From last few years, there has been an increased interest in the development of high performing solid oxide electrolysis cells (SOECs) due to production of highly pure hydrogen. The basic concept of SOECs technology has been developed based on SOFCs and their materials research. The most common electrolyte and hydrogen/steam electrode are yttria stabilized zirconia (YSZ) and Ni-YSZ cermet respectively, as in SOFC, already exhibited good electrochemical performance and stability. In terms of oxygen electrode materials La_1-xSr_xMnO₃ (LSM), La_0.58Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) and their composite with GDC or YSZ have been reported. Nevertheless, the electrochemical and thermo-mechanical stability of these materials during SOEC operation still requires further investigation.

Recently several researchers have focused their work on the degradation mechanism during SOEC operation. In short term (during first few hours) of ageing, the formation of Sr- and/or Co-rich particles on the top surface of dense LSCF samples has been reported by the authors while only surface Sr-enrichment is usually observed in aged porous oxygen electrode [1, 2]. When it is kept for long duration at operating condition then particularly the delamination of oxygen electrode at the electrode/electrolyte interface is the most common mode of failure [3, 4]. In general, the oxygen evolution reaction at the oxygen electrode leads to a locally high partial pressure of oxygen (pO₂) in the electrode and at the electrode/electrolyte interface in SOEC mode, further leads to increase in electrode overpotential [3]. So, the pO₂ and overpotential (η) at the electrode/electrolyte interface are the governing factors and should be treated carefully considering the specific interface structure. One way to avoid these problems could be to increase the ionic conductivity at the electrode/electrolyte interface.

Our current research work is focused on the oxygen electrode to avoid such kind of delamination by increasing the activity of oxygen electrode using infiltration of very active material like La_0.58Sr_0.4CoO_3-δ (LSC), for the efficient hydrogen production. The electrochemical performance of LSC infiltrated LSCF oxygen electrode is investigated for steam electrolysis and compared with blank LSCF electrode. Furthermore it is also tried to investigate at which overpotential the delamination of oxygen electrode starts. In this respect, the symmetrical half-cell as well as full cell containing LSCF oxygen electrode with and without LSC infiltration are characterized using electrochemical impedance spectroscopy in the temperature range 750-900 °C. The symmetrical half-cells “8YSZ//CGO//LSCF” are characterized in a three electrode set up using a reference electrode with the aim to obtain detailed information on the different electrochemical processes and degradation mechanisms. The polarization resistance (R_p) values obtained for symmetrical half-cells with and without infiltration are 24 mΩ.cm² and 32 mΩ.cm² respectively, at 800 °C. An improvement in the R_pvalue is observed for LSC infiltrated sample. The degradation experiment performed up to two weeks with an increase of potential 50 mV in each two days. The postmortem analysis performed to investigate the behavior of electrode and electrode/electrolyte interface using SEM-EDX. Interestingly, no delamination is observed at least after two weeks with LSC infiltrated symmetrical half-cell, contrary to the blank LSCF symmetrical half-cell.

The behavior of Ni-YSZ supported single cells “Ni-YSZ//8YSZ//CGO//LSCF" is also investigated from 750-900 °C temperature range under both SOFC and SOEC modes. A maximum current density value of 1.48 A.cm^-2 is obtained at 800 °C under an applied electrolysis voltage of 1.5 V with 50 % H₂O. The investigation of LSC infiltrated LSCF single cell is under progress. The comparison of electrochemical properties of symmetrical half-cells and single cells with and without infiltration will be presented and discussed in detail.

 Refrances
[1] L. C. Baqué, A. L. Soldati, E. Teixeira-Neto, H. E. Troiani, A. Schreiber, A. C. Serquis, Journal of Power Sources, 337 (2017) 166-172.
[2] J. Druce, I. Tatsumi, J. Kilner, Solid State Ionics, 262 (2014) 893-896.
[3] Anil V. Virkar, International Journal of Hydrogen Energy, 35 (2010) 9527-9543.
[4] J. R. Mawdsley, J. D. Carter, A. J. Kropf, B. Yildiz, V. A. Maroni, International Journal of Hydrogen Energy, 34 (2009) 4198-4207.