First principles of Si-doped BC2N single layer for hydrogen evolution reaction (HER)

Understanding the Hydrogen Evolution Reaction (HER) process is fundamental to use hydrogen as a sustainable (clean and renewable) energy source. Using first-principles calculations, we study the HER process when Si-doped a h-BC₂N single layer. The pristine BC₂N presents semiconducting properties with a band gap of 1.6–2.0 eV, being appropriate as a catalytic in the water splitting process. When Si is incorporated into the BC₂N monolayer, we obtain that the most stable site (lower formation energy) occurs when the Si atom replaces a C atom (Si_C). The Si atom moves out of the plane forming a buckling structure and the semiconducting properties are maintaining without spin effects. However, Si_B and Si_N give rise to two unpaired spin electronic levels inside the band gap and a magnetic moment of 1 μ_B. The adsorption energies of an H₂ molecule on the top of the Si atom are in the range of 50–100 meV, which are greater than the calculated ones for H₂ adsorbed on graphene and h-BN nanosystems but still low to be considered as an optimized medium for hydrogen storage. In addition, we observe that dispersive forces (van der Waals interactions) are responsible for half part of the adsorption energies. Strain due to the difference between the atomic radius of Si and C as well as the less stability of the Si–H bonds compared to the C–H ones leads to the Gibbs free energy (ΔG1) for hydrogen adsorbed on Si_C near zero, showing that Si-doped h-BC₂N is a potential system for HER.