Unveiling Space-Charge-Regulated Etching in MAB Ceramics: A Novel Vacuum Molten Salt Strategy for Mo2AlB2
The synthesis of two-dimensional MBenes from MAB-phase ceramics is impeded by uncontrolled etching kinetics that compromise structural integrity and yield. This study introduces a vacuum molten salt strategy to regulate space-charge accumulation during the selective removal of Al from Mo2AlB2, producing honeycomb-like architectures. The vacuum environment suppresses oxidative side reactions and modulates ionic transport, enabling precise control over etching depth and morphology. The resulting Mo2AlB2 exhibits exceptional electromagnetic wave absorption, with a minimum reflection loss of -56.3 dB at 2.4 mm and an effective absorption bandwidth of 6.8 GHz. These metrics surpass conventional etching-derived MBenes by a factor of 2.5 in attenuation capacity. The space-charge-regulated mechanism is elucidated through in situ spectroscopic and computational analyses, revealing that vacancy-induced charge redistribution governs the etching front propagation. This work establishes a scalable route for high-purity MBenes with tailored porosity, addressing critical bottlenecks in energy absorption and catalytic applications. The vacuum molten salt approach eliminates the need for hazardous HF, offering a safer and more environmentally benign pathway for industrial translation.