Sunlight-driven CO2 hydrogenation has drawn tremendous attention. However, selective CH4 formation via CO2 photoreduction is very challenging. Herein, we report a metal oxide semiconductor heterojunction consisting of BiVO4 and WO3 as a photocatalyst for the efficient conversion of carbon dioxide (CO2) selectively to methane (105 μmol g–1 h–1) under visible light in the absence of a sacrificial agent. Wise selection of the reaction medium and the strategically tuned heterojunction upon strain relaxation suppresses the competitive hydrogen generation reaction. The detailed photophysical, photoelectrochemical, and X-ray absorption spectroscopy studies pointed to the Z-scheme mechanism of electron transfer, which favors superior electron and hole separation compared to the individual components of the composite catalyst and other well-known photocatalysts reported for CO2 reduction. The observations are further corroborated by experimental diffuse reflectance infrared Fourier transform spectroscopy and theoretical density-functional theory calculations, which reveal that the heterojunction has a lower free-energy barrier for CO2 conversion to CH4 due to the larger stabilization of the *CH2O intermediate on the strain-relaxed heterojunction surface, in comparison to the pristine BiVO4 surface. The present work provides fundamental insights for constructing high-performance heterojunction photocatalysts for the selective conversion of CO2 to desired chemicals and fuels.

A facile non-template-assisted mechanical ball milling technique was employed to generate a PdBi alloy catalyst. The induced lattice strain upon the milling time caused a shift of the d-band center, thereby enhancing the oxygen reduction reaction (ORR) catalytic activity. Additionally, the Pd–O reduction potential and adsorbed OH coverage used as descriptors stipulated the cause of the enhanced ORR activity upon the increased milling interval. Redox properties of surface Pd are directly correlated with a positive shift in the Pd–O reduction potential and OH surface coverage. Hence, by deconvoluting the lattice strain and the role of the descriptor species we achieved a catalyst system with a specific activity 5.4× higher than that of commercial Pt/C, as well as an improved durability. The experimental observation is well-corroborated by a theoretical simulation done by inducing strain to the system externally.

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Ni1-x(Zn1/2Zr1/2)xW1-xNbxO4 (x = 0.0-1.0) compositions were synthesized via conventional solid-state reaction method. Structural and lattice vibrational characteristics of these compositions were studied with the help of powder X-ray diffraction and Raman spectroscopic measurements. Rietveld refinements confirm the formation of all these compositions in monoclinic wolframite structure with P2/c space group. When moving towards Ni(2+)-poor compositions, splitting in the X-ray reflections was observed and is explained with lattice parameter variation. With increasing value of x, Raman spectra show two additional Raman active modes and the possible reasons for observing these modes are discussed in terms of electronegativity difference of the randomly distributed cations in B-site of these compositions. X-ray photoelectron spectroscopic measurements were done to understand the chemical bonding states of different elements in these compositions. Surface morphology studies reveal that the average grain size increases with increasing x. Microwave dielectric properties such as dielectric constant and quality factor were measured using Hakki-Coleman and reflection cavity techniques and enhancement in these values with x is correlated with intrinsic parameters such as polarizability and 3d electrons present in the constituent ions of these compositions. Temperature coefficient of resonant frequency was measured using an invar cavity attached to a programmable hot plate and is explained with B-site octahedral distortion of these compositions. Well dense Ni1-x(Zn1/2Zr1/2)xW1-xNbxO4 (x = 0.0-1.0) compositions possess good microwave dielectric properties.

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