Interaction of water with nitrogen-doped graphene

We have studied the interaction of water and graphene doped with nitrogen in different configurations, namely, graphitic and pyridinic nitrogen, by means of the van der Waals density functional. We found that the local nitrogen configuration plays a key role in determining the stable water configuration, while the dispersion force is responsible for the water adsorption. With the graphitic nitrogen, water prefers to orient with its oxygen toward the surface, whereas for the pyridinic nitrogen it prefers to orient with its hydrogens toward the surface, because nitrogen is positively and negatively charged for the former and the latter, respectively. Our results have great implications for the modeling of the interface between water and nitrogen-doped graphitic systems.

Figure 1

Side (upper panel) and top (lower panel) views of the water adsorption configuration on pristine graphene for (a) 0-leg, (b) 1-leg, and (c) 2-leg configurations. In the 1-leg configuration, water molecule is inclined by ${4.51}^{\circ }$ with respect to the surface normal. H, C, and O atoms are represented by white, brown, and red spheres, respectively.

Figure 2

Interaction energy of water with pristine graphene as a function water-graphene distance.

Figure 3

Structures of graphene doped with (a) graphitic N, (b) pyridinic N and dangling C, and (c) pyridinic N and H-terminated C. White, brown, and silver spheres represent H, C, and N atoms, respectively.

Figure 4

Water adsorption configuration on graphene doped with graphitic N with difference N positions (N1–N4) for (a) 0-leg, (b) 1-leg, and (c) 2-leg configurations.

Figure 5

Interaction energy of water on graphene doped with graphitic N as a function of water-graphene distance with different N positions for (a) 0-leg, (b) 1-leg, and (c) 2-leg configurations.

Figure 6

Charge-density difference ($\mathrm{\Delta }\rho$) of water on graphitic N for (a) 0-leg, (b) 1-leg, and (c) 2-leg configurations with the most stable relative N positions (N3, N1, and N4, respectively). $\mathrm{\Delta }\rho$ in a plane containing the molecular plane is plotted. The maximum (minimum) value of $\mathrm{\Delta }\rho$ is $1.35\times {10}^{-2}$ ($-1.35\times {10}^{-2}$) $e$ Å${}^{-3}$.

Figure 7

Hartree potential difference ($\mathrm{\Delta }{V}_{\mathrm{H}}$) for graphitic N [(a) top and (c) side views] and that for pyridinic N [(b) top and (d) side views]. The maximum (minimum) value of $\mathrm{\Delta }{V}_{\mathrm{H}}$ is 1.1 ($-0.5$) eV. The red dotted line indicates the lattice plane for the side views.

Figure 8

Water adsorption configurations on graphene doped with pyridinic N and H-terminated C for (a) 0-leg configuration, (b) 1-leg configuration (orientation 1) (1-leg 1), and (c) 2-leg configuration (orientation 1).

Figure 9

Interaction energy of water with graphene doped with pyridinic N and H-terminated C, as a function of water-surface distance for difference water configurations.

Figure 10

Charge-density difference ($\mathrm{\Delta }\rho$) of water molecule on graphene doped with pyridinic N with H-terminated C for (a) 0-leg, (b) 1-leg, and (c) 2-leg configurations. $\mathrm{\Delta }\rho$ in a plane containing the molecular plane is plotted. The maximum (minimum) value of $\mathrm{\Delta }\rho$ is $1.35\times {10}^{-2}$ ($-1.35\times {10}^{-2}$) $e$ Å${}^{-3}$.