Impurity-engineered orbital contributions to the electronic heat capacity of highly stable monolayer h-B₂O

Monolayer honeycomb borophene oxide (h-B₂O) combines exceptional thermodynamic stability with nontrivial topology and prospective superconductivity, yet its thermodynamic behavior remains largely unexplored. Here, we construct an orbital-resolved tight-binding (TB) model based on the boron p_y and p_z orbitals and, through detailed analysis of the corresponding band structure (BS) and density of states (DOS), establish the metallic character of h-B₂O. We further determine, for the first time, its electronic heat capacity (EHC). At 300 K, the orbital components are and , with , reflecting the enhanced p_z-orbital DOS near the Fermi level. In the pristine limit, the low-temperature EHC exhibits a linear dependence below ≈25 K, consistent with the Sommerfeld model (C_e = γT), and shows a Schottky anomaly near 75 K. To assess the robustness of the EHC against disorder, we treat impurity scattering within the T-matrix formalism and calculate the corresponding self-energies for both n-type (u = +10 eV) and p-type (u = -10 eV) dopants over n_i = 0-10% at 300 K. The EHC does not follow a universal monotonic trend but instead exhibits pronounced orbital-selective modulation. For n-type doping, the total EHC closely follows the p_y channel, reaching a maximum increase of +13.1% at n_i = 1% and a minimum decrease of 26.2% at n_i = 9%. Under p-type doping, the response is dominated by the p_z orbital, increasing by +55.7% at n_i = 9% and decreasing by 26.4% at n_i = 10%. These results establish h-B₂O as a model system for investigating orbital-selective modifications of electronic thermodynamic properties induced by charged impurities. The calculated C_v provides a sensitive orbital-resolved thermodynamic descriptor that can support future studies of impurity effects and coupled thermal or electronic phenomena in two-dimensional boron-based materials.