High-yield Synthesis of Sodium Chlorides of Unconventional Stoichiometries.

Abnormal salt crystals with unconventional stoichiometries, such as Na 2 Cl, Na 3 Cl, K 2 Cl, and CaCl crystals that have been explored in reduced graphene oxide membranes (rGOMs) or diamond anvil cell, hold great promise in applications due to their unique electronic, magnetic, and optical properties predicted in theory. However, the low content of these crystals, only less than 1% in rGOM, limits their research interest and utility in applications. Here, w e report a high-yield synthesis of 2D abnormal crystals with unconventional stoichiometries achieved by applying negative potential on rGOM. W e obtained a more than ten-fold increase in the abnormal Na 2 Cl crystals using potential of -0.6 V, resulting in an atomic content of 13.4 ± 4.7% for Na on rGOM. Direct observations by transmission electron microscopy and piezoresponse force microscopy demonstrated a unique piezoelectric behavior arise from 2D Na 2 Cl crystals with square structure. The output voltage increased from 0 to ∼180 mV in broad 0°-150° bending angle regime, which meets the voltage requirement of most nanodevices in realistic applications. Density functional theory calculations reveal that the applied negative potential of the graphene surface can strengthen the effect of the Na + -π interaction and reduce the electrostatic repulsion between cations, making more Na 2 Cl crystals formed. This article is protected by copyright. All rights reserved.