Electrocatalytic performance of transition metal mono-carbides (TM: CrC, FeC, MnC, TiC, VC) decorated on palladium-encapsulated fullerenes (TM-Pd@C60) for hydrogen evolution reaction (HER): A DFT perspective

The search for efficient and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) is critical for advancing renewable energy technologies. This study employs density functional theory (DFT) at the MN12-SX/GenECP/Def2svp/LanL2DZ computational method to investigate the electronic, structural, and catalytic properties of modified fullerene (C₆₀) systems encapsulated with palladium (Pd) and doped with transition metal carbides: CrC, FeC, MnC, TiC, and VC. Frontier molecular orbital (FMO) analysis reveals significant changes in the HOMO-LUMO gap upon doping, indicating enhanced electronic conductivity essential for catalytic activity. The lowest energy gaps 0.081 eV for MnC–Pd@C₆₀ and 0.096 eV for VC-Pd@C₆₀ were observed thus showing their readiness in terms of electron transfer. HER activity was assessed through the calculation of Gibbs free energy changes (ΔG_H) for hydrogen adsorption. The results highlight TiC–Pd@C₆₀, FeC–Pd@C₆₀, and CrC–Pd@C₆₀ as having optimal ΔG_H values close to zero, suggesting their superior catalytic performance. Structural analysis confirms the stability of these doped systems, with minimal distortions observed in the fullerene framework upon metal encapsulation and doping. Vibrational analysis revealed that Pd@C₆₀ complexes show reduced M − C vibrations and the formation of M − H bonds, indicating efficient hydrogen adsorption, especially in MnC–Pd@C₆₀ and VC-Pd@C₆₀. Thermodynamics investigation show MnC–Pd@C₆₀ and VC-Pd@C₆₀ to exhibit highly exothermic and spontaneous hydrogen adsorption. Overall, Ti, Fe, and Cr-based catalysts show weaker interactions, which might favor the desorption step in HER. On the other hand, catalysts with V and Mn show strong hydrogen interactions via the Tafel step, which might benefit initial hydrogen adsorption but could require optimization to ensure efficient hydrogen release.