Using the DFT+U method, i.e., first principles density functional theory calculations with the inclusion of on-site Coulomb interaction, the effects of Pd doping on the O vacancy formation energy (E(vac)) in CeO(2) has been studied. We find that E(vac) is lowered from 3.0 eV in undoped ceria to 0.6 eV in the Pd-doped compound. Much of this decrease can be attributed to emerging Pd-induced gap states above the valence band and below the empty Ce 4f states. These localized defect states involve the Pd ion and its nearest neighbors, which are also the main acceptors of the extra electrons left on reduction. The effect of the Pd dopant on the geometric structure is very modest for CeO(2) but considerable for CeO(2-x).

One great challenge for supercapacitor is to achieve high energy capacity and fast charge/discharge rates simultaneously. Porous graphene with large surface area is a promising candidate for electrode materials of supercapacitor. Using first-principles calculations and non-equilibrium Green's function technique, we have explored the formation energies, mechanical properties, diffusion behaviors and electrical conductance of graphene sheets with various hole defects and/or nitrogen doping. Interestingly, graphene sheets with pyridinic-like holes (especially hexagonal holes) can be more easily doped with nitrogen and still retain the excellent mechanical properties of pristine graphene that is beneficial for the long cycle life. Porous graphene electrode with moderate hole diameter of 4.2-10 Å facilitates efficient access of electrolyte and exhibit excellent rate capability. In addition, doping with nitrogen as electron donors or proton attractors leads to charge accumulation and generates higher pseudocapacitance. Transmission coefficients of N-doped graphene sheets with pyridinic-like holes are only moderately reduced with regard to that of pristine graphene and are insensitive to the detailed geometry parameters. Overall, N-doped graphene with pyridinic-like holes exhibits exciting potentials for high performance energy storage in supercapacitor devices.

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The effects of noble metal (NM) dopants (NM = Pt, Rh) on the structural and electronic properties of ceria are studied using a density functional theory (DFT) method, with the inclusion of on-site Coulomb interaction (DFT+U). It is found that these NM dopants give rise to large perturbations of the atomic and electronic structures of ceria and induce metal-induced gap states at the Fermi level suitable for accommodating extra electrons, thereby lowering the reduction energy of ceria and making the NM-doped cerias more reducible than pure ceria. This mechanism for facilitating the reduction of ceria is different from that of Zr-doped ceria where the increased reducibility is largely due to the structural distortions and not to electronic modifications.

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Layered transition-metal oxides, LiMn x Co y Ni 1-x-y O 2 , have been considered as potential cathode materials for lithium batteries with high energy density. The crystal structures, reversible potentials and activation energies of LiMn x Co y Ni 1−x−y O 2 are studied by means of density functional theory (DFT) calculations within generalized gradient approximation (GGA) and projector-augmented-wave (PAW) method. The larger cell volume with increasing Ni content benefits the capacity of the cathode materials. Sufficient amount of Ni content in the LiMn x Co y Ni 1-x-y O 2 is beneficial for stabilizing the electrode voltage. Ni substitution is always beneficial to Li diffusion, whereas existence of Mn ions may hinder Li motion by increasing the activation energy. All these first-principles results reveal some general trends for the synergistic effects of TM ions and may guide finding optimal compositions in future experiments.

The effects of transition metal (TM) doping on Li-vacancy formation energies and electrode potentials of Li2S cathode materials for lithium batteries are investigated using first-principles calculations with density functional theory. In addition, the geometric and electronic structures for 1.56 at. % Fe-doped lithium sulfide are analyzed to further reveal the TM-doping effect. We find that Evac can be only moderately enhanced by the increasing atomic number of TM dopant. The Evac is lowered from 3.37 eV in pure Li2S to about 1.11–1.23 eV in the Fe-doped compounds. Such decrease can be mainly attributed to the electronic structures. Compared with Li2S, the downtrend of reversible electrode potential (U) value in the Cu-doped systems is indistinctive with increase in the dopant contents.

Herein, two-dimensional materials for photocatalytic water splitting are drawing more attention due to the larger surface areas for photocatalytic reactions and shorter migration distances for photogenerated carriers. In this present study, we systematically investigated the fundamental electronic properties of GaSTe monolayers (x = 0, 0.125, 0.25, 0.5, 0.75, 0.875, and 1) for water splitting based on density functional theory (DFT) using the HSE06 functional. The simulation of the defect formation energy under each experimental synthetic condition shows that the Te substitutional impurity in GaS can be relatively easily realized under Ga-rich conditions. Our results show that the GaSTe monolayer is a direct band gap (2.09 eV) semiconductor, which is attributed to the elevation of Te p/p states at the Γ point by the strain effect. Moreover, the GaSTe monolayer has appropriate band edge alignment with respect to the water redox potentials in both acidic and neutral environments. Additionally, the carrier effective mass of the GaSTe monolayer along the direction of Γ → K is smaller than those of pristine GaS and GaTe monolayers, which can cause the carriers to quickly transfer from the photogenerated center to the surface of the photocatalyst. These results imply that the GaSTe monolayer is a promising candidate as a visible-light water splitting photocatalyst, which should be properly synthesized and tested in further experimental investigations.