Dual functionality of the BiN monolayer: unraveling its photocatalytic and piezocatalytic water splitting properties.

To achieve scalable and economically viable green hydrogen (H) production, the photocatalytic and piezocatalytic processes are promising methods. The key to successful overall water splitting (OWS) for H production in these processes is using suitable semiconductor catalysts with appropriate band edge potentials, efficient optical absorption, higher mechanical flexibility, and piezoelectric coefficients. Thus, we explore the bismuth nitride (BiN) monolayer using density functional theory simulations, revealing intriguing catalytic properties. The BiN monolayer is a semiconductor with an indirect electronic bandgap () of 2.08 eV and displays excellent visible light absorption (approximately 10 cm). Detailed analyses show that the band edges satisfy the redox potential for photocatalytic OWS biaxial strain engineering and pH variation. Notably, the solar to hydrogen conversion efficiency () for the BiN monolayer can reach 17.18%, which exceeds the 10% efficiency limit of photocatalysts for economical green H production. The obtained in-plane piezoelectric coefficient of = 16.18 Å C m is superior to widely studied 2D materials. Moreover, the generated piezopotential under oscillatory strain stands at 28.34 V, which can initiate the water redox reaction the piezocatalytic mechanism. This originates from the mechanical flexibility coupled with higher piezoelectric coefficients. The result highlights the BiN monolayer's potential application in photocatalytic, piezocatalytic, and photo-piezo-catalytic OWS.