Development of Electrochemical Anion Doping Technique for Expansion of Functional Material Exploration

Abstract

Instead of conventional cation doping strategy, anion doping is a promising new strategy for advances of energy conversion and storage technologies such as batteries, catalysts, electrolysis, and fuel cells. To synthesize mixed‐anion compounds, novel synthesis techniques such as topochemical reaction, high‐pressure reaction, solvothermal reaction have been developed. Despite these excellent synthesis techniques, synthesizable mixed‐anion compounds are still limited. For further expansion of the material exploration of mixed‐anion compounds, herein, an electrochemical anion doping technique is developed, which can flexibly control a species of anion, the doping rate and the degree of anion doping. The concept of the new synthesis technique is verified by F doping to the perovskite oxide La0.5Sr0.5CoO3−δ. Quantitative control of F in the perovskite host material is succeeded by using an electrochemical reactor composed of La0.5Sr0.5CoO3−δ‐BaF2|BaF2|PbF2‐Pb, and phase‐pure F‐doped La0.5Sr0.5CoO3−δ powder is obtained. Moreover, nano‐size crystalline domains with amorphous phase are formed on the particle surface under the high‐rate F doping, suggesting that tuning the anion doping rate enables the control of the formation of metastable phase. As demonstrated, the electrochemical anion doping technique opens up new possibilities for advances of energy materials by utilizing function of anionic species.

Improved Catalytic Properties of Fluorine-Doped La0.6Sr0.4Co0.2Fe0.8O3-δ for Air Electrode with High-Performance Metal-Air Batteries

“…As displayed in Table S1, F doping increases the lattice parameters along the a, b, and c axes (with the c-axis parameter showing the greatest increase), resulting in volume expansion. Another probable reason for the crystalline expansion is the transformation of the Co(O/F) 6 octahedron due to the reduction of the Co/Fe ion by F doping [15]. In summary, lattice expansion due to F doping results from the charge compensation of anions and changes in the structure of the transition metal oxide; this will be discussed in the following XPS result analysis.…”

“…The O 2− site of perovskite oxide is partially substituted by F − in the presence of F sources, and the M-F-M ligands reduces the transition metals while decreasing their electron valence. Simultaneously, oxygen ions on the surface are activated, inducing highly oxidizing O 2− /O − species, which act as highly catalytic reactive sites for OER/ORR [15]. LSCF is well-known as a commercial material for fuelcell electrodes and various electrochemical energy storage devices, and it has gained attention as a bifunctional catalyst for OER/ORR.…”