Strain-tunable pure H- conduction in one-atom-thick hexagonal boron nitride for high-energy-density fuel cells

After proton conductor, hydride (H-) ion conductor with advantages of suitable-ionic-size fast conduction and strong reducing ability is exceptionally promising for high-energy-density fuel cells, but it is hindered by a very limited number of materials in oxyhydrides, metal hydrides and titanium-nitride thick membranes. So far, pure H- conduction is not demonstrated in two-dimensional (2D) materials. Here, we demonstrated a strain-tunable pure H- conduction in one-atom-thick hexagonal boron nitride (h-BN), being a new-type H- solid electrolyte of high-energy-density fuel cells. We studied adsorption behavior and migration process of H- ion on h-BN monolayer under different strains by using systematic first-principles calculations. It is found that structure of hBN primitive unit cell can tolerate compressive strain as big as -6 %. According to Bader charge analysis, H got 0.3 e to be H- ion, and H got more charge as the tensile strain increases, which was also proved by electronlocalization-function maps. H- ion has the lowest migration energy barrier of 0.730 eV on h-BN monolayer surface without external strain. Overall, the results have demonstrated a large-range strain-tunable fast pure Hconduction in 2D h-BN, and a promise of new-type ultrathin flexible solid electrolytes for next-generation fuel cells with high energy density.