High Throughput Study of Rare Earth Doping in Double Transition Metal MAX and MXenes

MXenes, two-dimensional (2D) transition metal carbides, nitrides, or carbonitrides, have grown rapidly as a nanomaterial family over the last decade for applications in energy storage, catalysis, electromagnetic interference (EMI) shielding, and beyond. The incorporation of rare-earth (RE) elements into MXenes can open a wide range of applications, from magnetic 2D materials for quantum computing and EMI shielding to electrocatalysis. However, until now, the instability of RE elements in the transition metal sites in previous studies during top-down etching has limited the synthesis of RE-containing MXene from their parent MAX phases. Recently, RE-doping in nanostructures ranging from semiconductors to inorganic–organic hybrids has resulted in tunable optical, electrical, magnetic, and catalytic properties. Here, we present a high-throughput synthesis study of a series of RE-doped MAX phases and their MXenes, using five MAX/MXene compositions with three RE dopants (Nd, Gd, Tb). This investigation involves systematically incrementing molar stoichiometric ratios of RE to transition metal elements in the MAX phases. To determine the RE-doping into the selected MAX phase, we used x-ray diffraction and scanning electron microscopy with energy dispersive x-ray spectroscopy. Afterward, the successful RE-doped MAX phases were etched to form MXenes. The selective etching and delamination experiments were tuned to minimize the harsh environmental effects, which could oxidize existing rare earth components. This high throughput study expands the available compositions of MXenes with the incorporation of RE, which may further explore 2D RE-MXenes in magnetic or quantum electronics.