Catalytic battle of activated carbon supported transition metal atom towards adsorption and dissociation of molecular hydrogen: Progress towards quantum chemical application on renewable energy resource

Density functional theory (DFT) investigation has been done to unravel the adsorption and dissociation nature of hydrogen molecule on 3d, 4d and 5d transition metal (M = Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt or Au) atom doped activated carbon (AC) surface. Transition metal doped AC are found to be active catalyst for storage of hydrogen and also gives the stability of M − H bonds formed after bond breakage of H₂ molecule. Transition metals are found to occupy the position on the five member ring rather than six member ring of the AC. Five member ring of the AC is seen to be more deformed than the six-member ring on metal doping. Higher values of LUMO-HOMO gap and vertical ionization potential and lower electron affinity signify the higher stability of hydrogen molecule adsorbed metal doped AC. Bond length and vibrational analysis of the adsorbed hydrogen molecule suggest the higher activation of hydrogen molecule on AC, where 4d and 5d metal doped ACs are found to be more efficient in comparison to 3d metal. Adsorbed hydrogen molecule on metal doped AC follows dissociation either via spill-over or via normal process. DFT evaluated rate constant and the transition states suggest that Ru, Rh, Os and Ir doped AC are found to be efficient in the dissociation of hydrogen molecule, while, Cu doped AC is seen to be worst in the same reaction. Deformed electron density, HOMO-LUMO isosurface, and density of states confirms the redistribution of electrons among H₂ and metal doped AC surface. ΔG_H values of Hydrogen evolution reaction also signifies the greater catalytic activities of Ru and Os supported activated carbon towards HER.