Nowadays, scientists are increasingly focused on finding new efficient 2D materials for hydrogen storage due to their large specific surface area, exceptional physisorption properties, and high gravimetric capacity. In this respect, we have analyzed the potential of new 2D orthorhombic (o)-B₂CN and o-B₂C₂ materials as lightweight solid mediums for hydrogen storage, employing lithium decoration through density functional theory (DFT) calculations. Both materials were found to be conductive and demonstrated excellent mechanical, dynamical and thermal stability. The binding energies of lithium adatoms to the monolayers during the decoration process were found to be −3.38 and −3.72 eV for o-B₂CN and o-B₂C₂, respectively. These values indicate strong interactions with both substrates and the lack of lithium clustering given that they are higher than its cohesive energy (−1.63 eV). The lithium decoration technique significantly improves the adsorption of H₂ molecules on both materials, where each system adsorbs 32 molecules with an average adsorption energy of 0.25 and 0.23 eV for 32H₂@8Li-B₂CN and 32H₂@8Li-B₂C₂, respectively, along with excellent gravimetric capacities of 12.87 and 13.29 wt% and desorption temperatures of 186 and 171 K. To assess dynamical stability, AIMD calculations were conducted on fully loaded H₂ systems at temperatures of 100, 200, 400 and 500 K, demonstrating complete H₂ desorption and confirming the reversibility of both systems. A radial distribution function (RDF) analysis was conducted to examine the thermal effects on Li–H atomic correlations and assess the stability of hydrogen adsorption at different temperatures. Based on these results, it can be concluded that Li-decorated o-B₂CN and o-B₂C₂ show considerable potential for hydrogen storage applications.