  For carbon-based materials, in contrast to metal surfaces, the relationship
between strain and reactivity is not yet established, even though there are
literature reports on strained graphene. Knowledge of such relationships would
be extremely beneficial for understanding the reactivity of graphene-based
surfaces and finding optimisation strategies which would make these materials
more suitable for targeted applications. Here we investigate the effects of
compressive and tensile strain (up to +/-5%) on the structure, electronic
properties and the reactivity of pure, N-doped and P-doped graphene, using DFT
calculations. We demonstrate the possibility of tuning the topology of the
graphene surface by strain, as well as by the choice of the dopant atom. The
reactivity of (doped) strained graphene is probed using H and Na as simple
adsorbates of great practical importance. Strain can both enhance and weaken H
and Na adsorption on (doped) graphene. In case of Na adsorption, a linear
relationship is observed between the Na adsorption energy on P-doped graphene
and the phosphorus charge. A linear relationship between the Na adsorption
energy on flat graphene surfaces and strain is found. Based on the adsorption
energies and electrical conductivity, potentially good candidates for hydrogen
storage and sodium-ion battery electrodes are discussed.
