Electrochemically Induced Phase Changes in La2CuO4 During Cathodic Electrocatalysis. Issue 19 (14th October 2019)

• Record Type: Journal Article
• Authors: Whittingham, Alexander W. H.; Smith, Rodney D. L.
• Is Part Of: ChemElectroChem. Volume 6:Issue 19(2019)
• Page Start: 5116
• Page End: 5123
• Publication Date: 2019-10-14
• Subjects: perovskite -- electrocatalysis -- amorphization; Electrochemistry -- Periodicals; 541.37
• DOI: 10.1002/celc.201901412
• Languages: English
• ISSNs: 2196-0216

Abstract

Abstract: The ability of layered perovskites to accommodate both oxygen vacancies and hyperstoichiometry provides a dimension of tunability that makes them appealing for electrocatalytic applications, but the resulting ionic conductivity enables electron transfer reactions within bulk crystals. We report on the stability of La2 CuO4 in the voltage regimes relevant to oxygen reduction, hydrogen evolution and CO2 reduction. Voltammetric experiments, X‐ray photoelectron spectroscopy and X‐ray diffraction reveal both surface and bulk electron transfer reactions. Application of anodic voltages results in expansion in the crystal c‐axis, while cathodic voltages induce contraction. The ability to catalyze each of the three cathodic reactions is confirmed, but X‐ray diffraction and electron microscopy reveal amorphization of the electrocatalyst at voltages below −0.4 V that affects both the oxygen reduction and CO2 reduction reactions. While the ionic conductivity of Ruddlesden Popper oxides introduces intriguing properties, it simultaneously introduces the risk of structural instability in catalytically relevant voltages. Abstract : Examination of the aqueous electrochemistry of La2 CuO4 over a wide voltage window reveals a series of electrochemically induced phase transitions. In addition to the well‐documented structural expansion that accompanies insertion of interstitial oxide ions upon electrochemical oxidation, the unit cell of the layered perovskite contracts when electrochemically reduced at moderate voltages, and amorphizes at more extreme voltages. Amorphization occurs at voltages relevant to CO2 reduction and lead to loss in catalytic performance.