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Direct methanol fuel cell (DMFC) running on hydrogen is an attractive alternative power source for a wide range of applications. Importantly, the required hydrogen can be in situ released from the stable liquid, which ensures its safe transformation and storage. However, the catalyst in DMFC is usually poisoned by the generated CO species, thus it is challenging to find an efficient and durable catalyst for practical applications. Here, the mechanism of methanol oxidation reaction (MOR) on the Mo2P monolayer is first studied using density functional theory. Compared with the initial C–H and C–O bond scissions, the initial O–H bond scission is found to be the most favorable. The reason is systematically analyzed based on steric effect, activation Gibbs free energy (Gact) decomposition and the Bronsted − Evans − Polanyi (BEP) relationships. The further dehydrogenation of CH2OH via the O–H bond scission has a significantly lower Gact than that of CH3O, thus the methanol decomposition on the Mo2P monolayer may proceed via two competitive pathways, i.e., CH 3 OH → CH 3 O → CH 2 O → CHO → CO and CH 3 OH → CH 2 OH → CH 2 O → CHO → CO . Then, through overcoming a relatively low barrier, the generated CO species can be combined with hydroxyl group from water dissociation on the Mo2P monolayer to produce formic acid, which can be easily desorbed from the catalyst surface to avoid the block of active sites. This study provides a better understanding of the MOR mechanism and paves the way for further advancing the catalyst in DMFCs.

The main objective of this study is density functional theory investigations on adsorption and decomposition of N 2 O on ZnO(0001)-G nanocomposite. The adsorption and decomposition of small molecules on the magnetic oxides containing transition metals are relatively rare due to the modeling difficulties using current density functional approximations. A molecular modeling of the reaction mechanism was studied in this work through ab initio modeling of the catalytic adsorption and decomposition of N 2 O on ZnO(0001)-G. DFT was used to study the molecular mechanism of conceivable elementary steps of the decomposition of N 2 O over the most stable (0001) surface. Three reactions including the N 2 O bond cleavage, the oxygen atom transfer, forming a surface peroxy group O 2 2− were studied. The horse-like (N N O), parallel (N N O) and lying-atop-011 (O N N) with all three atoms of the N 2 O molecule interacting with the surface have been found as more stable adsorption forms, which have adsorption energies of −0.27, −0.23 and −0.23 eV, respectively. The activation energies of the N 2 O decomposition through mentioned reactions were found to be 2.73, 0.48 and 0.63 eV, respectively. The obtained results reveal that ZnO(0001)-G is not only an efficient but also a green catalyst in comparison with others such as Mn-G.

A new category of two-dimensional electrode materials, i.e., V2Ch2O (Ch = S, Se and Te) monolayers was explored for K-ion batteries (PIBs) based on principle of chemical exfoliation, density functional theory and ab initio molecular dynamics simulations. The V2Ch2O monolayers show low cleavage energies and excellent thermal, dynamical and mechanical stabilities. Adsorption energies of a potassium atom on the V2Ch2O monolayers are exothermic, which are of benefit to prevent forming dendrites. The existence of electrode potentials substantially decreases the diffusion barriers of potassium atoms on the three V2Ch2O monolayers. The V2Ch2O monolayers are able to maintain their metallic characteristics and single surface phase during the whole K-intercalation process, avoiding the decrease in electronic conductivity and the appearance of potential hysteresis. The theoretical specific capacities of the V2S2O, V2Se2O and V2Te2O monolayers are predicted to be 883.6, 583.1 and 431.0 mAh g−1, respectively, and the corresponding average open-circuit voltages are 0.449, 0.390 and 0.293 V, respectively. The maximum percentage changes in lattice parameters are 4.21%, 6.07% and 7.26% for the V2S2O, V2Se2O and V2Te2O monolayers, respectively. All the calculated properties indicate that the V2Ch2O monolayers are promising electrode materials for PIBs with high capacities and long cycle lives.

Calcium sulfate hemihydrate (CaSO 4 ·0.5H 2 O, CSH) whiskers with high aspect ratio are promising reinforce materials which have drawn much attention. In order to obtain high quality CSH materials, effect of Mg 2+ ions on properties of the (0 0 2), (2 0 0) 1 and (2 0 0) 2 planes of CSH is investigated using an ab initio density functional theory (DFT) with a van der Waals (vdW) dispersion-correction. The computed results show that strong adsorption and substitution effects take place between Mg 2+ ion and (2 0 0) 1 plane. The adsorption energies of an Mg 2+ ion on the (0 0 2), (2 0 0) 1 and (2 0 0) 2 planes are −0.066, −0.571 and −0.047 eV, respectively. An insight into the electrostatic potential of pristine CSH planes has demonstrated that the (2 0 0) 1 plane is much more negatively charged than the (0 0 2) and (2 0 0) 2 planes. The energies of the substitution of a Ca atom with an Mg atom on the CSH (0 0 2), (2 0 0) 1 and (2 0 0) 2 planes are 1.572, 0.063 and 1.349 eV, respectively. It is found that Ca atoms on the (2 0 0) 1 plane are relatively easy to be substituted by Mg atoms. The calculation results of a Ca 2+ ion adsorption on the Mg-doped (2 0 0) 1 plane indicate that the adsorption energies increase apparently as the doping ratio varies from 0 to 1.0. Compared with K + , Na + and Al 3+ ions, Mg 2+ ion is the most promising additive to promote the growth of CSH along c axis.

Catalytic conversion of non-CO2 green house gases and other harmful gases is a promising way to protect the atmospheric environment. Non-metal atom-doped graphene is attractive for use as a catalyst in the conversion due to its unique electronic properties, relatively low price and leaving no burden to the environment. To make an attempt on the development of green catalysts for the conversion, ab initio density functional theory is used to investigate the mechanisms of N2O reduction by CO on Si- and Se-doped graphenes. We have calculated the geometries and adsorption energies of reaction species (N2O, CO, N2 and CO2) as well as energy profiles along the reaction pathways. The activation energies of N2O decomposition and CO oxidation on both Si- and Se-doped graphenes have been obtained. Our calculated results indicate that the catalytic activity of Si-doped graphene is better than the Fe+ in gas phase and comparable to the single Fe atom embedded on graphene. In the calculations, we found that van der Waals interactions and zero-point energy are two non-negligible factors for the predictions of the activation energies. Further discussion shows that Si-doped graphene can be one of efficient green catalysts for conversion of the airborne pollutants and Se-doped graphene can be a candidate for oxidizing CO by atomic oxygen.

By density functional theory (DFT) calculations, the early stages of the growth of graphene on copper (1 1 1) surface are investigated. At the very first time of graphene growth, the carbon atom sinks into subsurface. As more carbon atoms are adsorbed nearby the site, the sunken carbon atom will spontaneously form a dimer with one of the newly adsorbed carbon atoms, and the formed dimer will up-float on the top of the surface. We emphasize the role of the co-operative relaxation of the co-adsorbed carbon atoms in facilitating the sinking and up-floating of carbon atoms. In detail: when two carbon atoms are co-adsorbed, their co-operative relaxation will result in different carbon–copper interactions for the co-adsorbed carbon atoms. This difference facilitates the sinking of a single carbon atom into the subsurface. As a third carbon atom is co-adsorbed nearby, it draws the sunken carbon atom on top of the surface, forming a dimer. Co-operative relaxations of the surface involving all adsorbed carbon atoms and their copper neighbors facilitate these sinking and up-floating processes. This investigation is helpful for the deeper understanding of graphene synthesis and the choosing of optimal carbon sources or process.

Adsorption of carbon monoxide on different Ag + -exchange sites of Ag–ZSM-5 zeolite has been investigated using density functional theory. The coordination and local geometry of the Ag + ion in Ag–ZSM-5 as well as adsorption structures and energies of CO adsorbed on these sites are explored extensively. The structure of Ag + -exchange sites, location of the Al atom on the T site, and number of the Al atoms contained in the sites are considered in the theoretical calculations. The calculated results show that the Ag O coordination number of two is strongly preferred before and after CO adsorption. The Ag O bond lengths are in a broad range of 2.2–2.9 A, and the Ag C bond lengths for CO adsorbed on Ag–ZSM-5 zeolite are calculated to be 2.0–2.2 A. Both Ag O and Ag C bond lengths for CO–Ag–ZSM-5 complex are longer than those for CO–Cu–ZSM-5 complex. The calculated adsorption energy of CO adsorbed on the I2 sites is between 28.5 and 29.6 kcal/mol, and that on the Z5, Z6, M5 and M6 sites containing one Al atom on the T position is between 11.3 and 18.9 kcal/mol whereas the calculated adsorption energy of CO adsorbed on the M7 site containing one Al atom is 19.9 kcal/mol. The introduction of the two Al atoms to the Ag + -exchange site results in a reduction of CO adsorption energy. In general, the adsorption energy of CO on Ag–ZSM-5 is lower than that on Cu–ZSM-5. The predicted coordination of the Ag + ion, bond lengths of Ag O and Ag C as well as adsorption energy are in accord with available experimental results.