Two-dimensional in-plane transition metal boride, Mo1.33Y0.67B2-xTz i-MBene for enhanced energy and power densities in supercapacitor devices

Two-dimensional (2D) MBenes are the emerging members of the advanced 2D materials owing to their exceptional functional properties for applications such as energy storage. We report the fabrication of Mo₄/₃Y₂/₃B₂−xTz (Tz = -O, -F, or -OH) i-MBene through the wet-chemical etching method using concentrated hydrofluoric (HF) acid. The structural, morphological, optical, and analytical results assured the successful etching of Al atoms and the synthesis of a stable structured i-MBene, and the consequent interlayer opening facilitates fast ion diffusion and enhanced storage capacity. The three-electrode system achieved the maximum gravimetric capacitance of 1112 Fg−1 with an outstanding energy density of 38 Wh kg−1 and power density of 250 W kg-1 at 1 Ag−1, which is the highest compared to the other recent 2D materials such as MXenes. Furthermore, the two-electrode system (device) exhibited the gravimetric capacitance of 90 Fg−1, energy density of 15 Wh kg−1, with a high power density of 800 W kg−1 at 1 Ag−1. Moreover, with 80% capacity retention yield over 5000 cycles at 10 Ag−1, i-MBene proved to be a new and notable performance active 2D material for electrochemical energy storage applications.