Electrochemical Fluorination of La₂CuO₄: A Mild “Chimie Douce” Route to Superconducting Oxyfluoride Materials

Abstract

The fluorination of La(2)CuO(4) was achieved for the first time under normal conditions of pressure and temperature (1 MPa and 298 K) via electrochemical insertion in organic fluorinated electrolytes and led to lanthanum oxyfluorides of general formula La(2)CuO(4)F(x). Analyses showed that, underneath a very thin layer of LaF(3) (a few atomic layers), fluorine is effectively inserted in the material's structure. The fluorination strongly modifies the lanthanum environment, whereas very little modification is observed on copper, suggesting an insertion in the La(2)O(2) blocks of the structure. In all cases, fluorine insertion breaks the translation symmetry and introduces a long-distance disorder, as shown by electron spin resonance. These results highlight the efficiency of electrochemistry as a new "chimie douce" type fluorination technique for solid-state materials. Performed at room temperature, it additionally does not require any specific experimental care. The choice of the electrolytic medium is crucial with regard to the fluorine insertion rate as well as the material deterioration. Successful application of this technique to the well-known La(2)CuO(4) material provides a basis for further syntheses from other oxides.

Fluoride ion batteries – past, present, and future

“…The other example is the electrochemical fluorination of La2CuO4 in a classic three-electrode configuration using organic fluorinated electrolytes (in liquid state) and gold foil and Pt wire as counter and reference electrodes, respectively. 137 In this work, it was reported that 0.18 fluoride ions had been electrochemically inserted in the vacant interlayers of La2CuO4, resulting in an increase in the parameter c of the cell from 13.141 Å to 13.205 Å. The results were in good agreement with what was found using chemical fluorination methods using F2 gas.…”

Topochemical Fluorination of La2NiO4+d: Unprecedented Ordering of Oxide and Fluoride Ions in La2NiO3F2

“…Compounds with the Ruddlesden–Popper-type structure A n +1 B n O 3 n +1 are known for a variety of functional properties, among them superconductivity − and catalytic, ferroelectric, and magnetic , properties. The member with n = 1 (A 2 BX 4 , often referred to as K 2 NiF 4 -type structure) can be understood as being built of alternating layers of perovskite ABX 3 and rock salt AX layers.…”

Role of precursor chemistry in the direct fluorination to form titanium based conversion anodes for lithium ion batteries

“…4,6 Although conversion materials have been studied for decades the underlying mechanisms of these conversion reactions are still not well understood. [7][8][9] Fluorination reactions to form the electrode materials can be performed by a variety of methods including precipitation from a uorinated solution, reaction with HF, 10 direct reaction with F 2 (g), solid-state reactions with a uorinating agent such as NH 4 F, CuF 2 , ZnF 2 , XeF 2 , AgF 2 or NH 4 HF 2 , 11,12 electrochemical uorination 13 and reaction with poly(vinylidene uoride) (PVDF). 14 Experimental conditions including reaction time, temperature and uorine concentration can be used to control the level of uorine insertion and the homogeneity of the products.…”