Electrochemically Induced Phase Changes in La₂CuO₄ During Cathodic Electrocatalysis

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 La 2 CuO 4 in the voltage regimes relevant to oxygen reduction, hydrogen evolution and CO 2 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 À 0.4 V that affects both the oxygen reduction and CO 2 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.[a] A.

How Cation Substitutions Affect the Oxygen Reduction Reaction on La2−xSrxNi1−yFeyO4

“…This confirms that Fe‐doping is critical to the observed changes in electrocatalytic behavior. Electrocatalytic performance is frequently tied to catalyst instability, a feature which has been observed for related La 2 CuO 4 materials [26,27] . All samples in the La 2−x Sr x Ni 0.7 Fe 0.3 O 4+δ series exhibit a red shift in the A 1g (La−O) mode following 30 minutes of electrolysis (Figure 6B) and the magnitude of shift correlates to the onset of ORR observed in RRDE experiments (Figure 7E).…”

“…Electrocatalytic performance is frequently tied to catalyst instability, a feature which has been observed for related La 2 CuO 4 materials. [26,27] All samples in the La 2À x Sr x Ni 0.7 Fe 0.3 O 4 + δ series exhibit a red shift in the A 1g (LaÀ O) mode following 30 minutes of electrolysis (Figure 6B) and the magnitude of shift correlates to the onset of ORR observed in RRDE experiments (Figure 7E). The defect-induced feature at 610 cm À 1 correlates negatively to the average number of electrons transferred in the second ORR plateau, which is the voltage region in which electrolysis was performed (Figure 7F).…”

Perovskite Oxides for Cathodic Electrocatalysis of Energy‐Related Gases: From O2 to CO2 and N2

“…For example, in one of the recent studies, the irreversible contraction of La 2 CuO 4 was observed at a more negative potential than −0.4 V, and the resultant amorphization was believed to deteriorate its activity toward CO 2 RR. [ 27 ] Differently, Singh and co‐works reported that La 2 CuO 4 could break into La 2 O 3 and Cu 2 O. [ 108 ] The resulting Cu 2 O, which further underwent reduction and formed Cu metal in a reversible way, was considered to be responsible for the high selectivity toward C 2 H 4 .…”

“…Notably, perovskite oxides show advantages for CO 2 RR and NRR, such as the good adjustability in physicochemical properties, the high tolerances to both interstitial oxygen and oxygen vacancies, as well as economic and environmental friendliness, when compared with other catalysts. [26,27] Nevertheless, with insufficient studies, perovskite oxide-based electrocatalysts require further development, and breakthroughs are expected by understanding the catalytic trend on perovskite oxides.…”

Cation‐Deficiency‐Dependent CO2 Electroreduction over Copper‐Based Ruddlesden–Popper Perovskite Oxides

“…[11,12] On this basis,i fo ne could substitute the Cu element into the B-site cations of the RP perovskite oxides,t hey are anticipated to provide attractive CER catalytic properties.Asdemonstrated by af ew previous studies,t ypical examples including A 1.8 Sr 0.2 CuO 4Àd (A = La, Pr, and Gd) as well as La 2 CuO 4Àd were active toward the CER for the formation of high-order products. [14][15][16][17][18] Nonetheless,w ith the insufficient studies,t he Cu-based RP perovskite oxides for CER are in their infancy, but their catalytic performance is supposed to have plenty of space to promote.T ot his end, there is an urgent need for further rational design and development of highly efficient Cu-based RP perovskite oxides for CER.…”