Electro-Oxidation Reaction of Methanol over La2–xSrxNiO4+δ Ruddlesden–Popper Oxides

Abstract

How materials’ crystalline structure influences the underlying electronic configuration, along with redox properties, and plays a pivotal role in electrocatalysis is an intriguing question. Here, solution combustion-synthesized La2–xSrxNiO4+δ (x = 0–0.8) Ruddlesden–Popper (RP) oxides were explored for an electrocatalytic methanol oxidation reaction. Optimal doping of bivalent Sr2+ in the A site enabled the tetragonal distortion and oxidation of Ni2+ to Ni3+ that resulted ultimately in enhanced covalent hybridization of Ni 3d–O 2p with a closer proximity of the O 2p band to the Fermi level. The RP oxide La1.4Sr0.6NiO4+δ exhibited the highest methanol oxidation reactivity vis-à-vis the formation of HCO2H. The proposed mechanism over La1.4Sr0.6NiO4+δ considers a lattice oxygen-mediated methanol oxidation reaction, owing to Fermi-level “pinning” at the top of the O 2p band, which facilitated lattice oxygen atoms prone to oxidation. A high surface concentration of the key active species of Ni–OOH was observed to form during the methanol oxidation reaction with the help of lattice oxygen atoms and oxygen vacancies in La1.4Sr0.6NiO4+δ. The present study offers a uniquely comprehensive exploration of structural and surface properties of RP oxides toward methanol oxidation reactions.