First principles study within the density functional theory is addressed to study the energetic and electronic properties of β12 borophene nanosheet with adsorbed platinum (Pt). In addition, the potential use of Pt-decorated borophene as a catalytic material and molecular sensor is also studied. We observed that the most stable configuration (lower binding energy) for Pt be adsorbed on the β12 borophene nanosheet is on the center of a hexagon (Eb=−4.473 eV). The presence of Pt adsorbed does not modify the metallic properties of β12 borophene but gives rise to new electronic levels resonant with the conduction band (around 2.0 eV above the Fermi energy). The calculated Bader charge show a charge transference of 0.567 electrons from borophene to the Pt atom. When molecules are adsorbed on the Pt atom, the calculated adsorption energies, electronic density of states (DOS), work function, and charge transference show that there is a strong interaction between hazardous molecules and Pt-decorated β12 borophene. The only exception is CO2, which interact with Pt-decorated borophene via van der Waals forces. The comparative analysis of the DOS before and after the molecular adsorption shows that the Pt levels are spread out and shifted to the Fermi energy after the molecular adsorption. The results of the DOS, charge transference, as well as the change in the work function allow us to infer that Pt-decorated β12 borophene is a potential material to be used as catalyst and gas sensing. Display omitted •Understanding the energetics of Pt-decorated on β12 borophene.•Effects of molecular adsorption on Pt-decorated β12 borophene.•Use Pt-decorated β12 borophene for gas sensing.