A Compatibility in the Single Cell of the NiO / LSGM / LSCF

Received: 23rd July 2020 Revised: 21st October 2020 Accepted: 27th October 2020 Online: 31 October 2020 The compatibility between anode, electrolyte, and cathode in a solid fuel cell determines its performance. Research on the compatibility between fuel cell components is challenging, especially for SOFCs that operate at high temperatures. Therefore, efforts to reduce the operating temperature to become intermediate temperature SOFC (IT-SOFC) are essential to facilitate compatibility between its components. La0.6Sr0.4Co0.2Fe0.sO3(LSCF) has been recognized as one of the most promising cathode materials for (IT-SOFC) due to its high electronic conductivity and excellent electrical performance. While Lao.sSro.2Gao.sMgo.2O3(LSGM) has a high oxygen ion conductivity at low temperatures, its chemical stability is still not good. LSGM is known to have interface reactivity with other components such as NiO and LSCF in fuel cells. This study looked at the compatibility of NiO/LSGM/LSCF cells prepared by the solid chemical synthesis method. Compatibility evaluation is determined by the Thermal Expansion Coefficient (TEC) parameter using the dilatometric method, Area Specific Resistance (ASR), and TBF area morphology by Scanning Electron MicroscopeEnergy Dispersive Spectroscopy (SEM-EDS). While the conductivity of the cells is determined by Electrochemical Impedance Spectroscopy (EIS). NiO/LSGM/LSCF cells have good compatibility with a value of 78.05 kg1.K.A.s3.p2 at a temperature of 600 C. The ASR values of cells tend to decrease with increasing temperature and conductivity values at small TEC values. Based on these parameter values, delamination in NiO/LSGM/LSCF cells did not occur.


Introduction
The increasing need for energy is a challenge in developing alternative energy sources and supporting technology. Most of today's energy needs are obtained from non-renewable energy sources, especially fossil fuels such as petroleum, coal, and natural gas [1]. Therefore an electrochemical device is needed to convert chemical energy into electrical energy with very high efficiency, which is often referred to as Solid Oxide Fuel Cell (SOFC) [1,2]. SOFC is the most developed high-temperature solids fuel cell (range 6oo-iooo°C) due to its high efficiency and flexibility to hydrocarbon fuels due to its electrolytic material [ 3 ]. Its high operating temperature effectively δ  σ σ (LSGM). Meanwhile, cathode ioo°C was re-measured its expansion to determine the TEC value [18].

Fabrication of NiO / LSGM / LSCF Cell.
NiO / LSGM / LSCF cells were prepared by combining the three components, such as a sandwich consisting of anode / electrolyte / cathode, through gradual sintering, which was initiated by combining LSGM with NiO, followed by merging with LSCF. One side of the LSGM was coated with NiO anode slurry and then sintered at 900°C for 5 hours. After cooling, the other side was coated with an LSCF cathode and then sintered at 8oo°C for 2 hours. This sintering process can also simultaneously remove cellulose acetate binders dissolved in DMF. The two sides of the NiO / LSGM / LSCF cells were then coated with silver paste (Ag) as a current collector at each electrode. The cells were sintered again to 6oo°C [6] and then tested their electrochemical performance using EIS (LCR meter GW Instek 8105 G).
The morphology between anode-electrolyte and electrolyte-cathode was observed by SEM -EDS (EDS (SEM: JEOL JSM -636 OLA, SEM-EDS: Hitachi-EDAX Team) to ascertain the level of chemical reactivity that may occur.

. Area Specific Resistance (ASR)
ASR is determined by impedance spectroscopy technique (LCR meter GW Instek 8105 G) at a frequency of 20-5000 Hz with a temperature range of 300 -600°C, signal AC = 1.00V. The ASR value is calculated from the total measured resistance.

Total Conductivity
The total conductivity is determined from the total resistance value ( Rtot ) measured by the EIS. This total resistance consists of electrolyte ohmic resistance ( Rs ), electrode ohmic polarization resistance (R 0 ), charge transfer resistance ( Ret ), and electrode diffusion resistance (Rdif ). This total conductivity is calculated using the following equation: Lao.8Sro.2Gao.8Mgo.2O3 materials that are often chosen include lanthanum strontium cobaltite (LSCo) or lanthanum strontium cobalt ferrite (LSCF), and NiO for the anode. The selection of the right fuel cell components between electrolyte, anode, and cathode is critical to decreasing the operating temperature by reducing the electrodes' energy loss [6].
LSCF has a high level of electronic conductivity and has an electrical performance as a cathode material [ 15 ].
Meanwhile, Ni / YSZ anode has been widely used as a SOFC anode because of its high electrochemical activity against H2 oxidation as well as high stability at high operating temperatures [6,16]. Therefore, this study made NiO / LSGM / LSCF single cells to test their compatibility. The performance of similar cells, such as Ni-Sc / LSGM / LSCF -Ag and YSZ / Ni-LSGM-LSCF, has been previously reported [6,17 ], which was measured at a temperature of 6oo°C. In this study, the cell performance was measured at lower temperatures, i.e., from 300 -6OO°C, to determine its electrochemical character at lower temperatures.

Materials and Tools
The tools used in this research are mortar, analytical balance, ball mill agate, furnace, oven, pellet maker, and glassware. Electrolyte, anode, and cathode morphology was determined by SEM-EDS (SEM: JEOL JSM -636 OLA, SEM -EDS: Hitachi-EDAX Team), while structural measurements were used XRD (Rigaku: MiniFlex6oo) to determine the ASR value and total conductivity, used Impedance spectroscopy (LCR meter GW Instek 8105 G), TEC values were used with a micrometer screw.
The materials used in this study include LSGM ( 99 % trace rare earth metal basic) as an electrolyte, silver paste, NiO ( 99.999 % trace metals basic) as an anode, LSCF ( 6428 Sigma-Aldrich) as a cathode, DMF, and cellulose acetate as a binder. The material used was previously characterized by its structure with XRD (Rigaku: MiniFlex6oo).

Preparation of NiO, LSGM, and LSCF Pellet
NiO, LSGM, and LSCF pellets were made with a diameter of 0.798 ± 1.045 cm, a cross-sectional area of 5.003 ± 8.58 cm 2 ' and a thickness of 0.2425 ± 0.353 cm.
Each pellet was compacted under a pressure of 6000 kg.cm 2 .

Coefficient (TEC) of NiO / LSGM / LSCF
The TEC of the NiO, LSGM, and LSCF fuel cell components were determined by dilatometric techniques using micrometer couplers. Each compacted NiO, LSGM, and LSCF pellet was then heated in a specially designed furnace to noo°C, and each increase in temperature of

. Results and Discussion
The determination of the compatibility of NiO, LSGM, and LSCF was completed by the analysis of the structure and surface and cross-section morphology of each cell component, then analysis of TEC and ASR.  hollow anode and cathode regions. The possible chemical reactivity in this area indicates a fusion of the electrolyte-anode boundary, which means that the electrodes are likely to have diffused into the electrolyte, which allows a deficiency in electrochemical performance. In the study, it could be concluded that there was no significant reactivity for both NiO / LSGM and alsoLSGM / LSCF [ 19 ].

. Characterization of
The anode pores are useful for passing hydrogen, which then diffuses into the Triple Phase Boundary (TPB). The unsuitable cavity size can result in H20 molecules trapped in the cavity. If H20 evaporation is slower than formation, the H20 molecule affects SOFC cell compatibility, namely in the form of SOFC resistance. To ensure reactivity in the border area, an analysis of the area elements was carried out ( Figure 2). Meanwhile, the cavity in the cathode functions so that oxygen gas can diffuse through the cavity. The probability of meeting electrons, oxygen gas, and electrolytes on the TPB can increase. On the other hand, electrolytes must have low porosity and be relatively dense to prevent the diffusion of oxygen gas into the bulk phase of the electrolyte, which can interfere with the electrochemical reaction process [20,21].
In addition to the morphological observations between the electrodes on the cell components, the chemical reactivity of these cells was also confirmed by the composition of the elements at the boundary area of the components tested by EDS (Figure 3 ). Based on Figure 3 , the previous conclusion that there is no chemical activity between the anode and cathode with electrolytes is strengthened by the absence of other elements besides the constituents of NiO, LSCF, and LSGM (Table 1 and Table 2). LSGM single phase which refers to ICSD standard No. 98 -009 -8170 has a cubic crystal form with a space group Pm-3 m ( a = b-3.92 (2); c = 3.92 (2)), where the typical peak is located at 2 = 32.340 (0 1 1). While the typical peak of NiO is at 2 = 43.09°( 0 0 2), which adopts (1)). Likewise, LSCF shows a typical peak at 2 = 32.44 (0 11) refers to ICSD 98 -015 -8799 , with a cubic structure with space group Pm -3 m ( a = b = 3.88 (2); c = 3.88 (2) A).      4 ).
The TEC NiO pattern is relatively different compared to LSCF and LSGM, which tend to continue to rise at a temperature of 8oo°C, meaning that the maximum value has not been reached. A high increase in the TEC value can significantly increase the coefficient of expansion. This can affect other parameter values, which also affect cell compatibility. The comparison of TEC values from NiO, LSCF, and LSGM in literature and research results is presented in Table 3 . Madelung e t a l . [ 25 ] 13.9 Corbel eta /. [26] 16

Thermal Expansion Coefficient (TEC)
One of the eligibility requirements of a SOFC cell is that the TEC value of the electrode material must be slightly higher than that of the electrolyte. Flowever, a mismatch that is too large can cause the electrolyte to break down easily, and this can change the structure of the SOFC cell as the operating temperature rises. In this study, quite a large difference in TEC was found at the LSCF cathode. The cause of the decrease in TEC value from LSCF in this study cannot be explained; however, cell damage at the time of fabrication was not found. The difference in the TEC value, which is very large between the results of this study and the references that have been reported, can be caused by several things, including differences in the morphology of LSCF due to differences in the synthesis method used.

. ASR Value and Cell Conductivity
EIS testing was carried out in a temperature range of 300 -600°C using an LCR meter at a frequency of 20-5000 Hz. Data displayed is data in the form of real Z (Z ' ) and imaginary Z (Z " ) of NiO / LSGM / LSCF cells (Table 4 ). In this study, TEC measurements were carried out at a temperature of 25 -8oo°C [22,23 ]. The increase in sample dimensions (diameter and height of pellets) is measured using a screw micrometer. The length of LSCF, The NiO / LSCF / LSGM SOFC cells' compatibility is shown in the Nyquist diagram ( Figure 5 ). The Nyquist diagram is generally a semicircular curve, both in response to grain phase resistance and phases between grains, but it is more like a quarter circle in this study. This difference can occur due to different types of electrochemistry in the cell.

. Total conductivity of NiO / LSGM / LSCF cell
The total conductivity value is calculated from the total resistance measured Rtotai ( Rs+Ri+W ). A pellet with a thickness of ( 1 ) 0.15 cm and a cross-sectional area of pellets (A) 0.7857 cm 2 , the total conductivity values for NiO / LSGM / LSCF cells are summarized in Table 6. The higher the operating temperature, the higher the cell conductivity ( Figure 6). This means that up to a temperature of 6oo°C, compatibility between components is maintained. -58 -56 -54 -1 It is necessary to quantify the Nisquist profile to map the measured polarization resistance and ohmic resistance values in NiO / LSGM / LSCF cells. Based on the resulting Nisquist profile, it is difficult to separate the resistance resulting from the grain phase and grain boundaries, as well as the polarization at the electrodes in NiO / LSGM / LSCF cells. The resulting Nyquist diagram has a dominant form of loop inductance, where the reactance is inductive. Inductive is a type of resistance that resists changes in direction in an AC circuit. When AC passes through a component containing a reactance, energy can be stored and released in the form of a magnetic field. In this case, the reactance is inductive, as mentioned in the previous literature [ 27 ]. Table 5 . ASR values for single-cell NiO / LSGM / LSCF.  The decrease in the ASR value occurs with the increase in temperature. In the SOFC principle, the higher the temperature, the smaller the resistance or ASR. From the results of calculations in this study, it can be seen that the inductance (L) value also decreases with the increase in temperature. This temperature increase also affects the increase in the electrons' conductivity in the grain and grain boundaries of the anode as the temperature increases and the resistance decreases. The ASR value, which decreases with increasing temperature, indicates that the resulting cells are compatible. The decrease in the ASR value and the increase in temperature can occur because the resistance and reactance values in SOFC cells have decreased, which affects ASR. These results are confirmed by the results of the calculations in Table 5 .  Compatibility value of NiO / LSGM / LSCF cell is in the quartile range Q 3 -Q 4 ( Table 8). Thus, NiO / LSGM / LSCF cells have an adequate cell compatibility level, both thermal and reactivity levels. The low reactivity between the electrolyte and the electrodes does not significantly affect the cell's electrochemical activity. This fact is supported by the relatively small ASR value of the cell 0.9266 Q .cm 2 , the relatively high total conductivity ( 0.0093 S.cnr 1 ) at an operating temperature of 6oo°C.

. Conclusion
Single