  Cubic gauche nitrogen (cg-N) has received wide attention due to its high
energy density and environmental friendliness. However, existing synthesis
methods for cg-N predominantly rely on the high-pressure techniques, or the
utilization of nanoconfined effects using highly toxic and sensitive sodium
azide as precursor, which significantly restrict the practical application of
cg-N as high energy density materials (HDEM). Here, based on the
first-principles simulations, we find that the adsorption of potassium on the
cg-N surface exhibits superior stabilization compared to sodium. Then, we chose
the safer potassium azide as raw material for synthesizing cg-N. Through
plasma-enhanced chemical vapor deposition treatment, the free-standing cg-N was
successfully synthesized without the need of high-pressure and nanoconfined
effects. Importantly, it demonstrates excellent thermal stability up to 760 K,
and then a rapid and intense thermal decomposition occurs, exhibiting typical
behaviors of HDEM thermal decomposition. Our work has significantly promoted
the practical application of cg-N as HDEM.
