“…MXenes are therefore potentially promising 2D HER catalysts, but are limited to carbide, nitride, and carbonitride phases due to compositional limitations of the parent MAX phases. In addition to metal carbides, metal borides also have been gaining attention as HER catalysts, − especially molybdenum borides that include α-MoB, β-MoB, Mo 2 B, and MoB 2 . , However, efforts to access high surface area metal boride materials are challenging, particularly for the molybdenum-based systems that are of greatest interest for their high activity and stability. The ability to access MXene-like 2D borides through etching boride analogues of MAX phases would significantly expand the diversity of available MXene materials .…”