Surface oxygen exchange of LaSrCoO

Abstract

The surface oxygen exchange of Lao.3Sro,, Co0,_6 has been studied by 'SO/'hO exchange followed by dynamic SIMS analysis in the temperature region 700-900°C at a po, of 2.1 X lo4 Pa. The activation energy for the surface exchange rate (k) is 283 kJ mol -' and for the oxygen tracer diffusion coefficient (D *) 56t4 kJ mol-' The absolute values for both k and D * are among the highest known in the literature. The characteristic thickness at a po, of 2.1 X lo4 Pa is calculated to lie in the range 0.70 to 1.3 mm and is a function of temperature. The latter reflects the different activation energies for k and D*. The surface oxygen exchange coefficient is proportional to p& with n =0.41 to.02 at WYC, which has been explained by a rate determining step involving an adsorbed oxygen species and an oxygen vacancy. No oxygen pressure dependence for the tracer diffusion coefficient was observed at this temperature.

Direct Observation of Rate Determining Step for Nd2NiO4+^|^delta; SOFC Cathode Reaction by operando Electrochemical XAS

“…In contrast, when the electrode reaction is governed by bulk diffusion or ion transfer at the electrode/electrolyte interface, the oxygen potential profile should be as shown in (iii) Previously, the impedance measurement and the isotopic exchange depth profile coupled with secondary ion mass spectroscopy measurement implied the rate-determinig step is surface reactionis for (La, Sr)CoO 3 system. 18,20 The experimental results in this study are good agreement with the previous studies and provide direct evidence for the rate-determining step of surface reactions in SOFC cathode reaction. Enhancing surface reactions is the most important strategy for further improvement of cathode materials.…”

Materiales conductores mixtos para la Oxidación Parcial de Hidrocarburos

“…On the contrary, surface exchange control yields values of j independent of the membrane thickness, whereas JO 2 increases with thickness. Changes both in j and JO 2 with membrane thickness indicate mixed control, which occurs when the thickness of the membrane is close to a critical value L c =k/D, k being a surface exchange coefficient and D the diffusion coefficient [4]. A numerical method was used to solve Eqs.…”

“…The fractions of hydrogen and CO typically reach maxima at pO 2 close to 10 -20 atm and then decrease for more oxidising conditions, yielding CO 2 and H 2 O. These stability requirements are excessive for mixed conducting materials based on LaCoO 3 [3][4][5], (Fig.2). Other materials (e.g.…”

“…A relatively wide range of mixed conductors has been studied for these membrane reactors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], including single phase and composite materials consisting of a metallic conductor and a good ionic conductor. This concept is widely discarded because these composite materials are either based on noble metals of prohibitive cost, or fail to meet the required stability (e.g.Ag/Bi(Er)O 1.5 ) or oxidation resistance conditions.…”

“…This concept is widely discarded because these composite materials are either based on noble metals of prohibitive cost, or fail to meet the required stability (e.g.Ag/Bi(Er)O 1.5 ) or oxidation resistance conditions. The emphasis has thus been on mixed conducting ceramics, mainly single phase [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], and occasionally 2-phase ceramic/ceramic composites [17]. Perovskite materials Sr 1-x La x CoO 3-δ [3][4][5] and Sr 1-x La x FeO 3-δ possess the highest permeability, limited stability, and excessive thermal and chemical expansion.…”