# Femtosecond Laser Additive Manufacturing of Multi-Material Layered Structures
## 3 Results and Discussion
### Three-Layered Cell Testing and Analysis  
Figure 6a is a photo of the SOFC cells made from the same batch. Consistent and uniform three layered cells were made in our laboratories with up to a \(30\times 30\) mm active area. Figure 6b shows that the high strength of Ni-YSZ supporting anode can be achieved with controlled porosity at properly adjusted laser power and scan speed.  
We have developed a process to control the laser power, scan speed, and scan patterning to obtain complete cell unit fabrication (anode, electrolyte, and cathode). Over 50% yield of complete SOFC cells was achieved from the anode substrates. The boundary and porosity were well controlled to achieve desired values as described in Table 1. A complete SOFC cell was sent to a third party (Fiaxell, Lausanne, Switzerland) for performance tests including polarization (I-V) curve and electro impedance spectroscopy (EIS). Figure 6c,d show the cell before and after the performance tests. Of note, since there is no interconnect integrated with the cell sample, it is a challenge for the Au grid attached to the cell to have a perfect contact. This may impact the final results. However, the purpose of this publication is to demonstrate that the basic three-layered structure (anode, electrolyte, and cathode) made with LAM can generate a current.  
The testing results are shown in Figure 7. The cell sample was functional and an electrical current was generated. Two measurements were implemented to reflect the time dependent performance. Data with solid markers were taken right after injecting the H2 into the cell. The cell was then kept in a protective atmosphere (200 mL/min of 92%N2 + 8%H2) overnight. Data with open markers were taken after 18 h in 92%N2 + 8%H2, followed by the injection of H2. Three temperatures (700 \({}^{\circ}\)C, 800 \({}^{\circ}\)C, and 900 \({}^{\circ}\)C) were sequentially tested. The resistance of cells was found to be much higher than the SOFC made by conventional approaches such as cold spray. The higher resistance causes a lower voltage and lower current at the same time. Based on our current LAM process, the high resistance may be caused by the thickness control of the YSZ electrolyte, with the thickness being either too large or non-uniform. The second possibility is the YSZ electrolyte layer does not connect well with both the Ni-YSZ anode and LSM cathode layer (disconnection). The third issue may come from the Au grid attachment in testing. The Au grid might not be in physical contact with the testing cell during the 18 h testing period. All these issues are related to the uniformity control of the LAM process over the entire SOFC area, especially the surface roughness of the Ni-YSZ anode and thin layer printing uniformity of the YSZ electrolyte. We are currently working to improve the control process.  
Figure 6: (**a**) Complete three layered cell samples (\(30\times 30\) mm); (**b**) cross-section SEM image of the interfaces for a complete cell sample; (**c**) a cell sample is mounted with a Au grid for testing I-V curve and EIS; (**d**) the cell sample after testing.  
In future activities, a full temperature range, temperature cycling, and damp heat will be used to test its reliability and endurance. A model related to the LAM process will be built to analyze its failure mode and mechanism.