High Catalytic Performance of MB MBenes in Aqueous Li-N Battery Cathodes: A Theoretical Study.

Aqueous Li-N batteries are promising electrochemical energy storage devices, but their reaction mechanisms remain controversial. This study employed density functional theory to investigate the catalytic mechanism of MB MBenes (M = Ti, Zr, Hf, Cr, Mo, and W) as cathodes for aqueous Li-N batteries. MB MBenes exhibit high conductivity due to strong d-electron states crossing the Fermi level. IVB-group MBenes (TiB, ZrB, and HfB) preferentially adsorb N in side-on modes at hcp sites, while VIB-group MBenes (CrB, MoB, and WB) favor face-centered cubic sites, with adsorption strength inversely correlated to metal atomic number. The reaction cycle involves N adsorption, LiN formation via discharge, ammonia synthesis through LiN hydrolysis, and LiOH decomposition during charging. The higher discharging overpotential compared to charging suggests that Li-N batteries operate in a discharge-controlled manner. Both discharge and charge overpotentials follow HfB > ZrB > TiB and WB > MoB > CrB. The difference in catalytic activity between the IVB-group and VIB-group MBenes arises from distinct adsorption sites and configurations. Notably, CrB MBene demonstrates exceptional catalytic performance (0.69 V discharge/0.16 V charge overpotentials) attributed to its high d-band center enhancing N adsorption/activation and the distinctive LiNN* intermediate configuration where two Li atoms concentrate at one N terminus facilitating subsequent lithiation. This study establishes a theoretical foundation for designing high-performance Li-N batteries by utilizing tunable electronic properties of MBenes.