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

Abstract

To achieve scalable and economically viable green hydrogen (H₂) production, the photocatalytic and piezocatalytic processes are promising methods. The key to successful overall water splitting (OWS) for H₂ 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 (E_g) of 2.08 eV and displays excellent visible light absorption (approximately 10⁵ cm⁻¹). Detailed analyses show that the band edges satisfy the redox potential for photocatalytic OWS via biaxial strain engineering and pH variation. Notably, the solar to hydrogen conversion efficiency (η_STH) for the BiN monolayer can reach 17.18%, which exceeds the 10% efficiency limit of photocatalysts for economical green H₂ production. The obtained in-plane piezoelectric coefficient of e₁₁ = 16.18 Å C m⁻¹ 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 via 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.