Effect of Morphology Structures on Hydrogen Evolution Reaction and Oxygen Evolution Reaction Performances of Mo₂CO₂ MXene

Currently, single atom (SA), quantum dots (QDs) and heterogeneous interfaces have been extensively employed for the design of novel catalysts for overall water splitting. However, there are still few literatures about the hydrogen (HER) and oxygen (OER) evolution performances for three different morphologies of the same metal loaded on MXenes substrates. Herein, the HER and OER performances of Mo₂CO₂ modified by transition metals (TM, TM=Fe, Co, and Ni) with different SA loading (S_TM/Mo₂CO₂), QDs (Q_TM/Mo₂CO₂) and heterogeneous interface (I_TM/Mo₂CO₂), and TM loading and N₃ (TMN₃/Mo₂CO₂) or N₄ doping co-modification (TMN₄/Mo₂CO₂) are investigated by density functional theory (DFT) calculations. The results show that the HER and OER performances of S_TM/Mo₂CO₂ are better than those of I_TM/Mo₂CO₂ and Q_TM/Mo₂CO₂. Especially, S_Ni/Mo₂CO₂ exhibits the best HER and OER properties among the studied structures, with the corresponding ΔG_H* and η_OER of −0.04 eV and 0.53 V, respectively. It is noteworthy that the ΔG_H* absolute value, η_OER, work function (Φ) and TM valence charges are significantly correlated, where ΔG_H* absolute value, η_OER, and Φ all present an increase trend following the order of S_TM/Mo₂CO₂, I_TM/Mo₂CO₂, and Q_TM/Mo₂CO₂, whereas TM valence charges exhibit a decrease trend with the above order. Furthermore, integral crystal orbital Hamilton population (ICOHP) results indicate that the more negative the ICOHP, the stronger bonding strength between TM and H atoms, and the better the corresponding HER performance in S_TM/Mo₂CO₂. Campared with S_Ni/Mo₂CO₂, Ni loading and N₃ doping co-modification Mo₂CO₂ (NiN₃/Mo₂CO₂) shows better HER (ΔG_H*=−0.01 eV) and OER catalytic activities (η_OER=0.36 V). Molecular dynamics simulations results indicate that most of the modified systems are stable at reaction temperature. In summary, NiN₃/Mo₂CO₂ can be used as an efficient electrocatalyst for overall water splitting.