Understanding the oxidation chemistry of Ti_(3)C_(2)T_(x)(MXene)sheets and their catalytic performances

Transition metal carbides and nitrides(MXenes)nanosheets are attractive two-dimensional(2D)materials,but they suffer from oxidation/degradation issues during storage and/or applications due to their sensitivity to water and oxygen.Despite the great research progress,the exact oxidation kinetics of Ti_(3)C_(2)T_(x)(MXene)and their final products after oxidation are not fully understood.Herein,we systematically tracked the oxidation process of few-layer Ti_(3)C_(2)T_(x) nanosheets in an aqueous solution at room temperature over several weeks.We also studied the oxidation effects on the electrocatalytic properties of Ti_(3)C_(2)T_(x) for hydrogen evolution reaction and found that the overpotential to achieve a current density of 10 mA cm^(-2)increases from 0.435 to 0.877 V after three weeks of degradation,followed by improvement to stabilized values of around 0.40 V after eight weeks.These results suggest that severely oxidized MXene could be a promising candidate for designing efficient catalysts.According to our detailed experimental characterization and theoretical calculations,unlike previous studies,black titanium oxide is formed as the final product in addition to white Ti(IV)oxide and disordered carbons after the complete oxidation of Ti_(3)C_(2)T_(x).This work presents significant advancements in better understanding of 2D Ti_(3)C_(2)T_(x)(MXene)oxidation and enhances the prospects of this material for various applications.

Intrinsic hard magnetism and thermal stability of a ThMn_(12)-type permanent magnet

Herein,we theoretically demonstrate that simple metal(Ga and Al)substitutional atoms,rather than the conventional transition metal substitutional elements,not only stabilize the ThMn_(12)-type SmFe_(12) and Sm(Fe,Co)_(12)phases thermodynamically but also further improve their intrinsic magnetic properties such that they are superior to those of the widely investigated SmFe_(11)Ti and Sm(Fe,Co)_(11)Ti magnets,and even to the state-of-the-art permanent magnet Nd_(2)Fe_(14)B.More specifically,the quaternary Sm(Fe,Co,Al)_(12)phase has the highest uniaxial magnetocrystalline anisotropy(MCA)of about 8 MJ m^(−3),anisotropy field of 18.2 T,and hardness parameter of 2.8 at room temperature and a Curie temperature of 764 K.Simultaneously,the Al and Ga substitutional atoms improve the single-domain size of the Sm(Fe,Co)_(12)grains by nearly a factor of two.Numerical results of MCA and MCA-driven hard magnetic properties can be described by the strong spin-orbit coupling and orbital angular momentum of the Sm 4f-electron orbitals.