Ultra-high capacity hydrogen storage in a Li decorated two-dimensional C2N layer

Owing to naturally existing uniform periodic pores in two-dimensional (2D) C2N layers, they can be an ideal candidate for hydrogen storage materials among other 2D materials. Here, we explored the potential application of ultra-high capacity hydrogen storage using the first principles method. Remarkably, Li was strongly bonded with the C2N layer via a Kubas-type interaction with a large binding energy of 3-5 eV. This unique interaction does not exist in graphene or other 2D materials, and it rules out the possibility of Li alkali metal cluster formations. We found that the Li-decorated C2N could show a very high theoretical gravimetric density of 13 weight percentage (wt%). Very interestingly, this gravimetric density is not only 40% and 30% higher than those found in MgH2 and C60 but also significantly higher than the values obtained in alkali metal decorated graphene, MoS2 and phosphorene. Irrespective of the theoretical capacity, the most important physical quantity is the practical capacity (the difference in the number of adsorbed and desorbed hydrogen molecules) under ambient conditions of pressure and temperature. Our thermodynamic analysis showed that 75% of the adsorbed hydrogen molecules could be released under practical conditions of temperature and pressure and the practical capacity is about 10 wt%. Our findings suggest that the Li decorated C2N can be a very promising material for room-temperature hydrogen storage under realistic conditions.