Surface Modification of NiFe Anode-Support for Thin-Film Solid-Oxide Fuel Cell

Abstract

A dense NiO-Fe₂O₃ (NiFe) pellet has been developed as a potential anode-support for thin-film solid oxide fuel cells (SOFCs). However, preparation of dense NiFe is very challenging. Hole-formed NiFe pellets or porous NiFe pellets are frequently formed, which cannot be used as a support (substrate) for thin-film SOFCs. Therefore, this hole-formed NiFe support is simply wasted. In this report, we attempt to re-qualify this NiFe support to be a valuable substrate, which can be used for fabricating thin-film SOFCs. By deposition of smaller NiFe particles to cover the hole-formed NiFe support, the surface of this NiFe pellet is modified. Large holes on the surface disappear. The newly formed NiFe support can be used for fabricating a single cell with La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ as thin-film electrolyte operated at intermediate temperature. Maximum power density generated from this cell is 0.45, 0.86 and 1.28 W cm⁻² at 873, 923 and 973 K, respectively.

1. Introduction

Large ohmic loss generated mainly from thick electrolyte in an electrolyte-support solid oxide fuel cell (SOFC) is a common problem in conventional SOFCs, which enables them to operate effectively only at higher temperature (>1023 K).^1,2 To reduce the cost of electricity produced from fuel cell systems, development of low-temperature (673–873 K) or intermediate-temperature (873–1023 K) fuel cell is a new target for positioning fuel cells as main technologies for clean energy production in the future.³ One of the most successful resolutions to reduce the ohmic loss is decreasing the thickness of electrolyte to a thin-film electrolyte.⁴ Therefore, anode-support and metal-support cells were subsequently developed. Various techniques were developed to deposit thin-film electrolytes for fabricating a high performant cell, which can be operated at lower temperatures compared to that of conventional cells.^5–7 To fabricate thin-film SOFCs, high-quality anode-support or metal support must be developed.

Our group has successfully developed high-quality NiO-Fe₂O₃ (NiFe) anode-support for thin-film SOFCs, which could be operated at temperature range of 773–973 K.^8–10 NiFe composite particles were pelletized by pressing and sintering processes. The initial structure of NiFe anode was a dense pellet. However, during cell operation, anode is exposed to H₂ and reduced to Ni-Fe metal with porous structure. This porous NiFe support is an excellent structure for SOFC’s anode. To achieve better quality of the NiFe anode-support, important criteria much be included, such as dense pellet (∼99 % of relative density), small shrinkage of pellet’s size after reduction (<5 %) and high porosity after reduction (>30 %).^8–10 However, it is very challenging to fabricate this perfect structure of NiFe support. Problem of hole formation on the surface of NiFe pellets was frequently observed. Based on our experiences, hole formation might be due to one of the reasons: (1) an inhomogeneous mixture of Fe loading on the NiO, or (2) changes of NiO particle structure (e.g., size or size distribution). Pellets formed with pores cannot be used for fabricating cells. Therefore, optimization of NiFe pellet preparation, such as sintering temperature, ball-milling processes must be re-evaluated, which are considered as time and resource-consuming.

In this report, we aim to develop a process to restructure the hole-formed NiFe support to re-qualify this waste support to a valued one. We deposit a layer of small particles on this NiFe support, covering the holes to form a new surface. Large holes are covered by newly deposited particles, enabling successful deposition of a thin-film electrolyte for fabricating an anode-supported thin-film SOFC.

2. Experimental

2.1 Material synthesis and anode-support preparation

Anode material and anode-support preparation: NiO-Fe₂O₃ was prepared by impregnating Fe(NO₃)₃·9H₂O (99.9 %, Wako Pure Chemical Industries Co., Ltd., Japan) onto NiO (98 %, Kishida, Japan). 10.48 g of NiO and 6.36 g of Fe(NO₃)₃·9H₂O were dispersed in 200 mL de-ionized water (DI) in a 250 mL beaker by magnetic stirring. The weight ratio of Ni and Fe was fixed at 9 : 1, which was determined to be the optimal composition based on our previous work.^8–10 This mixture was heated to 553 K and kept until complete evaporation of water occurred. The remaining solid was then fired at 673 K for 2 hours to decompose the nitrate species. After grinding with a pestle and mortar, this composite powder was annealed at 1473 K for 6 hours in air. The annealed powder was ground by ball-milling process (with 20 zirconium balls, each 5 mm of diameter) at 300 rpm in ethanol for 2 hours. The powder was dried under an infrared (IR) lamp and subsequently ground with a pestle and mortar for 10 minutes. The produced powder was placed into a vial and placed in a vacuum oven at 393 K overnight.

2 g of NiO-Fe₂O₃ was pelletized by pressing at 40 MPa. The formed pellet was subsequently conducted cold isostatic pressing (CIP) at 250 MPa for 30 minutes. Later, pellet was sintered at 1273 K for 6 hours with a temperature increasing rate of 473 K h⁻¹. After sintering, the pellet was slightly polished by using silicon carbide sandpaper (500 grit, 1000 grit, 2000 grit, Fuji Star, Japan) to make surface smoother. The pellet was then re-sintered at 1773 K for 6 hours with increasing temperature rates of 473 K h⁻¹ for room temperature to 1273 K and 373 K h⁻¹ from 1273 to 1773 K. The size of final NiFe pellet is 18 mm and 1.8 mm of diameter and thickness, respectively.

Cathode materials: Sm_0.5Sr_0.5CoO_3−δ (SSC) was synthesized by sol-gel method, as reported in our previous work.¹⁰ All metal precursors, including 7 mmol of Sm(NO)₃·6H₂O (99.5 %, Wako Pure Chemical Industries Co., Ltd., Japan), 7 mmol of Sr(NO)₃ (98 %, Wako Pure Chemical Industries Co., Ltd., Japan), and 14 mmol of Co(NO₃)₂·6H₂O (99.5 %, Wako Pure Chemical Industries Co., Ltd., Japan), were dissolved in 200 mL of DI water with magnetic stirring. Then, 56 mmol of citric acid (C₆H₈O₇·H₂O, 99.5 %, Wako Japan) and 10 mL of polyethylene glycol 400 (PEG400, H(OCH₂CH₂)_nOH, Wako Pure Chemical Industries Co., Ltd., Japan) were subsequently added to prepare a metal precursor solution with a total concentration of 0.14 mol L⁻¹. This mixture was heated to 553 K, and kept until complete evaporation of water occurred. The solid product was fired at 673 K for 2 hours and annealed at 1173 K for 3 hours under ambient conditions. Finally, the synthesized powder was ground using a pestle and mortar before use.

Electrolyte materials and pulse laser deposition (PLD) target preparation: La_0.67Sr_0.1Ga_0.73Mg_0.38O_3−δ (LSGM) was used as PLD target from our optimization carried out in our previous works after slight modifications.^8–10 LSGM target powder was synthesized via a solid-state reaction. Using the stoichiometric ratio of LSGM target above, 9.79 g of powder mixture composed of La₂O₃ (99.99 %, Kishida, Japan), Sr(CO₃) (99.99 %, Wako Pure Chemical Industries Co., Ltd., Japan), Ga₂O₃ (99.99 %, Wako Pure Chemical Industries Co., Ltd., Japan), MgO (99.9 %, Wako Pure Chemical Industries Co., Ltd., Japan) was mixed with ethanol using planetary ball-milling process (20 zirconia balls, 5-mm diameter) for 12 hours (48 cycles of 15-min runs and 5-min rests). Then, LSGM powder was annealed at 1273 K for 6 hours in air. 2 g of LSGM powder was pressed at 20 MPa to make a target pellet. This formed pellet was conducted CIP at 250 MPa for 30 min, and sintered at 1773 K for 6 hours.

Functional layer materials and PLD target preparation: Sm_0.2Ce_0.8O₂ (SDC) was purchase from Daiichi Kigenso Kagaku-Kogyo Co., Ltd., Japan. The preparation of the PLD target was the same as for the LSGM PLD target. However, the final sintering temperature for the SDC pellet target was 1473 K for 6 hours.

2.2 Cell fabrication

Two types of supports, dense NiFe and pore-formed NiFe support, were selected for study in this work. The dense support was used to directly deposit LSGM electrolyte. For hole-formed support, NiFe particles were deposited on the surface by spin-coating method and sintered at 1073 K for 2 hours.

Thin-film LSGM electrolyte and SDC functional layer were deposited using a PLD system (PLD-7, PASCAL, Japan). Film deposition was conducted at 1073 K under oxygen partial pressure of 0.67 Pa, using a laser intensity of 180 mJ per pulse at a frequency of 10 Hz.¹⁰ Deposition durations for LSGM and SDC were 8 hours and 30 minutes, respectively, to achieve thickness of 5 µm and 0.5 µm. It is noted that the LSGM target compositions were optimized to obtain the best stoichiometry of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ. After deposition, the NiFe/LSGM half-cell was annealed at 1073 K for 1 hour in air with a temperature ramp rate of 373 K h⁻¹. SSC air electrode was deposited onto the LSGM electrolyte using screen-printing method to form a single cell. A Pt wire was connected on LSGM electrolyte by Pt paste near the air electrode as a reference electrode. Finally, the cell was annealed at 1073 K for 1 hour in air before analysis.

2.3 Analysis and characterizations

Morphologies and microstructures were analyzed using scanning electron microscopy (SEM) (Versa 3D Hivac, FEI, USA). Crystal structure was studied by X-ray diffraction (XRD) (CuKa line, Rigaku Rint 2500, Rigaku Corporation, Japan). Elemental mapping was conducted by energy-dispersive X-ray spectroscopy (EDS) (Versa 3D Hivac, FEI, USA). Elemental composition was analyzed by X-ray fluorescence spectroscopy (XRF) (XRF-1800, Shimadzu, Japan).

Electrochemical analysis of cell was conducted in accordance with our previous setup.¹¹ Pt mesh, serving as a current collector, was covered on both anode and cathode areas. Pt wire was used to connect the electrodes to electrochemical equipment. Glass sealing was performed by increasing the temperature of reactor to 1073 K for 1 hour. Before electrochemical measurement, the NiFe anode was reduced by humid hydrogen at 973 K for 1 hour. During cell analysis, 100 mL of humidified hydrogen was supplied to the anode, and 100 mL oxygen was supplied to the cathode site (air electrode). Electrochemical analysis of cells, such as current-voltage-power (I-V-P) measurement, was conducted over a reaction temperature range of 873–973 K using four-wire method, also known as separate current and voltage leads. The current across the cell was controlled by using a Potentiostat/Galvanostat (HAL3001, Hokuto Denko, Japan), and the terminal voltage was measured with a digital multimeter (R6451A, Advantest, Japan). Electrochemical impedance spectra (EIS) were measured by an impedance/gain-phase analyzer (SI 1260 impedance analyzer and SI 1287, Solartron, Farnborough, UK) with commercial Z-view software under open-circuit condition at an AC voltage of 10–25 mV and a frequency range of 10⁵ to 0.1 Hz.

3. Results and Discussion

Before cell fabrication, characterizations of the NiFe support were conducted for quality checks, including investigation of morphological structure, crystal phase, composition, and reduction behavior. Surface structure is one of the most important criteria for an anode-support used in thin-film-based SOFCs. SEM images of the dense and hole-formed (porous) support are depicted in Fig. 1. The dense-surface NiFe support provides an excellent structure for thin-film deposition (Fig. 1a). However, large holes are randomly found on the hole-formed NiFe pellet (Fig. 1b). The hole-formed structure of NiFe cannot be used for cell fabrication. Thin electrolyte film might not completely cover these holes, which are unable to separate the reactive gases between the anode and cathode side. Therefore, we deposited small NiFe particles on this NiFe support (also called NiFe-NiFe) to cover these large holes. As a result, the large holes on this NiFe support were successfully covered by NiFe particle layer (see Fig. 2). Large holes on NiFe support disappeared. At higher magnification, it was clearly seen that the surface was porous with very tiny pores (Fig. 2b). However, these pores were very small, which suggested that they might be covered by thin-film electrolyte deposited by PLD. Elemental composition of both NiFe powder and pellet determined by XRF closely matched to our stoichiometric preparation, with an Fe/Ni ratio of 9 wt%. The shrinkage and porosity of these pellets were analyzed after reduction at 973 K under H₂ for 1 hour. The shrinkages after reduction of pore-formed NiFe and NiFe-NiFe pellet were 7.72 and 7.28 %, respectively. Because the particle layer was deposited only on the surface of NiFe substrate, the shrinkage was not significantly changed. The porosity of the Ni-Fe substrate slightly increased from 27 % to 32 % after the deposition of NiFe particle layer. As shown in SEM images, the NiFe particle layer is a porous layer. Therefore, porosity of pellet substrate should also be increased.

Figure 1.

SEM images of surface of the dense NiFe pellet and the hole-formed NiFe support.

Figure 2.

SEM images at different magnifications of the surface’s supports and their corresponding camera images (a) the hole-formed NiFe, (b) the NiFe particle layer deposited on NiFe support (NiFe-NiFe) and (c) the LSGM deposited on the NiFe-NiFe support.

The new formed NiFe-NiFe support was attempted to be used as a substrate for thin-film SOFCs. Therefore, we deposited an LSGM thin film by PLD for 8 hours to achieve a thickness of around 5 µm. Figure 2c shows the surface of the LSGM deposited on NiFe-NiFe support. Porous surface turned into a dense surface after LSGM deposition. The dense surface of LSGM film indicates the feasibility of fabricating a single cell.

XRD was used to analyze the crystal structures of both NiFe powder and NiFe support. XRD spectra in Fig. 3 depict the crystal structure of NiFe support before and after NiFe particle and LSGM deposition. The crystal phases of NiFe powder and pellet were identical, consisting of NiO and NiFe₂O₄ (Fig. 3a). Because the support and particle layer were made from the same materials, no change in crystal structure (NiO and NiFe₂O₄) was observed after NiFe particle deposition. However, NiFe’s XRD peaks disappeared after LSGM deposition. These new diffraction peaks were indexed very well to JCPDS#01-075-9521 of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ. Sharp XRD peaks infer that the deposited LSGM film was well-crystallized, which should be good for oxide ion transport for SOFC applications.^8,9 No impurity peaks were detected. In fact, before cell deposition, LSMG film quality was optimized by using different target compositions. As in the supplementary information, Fig. S1 and Table S1, LSGM film with desired composition (La_0.9Sr_0.1Ga_0.8Mg_0.2O₃) and high crystallinity was obtained with target composition of La_0.67Sr_0.1Ga_0.73Mg_0.38O_3−δ. Therefore, the LSGM film deposited on NiFe support should also have good quality in terms of phase and composition.

Figure 3.

(a) XRD spectra of the hole-formed NiFe support (NiFe) before and after NiFe particle layer and LSGM deposition, and (b) fitting and indexing XRD spectrum of the LSGM deposited on the NiFe-NiFe support with standard diffraction data.

Surface and crystal structures confirmed that the LSGM electrolyte was well deposited on the newly formed NiFe-NiFe support. Next, we fabricated a single cell for analyzing its electrochemical performance. SSC was deposited as the cathode on the top of the LSGM surface with a size of ∼0.2 cm², which was used to calculate the power density generated during cell analysis. An image of cell is shown in Fig. 4a. Cell analysis was conducted at 973 K under humid H₂ and dried O₂. The open circuit voltage (OCV) of cell (NiFe-NiFe|LSGM|SSC) was 0.83 V. The maximum power density generated from our cell was ∼0.81 W cm⁻² (Fig. 4b). The low OCV observed on this cell might be assigned to the pin hole or small crack in LSGM film deposited on this porous support. Gas leakage through a defected electrolyte film (e.g., crack or pin hole) could decrease OCV. Although this defected electrolyte film was hard to observe by SEM analysis, we experienced the difficulty in achieving a highly dense structure of 5-µm LSGM electrolyte deposited on this porous support. However, for cell made from dense support, OCV was up to 1.06 V, as previously reported.^8–10

Figure 4.

(a) A digital photograph of the cell and the comparison of cell performance at 973 K between the cell made with and without SDC functional layer, (b) I-V-P curves, (c) and (d) impedance spectra (Nyquist plots) and their equivalent circuits (insets).

After I-V-P analysis, impedance analysis of the cell was conducted and plotted in Fig. 4c. The semi-cycle shape of impedance comprises ohmic resistance and polarization resistance. Ohmic resistance (intercept on x-axis, Rs) is derived from the highest frequency and is attributed to resistance of electrode, electrolyte, current collectors, and others.¹² Polarization resistance (Rp) is calculated by subtracting the highest-frequency intercept from the lowest one. Rp originates from charge transfer resistance (electron transfer and ion transfer process at the interfaces between current collector and electrodes, or/and electrodes and electrolyte) at high-frequency arc (R₁), and mass transfer resistance (adsorption/desorption of oxygen, oxygen diffusion at gas-cathode surface/interface, surface diffusion of oxygen intermediates) at the low-frequency arc (R₂).^13–15 Ohmic (Rs) and total polarization resistance (Rp) of this cell were 0.73 Ω cm⁻² and 1.2 Ω cm⁻², respectively.

After the power generation measurement, the cross-section of the cell was analyzed with SEM and EDS elemental mapping to investigate its microstructure and elemental composition of layers. In Fig. S2, a dense layer was identified as LSGM electrolyte with a thickness of ∼5 µm deposited on the porous NiFe layer. It was clearly observed that some parts of LSGM electrolyte were not well-contacted to the NiFe support (Fig. S2b). A NiFe particle layer (∼10 µm) was located between LSGM electrolyte and NiFe support. Generally, holes were not observed on the surface of the NiFe support. However, holes located inside the support were still remained. This suggests that the surface holes were filled with small NiFe particles. It was noted that the shrinkage of porous support with and without NiFe particle layer was not significantly changed. However, the cell was still stable enough to be analyzed. It seems that the NiFe particle layer serves multiple functions in this cell. (1) The NiFe particle layer covers the holes on the surface of the porous NiFe support, enabling the deposition of a dense LSGM electrolyte film. (2) The NiFe particle layer might help in reducing the mechanical stress between LSGM electrolyte and NiFe support. Even though the NiFe support shrinks, LSGM film still maintains a dense structure. We observed that without the NiFe particle layer, the cells using the hole-formed NiFe support show negligible OCV, or the OCV dropped shortly during reduction. LSGM electrolyte was fully broken/delaminated during reduction. Therefore, the advantages of NiFe particle layer were clearly demonstrated from this result. Although the OCV of this cell was low, a single cell with reasonable performance can be prepared by using this waste support.

To improve the cell performance, an SDC functional layer was deposited between NiFe-NiFe support and the LSGM electrolyte to form a new structure of NiFe-NiFe|SDC|LSGM|SSC. Before deposition on the cell, the SDC film deposited on alumina substrate was analyzed the phase and composition (see Fig. S3). Because the thickness of SDC layer was thin, almost no change in the surface structure of the NiFe particle layer was observed (Fig. S4a). The porous structure of NiFe particle layer was observed on the surface of SDC/NiFe-NiFe. Using EDS elemental mapping, it was shown that the SDC layer fully covered the NiFe particle layer (Figs. S4b–S4e). However, after LSGM deposition, the porous surface changed to a dense surface (Fig. S5a). The structure of LSGM film was almost identical to that of the previous cell without the SDC functional layer. EDS elemental mapping shows a homogenous distribution of La, Sr, Ga and Mg, which are the elemental composition of LSGM film. Almost no EDS signal was observed for Ce, Sm, Ni and Fe, which suggests that LSGM completely covered the SDC functional layer and NiFe support. A single cell was fabricated with SSC as the cathode and measured electrochemical performance.

As expected, the SDC functional layer significantly improved the cell’s performance. The OCV of th cell increased to 0.93 V, and the power density also increased to 1.28 W cm⁻² at 973 K reaction (Fig. 4b). Impedance spectra reduced significantly with SDC as a functional layer between LSGM electrolyte and anode-support. The cell made with an SDC functional layer was further operated at different temperatures ranging from 873–973 K (Fig. 5). I-V-P curves show that the maximum power density of cell is 0.47, 0.86 and 1.28 W cm⁻² at 873, 923 and 973 K, respectively. The cell’s performance is summarized in Table 1. This cell generated very small polarization resistance and activation energy (0.11 eV).

Figure 5.

The performance of the cell made with SDC functional layer operated at 873, 923 and 973 K (a) I-V-P curves, (b) cell’s impedance and (d) the Arrhenius plots of (b).

Table 1. Performance of cell (NiFe-NiFe|SDC|LSGM|SSC) at 873–973 K.

Temp. (K)	OCV (V)	Power density (W cm−2)	Rs (Ω cm−2)	Rp (Ω cm−2)
873	0.88	0.47	0.17	0.21
923	0.92	0.86	0.11	0.11
973	0.93	1.28	0.10	0.06

After the reaction, the microstructure of the cell was studied by SEM analysis and EDS elemental mapping. The cross-section of the cell allows us to identify each layer of deposited film. The thick part at the bottom of the cell is NiFe anode-support pellet. The center film with a dense structure is LSGM electrolyte with a thickness of around ∼5 µm. The porous layer located between the LSGM electrolyte and the NiFe support is the NiFe particle layer (∼10 µm). The top part is the cathode layer of SSC (> 10 µm) (Fig. 6a). The SDC functional layer is very thin, making it hard to observe by low-magnification images. However, a high-magnification SEM image in Fig. 6b clearly shows that the SDC layer strongly contacts the LSGM electrolyte. This is further confirmed by EDS mapping of all elements of LSGM and SDC in Figs. 6c–6h. The thickness of SDC functional layer is about 0.5 µm. Microscopic analysis concludes that all layers of targeted cell’s structure were successfully deposited on the NiFe anode-support.

Figure 6.

(a) SEM images of the cell’s cross-section after reaction, (b) high-magnification of (a) at the SDC layer, (c)–(h) EDS elemental mapping of SDC and LSGM elements.

From microscopic observation of the cell after the measurement, the effect of the SDC functional layer was clearly observed. The strong contact between the LSGM electrolyte and the NiFe-NiFe support was observed by the introduction of the thin SDC layer. The weak contact between the LSGM electrolyte and the NiFe-NiFe support was resulted in a large ohmic resistance. During the cell operation, the LSGM electrolyte film locally was delaminated (Fig. S2b). This was further confirmed by the OCV in Fig. S6a. The OCV of the cell without SDC functional layer was slowly dropped after electrochemical measurements, particularly after EIS analysis. The OCV of the cell with SDC functional layer was much stable (Fig. S6b). Although the cell underwent electrochemical measurements for several cycles, the contact between the LSGM electrolyte and the NiFe-NiFe support remained tight, and no delamination observed (Fig. 6b). Therefore, the SDC functional layer is highly effective in achieving stable and high performance of power generation property of the LSGM cell.

The deposition of a small NiFe particle layer was successfully used to modify the surface of the hole-formed NiFe support. We attempted to deposit other particles such as SDC, Ti-LDC or Ni-SDC. However, these materials used as hole-covering layers generated low-performing cells. Our NiFe-NiFe|SDC|LSGM|SSC cell generates outstanding performance, which is better than that of similar cells reported.^12,16,17 Wang et al. fabricated Ni-SDC anode-support SOFC with tri-layer-sandwich electrolytes composed of SDC|LSGM|SDC, enabling the generation of a maximum power density of 0.74 W cm⁻² at 973 K.¹² Recently, Solovyev et al. prepared multi-layer cells using NiO-YSZ as anode-support and YSZ|GDC film as electrolyte. The maximum power generated from this cell was 0.65 W cm⁻² at 973 K,¹⁷ which was also lower than that of ours. However, when compared to GDC electrolyte-based anode-support cells with nanoparticle-infiltrated catalysts as cathode reported by Miura et al.,¹⁸ our cell produces a lower power density. Typically, when compared to cells made with dense NiFe anode-support, our cell generates a poorer power density.^8–10 It is not surprising that high-quality LSGM electrolyte could be deposited on dense NiFe support, resulting in a high-performing cell. However, our method is very promising to modify the hole-formed NiFe support, enabling the transformation of waste support into usable support.

4. Conclusion

A method to modify the hole-formed NiFe support, previously considered waste, into a usable NiFe anode-support for thin-film SOFCs, has been developed. The deposition of a small NiFe particle layer enabled the elimination of large holes on hole-formed NiFe support. The newly formed NiFe-NiFe pellet was utilized to fabricate a single cell of thin-film SOFC with LSGM as the electrolyte film. The fabricated cell, composed of NiFe-NiFe|SDC|LSGM|SSC, generated remarkable performance at intermediate temperature. The maximum power density was 0.47, 0.86 and 1.28 W cm⁻² at 873, 923 and 973 K, respectively. Although the performance of the cell made from this re-qualified NiFe-support was lower than made with dense NiFe, the developed process should be valued because the hole-formed NiFe-support could not previously be used for cell fabrication. Before developing this method, this hole-formed NiFe-support was just waste. By using our developed method, waste can be transformed into a valued product, which is very innovative approach. This method would be applicable not only to NiFe materials but also other materials.

Acknowledgments

Part of this study was financially supported by New Energy and Industrial Technology Development Organization (NEDO, No. JPNP20003), Japan.

Data Availability Statement

The data that support the findings of this study are openly available under the terms of the designated Creative Commons License in J-STAGE Data at https://doi.org/10.50892/data.electrochemistry.25224143.

• 1) A dense NiO-Fe₂O₃ (NiFe) pellet has been developed as a potential anode-support for thin-film solid oxide fuel cells (SOFCs). However, preparation of dense NiFe is very challenging. Hole-formed NiFe pellets or porous NiFe pellets are frequently formed, which cannot be used as a support (substrate) for thin-film SOFCs. Therefore, this hole-formed NiFe support is simply wasted. In this report, we attempt to re-qualify this NiFe support to be a valuable substrate, which can be used for fabricating thin-film SOFCs. By deposition of smaller NiFe particles to cover the hole-formed NiFe support, the surface of this NiFe pellet is modified. Large holes on the surface disappear. The newly formed NiFe support can be used for fabricating a single cell with La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ as thin-film electrolyte operated at intermediate temperature. Maximum power density generated from this cell is 0.45, 0.86 and 1.28 W cm⁻² at 873, 923 and 973 K, respectively.

CRediT Authorship Contribution Statement

Sovann Khan: Conceptualization (Lead), Data curation (Lead), Formal analysis (Lead), Investigation (Lead), Methodology (Lead), Writing – original draft (Lead), Writing – review & editing (Lead)

Jun Tae Song: Formal analysis (Supporting), Investigation (Supporting), Writing – review & editing (Supporting)

Motonori Watanabe: Formal analysis (Supporting), Investigation (Supporting), Writing – review & editing (Supporting)

Tatsumi Ishihara: Conceptualization (Lead), Data curation (Lead), Formal analysis (Lead), Funding acquisition (Lead), Investigation (Lead), Supervision (Lead), Writing – review & editing (Lead)

Conflict of Interest

Authors declare no conflict of interest in the manuscript.

Funding

New Energy and Industrial Technology Development Organization: JPNP20003

Footnotes

S. Khan, J. T. Song, and T. Ishihara: ECSJ Active Members

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