Identifying suitable electrodes materials with desirable electrochemical properties is urgently needed for the next generation of renewable energy technologies. Here we report an ideal candidate material, Mo2C monolayer, with not only required large capacity but also high stability and mobility by means of first-principles calculations. After ensuring its dynamical and thermal stabilities, various low energy Li and Na adsorption sites are identified, and the electric conductivity of the host material is also maintained. The calculated minor diffusion barriers imply a high mobility and cycling ability of Mo2C. In addition, the Li-adsorbed Mo2C monolayer possesses a high theoretical capacity of 526 mAh·g(-1) and a low average electrode potential of 0.14 eV. Besides, we find that the relatively low capability of Na-adsorbed Mo2C (132 mAh·g(-1)) arises from the proposed competition mechanism. These results highlight the promise of Mo2C monolayer as an appealing anode material for both lithium-ion and sodium-ion batteries.

To enhance the photocatalytic activity of monoclinic BiVO4 for O2 evolution from water, Ce-doped BiVO4 was prepared using the one-pot facile solvothermal method and characterized via XRD, Raman, XPS, and electrochemical impedance spectroscopy (EIS). The XPS spectra confirm that Ce component is Ce3+ ions instead of Ce4+ ions. From the structural characterization and the calculations of formation energies it has been stated that the doping of Ce3+ ions takes place at Bi3+ sites without changing the host structure. The as-prepared Ce-doped BiVO4 samples display significantly enhanced photocatalytic O2 evolution activities from water compared to pristine BiVO4. Density of states calculations indicate that Ce3+ ions act as hole traps, thereby delaying the recombination of photogenerated electrons and holes. The results demonstrate that the substitution of the remaining monoclinic crystal structure may offer an attractive alternative approach for the doping of BiVO4 to enhance the evolution activity of photocatalytic O2.

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Graphane, graphone and hydrogenated graphene (HG) have been extensively studied in recent years due to their interesting properties and potential use in commercial and industrial applications. The present study reports investigation of hydrogenated graphene/TiO 2-x (HGT) nanocomposites as photocatalysts for H 2 and O 2 production from water without the assistance of a noble metal co-catalyst. By combination of several techniques, the morphologies, bulk/atomic structure and electronic properties of all the powders were exhaustively interrogated. Hydrogenation treatment efficiently reduces TiO 2 nanoparticles, while the graphene oxide sheets undergo the topotactic transformation from a graphene-like structure to a mixture of graphitic and turbostratic carbon (amorphous/disordered) upon altering the calcination atmosphere from a mildly reducing to a H 2 -abundant environment. Remarkably, the hydrogenated graphene-TiO 2-x composite that results upon H 2 -rich reduction exhibits the highest photocatalytic H 2 evolution performance equivalent to low loading of Pt (~0.12 wt%), whereas the addition of HG suppresses the O 2 production. We propose that such an enhancement can be attributed to a combination of factors including the introduction of oxygen vacancies and Ti 3+ states, retarding the recombination of charge carriers and thus, facilitating the charge transfer from TiO 2-x to the carbonaceous sheet.

The electronic structure and related photocatalytic properties of Bi2MO6 (M = W, Mo) with various intrinsic defects are studied based on the first-principles density functional theory (DFT). Our results indicate that O vacancies form easily in both Bi2WO6 and Bi2MoO6 under Bi rich/O poor conditions. The near-infrared light transitions can be realized involving electrons from the O vacancy induced impurity states within the band gap to the conduction band. Rather than acting as photogenerated carrier recombination centers, the impurity states caused by O vacancies favor the transfer of photogenerated holes and further benefit the photocatalytic process due to the delocalized nature. The spatial separation of photogenerated carriers among different layers can be realized, which reduces the carrier recombination and improves the photocatalytic activity. In addition, Bi2WO6 with O vacancies is desirable for having better near-infrared photocatalytic performance than Bi2MoO6 due to the larger mobility of photogenerated holes.