Reducibility of ZrO2/Pt3Zr and ZrO2/Pt 2D films compared to bulk zirconia: a DFT+U study of oxygen removal and H2 adsorption

Surface Passivation of LiCoO2 by Solid Electrolyte Nanoshell for High Interfacial Stability and Conductivity

The practical application of lithium cobalt oxide (LiCoO2 ) cathodes at high voltages is hindered by the instability of the surface structure and side reactions with the electrolyte. Herein, we prepared a multifunctional hierarchical core@double-shell structured LiCoO2 (MS-LCO) cathode material using a scalable sol-gel method. The MS-LCO cathode material comprised an outer shell with fast lithium-ion conductivity, a La/Zr co-doped inner shell, and a bulk LiCoO2 core. The outermost shell prevented direct contact between the electrolyte and LiCoO2 core, which alleviated the electrolyte decomposition and loss of active cobalt, while the La/Zr co-doped shell improved the structural stability at higher voltages in a half-cell with a liquid electrolyte. The MS-LCO cathode exhibited a stable capacity of 163.1 mAh g-1 after 500 cycles at 0.5 C, and a high specific capacity of 166.8 mAh g-1 at 2 C. In addition, a solid lithium battery with the surface-passivated MS-LCO cathode and a polyethylene oxide (PEO)-based inorganic/organic composite electrolyte retained 85.8 % of its initial discharge capacity after 150 cycles at a charging cutoff voltage of 4.3 V. Thus, the introduction of a surface-passivating shell can effectively suppress the decomposition of PEO caused by highly reactive oxygen species in LiCoO2 at high voltages.

Probing the nature of Lewis acid sites on oxide surfaces with 31P(CH3)3 NMR: a theoretical analysis

The characterization of catalytic oxide surfaces is often done by studying the properties of adsorbed probe molecules. The ³¹P NMR chemical shift of adsorbed trimethylphosphine, P(CH₃)₃ or TMP, has been used to identify the presence of different facets in oxide nanocrystals and to study the acid-base properties of the adsorption sites. The NMR studies are often complemented by DFT calculations to provide additional information on TMP adsorption mode, bond strength, etc. So far, however, no systematic study has been undertaken in order to compare on the same footing the chemical shifts and the adsorption properties of TMP on different oxide surfaces. In this work we report the results of DFT+D (D = dispersion) calculations on the adsorption of TMP on the following oxide surfaces: anatase TiO₂(101) and (001), rutile TiO₂(110), tetragonal ZrO₂(101), stepped ZrO₂(134) and (145) surfaces, rutile SnO₂(110), (101) and (100), wurtzite ZnO(101̄0), and cubic CeO₂(111) and (110). Beside the stoichiometric surfaces, also reduced oxides have been considered creating O vacancies in various sites. TMP has been adsorbed on top of variously coordinated Lewis acid cation sites, with the aim to identify, also with the support of machine learning algorithms, trends or patterns that can help to correlate the ³¹P chemical shift with physico-chemical properties of the oxide surfaces such as adsorption energy, Bader charges, cation-P distance, work function, etc. Some simple correlation can be found within the same oxide between the ³¹P chemical shift and the adsorption energy, while when the full set of data is considered the only correlation found is with the net charge on the TMP molecule, a descriptor of the acid strength of the adsorption site.

Inverse ZrO2/Cu as a highly efficient methanol synthesis catalyst from CO2 hydrogenation

Enhancing the intrinsic activity and space time yield of Cu based heterogeneous methanol synthesis catalysts through CO₂ hydrogenation is one of the major topics in CO₂ conversion into value-added liquid fuels and chemicals. Here we report inverse ZrO₂/Cu catalysts with a tunable Zr/Cu ratio have been prepared via an oxalate co-precipitation method, showing excellent performance for CO₂ hydrogenation to methanol. Under optimal condition, the catalyst composed by 10% of ZrO₂ supported over 90% of Cu exhibits the highest mass-specific methanol formation rate of 524 g_MeOHkg_cat⁻¹h⁻¹ at 220 °C, 3.3 times higher than the activity of traditional Cu/ZrO₂ catalysts (159 g_MeOHkg_cat⁻¹h⁻¹). In situ XRD-PDF, XAFS and AP-XPS structural studies reveal that the inverse ZrO₂/Cu catalysts are composed of islands of partially reduced 1–2 nm amorphous ZrO₂ supported over metallic Cu particles. The ZrO₂ islands are highly active for the CO₂ activation. Meanwhile, an intermediate of formate adsorbed on the Cu at 1350 cm⁻¹ is discovered by the in situ DRIFTS. This formate intermediate exhibits fast hydrogenation conversion to methoxy. The activation of CO₂ and hydrogenation of all the surface oxygenate intermediates are significantly accelerated over the inverse ZrO₂/Cu configuration, accounting for the excellent methanol formation activity observed.

Enhancing the intrinsic activity and space time yield of Cu based heterogeneous methanol synthesis catalysts is one of the major topics in CO₂ hydrogenation. Here the authors develop a highly active inverse catalyst composed of fine ZrO₂ islands dispersed on metallic Cu nanoparticles.

Enhanced Adhesion Energy at Oxide/Ag Interfaces for Low-Emissivity Glasses: Theoretical Insight into Doping and Vacancy Effects

Low-emissivity glasses rely on multistacked architectures with a thin silver layer sandwiched between oxide layers. The mechanical stability of the silver/oxide interfaces is a critical parameter that must be maximized. Here, we demonstrate by means of quantum-chemical calculations that a low work of adhesion at interfaces can be significantly increased via doping and by introducing vacancies in the oxide layer. For the sake of illustration, we focus on the ZrO₂(111)/Ag(111) interface exhibiting a poor adhesion in the pristine state and quantify the impact of introducing n-type dopants or p-type dopants in ZrO₂ and vacancies in oxygen atoms (nV_O; with n = 1, 2, 4, 8, 10, 16), zirconium atoms (mV_Zr; with m = 1, 2, 4, 8), or both (nV_O + mV_Zr; with m/n = 1:2, 1:4, 2:2, 2:4). In the case of doping, interfacial electron transfer promotes an increase in the work of adhesion, from initially 0.16 to ∼0.8 J m^-2 (n-type) and ∼2.0 J m^-2 (p-type) at 10% doping. A similar increase in the work of adhesion is obtained by introducing vacancies, e.g., V_O [V_Zr] in the oxide layer yields a work of adhesion of ∼1.5-2.0 J m^-2 at 10% vacancies. An increase is also observed when mixing V_O and V_Zr vacancies in a nonstoichiometric ratio (nV_O + mV_Zr; with 2n ≠ m), while a stoichiometric ratio of V_O and V_Zr has no impact on the interfacial properties.

Electronic structure of CuWO4: dielectric-dependent, self-consistent hybrid functional study of a Mott-Hubbard type insulator

CuWO₄ is a semiconducting oxide with interesting applications in photocatalysis. In this paper we present an accurate study of the electronic properties of stoichiometric and oxygen deficient CuWO₄ based on a dielectric dependent hybrid density functional. In CuWO₄ the Cu ions (Cu²⁺) are in a 3d⁹ configuration, so that the material must be classified as a magnetic insulator. Various magnetic configurations of CuWO₄ have been considered, the most stable configuration being anti-ferromagnetic. The band structure, described in terms of density of states (DOS), exhibit the presence of a wide band dominated by W 5d states, separated by about 5 eV from the top of the valence band (VB), consisting of O 2p states partly mixed with Cu 3d states. The empty component of the Cu 3d orbitals forms a narrow band 3.6 eV above the VB maximum. The electronic structure emerging from the DOS curves and the Kohn-Sham energies is hard to reconcile with an experimental band gap of 2.1-2.3 eV. This gap can be rationalized within the Mott-Hubbard model of magnetic insulators, and has been computed from the total energies of the system with one electron removed from the O 2p band and one electron added to the Cu 3d states. Computing the charge transition levels for CuWO₄, we come to a theoretical band gap of 2.1 eV, in excellent agreement with the experimental observations. We also studied the nature of the oxygen vacancy in CuWO₄ with particular attention to the electron redistribution following the oxygen removal. The excess electrons, in fact, can occupy the localized 3d states of Cu or the localized 5d states of W. The resulting solution depends on various factors, including the concentration of oxygen vacancies.

Controlling the charge state of supported nanoparticles in catalysis: lessons from model systems

Model systems are very important to identify the working principles of real catalysts, and to develop concepts that can be used in the design of new catalytic materials.