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

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+delta (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+delta exhibited the highest methanol oxidation reactivity vis-a-vis the formation of HCO2H. The proposed mechanism over La1.4Sr0.6NiO4+delta 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+delta. The present study offers a uniquely comprehensive exploration of structural and surface properties of RP oxides toward methanol oxidation reactions.

Automated summary

The study demonstrates that optimal doping of Sr2+ in La1.4Sr0.6NiO4+delta leads to the highest reactivity for methanol oxidation, with a lattice oxygen-mediated reaction mechanism facilitating the process.