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 × 105 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
d31 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 d11 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.