DFT study of hydrogen adsorption on Co-decorated C 12 carbyne ring

Abstract Efficient and reversible hydrogen storage still hinders the practicality of hydrogen-based energy systems. Carbon-based nanostructures have shown promise with adsorption energies within the targets set by the US-DOE but could still be improved with more efficient energy density. Recent studies have demonstrated that decorating carbon materials with transition metals can enhance hydrogen storage capacities by facilitating adsorption of H 2 molecules while increasing surface area. This study investigates the hydrogen adsorption capability of Co-decorated C₁ 2 carbyne ring using Density Functional Theory (DFT). The hollow, single bond, and triple bond adsorption sites were chosen. All calculations employed the GGA-PBE exchange-correlation functional with spin polarization. Cell parameters 20 Å × 20 Å × 20 Å was used to avoid self-interaction, while 1×1×1 k-point sampling was chosen due to the non-periodic nature of the system. Calculations were performed using DFT implemented in Quantum ESPRESSO. Adsorption energies at the single and triple bond sites indicated that H 2 is adsorbed through chemisorption in these configurations. While the hollow site adsorbs H 2 through physisorption. 8 H 2 molecules were incrementally added around the Co site and geometry optimization performed for each configuration. 6 H 2 molecules were successfully adsorbed with 4 exhibiting adsorption energies ranging from -0.22 eV and -0.41 eV, falling within the ideal range for reversible storage. This yielded a gravimetric weight of 3.82 wt% which is under US-DOE targets but still promising for a single molecule of Co-decorated C 12 carbyne ring.