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First-principles calculations based on spin-polarised density functional theory have been used here to investigate the structural, electronic and magnetic properties of tape-heme monolayer (THM) with gas molecules (H2O, N2, HCN, NH3, NO2 and SO2) adsorption. Our results suggest that H2O and NH3 are physisorbed on THM while N2, HCN, NO2 and SO2 are adsorbed on THM by chemisorption. The toxic HCN, NH3, NO2 and SO2 can be effectively captured by THM according to their adsorption energy (> 0.50 eV). The adsorption of NO2 (or SO2) can partly (or completely) decrease the spin moment of THM and induce the transition from the metallic property into half-metallic (or semiconductor) behaviour. The magnetism of the NO2 adsorption system is sensitive to tensile strain while that of the SO2 adsorption system is invariably non-spin polarised regardless of the compressive or tensile strain. The electronic structure of the NO2 and SO2 adsorption system can be effectively modulated by external biaxial strain. Our findings reveal that THM could effectively detect toxic NO2 and SO2 in an environment with high sensitivity and selectivity and reactivity, indicating that it possesses a potential application in the field of heme-based gas sensors. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is the key bottleneck in the performance of fuel cells. The rational design of efficient and inexpensive ORR electrocatalysts is a common goal for the large-scale application of fuel cells. Herein, by means of density functional theory calculations, we demonstrate that two-dimensional (2D) biphenylene (BPN) with doping B/N are metal-free single-atom catalyst candidates with the overpotentials comparable to those noble metal benchmark catalysts. The B/N doping effectively modulates the charge distribution in BPN sheets, promotes the electron transfer between doped BPN and the oxygen-containing intermediates, which results in enhancing their binding strength, and facilitating their electrochemical ORR catalytic activity. This work not only provides metal-free single-atom catalysts for ORR, but also promotes BPN nanomaterials for single-atom catalysts development and practical applications. [Display omitted] • 2D biphenylene with doping B/N are metal-free single-atom catalysts. • N 2 -BPN exhibits superior ORR performance with a overpotential of 0.40 V. • N substituting C 2 atom in BPN could tune charge redistribution of active C 1 atom. • N 2 -BPN exhibits a suitable adsorption free energy and shows high ORR activity. [ABSTRACT FROM AUTHOR]