybrid density functional theory (DFT) calculations. First, we delve into monolayers’ structural, electronic, ferroelectric, and optical properties. This reveals that NbP and NbN can drive the photocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, in the visible region of the solar spectrum and can also be used in designing a z -scheme photocatalyst for efficient overall water splitting. Particularly, strong photon absorption of 4 × 10 5 cm –1 with 89% absorption efficiency makes these monolayers ideal candidates to explore. It further reveals that the presence of robust out-of-plane ferroelectricity induces an intrinsic electric field which helps in enhancing the separation of photoinduced charge carriers. We also explore the elastic and piezoelectric properties of these monolayers to understand their piezocatalytic behavior. The low Young’s modulus of 51.76 N m –1 for NbP and 104.65 N m –1 for NbN monolayers demonstrates the higher mechanical flexibility. A sizable vertical piezoelectricity d 31 of 0.81 pm V –1 and 0.56 pm V –1 for NbP and NbN, respectively, is highest among the similar type buckled honeycomb group III–V monolayers. In addition, the in-plane piezoelectricity d 11 of 36.02 pm V –1 and 17.61 pm V –1 for NbP and NbN monolayers, respectively, results in the generation of sufficient piezopotentials to demonstrate their piezocatalytic water splitting ability. These properties reveal the potentiality of NbP and NbN for designing efficient piezo- and photo-catalysts for green hydrogen generation.