Vanadium oxynitrides as stable catalysts for electrochemical reduction of nitrogen to ammonia: the role of oxygen
JOURNAL OF MATERIALS CHEMISTRY A
Authors: Pan, Jaysree; Hansen, Heine Anton; Vegge, Tejs
Abstract
Electrochemical reduction of nitrogen to ammonia can potentially replace the existing centralized fossil fuel-based Haber-Bosch process with small, decentralized units relying on electrical energy from renewable sources, thus supporting a sustainable food and energy infrastructure. Recent activities in the development of transition metal nitride electrocatalysts for this reaction have shown promise, but oxynitrides remain unexplored. We have performed a rigorous computational study of the highly promising vanadium oxynitride (VON) to establish for the first time the nitrogen reduction pathway in oxynitrides and the role of the mixed anions that can lead to improved stability of the active surface-states, activity, and selectivity over hydrogen evolution. The electrocatalytic properties are best enhanced at low oxygen content (12.5%) due to optimal balance between consecutive protonation preference at N-sites over V-sites, low onset potential (0.4 V-RHE), and facile N-2 adsorption at N-vacancy sites, while a higher oxygen containing VON (31.25%) shows the lowest N-2 adsorption/dissociation barrier (similar to 0.3 eV) on the anion vacancy and can also be a potential N2RR catalyst with a higher NH3 turn over frequency, albeit with a lower stability and higher overpotential (0.6 V-RHE) compared to x = 12.5%. The critical N-vacancy active sites are protected from self-annihilation by the mixed-valency anions, large kinetic barriers, and site blocking by O*/OH*/H* due to highly favorable N-2 absorption.
Facile synthesis of alpha-Zn2V2O7 and its catalytic role for the photo mediated conversion of benzyl alcohol
MATERIALS LETTERS
Authors: Shrivastava, Vipul; Nagarajan, Rajamani
Abstract
The hydroxide co-precipitation approach is demonstrated to prepare Zn2V2O7 in a reproducible and straightforward manner. Based on the structural refinement of the PXRD pattern along with FTIR, Raman spectra, and microscopic analysis, the thortveitite structure for Zn2V2O7 is confirmed. The sample shows a surface area of 45.3 m(2)/g (BET) and has pores with a mean pore diameter of 30.9 nm. The V5+-O2- charge transfer transition manifests as intense absorbance in the UV region, yielding a bandgap of 2.9 eV. The sample catalyzed the photo-oxidation of benzyl alcohol to benzaldehyde (86%) and benzoic acid (14%) in 120 min. (C) 2020 Elsevier B.V. All rights reserved.