Computational Evaluation of Lithium-Functionalized Carbon Nitride (g

Article pubs.acs.org/JPCC

Computational Evaluation of Lithium-Functionalized Carbon Nitride (g‑C6N8) Monolayer as an Efficient Hydrogen Storage Material Tanveer Hussain,*,† Marlies Hankel,† and Debra J. Searles†,‡ †

Centre for Theoretical and Computational Molecular Science, Australian Institute for Bioengineering and Nanotechnology, and School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia

‡

ABSTRACT: Quantum chemical density functional theory calculations have been used to study the structural, electronic, and hydrogen storage properties of a monolayer that is a stable allotrope of carbon nitride (g-C6N8). It was observed that a 2 × 2 supercell can bind three, six, and eight lithium (Li) adatoms in different configurations with a binding energy much higher than the cohesive energy of Li, indicating that a distribution of Li over the monolayer can form without clustering of Li occurring. Density of states calculations suggests that adding Li atoms transforms the semiconducting (g-C6N8) monolayer into a conducting one. A significant amount of charge is transferred from Li to the monolayer that induces a partial positive charge on each Li adatom. This facilitates the polarization of the H2 molecules exposed to Li, which are then held by it through electrostatic and van der Waals interactions. Each Li can adsorb multiple H2 molecules with adsorption energies that lie within the desired range for an efficient and reversible H2 storage material with a storage capacity of 7.55 wt %.

1. INTRODUCTION Because of its high energy density per mass, abundant availability, and zero emission on burning, hydrogen (H2) is considered as a perfect energy carrier for the future. However, identification of a suitable storage media has been the biggest bottleneck toward the realization of a H2-based economy. Because of the apprehensions associated with conventional storage methods, liquefaction, and storage under pressure, materials-based H2 storage seems to be the most practical route. However, the pursuit of ideal materials that are suitable for a range of applications including mobile storage remains a serious challenge that needs to be overcome.1−3 Among many others, the carbon-based materials have been widely pursued over the past decades as energy storage materials.4−6 Graphitic carbon nitride is a porous graphene-like membrane, and two structures exist with different pore sizes.7−13 The smaller pore size material is based on triazine units, C3N3, connected via a nitrogen and forms triangular pores surrounded by three C3N3 rings. The second one is based on heptazine units, C6N7, again connected via nitrogen and forms much larger triangular pores. Since first being predicted by Liu and Cohen14 to be a superhard material, these carbon nitrides (g-C3N4 and g-C6N8) have attracted considerable attention due to their promising application in mechanical, optical, and electronic devices.10 The most stable and readily available allotrope is g-C6N8 while g-C3N4 has only recently been synthesized.12 The majority of studies of graphitic carbon nitride are on its photocatalytic and photoelectronic properties. However, it has also been investigated for metal and transition metal decoration and subsequent hydrogen storage.15−19 The pore structure of graphitic carbon nitride facilitates a good dispersion of the metal or transition metal atoms on the surface, and since the adsorption energy between the surface and the © 2016 American Chemical Society

metal is usually high, it avoids clustering of the metal. Nair et al.15 experimentally investigated hydrogen storage on palladium-decorated graphitic carbon nitride. They found that the hydrogen storage capacity of Pd-decorated g-C3N4 reaches 2.6 wt % at 25 °C and 4 MPa. Ruan et al.16 investigated the physical properties of Li-doped g-C3N4 employing density functional theory (DFT) methods. They found that Li binds preferable in the pores with adsorption energy of −2.11 eV for a single Li in a 2 × 2 supercell. Zhang et al.17 used DFT to show that g-C3N4 provides an excellent template for stable and well-dispersed decoration of Li and 3d transition metal atoms. They found that the most stable transition metals are Ti and Sc and that they show high capacity of hydrogen adsorption with energies that are suitable for mobile applications. Wu et al.18 studied hydrogen adsorption on Li decorated g-C3N4, g-C4N3, and g-C6N8 using DFT calculations. They found that up to three H2 per Li could be adsorbed on Li2C3N4, which corresponds to 10.2 wt % and up to five H2 can adsorb on Li2C6N8, which corresponds to 4.8 wt %. Zhu et al.19 also studied the hydrogen storage on Li decorated g-C3N4. They found adsorption energy of H2 of −3.48 kcal/mol (−0.15 eV) and a hydrogen uptake of 4.5 wt %. Most theoretical studies on hydrogen storage have concentrated on g-C3N4, with only one study reporting results for hydrogen storage on g-C6N8,18 despite the fact that this allotrope has been more readily available for experiment. In their work, Wu et al.18 decorated the g-C6N8 with lithium and demonstrated that it is a promising H2 storage material, and we consider this system here. We extend the work of Wu et al.18 by Received: June 19, 2016 Revised: October 17, 2016 Published: October 21, 2016 25180

DOI: 10.1021/acs.jpcc.6b06182 J. Phys. Chem. C 2016, 120, 25180−25188

Article

The Journal of Physical Chemistry C

Figure 1. Optimized structure of the 2 × 2 supercell of the g-C3N4 carbon nitride monolayer. Black and orange balls represent C and N atoms, respectively.

where m the number of adsorbed H2 molecules.

including dispersion corrections in the DFT calculations of the Li adsorption, using a large supercell for the calculations and considering different Li decorations and their effect on the H2 storage capacity.

3. RESULTS AND DISCUSSION This section of the paper is divided into two parts. In the first part the structural properties and the binding mechanism of Li dopants on the carbon nitride monolayer are briefly described. The second part deals with the adsorption of H2 on the Li functionalized carbon nitride monolayer. 3.1. Structural Properties and Li Binding. The lattice parameters of the unit cell were optimized and found to be a = b = 7.132 Å. The optimized bond lengths of C−N in a 2 × 2 supercell (shown in Figure 1) are found to be 1.39 Å for the C−N bonds that are part of six-member rings; however, the C and N atoms which link the two rings have a larger bond length of 1.47 Å. To find the most stable adsorption site of Li on the carbon nitride sheet, all the likely sites were studied: above the C atom, above the N atom, above bonds, and above the rings (pores). As was found for g-C3N4 in previous studies, the Li preferably adsorbs over the large pore. Various loadings and adsorption sites were identified and are discussed here. The adsorption energy (eq 1) of one Li in the large pore is Eads(Li) = −6.23 eV, and it is observed that the heptazine units slightly twist to accommodate the lithium atom, which sits in the middle of the pore in the membrane plane. If one lithium atom is placed in the same position on either side of the membrane, no distortion of the membrane is found, but the two Li atoms move slightly off the center of the pore and the adsorption energy per Li is reduced to −3.08 eV. This indicates that symmetric placement of the atoms which prevents distortion results in a significant lowering of the binding energy. If three Li are placed into the same pore, they sit above the pore with Eads(Li) = −3.29 eV and that the inner nitrogens of the pore are displaced toward the lithium atoms. Interestingly, placement of four Li atoms into one pore (Eads(Li) = −3.05 eV), one in each corner of the pore and one in the middle, leads to the middle Li moving into the membrane plane while the other three stay above the membrane plane, and again, the nitrogens inside the pore move above the plane, toward the lithium atoms. The calculated

2. COMPUTATIONAL DETAILS The DFT calculations in the current project are carried out using the VASP code.20−22 Three-dimensional periodic boundary conditions were applied to simulate infinitely large periodic systems. A 20 Å vacuum space between two sheets was set to prevent the interaction between the two carbon nitride layers. The Brillouin zone for a 2 × 2 supercell was sampled using a 3 × 3 × 1 k-point mesh for structural optimization and a 5 × 5 × 1 k-point mesh for density of states (DOS) calculations.23 These values were selected to be optimal in terms of accuracy and computational time using results of preliminary calculations. The electronic structure of the system was treated using the generalized gradient approximation (GGA) with the PBE functional.24 van der Waals interactions were added to the standard DFT description by Grimme’s scheme (D2).25 An energy cutoff of 500 eV with convergence criteria of 10−5 eV for energies has been used, and optimization of the structures was performed until the forces acting on each ion became less than 0.05 eV/Å. The transfer of electronic charge between the Li dopant and the monolayer was approximated by Bader charge analysis.26 The adsorption energy of the Li dopants on the carbon nitride monolayer Eads(Li) is given by Eads(Li) = {E(Li nC24 N32) − E(C24 N32) − nE(Li)}/n (1)

where n is the number of adsorbed Li atoms and E(X) is the energy of the atom, molecule, or composite, X. With this definition, negative adsorption energy indicates a favorable adsorption. The adsorption energies of H2 molecules to the functionalized systems Eads(H2) were calculated using Eads(H 2) = {E(mH 2@Li nC24 N32) − E(Li nC24 N32) − mE(H 2)}/m

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Figure 2. Optimized structure with three lithium atoms on the supercell of the carbon nitride monolayer. The Li atoms are approximately 1.92 Å above the membrane plane. Black, orange, and red balls represent C, N, and Li atoms, respectively.

Figure 3. Optimized structure (extended) of the Li6-functionalized carbon nitride monolayer. The Li atoms are between 1.4 and 1.8 Å above the membrane plane. Black, orange, and red balls represent C, N, and Li atoms, respectively. The supercell used in the calculations is indicated.

adsorption energy of Li on the carbon nitride monolayer is much higher than the Li cohesive energy (−1.63 eV), which indicates a uniform distribution of Li dopants that are not clustered. In the optimized structure as shown in Figure 2, the distance between Li and the neighboring N atoms is 1.908 Å for each Li. The distance between adsorbed Li atoms, Li−Li, is found to be 2.764 Å.

The g-C3N4 with three Li atoms above the membrane plane (Figure 2) was anticipated to have a high potential H2 storage capacity due to the number of Li atoms and the available space, so this system was considered for this purpose in the next section. However, as will be shown below, the H2 storage capacity remains less than 5.5 wt %, a target proposed by the DOE to be met by 2020.27 Thus, to increase the H2 storage capacity, more Li atoms were introduced to the monolayers, 25182


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Figure 4. Optimized structure (extended) of the Li8-functionalized carbon nitride monolayer. Where there is a single Li atom in the pore the Li lie in the membrane plane. Where there are three Li in one pore the Li atoms are between 1.45 and 1.89 Å above the membrane plane. Black, orange, and red balls represent C, N, and Li atoms, respectively. The supercell used in the calculations is indicated.

Figure 5. PDOS of (top) pure and (bottom) Li3-functionalized carbon nitride monolayer. The energy is shown relative to the Fermi energy. PDOS are shown for a selected Li atom and C and N atoms closest to the selected Li atom.

energy for both configurations ensure the stability of the Li functionalized carbon nitride monolayers and that a number of H2 molecules can be adsorbed. The optimized structures of these configurations are shown in Figure 3 (six Li) and Figure 4 (eight Li). In the case when six Li atoms are adsorbed on the

with the expectation that they would remain uniformly distributed over the sheet without forming clusters. Two different configurations were observed, with six and eight Li attached to the sheet with adsorption energies of −2.79 and −3.14 eV per Li, respectively. The high values of adsorption 25183


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Figure 6. PDOS of (top) Li6- and (bottom) Li8-functionalized carbon nitride monolayer. The energy is shown relative to the Fermi energy. PDOS are shown for a selected Li atom and C and N atoms closest to the selected Li atom.

membrane (see Figure 3), three of the Li are located together in a pore. This results in a configuration where all the Li are adsorbed on the same side of the membrane and with all Li at an equal distance above the membrane, similar to the configuration with three Li. To obtain a configuration of eight Li atoms adsorbed on the membrane (see Figure 4), a single Li atom was added to each of the empty pores of configuration shown in Figure 3 with six Li. In this system the three Li located together in a pore sit at a distance above the membrane whereas the single Li in a pore sit in the membrane plane. These two configurations with six and eight Li atoms were selected to ensure reasonable space for H2 to adsorb around the Li on both sides of the membrane. The binding of Li with the carbon nitride monolayer has also been investigated by studying the electronic DOS which indicate that the g-C6N8 monolayer is semiconducting, and it becomes conducting on addition of Li atoms. In Figures 5 and 6 the partial density of states (PDOS) for the s orbital of a selected Li atom and p orbitals of the C and N atoms that are located closest to the selected Li atom are shown. The PDOS of the pristine monolayer shown in the top panel of Figure 5 indicates that the valence band is dominated by N(p) and the conduction band by C(p). However, through the introduction of Li atoms, mid band states appear just before and at the Fermi level as shown in the lower panel of Figure 5 (C24N32Li3). A strong overlap between the N(p) and Li(s) close to the Fermi level indicates the existence of binding of the Li to the monolayer. A similar trend can be seen in the top and lower panel of Figure 6, which show the PDOS of C24N32Li6 and C24N32Li8, respectively. To further examine the type of bonding between the Li and the carbon nitride monolayer, the charge transfer mechanism was studied using a Bader analysis. Since the electronegativities of both C and N are higher than that of Li, the electric charge will be transferred from the Li adatoms toward the monolayer.

An analysis of the results shows that each Li loses approximately 0.82 e− of its charge to the N atoms of the monolayer that are in the vicinity of the Li atoms. 3.2. Hydrogenation of C24N32Li3. So far the results presented establish that the Li-functionalized carbon nitride monolayers (C24N32Li3, C24N32Li6, and C24N32Li8) are stable structures with Li atoms adsorbing strongly to the monolayer. Now the capacity of the doped system for adsorption of H2 molecules (hydrogenation) by the introduction of H2 around each Li in a stepwise manner is considered. First, C24N32Li3 is discussed in detail. The Bader charge analysis indicates that each Li atom transfers a significant amount of charge to the sheet and becomes positively charged. Initially one H2 molecule was placed near each Li (3H2 in total) on one side of the membrane, and the geometry of the system is allowed to optimize. The cationic nature of the Li induces a partial charge on H2 molecules in its vicinity, which are then held by the Li through electrostatic interaction. Along with electrostatic forces, there is a weak van der Waals interaction between the H2 and Li, and thus inclusion of the van der Waals corrections was important. The adsorption energy of H2 was calculated using eq 2 and is found to be −0.29 eV per H2 (GGA = −0.19 eV). Additional H2 molecules were added to each Li, and the system was reoptimized after each adsorption. As H2 molecules acquire a fraction of the charge from the Li, a reasonable distance needs to be maintained between the H2 to avoid the unwanted repulsion and to achieve multiple adsorptions of H2. The maximum number of H2 adsorbed on each Li in the case of C24N32Li3 is three; the fourth H2 molecule was repelled by the saturated system. The second and third H2 molecules adsorb to the system with energies of −0.221 eV (−0.13) and −0.185 eV (−0.07 eV), respectively. The values in parentheses are GGA results without van der Waals correction. The adsorption energies decrease with the increase of H2 molecules, which 25184


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physisorption. The optimized structures of C 24 N 32 Li 3 , C24N32Li6, and C24N32Li8 loaded with maximum H2 molecules are shown in Figures 7−9, respectively. Table 1 shows that the maximum storage capacity that is predicted to be able to be achieved with three lithium atoms in the supercell (i.e., C24N32Li3), and adsorption of hydrogen to just one side of the membrane is 2.32 wt %. On increasing the number of Li atoms in the supercell to six (i.e., C24N32Li6), it was still possible to adsorb three H2 per Li, leading to a maximum storage capacity of 4.23 wt %, which is a significant improvement over C24N32Li3. Figure 8 shows the positions of the hydrogen atoms in this case. Further improvement on the capacity was obtained by increasing the number of Li atoms in the unit cell to eight, although the calculations indicated that it was no longer possible to bind three H2 per Li on one side of the membrane due to crowding, and a maximum capacity of 5.42 wt % was achieved. Wu et al.18 were able to achieve a capacity of 4.8 wt % H2 adsorption. Note, however, that there are several differences between their calculations and those presented in this article. First the dispersion corrections were not considered for the lithium adsorption in their calculations, which would tend to lead to underestimations of the capacity. Second, the supercell considered was smaller (1 × 1 rather than 2 × 2 in this work). This has several effects including prevention of distortion of the membrane, decreasing the number of lithium atoms that can be accommodated in a single pore since all pores will be filled (structures like those shown in Figures 2−4 will not be

reflects that only a limited number of H2 could be adsorbed to the system. The complete results for the adsorption energies, Li−H2 distance, H−H bond lengths, and H2 storage capacities of different systems are given in Table 1. It is evident from the Table 1. Average H2 Adsorption Energies (GGA, vdW), Li− H2 Distances, H−H Bond Lengths, and Amount of H2 Adsorbed on Li-Functionalized Carbon Nitride Monolayers adsorption energy per H2 (eV)

system

GGA

GGA +vdW

Li−H2 distance (Å)

C24N32Li3+3H2 C24N32Li3+6H2 C24N32Li3+9H2 C24N32Li6+6H2 C24N32Li6+12H2 C24N32Li6+18H2 C24N32Li8+14H2 C24N32Li8+23H2 C24N32Li8+32H2

−0.190 −0.130 −0.070 −0.138 −0.101 −0.050 −0.073 −0.047 −0.027

−0.290 −0.220 −0.185 −0.230 −0.219 −0.200 −0.251 −0.217 −0.194

2.04 2.11 2.15 2.06 2.12 2.17 2.24 2.29 2.32

H−H bond length (Å)

hydrogen storage capacity (wt %)

0.766 0.761 0.759 0.768 0.760 0.758 0.763 0.760 0.761

0.79 1.56 2.32 1.52 3.00 4.23 3.45 5.42 7.55

table that the H−H bond lengths are slightly longer than those in pure H2, but it suggests molecular adsorption. The average distances of adsorbed H2 to the Li atoms tend to increase with the increase in H2 adsorbed, and the energies are indicative of

Figure 7. Optimized structure of hydrogenated C24N32Li3 monolayer. All lithium atoms and hydrogen molecules are on the same side of the membrane. Black, orange, red, and green balls represent C, N, Li, and H atoms, respectively. 25185


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Figure 8. Optimized structure (extended) of hydrogenated C24N32Li6 monolayer. All lithium atoms and hydrogen molecules are on the same side of the membrane. Black, orange, red, and green balls represent C, N, Li, and H atoms, respectively. The supercell used in the calculations is indicated.

Figure 9. Optimized structure (extended) of hydrogenated C24N32Li8 monolayer. In cases where there are three lithium atoms in a pore, they are all on the same side of the membrane. In cases where there is one lithium atom in the pore it is in the plane of the membrane. Hydrogen molecules are on either side of the membrane. Black, orange, red, and green balls represent C, N, Li, and H atoms, respectively. The supercell used in the calculations is indicated.

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(6) Hussain, T.; Maark, T. A.; De Sarkar, A.; Ahuja, R. Polylithiated (OLi2) functionalized graphane as a potential hydrogen storage material. Appl. Phys. Lett. 2012, 101, 243902−243905. (7) Thomas, A.; Fischer, A.; Goettmann, F.; Antonietti, A.; Müller, J.O.; Schlögl, R.; Carlsson, J. M. Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts. J. Mater. Chem. 2008, 18, 4893−4908. (8) Holst, J. R.; Gillan, E. G. From Triazines to Heptazines: Deciphering the Local Structure of Amorphous Nitrogen-Rich Carbon Nitride Materials. J. Am. Chem. Soc. 2008, 130, 7373−7379. (9) Jürgens, B.; Irran, E.; Senker, J.; Kroll, P.; Müller, H.; Schnick, W. Melem (2,5,8-Triamino-tri-s-triazine), an Important Intermediate during Condensation of Melamine Rings to Graphitic Carbon Nitride: Synthesis, Structure Determination by X-ray Powder Diffractometry, Solid-State NMR, and Theoretical Studies. J. Am. Chem. Soc. 2003, 125, 10288−10300. (10) Dong, G.; Zhang, Y.; Pan, Q.; Qiu, J. A fantastic graphitic carbon nitride (g-C3N4) material: Electronic structure, photocatalytic and photoelectronic properties. J. Photochem. Photobiol., C 2014, 20, 33− 50. (11) Wei, W.; Jacob, T. Strong excitonic effects in the optical properties of graphitic carbon nitrideg-C3N4 from first principles. Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 87, 085202−085207. (12) Algara-Siller, G.; Severin, N.; Chong, S. Y.; Björkman, T.; Palgrave, R. G.; Laybourn, A.; Antonietti, M.; Khimyak, Y. Z.; Krasheninnikov, A. V.; Rabe, J. P.; Kaiser, U.; Cooper, A. I.; Thomas, A.; Bojdys, M. J. Triazine-based graphitic carbon nitride: a twodimensional semiconductor. Angew. Chem., Int. Ed. 2014, 53, 7450− 7455. (13) Fina, F.; Callear, S. K.; Carins, G. M.; Irvine, J. T. S. Structural Investigation of Graphitic Carbon Nitride via XRD and Neutron Diffraction. Chem. Mater. 2015, 27, 2612−2618. (14) Liu, A. Y.; Cohen, M. L. Prediction of new low compressibility solids. Science 1989, 245, 841−842. (15) Nair, A.; Sundara, R.; Anitha, N. Hydrogen storage performance of palladium nanoparticles decorated graphitic carbon nitride. Int. J. Hydrogen Energy 2015, 40, 3259−3267. (16) Ruan, L.; Xu, G.; Gu, L.; Li, C.; Zhu, Y.; Lu, Y. The physical properties of Li-doped g-C3N4 monolayer sheet investigated by the first-principles. Mater. Res. Bull. 2015, 66, 156−162. (17) Zhang, Y.; Sun, H.; Chen, C. New template for metal decoration and hydrogen adsorption on graphene-like C3N4. Phys. Lett. A 2009, 373, 2778−2781. (18) Wu, M.; Wang, Q.; Sun, Q.; Jena, P. Functionalized Graphitic Carbon Nitride for Efficient Energy Storage. J. Phys. Chem. C 2013, 117, 6055−6059. (19) Zhu, G.; Lü, K.; Sun, Q.; Kawazoe, Y.; Jena, P. Lithium-doped triazine-based graphitic C3N4 sheet for hydrogen storage at ambient temperature. Comput. Mater. Sci. 2014, 81, 275−279. (20) Hohenberg, P.; Kohn, W. Inhomogeneous Electron Gas. Phys. Rev. 1964, 136, 864−871. (21) Kresse, G.; Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 59, 1758−1775. (22) Kresse, G.; Hafner, J. Ab initio molecular-dynamics simulation of the liquid-metal−amorphous-semiconductor transition in germanium. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 49, 14251− 14269. (23) Monkhorst, H. J.; Pack, J. D. Special points for Brillouin-zone integrations. Phys. Rev. B 1976, 13, 5188−5192. (24) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865−3868. (25) Grimme, S. Semiempirical GGA-type density functional constructed with a long-range dispersion correction. J. Comput. Chem. 2006, 27, 1787−1799. (26) Bader, R. F. W. Atoms in Molecules - A Quantum Theory; Oxford University Press: Oxford, 1990.

possible), and changing the number of lithium atoms that can be stored on the material. Finally, Wu et al.18 allowed the hydrogen to be adsorbed on both sides of the membrane. Allowing adsorption on both sides will increase the capacity and therefore this possibility has been considered for the C24N32Li8 supercell. A capacity of 7.55 wt % was able to be obtained, and the configuration is shown in Figure 9.

4. CONCLUSION In order to identify a material to store H2 van der Waals corrected DFT calculations on a stable allotrope of the carbon nitride (g-C6N8) monolayer were performed. Like several carbon-based nanostructures, the g-C6N8 monolayer cannot bind H2 in its pristine form; hence, it has been functionalized with Li adatoms. The binding energy of Li to g-C6N8 is calculated to be much higher than the Li atom’s cohesive energy for systems with eight Li atoms on a 2 × 2 supercell, indicating that a stable Li-functionalized g-C6N8 monolayer could potentially be formed without clustering of the Li. The introduction of Li also changes the electronic properties of gC6N8 monolayer by transforming it from a semiconductor into a conductor. Bader charge analysis reveals the existence of a Li cation due to charge transfer from the Li to the monolayer, which can adsorb multiple H2 molecules by electrostatic as well as van der Waals interaction. A maximum capacity of 7.55 wt % is predicted from the calculations by careful tuning of the amount of Li doping and placement of the atoms. The results of H2 adsorption energies indicate that the Li-doped g-C6N8 monolayer is an interesting option for reversible storage of H2 at ambient conditions.

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AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected]; Tel +61 7 33463976. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was undertaken with the assistance of resources provided at the NCI National Facility systems at the Australian National University through the National Computational Merit Allocation Scheme supported by the Australian Government and support from the Queensland Cyber Infrastructure Foundation (QCIF) and the University of Queensland Research Computing Centre. This work was supported by resources provided by The Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia.

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REFERENCES

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Computational Evaluation of Lithium-Functionalized Carbon Nitride (g

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