Square-Octagon Structure of a BCN Monolayer: Near-Zero Poisson's Ratio, High Carrier Mobility, and Excellent Photocatalytic Activity for Overall Water Splitting

We predicted a square-octagon structure of a BCN monolayerwithfantastic mechanical properties, high carrier mobility, and excellentphotocatalytic activity for overall water splitting. The BCN monolayerhas unique mechanical properties with a very small negative valueof Poisson's ratio of -0.0058 and -0.0045 alongthe x- and y-direction, respectively,and remarkable flexibility under tensile strain. The electronic structurecalculation suggests that the BCN monolayer has a direct bandgap of2.82 eV and its band edges straddle the redox potentials for H+/H-2 and O-2/H2O. Additionally,the BCN monolayer exhibits a high intrinsic conductivity with an exceptionalhigh hole mobility of similar to 2.8 x 10(5) cm(2) V-1 s(-1). The drastically differentmobilities of electrons and holes in the BCN monolayer may reducethe rate of electron-hole recombination, resulting in improvedphotocatalytic activity. With excellent stability, ideal band edgepositions, high conductivity, and efficient visible-light absorption,the BCN monolayer well satisfies the strict requirements for idealphotocatalytic overall water splitting. The unique mechanical andelectronic properties of the BCN monolayer also make it an attractivematerial for use in advanced nanomechanical and electronic devices.