Optimization of BSCF-SDC composite air electrode for intermediate temperature solid oxide electrolyzer cell Dorna Heidari a,b,⇑ , Sirus Javadpour a , Siew Hwa Chan b a School of Material Science and Engineering, Shiraz University, Iran b School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore article info Article history: Received 3 September 2016 Received in revised form 3 January 2017 Accepted 4 January 2017 Keywords: Solid oxide electrolyzer cell Composite air electrode BSCF-SDC composite air electrode Intermediate temperature solid oxide electrolyzer cell abstract Solid oxide electrolyzer cells (SOECs) are devises which recently have attracted lots of attention due to their advantages. Their high operating temperature leads to mechanical compatibility issues such as ther- mal expansion mismatch between layers of material in the cell. The aim of this study is to mitigate the issue of thermal expansion mismatch between Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3d (BSCF) and samaria doped ceria, Sm 0.2 Ce 0.8 O 1.9 (SDC), enhance the triple-phase boundaries and improve the adhesion of the electrode to the electrolytes, hence improve the cell performance. To make BSCF more thermo-mechanically com- patible with the SDC electrolyte, the formation of a composite electrode by introducing SDC as the com- positing material is proposed. In this study, 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.%, and 50 wt.% of commercial SDC powder was mixed with BSCF powder, prepared by sol-gel method, to make the composite air elec- trode. After successfully synthesizing the BSCF-SDC/YSZ-SDC/Ni-YSZ electrolyzer cell, the electrochemical performance was tested for the intermediate-temperature SOEC (IT-SOEC), over the temperature range of 650–800 °C. The microstructure of each sample was studied by field emission electron microscopy (FESEM, JEOL, JSM 6340F) for possible pin holes. The result of this study proves that the sample with 20% SDC-80% BSCF shows the highest performance among the investigated cells. Ó 2017 Published by Elsevier Ltd. 1. Introduction Based on the type of the electrolyte used in the fuel cells they are classified into five types: (1) polymer electrolyte membrane fuel cell (PEMFC) [1], (2) phosphoric acid fuel cell (PAFC), (3) mol- ten carbonate fuel cell (MCFC) [2], (4) alkaline fuel cell (AFC), and (5) solid oxide fuel cell (SOFC). More information about these five types of fuel cell technology can be found in Table 1. Furthermore by multi-stacking the architecture of fuel cells, their efficiency, reliability, and flexibility improves [3]. Among all, SOFCs/SOECs have advantages including hydrogen fuel production, long-term stability, excellent fuel flexibility, low emissions, and low operat- ing costs. However, they have few disadvantages regarding hydro- gen storage, hydrogen infrastructures and high cost of hydrogen production. But their greatest disadvantage is the high operating temperature, which results in long start-up and shut down times. Among other types of fuel cells, proton exchange membrane fuel cells (PEMFCs) do not have this issue as they operate at low tem- peratures [4] and therefore the relationship between proton con- ductivity and temperature is very important in PEMFCs [5]. The power converter topology is submitted to severe con- straints in terms of current and voltage [7]. As it is known that in the intermediate operating temperature range, the performance of air electrode of the cell tends to limit the cell’s performance [8]. Therefore it is necessary to optimize the air electrode material and its performance [9,10]. Conventional solid oxide cells (SOCs) are composed of yttria stabilized zirconia (YSZ) electrolyte, Ni- YSZ cermet fuel electrode [11] and La 0.8 Sr 0.2 MnO 3 (LSM) air elec- trode [12], and they operate at around 1000 °C. The high operating temperature is beneficial for decreasing the electrolyte’s ohmic resistance and increasing the electrode’s reaction kinetics [13]. However, it also brings about severe drawbacks, such as increasing electrode sintering rate, difficulties in cell sealing and interconnec- tion, and promoting the interfacial reactions between cell compo- nents [14]. High operating/materials costs and inadequate operational stability are the two major factors hindering the wide- spread application of high-temperature SOCs. It is generally agree- able that the reduction of SOCs operating temperature to intermediate temperature range of 500–800 °C can greatly speed up the commercialization of the technology [15]. As it is very cru- cial to evaluate a technology for practical application, Han et al. http://dx.doi.org/10.1016/j.enconman.2017.01.007 0196-8904/Ó 2017 Published by Elsevier Ltd. ⇑ Corresponding author at: NO. 9, Unit 3, Alley 2, Nastaran 1 Street, Maaliabad Boulevard, Shiraz, Fars 7188654141, Iran. E-mail address: dorn0001@e.ntu.edu.sg (D. Heidari). Energy Conversion and Management 136 (2017) 78–84 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman