Tuning quantum capacitance in MGa 2 S 4 for supercapacitors via S-vacancy and light/transition-metal doping

As a member of the extended MA2Z4 family, current research on MGa2S4 (M = Mg, Ca, Sr) primarily focused on its potential applications in energy conversion. In this work, the geometric structure, quantum capacitance (CQ), and charge storage capacity (Q) of MGa2S4 (M = Mg, Ca, Sr) were investigated based on density functional theory (DFT) method. The effects of S-vacancy, light-element doping (B, N, O, Al, Si, P) and transition-metal doping (Sc, Ti, V, Cr, Mn, Fe) on capacitance properties of MGa2S4 were also systematically examined. The results indicated that pristine MGa2S4 structures exhibited excellent CQ and Q under negative voltage, and SrGa2S4 possessed the largest CQ (395.94 μF/cm²) at −0.6 V. Under negative bias, the introduction of S-vacancy increased the maximum CQ of MgGa2S4 and CaGa2S4 by 10.68–15.03 μF/cm². Light-element doping led to a further increase in the CQ, with N-doped SrGa2S4 achieving the most remarkable value of 527.85 μF/cm². Interestingly, transition-metal doping induced multiple peaks in the CQ-voltage profiles, especially under positive bias. Under positive bias, Ti-doped MGa2S4 exhibited the most significant CQ values (217.78–245.08 μF/cm²). Overall, the findings of this study are expected to advance the development of high-capacitance electrodes based on MGa2S4 materials.