Photo-induced water-splitting on hematite (Fe 2 O 3) is investigated by first-principles calculations.

We used density functional theory to study CO oxidation catalyzed by TiO 2 (110), in which some Ti atoms on the surface are replaced with V, Cr, Mo, W, or Mn. We find that in the presence of O, V, Cr, Mo, and W dopants at the surface bind an oxygen atom so that the dopant has formula MO (M ) V, Cr, Mo, W). Rutile doped with Mn does not take an oxygen atom from the gas phase. We find that these materials oxidize CO by a Mars-van Krevelen mechanism in which the role of the dopant is to facilitate the formation of oxygen vacancies. The energy of CO reaction with an oxygen atom from the surface layer decays linearly with the energy of vacancy formation ∆E v , whereas the energy of adsorption of O 2 at a vacancy is a linear function of ∆E v . These are the only two reactions in the mechanism whose energy varies from one doped oxide to another. Because they both depend on the energy of oxygen vacancy formation, the latter quantity is a good descriptor of catalytic activity. In deciding which intermediate reactions are most likely from an energetic point of view, we impose a "spin conservation" rule: a reaction that requires "flipping a spin" is too slow for catalysis. Because of this, we only consider reactions that conserve spin. We find that all the dopants studied here lower the energy of vacancy formation; therefore, the doped oxides are better oxidants than the undoped ones.

We use density functional theory to examine some of the important aspects of methanol oxidation to formaldehyde catalyzed by isolated MO 3 (M ) V, Mo, and Cr) clusters supported on rutile, TiO 2 (110). Thermodynamic analysis led us to conclude that in the presence of oxygen, the M (M ) V, Mo, and Cr) atom takes three oxygen atoms from the gas phase and this MO 3 species is the oxidant in the catalyst. We calculate the structure of these clusters, their Bader charge, the structure of the methoxide formed by methanol adsorption, and the activation energy for the dehydrogenation of the methyl group in the methoxide. We find that VO 3 is a substantially better catalyst than MoO 3 or CrO 3 .

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Enhanced electrocatalytic activity of the oxygen evolution reaction (OER) can be achieved through modulation of the electronic structure of the electrocatalytic active sites. This modulation can also be achieved through stabilization of metastable or non-native polymorphs of the electrocatalyst. Non-native (NN) crystal structures differ in their discrete translational symmetry from the bulk native (N) crystal. The variable oxygen evolution reactivity in a basic medium of different polymorphs is demonstrated by synthesizing β/N-, γ/N-NN1-, r/NN1-, α/NN2-, and δ/NN3-MnO 2 polymorphs of MnO 2 which show different active site densities on the surface, XPS-derived oxidation state of Mn, and bulk electronic conductivity. The specific OER activity [activity per electrochemical surface area (ECSA)] of MnO 2 is codependent on the oxidation state of Mn and electronic conductivity. A volcano-based relationship is observed for the specific OER activity of MnO 2 polymorphs with the universal descriptor ΔG O* − ΔG HO* , computed from density functional theory (DFT). Both δ/NN3-MnO 2 and α/NN2-MnO 2 lie closer to the volcano peak but on opposite legs of the volcano. δ/NN3-MnO 2 shows higher specific activity due to its low oxidation state (+3.5) of Mn, which is confirmed through the calculated average oxidation states (AOS) from XPS and Bader charge from DFT studies. α/NN2-MnO 2 shows higher specific activity due to higher electronic conductivity, which is correlated with its low oxygen vacancy formation energy. Further, the electronic origin of high OER activity in two of the most non-native polymorphs (δ/NN3-MnO 2 and α/NN2-MnO 2 ) is ascribed to a shift in the valence Mn-d band closer to the Fermi level leading to stronger O adsorption. The present study demonstrates the efficacy of utilizing non-native polymorphs for OER and unfolds the correlation between OER and variable oxidation states and electronic conductivities, thereby providing directions toward the generalization of these effects to other polymorphic compounds.

The concentration of Eu 3+ ion/dopant in the LaVO 4 monazite nanocrystal phase cannot be increased by the conventional synthetic procedures. We demonstrate a unique three-step methodology to increase the doping concentration of Eu 3+ in the LaVO 4 monazite nanocrystals. In the first step, Eu 3+ is doped (10%) in the zircon LaVO 4 nanocrystal phase, which does not have a limitation in terms of Eu 3+ ion loading. In the second step, high pressure (∼5 GPa) is utilized to transform the zircon crystal phase to the monazite phase. In the third step, the pressure is brought back to the atmospheric level, wherein it is observed that the monazite crystal phase is retained in its metastable phase with the 10% Eu 3+ ion doping concentration. The phase transitions have been characterized via electrical resistivity data, XRD, Raman spectroscopy, fluorescence spectroscopy, TEM, and density functional simulations.

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An approach to decreasing the overpotential, increasing the stability, and optimizing the noble‐metal composition of electrocatalysts for the oxygen evolution reaction (OER) in acidic media is demonstrated. Essential components of this approach are: 1) combining an active (unstable Ru) component with a dopant (Zn)‐activated passive (stable Ti) element, 2) blending these elements by co‐electrodeposition in an acidic environment in which dissolution of the unstable component (excess Ru) promotes roughness, and 3) further increasing the roughness of the resultant electrode through chemical inhomogeneity by the incorporation of Ti and through structural inhomogeneity by incorporation of Zn in RuO2. The composition of the electrode with the maximal activity is Ru0.258Ti0.736Zn0.006Ox, and its activity is four times higher than that of RuO2. The electrochemical stability towards the OER follows the order RuTiZn>RuTi>RuZn>Ru. This design strategy provides a facile method to improve activity without compromising stability.