Next Article in Journal
A Series of New Manganese(II) Polynuclear Complexes Based on Nitrothiacalix[4]arenes: The Study of Interplay between Macrocycle Platform Flexibility and Structural Diversity of Coordination Compounds
Next Article in Special Issue
Comparison of the Electrochemical Performances of Solid Oxide Fuel Cells with Sputtered Thin Barrier Layers Fueled by Hydrogen or Ammonia
Previous Article in Journal
Investigation of Microstructure and Density of Atmospheric Ice Formed by High-Wind-Speed In-Cloud Icing
Previous Article in Special Issue
Recent Advances and Challenges in Thin-Film Fabrication Techniques for Low-Temperature Solid Oxide Fuel Cells
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Crystals
Volume 13
Issue 7
10.3390/cryst13071016
crystals-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Laser Machining of Nickel Oxide–Yttria Stabilized Zirconia Composite for Surface Modification in Solid Oxide Fuel Cells

by
Miguel Morales
1,2,*,
Sandra García-González
1,2,
Michaela Plch
1,2,
Dario Montinaro
3 and
Emilio Jiménez-Piqué
1,2
1
CIEFMA—Department of Materials Science and Engineering, EEBE—Campus Diagonal Besòs, Universitat Politècnica de Catalunya—BarcelonaTech, C/Eduard Maristany, 16, 08019 Barcelona, Spain
2
Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya—BarcelonaTech, C/Eduard Maristany, 16, 08019 Barcelona, Spain
3
SolydEra SpA, Viale Trento 115/117, 38017 Mezzolombardo, TN, Italy
*
Author to whom correspondence should be addressed.
Crystals 2023, 13(7), 1016; https://doi.org/10.3390/cryst13071016
Submission received: 29 May 2023 / Revised: 21 June 2023 / Accepted: 22 June 2023 / Published: 26 June 2023
(This article belongs to the Special Issue Advances of Solid Oxide Fuel Cells)
Browse Figures
Versions Notes

Abstract

:
Laser machining of the nickel oxide–yttria-stabilized zirconia (NiO–YSZ) composite in Solid Oxide Fuel Cells (SOFCs) may be an effective approach to enlarge the electrode–electrolyte interface and improve the cell performance. However, laser energy can cause thermal damage to the composite surface during the machined operation. In this work, the microstructure changes and the collateral damage caused by pulsed laser machining on the sintered NiO–YSZ of the state-of-the-art SOFCs were evaluated using complementary analysis techniques. Laser patterns consisting of parallel tracks on sintered NiO–YSZ were processed, varying the laser parameters such as frequency and laser beam energy density. The analyses evidenced a heat-affected zone (HAZ) limited to around 2 µm with microcracking, porosity reduction, and recrystallization. The changes in chemical composition, phase transformation of YSZ and mechanical properties at the machined surface were quite limited.

1. Introduction

In recent decades, numerous strategies for improving the performance and reliability of Solid Oxide Fuel Cells (SOFCs) have been proposed, e.g., from the cell configuration [1,2,3] to the improvements in the materials used as electrolyte and electrodes [4,5], among others. In the case of fuel electrode, the state-of-the-art material is composed of nickel-based yttria-stabilized zirconia (Ni–YSZ). The optimization of the several microstructure parameters in the electrode—such as the percentage of electrode constituents [6,7], the tortuosity [8,9,10], the three-phase boundaries (TPBs) [11,12], and the porosity of Ni–YSZ support [13,14,15,16]—has significantly improved the power density of SOFCs. More recently, many works have reported enhancements at the electrode–electrolyte interfaces, because the conventional interfaces cause a remarkable increase to the total ohmic and polarization resistances of SOFCs [17]. An effective approach for reducing the interfacial resistance is to increase the electrode–electrolyte interface area. In this regard, micro-patterning processes based on conventional ceramic technologies—such as powder metallurgy [18], spray deposition of YSZ particles [19], and mesh pressing of tape-casted sheets [20,21]—have been developed. Alternatively, advanced processing techniques—such as atmospheric plasma spraying [22], thermal spray [23], micro-powder imprinting method [24], inkjet printing techniques [25,26], lithography [27,28] and stereolithography [29,30]—allowed us to obtain highly complex electrode–electrolyte interfaces with excellent control and reproducibility.
Within the above framework, laser machining has emerged as an effective method for enlarging the electrode–electrolyte contact area in a controlled, flexible, and reproducible manner [31]. Another positive point of this approach is the incorporation of the laser machining step into the typical cell processing, maintaining the state-of-the-art material components and techniques already proven in the SOFC field. For the electrolyte-supported cell configuration, Cebollero et al. engraved square arrays with a lattice parameter of 28 µm and a depth up to 7 µm on YSZ [32] and hexagonal arrangements of ∼22 µm depth with 24 µm lattice parameter [33], significantly reducing their polarization resistance at the oxygen electrode–electrolyte interface. The same researchers also processed thin self-supported YSZ electrolytes to decrease strongly the ohmic resistance [34]. Using the same approach, Cai et al. [35] employed laser micro-processing on the electrolyte-supported surfaces in order to modify the electrolytes with windows-like and dimples-like array structures with 12–27 µm depth and 38–60 µm diameter. Other researchers proposed to increase the electrode–electrolyte contact area using laser-machining on the NiO–YSZ fuel electrode, which is particularly interesting for the current state-of-the-art anode-supported SOFCs. In this regard, the 2D and 3D numerical simulation studies of Konno et al. [36], Seo et al. [37] and Jin et al. [38] demonstrated that the surface enlargement with a wavy electrode–electrolyte interface is the most effective way for an anode-supported cell. Zhang et al. [39] reported an increase of 55% in power density with a wavy interface based on the pits array (80 µm depth and 110–160 µm diameter) in the NiO–YSZ anode. Furthermore, laser drilling of cylindrical hole patterns in porous Ni–YSZ cermet was implemented by Gurauskis et al. [40] and Gu et al. [41]. These researchers successfully fabricated straight open finger-like pores to increase the gas transport along the fuel electrode, thereby reducing the concentration polarization of SOFCs.
Compared to other advanced and conventional ceramic techniques, laser machining may present much higher flexibility, precision and reproducibility. However, it presents a relevant issue related to the process effectivity and quality of the laser-machined surface, because this technique usually involves a combination of photochemical evaporation and photothermal melt expulsion [42,43]. The effectivity of laser machining mainly depends on input process parameters such as beam characteristics (pulse energy, pulse width, duration and the number of pulses, beam quality, wavelength); laser characteristics (laser power, focal distance, focal distance, assist gas pressure, nozzle diameter); and drilling characteristics (angle, depth and diameter of drilling) [43,44,45,46]. The laser machining process usually causes damage to the substrate around the laser pattern. Thus, the output performance properties of laser ablation must be analyzed after laser treatment, and mainly depends on the quality characteristics (material removal rate, surface roughness, etc.); geometrical characteristics (hole/track taper, circularity…); microstructure characteristics (spatter formation, recast layer thickness, thermal damage, heat affected zone (HAZ), microcracks…) [47,48]. Previous works reported that the ablation rate of sintered NiO–YSZ substrate is lower than that of the green state of NiO–YSZ [40,49,50]. Meanwhile, the laser ablation of Ni–YSZ cermet results in a poor-quality surface. Using the optimized laser ablation parameters, the green NiO–YSZ substrates were machined to desired structures without significant changes within the microstructure of the final Ni–YSZ cermet. Despite the clear advantages of laser ablation on unsintered NiO–YSZ, some processing routes for the state-of-the-art and future SOFC generations could require post-processing treatments, using laser machining on pre-sintered or sintered NiO–YSZ. For these cases, it would be very interesting to know the effects of laser machining technology on the sintered substrate. Unfortunately, detailed damage evaluation of laser treatment in sintered NiO–YSZ is scarce in the literature. Following the above idea, the authors of this study have reported several studies about the microstructure changes caused by laser patterning in dental-grade zirconia [51,52,53] and recently YSZ for SOFC applications [54].
This work aimed to evaluate the damage produced by laser machining on sintered NiO–YSZ composites, focusing on the changes in surface topography, chemical composition, microstructure and mechanical properties. For this purpose, sintered NiO–YSZ substrates of SOFCs fabricated using industrially scalable techniques (i.e., tape casting) were machined under distinct laser machining conditions to obtain linear patterns. The surface of the laser-machined NiO–YSZ substrates was characterized using complementary microanalysis and microscopy techniques. Additionally, special attention was paid to the study of the mechanical properties at the scale of the NiO–YSZ microstructure using the instrumented Nanoindentation technique, as these properties could be critical for the functionality and structural integrity of machined NiO–YSZ anode-supported cells.

2. Materials and Methods

2.1. Preparation of NiO–YSZ Substrates

Porous NiO–YSZ substrates with a thickness of 250 μm and a surface area of 10 × 10 cm2 were manufactured by SolydEra company, which are used as anode support for state-of-the-art planar SOFCs. The processing of the substrates was optimized for the maximization of performance and stability, using commercially viable manufacturing techniques. Thus, NiO–YSZ composite was manufactured by tape-casting using water suspensions and sintered at ∼1400 °C [55,56]. Further experimental details can be found in previous works. Afterward, NiO–YSZ plates were cut to obtain specimens of 20 × 20 mm2. The surfaces of the plates were ground with 600-, 800- and 1200-grit SiC papers, and polished using 30 μm and 3 μm diamond suspensions (Norton). The density of NiO–YSZ substrates at the surface was determined using the free, open-source software, ImageJ.

2.2. Laser Machining Treatment

A solid-state Nd:YLF Q-switched laser set-up (Spectra-Physics Explorer One 349–120) was employed to machine linear tracks on the NiO–YSZ surfaces. The laser is capable of emitting laser beams at 349 nm wavelength and a pulse width of up to 5 ns. The maximum output characteristics of the laser are a nominal output power of 60 W, a beam type TEM00, and a quality factor M2 < 1.3. As shown in Figure 1, the set-up was equipped with a platform consisting of a 2-axis laser beam deflection unit that controls the movement of the focus point on the XY-plane, together with two mirrors that adjust the trajectory of the laser beams. The sample is fixed on the sample holder, which is equipped with Vernier calipers along the x-, y- and z-axis. In this work, the laser beam was incident on the target surface at a 90-degree angle, a spot size diameter of 30 μm, and a scan rate of 6.0 mm/s. Preliminary work was focused on analyzing the influence of laser machining parameters—mainly the beam laser energy density (2.9–5.1 J/cm2) and the frequency (0.4–2.0 kHz)—on the surface quality and geometry of the track. For this purpose, laser patterns consisting of parallel tracks with a pitch of 100 μm between the parallel line tracks were chosen. Adequate laser-ablation conditions were selected combining complementarily optical and scanning electron microscopy inspection of all the machined tracks, maximizing a good balance between the track height, and the surface quality. For the next experiments, of the selected tracks, the line pitch between the parallel tracks was adjusted to the dimensions of the track-like features.

2.3. Characterization Techniques

Since laser machining may induce irreversible changes, special attention was paid to evaluating possible damage induced at the surface of the machined tracks. The surface integrity evaluation was conducted through complementary analytical, microstructural and mechanical techniques.

2.3.1. Surface Topography

The topography of the laser-machined surfaces was characterized using a Contact Profilometer (Dektak 150 Stylus, Bruker, Billerica, MA, USA). A tip with a radius of 50 nm was employed at a force of 5 mg for scanning a total length of 400 µm. Confocal Laser Optical Profilometer (Olympus Lext OLS30, Tokio, Japan) equipped with several lens objectives from ×10 to ×100 was employed to determine the surface roughness of the local regions in the laser tracks. The surface roughness parameter (Ra) of blank, pile-up and valley regions for samples was determined, using the profilometer software, from the average of 5 measurements with a cut-off length of 128 µm.

2.3.2. Scanning Electron Microscopy (SEM)

The microstructure of machined samples was carried out employing a field emission scanning electron microscope (Carl Zeiss Merlin FESEM, Oberkochen, Germany) equipped with Energy Dispersive Spectroscopy (EDS) (Oxford Instruments INCA-350 system, United Kingdom). Samples were coated with carbon to minimize the electrical charge of the surface. Image analysis was performed on the top and cross-section surfaces of the laser tracks. Focused Ion Beam (FIB, Carl Zeiss Neon 40, Oberkochen, Germany) was used to prepare the cross-sections to observe the microstructure of the material, below the machined surface, with FESEM.

2.3.3. X-ray Diffraction (XRD)

The study of the crystalline phases was performed via X-ray diffraction (XRD, Bruker, D8-Advance, Karlsruhe, Germany) using Cu Kα radiation (40 kV and 40 mA). Phase identification was carried out using the JCPDS database and the DIFFRACplus EVA software by Bruker AXS.

2.3.4. Raman Spectroscopy

The location of secondary phases was determined using Raman spectroscopy (inVia Qontor, Renishaw) at a wavelength of 532 nm as the applied excitation line, and 100× objective in an optical microscope was employed.

2.3.5. X-ray Photoelectron Spectroscopy (XPS)

The chemical composition at the surface was determined with X-ray Photoelectron Spectroscopy (XPS) with a SPECS system (Surface Nano Analysis GmbH) equipped with an Al anode XR50 source operating at 150 W and a PHOIBOS 150 EP hemispherical energy analyzer with MCD-9 detector. The fitting and peak integration of spectra was carried out using Casa XPS software. The binding energies were calibrated to the C 1s peak (284.6 eV) to compensate for any charging effects.

2.3.6. Nanoindentation Tests

The mechanical properties of laser-machined surfaces were determined with the instrumented indentation technique. Tests were performed using an MTS Nanoindenter XP with a continuous stiffness measurement module. A Berkovich diamond tip was employed, which was calibrated with a fused silica standard. Experimental data were analyzed with the Oliver and Pharr method [57]. The laser-machined samples were encapsulated in a resin (Buehler, Lake Bluff, IL, USA) before the polishing and laser machining processes. In this case, the surfaces were ground with 600-, 800-, and 1200-grit SiC papers, polished using 30 μm and 3 μm diamond suspensions, and the last step with colloidal silica. Tests were carried out on the top surface of the valley and pile-up tracks, and the untreated surface. For each region explored, two arrays of 25 imprints (5 × 5) were performed at 2000 nm of maximum displacement into the surface. A constant distance of 50 μm between contiguous imprints was held to prevent the overlapping effect between imprints and to ensure the test at the center of the laser track.

3. Results and Discussion

3.1. Surface Topography

Figure 2a shows the schematic definition of the height and width for a laser track, and the effect of laser parameters (energy density and frequency) on the surface topography. Figure 2b,c exhibit the surface topography as a function of the energy density at 1.0 kHz, and varying the laser frequency at 4.3 J/cm2, respectively. Additionally, Figure 3 and Figure 4 illustrate the 3D images of surface topography as a function of the energy density and the laser frequency, respectively. Table 1 summaries the dimension values of valley and pile-up for each laser condition. Increasing the energy density from 2.9 to 5.1 J/cm2 at 1.0 kHz, Ht and Wt were increased from 0.87 μm to 3.38 μm, and from 18.5 μm to 37.1 μm, respectively. On the other side, frequencies between 0.4 kHz and 2.0 kHz at 4.3 J/cm2 generated tracks of 0.91–2.08 µm Ht and 20.8–35.1 µm Wt. For the explored conditions, the pile-up induced with the laser track contributed between 24% and 29% of the total track depth. The width attributed to the sum of the two pile-ups (Wp) was between 39% and 48% of the total track width (Wt). The pile-up may enlarge the contact surface between the electrode and electrolyte. However, the pile-up is generated with molten and evaporated material as well as splashes of redeposited material from the laser track. Therefore, its microstructure and chemical composition could be quite different compared to the unmachined material, decreasing the electrochemical and mechanical performance of the cell. The extension of material pile-up mainly depends on the accuracy of the laser. Compared with pico- or femtosecond lasers, the accuracy of our laser is much lower, which also generates a wider laser track [58].
On the other hand, laser machining produces splashes of redeposited material and cracks, which generates significant roughness along the valley and pile-up surfaces. Therefore, the roughness of the laser trench is an interesting parameter to evaluate the surface quality. Table 2 shows the roughness (Ra) determined parallel to the laser track. Ra values between 0.14 and 0.31 μm in the valley surfaces were obtained. Ra obtained for pile-up was close to that of the valley, however, these values are in the same order as the height of the pile-up, and therefore, this roughness does not seem controllable. The roughness results at the valley were larger than those of a polished surface (Ra < 0.1 μm). Therefore, the laser machining generated a roughness on the polished surface much lower than the tape-casted NiO–YSZ composite (Ra > 1 μm). Furthermore, the presence of this roughness may enhance the electrode and electrolyte adhesion.
The specific goal of this work was to reproduce laser tracks within the typical range of energy density (3.3–6.4 J/cm2) [31,49,58] for SOFC materials with good surface quality to analyze the damage and possible microstructure changes. Accordingly, laser parameters selected for the processing of laser tracks were at 4.3 J/cm2 and 1.0 kHz, thus obtaining a valley depth close to 2 μm with a roughness lower than 0.20 μm and a minimized pile-up size. This laser track presented a valley depth smaller than that required for a remarkable modification of the electrode–electrolyte interface in an anode-supported SOFC, as the valley typically presents from a few to tens of micrometers [32,33,34,35,36,37,38,39,40,41,58]. Therefore, it is assumed that this laser track was satisfactory for subsequent studies related to microstructure and phase changes, and chemical and mechanical tests. Concerning the laser patterns, two series of samples were prepared: one with the line pitch adjusted to 100 µm for SEM and Nanoindentation tests, and another with 20 µm for FIB-SEM, XRD, Raman and XPS analyses to increase the signal of possible effects due to the laser–material interaction.

3.2. Microstructure

Figure 5 shows the FESEM surface images of laser tracks fabricated at 4.3 J/cm2 and 1.0 kHz, compared to a blank surface of NiO–YSZ. The valley region of the laser track presented microcracks and a surface microstructure denser than the blank one, which is attributed to the thermal effects of laser treatment. In addition, the microstructure of the pile-up region also exhibited a lower porosity than untreated NiO–YSZ (Figure 5 and Figure 6). It is due to the material vaporization of the laser-track valley, which can be partly deposited, in nanoparticle form, on top of the pile-up surface and a region close to the valley region. The presence of the denser layer with larger NiO and YSZ mean grain size at the laser tracks could lead to undesirable effects, such as the loss of gas transport, electrical connectivity and mechanical reliability of the final product, which is a porous Ni–YSZ cermet. Therefore, it could affect the electrochemical and mechanical properties of Ni–YSZ anode in a real application. However, the reduction of the NiO–YSZ composite to Ni–YSZ cermet at the typical conditions (750 °C using from 5% H2/Ar to 100% H2) evidenced the change in this layer to form a Ni–YSZ microstructure with ~18% porosity (Figure 6).
The extension of the HAZ was studied with the FIB-FESEM images of a cross-sectional laser track and blank NiO–YSZ (Figure 7). The HAZ affected a first layer of grains (around 2 µm) below the machined surface, presenting recrystallization to equiaxial grains and decreasing the porosity in the vicinity of the machined areas (Figure 7a,b). In addition, intergranular micro-cracks were observed at the top-surface, which propagated perpendicularly to the surface (Figure 7a). This particular microstructure at the surface is typically generated due to the photothermal-mechanical process of the laser ablation, in which the material is essentially removed due to the thermal mechanisms activated through the laser radiation [42,43]. Below the recrystallized material, the microstructure of laser machined exhibited typical properties similar to the blank material (Figure 7b,c).

3.3. Crystalline Phases

The XRD spectra of the NiO–YSZ samples, before and after the laser machining process, are shown in Figure 8. Both samples presented tetragonal and two monoclinic peaks (at 28° and 31°) corresponding to YSZ. However, the monoclinic peaks were more intense in the machined sample, as these exhibited an intensity about four times higher than the blank sample (unmachined). In addition, the comparison of both XRD spectra evidenced that the most intense peak of NiO (at 43°) presented a decrease in intensity of around 6% for the machined sample. It may be mainly attributed to the major evaporation and ejection of NiO compared to YSZ during laser treatment, which is in good concordance with no presence of metallic Ni, in the position of the most intense peak at 45°, detected in the XRD of the machined sample.
To assess the location of the monoclinic phase at zirconia transformed due to the thermal effect of laser treatment on the NiO–YSZ surface, FESEM and Raman spectroscopy were combined. Figure 9 shows a FESEM image at the valley of a laser track, and Raman spectra at different points near a crack generated during the laser treatment. When qualitatively observing the Raman spectra, the monoclinic phase is mainly located close to the crack. In contrast, the zones far away from the micro-crack (points 1 and 5) presented only a tetragonal phase. These results are in good agreement with our previous work of laser treatment on the YSZ surface, in which the tetragonal phase was mainly transformed to monoclinic in the regions close to cracks [54].

3.4. Chemical Composition

The XPS technique was employed to determine the changes in the elemental composition at the surface due to the laser-machining treatment. Figure 10 shows the XPS spectra of the main elements for the unmachined and laser-machined NiO–YSZ surfaces. In Figure 10a, the Zr 3d core-level spectrum, peaks corresponding to Zr 3d3/2 (at ∼184.5 eV) and Zr 3d5/2 (at ∼182 eV) indicated the presence of Zr–O bonds typically observed in ZrO2 and YSZ [59,60]. Similarly, the Y 3d core-level spectrum consisted of two deconvoluted peaks at 157 and 159 eV, which correspond to Y 3d5/2 and Y 3d3/2 of Y–O bindings, respectively (Figure 10b). In terms of the Y2O3 dopant concentration, the estimated Y/Zr ratio after laser machining was close to the unmachined sample with a difference of less than 4%. In Figure 10c, the deconvolution of two peaks at 854 and 856 eV belong to Ni 2p3/2, and the satellite peak at 861 eV, corresponded to nickel oxide with Ni2+ and Ni3+ states, respectively [61,62,63]. The laser-machined NiO–YSZ composite presented a slight decrease in Ni, which corresponded to a reduction of about 5% for the machined sample and was in good concordance with the XRD results. The O 1s spectrum was deconvoluted in three peaks at 529, 531 and 532 eV probably associated with metal–oxygen lattice, oxygen vacancy and chemisorbed oxygen species, respectively (Figure 10d) [64,65,66]. Thus, no significant elemental segregation was detected at the surface. Both the Ni content and the Y2O3 dopant concentration in YSZ were maintained, which is crucial for guaranteeing good electronic and ionic conductivity at the anode.

3.5. Mechanical Properties

The mechanical properties of laser-treated surfaces were studied using the instrumented Nanoindentation technique, assessing the evolution of Elastic Modulus (E) and Hardness (H) with the indenter indentation depth. Figure 11 shows the mechanical properties at the valley and the pile-up of laser-machined surfaces, which were compared to the blank surface. Both E and H of the blank surface and the pile-up surface gradually decreased with increasing indentation depth. This decrease in E and H was attributed to the internal defects, such as porosity and voids, present in the NiO–YSZ composite. In contrast, the mechanical properties at the valley of laser-treated surfaces presented a significant decrease at low indentation depths (within the range of 0–200 nm), which were recovered as the indenter penetrated further into the laser-machined surfaces. This drop at low indentation depths could be due to the presence of microcracks and certain roughness at the laser-treated surface, due to the thermal effects and the induced topography caused by laser treatment. Finally, the values of E and H determined for the laser-machined NiO–YSZ surfaces were close to those reported in previous works using the nanoindentation technique [67,68].

4. Conclusions

The surface topography of the state-of-the-art NiO–YSZ composites for SOFCs was modified using a pulsed laser to explore its thermal effects on microstructure and surface quality. The main conclusions are as follows:
-
The laser machining generated up to 2 µm thick laser-affected region, which presented intergranular microcracks and recrystallization with equaxial grains. The valley surface of laser tracks presented micro-cracks and a denser microstructure than the blank one, which was attributed to the thermal effects of laser machining. The microstructure of the pile-up region also exhibited a lower porosity than the blank surface, due to the partly deposited material from vaporization.
-
XRD and XPS analyses evidenced a small decrease in Ni (<5%) in the machined sample, which was mainly due to the major evaporation and ejection of NiO compared to YSZ during laser treatment. In addition, laser machining induced the doped zirconia transformation from the tetragonal to monoclinic phase on the treated surface, which was limited to only the regions close to cracks.
-
Nanoindentation tests showed that the laser-treated surfaces only presented a decrease in elastic modulus and hardness at low indentation depths (within the range of 0–200 nm). It was attributed to the presence of micro-cracks, and certain roughness at the laser-treated surface, due to the thermal effects and the induced topography caused by laser treatment. Therefore, this corroborated that the damage and the extension of HAZ induced during the laser treatment were very limited.
All in all, laser machining could be an interesting post-processing treatment for sintered NiO–YSZ composites, as the laser-affected region at the surface was local to the selected conditions. However, the microstructure changes should be evaluated to ensure the functionality, in terms of electrochemical performance, structural integrity and reliability, of the laser-machined NiO–YSZ composites used as anode precursors in SOFC applications.

Author Contributions

Conceptualization, M.M., M.P. and E.J.-P.; methodology, M.M., S.G.-G., M.P., D.M. and E.J.-P.; software, M.M. and M.P.; validation, M.M., S.G.-G. and M.P.; formal analysis, M.M., M.P., D.M. and E.J.-P.; investigation, M.M., S.G.-G., M.P. and E.J.-P.; resources, M.M., D.M. and E.J.-P.; data curation, M.M. and M.P.; writing—original draft preparation, M.M.; writing—review and editing, M.M., S.G.-G., M.P., D.M. and E.J.-P.; visualization, M.M. and M.P.; supervision, M.M., S.G.-G., M.P., D.M. and E.J.-P.; project administration, M.M., D.M. and E.J.-P.; funding acquisition, M.M. and E.J.-P. All authors have read and agreed to the published version of the manuscript.

Funding

This research has been supported by grant PID2021-126614OB-I00, funded by MCIN/AEI/10.13039/501100011033, and AGAUR, Agency for Administration of University and Research (Agència de Gestió d’Ajuts Universitaris i de Recerca) (2021 SGR 01053). Miguel Morales Comas is Serra Húnter Lecturer Professor and he is grateful to Serra Húnter program (Generalitat de Catalunya).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Stambouli, A.B.; Traversa, E. Solid Oxide Fuel Cells (SOFCs): A Review of an Environmentally Clean and Efficient Source of Energy. Renew. Sustain. Energy Rev. 2002, 6, 433–455. [Google Scholar] [CrossRef]
  2. Singhal, S.C.; Kendall, K. High-Temperature Solid Oxide Fuel Cells: Fundamentals, Design, and Applications; Elsevier: Amsterdam, The Netherlands, 2003; p. 405. [Google Scholar]
  3. Zakaria, Z.; Abu Hassan, S.H.; Shaari, N.; Yahaya, A.Z.; Boon Kar, Y. A Review on Recent Status and Challenges of Yttria Stabilized Zirconia Modification to Lowering the Temperature of Solid Oxide Fuel Cells Operation. Int. J. Energy Res. 2020, 44, 631–650. [Google Scholar] [CrossRef]
  4. Hussain, S.; Yangping, L. Review of Solid Oxide Fuel Cell Materials: Cathode, Anode, and Electrolyte. Energy Transit. 2020, 4, 113–126. [Google Scholar] [CrossRef]
  5. Mahato, N.; Banerjee, A.; Gupta, A.; Omar, S.; Balani, K. Progress in Material Selection for Solid Oxide Fuel Cell Technology: A Review. Prog. Mater. Sci. 2015, 72, 141–337. [Google Scholar] [CrossRef]
  6. Lee, J.H.; Moon, H.; Lee, H.W.; Kim, J.; Kim, J.D.; Yoon, K.H. Quantitative Analysis of Microstructure and Its Related Electrical Property of SOFC Anode, Ni–YSZ Cermet. Solid State Ionics 2002, 148, 15–26. [Google Scholar] [CrossRef]
  7. Morales, M.; Laguna-Bercero, M.Á. Influence of Anode Functional Layers on Electrochemical Performance and Mechanical Strength in Microtubular Solid Oxide Fuel Cells Fabricated by Gel-Casting. ACS Appl. Energy Mater. 2018, 1, 2024–2031. [Google Scholar] [CrossRef] [Green Version]
  8. Brus, G.; Miyawaki, K.; Iwai, H.; Saito, M.; Yoshida, H. Tortuosity of an SOFC Anode Estimated from Saturation Currents and a Mass Transport Model in Comparison with a Real Micro-Structure. Solid State Ionics 2014, 265, 13–21. [Google Scholar] [CrossRef]
  9. Morales, M.; Laguna-Bercero, M.A.; Navarro, M.E.; Espiell, F.; Segarra, M. The Effect of Anode Support on the Electrochemical Performance of Microtubular Solid Oxide Fuel Cells Fabricated by Gel-Casting. RSC Adv. 2015, 5, 39350–39357. [Google Scholar] [CrossRef] [Green Version]
  10. Tjaden, B.; Brett, D.J.L.; Shearing, P.R. Tortuosity in Electrochemical Devices: A Review of Calculation Approaches. Int. Mater. Rev. 2016, 63, 47–67. [Google Scholar] [CrossRef] [Green Version]
  11. Smith, J.R.; Chen, A.; Gostovic, D.; Hickey, D.; Kundinger, D.; Duncan, K.L.; DeHoff, R.T.; Jones, K.S.; Wachsman, E.D. Evaluation of the Relationship between Cathode Microstructure and Electrochemical Behavior for SOFCs. Solid State Ionics 2009, 180, 90–98. [Google Scholar] [CrossRef]
  12. Bertei, A.; Ruiz-Trejo, E.; Kareh, K.; Yufit, V.; Wang, X.; Tariq, F.; Brandon, N.P. The Fractal Nature of the Three-Phase Boundary: A Heuristic Approach to the Degradation of Nanostructured Solid Oxide Fuel Cell Anodes. Nano Energy 2017, 38, 526–536. [Google Scholar] [CrossRef]
  13. Morales, M.; Laguna-Bercero, M.A. Microtubular Solid Oxide Fuel Cells Fabricated by Gel-Casting: The Role of Supporting Microstructure on the Mechanical Properties. RSC Adv. 2017, 7, 17620–17628. [Google Scholar] [CrossRef] [Green Version]
  14. Su, H.; Hu, Y.H. Progress in Low-Temperature Solid Oxide Fuel Cells with Hydrocarbon Fuels. Chem. Eng. J. 2020, 402, 126235. [Google Scholar] [CrossRef]
  15. Bernadet, L.; Morales, M.; Capdevila, X.G.; Ramos, F.; Monterde, M.C.; Calero, J.A.; Morata, A.; Torrell, M.; Tarancón, A. Reversible Fuel Electrode Supported Solid Oxide Cells Fabricated by Aqueous Multilayered Tape Casting. J. Phys. Energy 2021, 3, 024002. [Google Scholar] [CrossRef]
  16. Morales, M.; Laguna-Bercero, M.A.; Jiménez-Piqué, E. Direct-Methane Anode-Supported Solid Oxide Fuel Cells Fabricated by Aqueous Gel-Casting. J. Eur. Ceram. Soc. 2023, 43, 2740–2751. [Google Scholar] [CrossRef]
  17. He, S.; Jiang, S.P. Electrode/Electrolyte Interface and Interface Reactions of Solid Oxide Cells: Recent Development and Advances. Prog. Nat. Sci. Mater. Int. 2021, 31, 341–372. [Google Scholar] [CrossRef]
  18. Tsumori, F.; Xu, Y.; Tanaka, Y.; Osada, T.; Miura, H. Micrometer-Scale Imprinting Process for Ceramic Sheet from Powder Compound Material. Procedia Eng. 2014, 81, 1433–1438. [Google Scholar] [CrossRef] [Green Version]
  19. Dai, H.; He, S.; Chen, H.; Guo, L. A Novel Method of Modifying Electrolyte Surface at Mesoscale for Intermediate-Temperature Solid Oxide Fuel Cells. Ceram. Int. 2016, 42, 2045–2050. [Google Scholar] [CrossRef]
  20. Timurkutluk, C.; Altan, T.; Yildirim, F.; Onbilgin, S.; Yagiz, M.; Timurkutluk, B. Improving the Electrochemical Performance of Solid Oxide Fuel Cells by Surface Patterning of the Electrolyte. J. Power Sources 2021, 512, 230489. [Google Scholar] [CrossRef]
  21. Timurkutluk, C.; Altan, T.; Onbilgin, S.; Yildirim, F.; Yagiz, M.; Timurkutluk, B. Mesh Patterned Electrolyte Supports for High-Performance Solid Oxide Fuel Cells. Int. J. Energy Res. 2022, 46, 10689–10703. [Google Scholar] [CrossRef]
  22. Gao, M.; Li, C.X.; De Wang, M.; Wang, H.L.; Li, C.J. Influence of the Surface Roughness of Plasma-Sprayed YSZ on LSM Cathode Polarization in Solid Oxide Fuel Cells. Key Eng. Mater. 2008, 373–374, 641–644. [Google Scholar] [CrossRef]
  23. Wang, X.M.; Li, C.X.; Huang, J.Y.; Yang, G.J.; Li, C.J. Deposition Mechanism of Convex YSZ Particles and Effect of Electrolyte/Cathode Interface Structure on Cathode Performance of Solid Oxide Fuel Cell. Int. J. Hydrogen Energy 2014, 39, 13650–13657. [Google Scholar] [CrossRef]
  24. Xu, Y.; Tsumori, F.; Osada, T.; Miura, H. Improvement of Solid Oxide Fuel Cell by Imprinted Micropatterns on Electrolyte. Micro Nano Lett. 2013, 8, 571–574. [Google Scholar] [CrossRef]
  25. Farandos, N.M.; Kleiminger, L.; Li, T.; Hankin, A.; Kelsall, G.H. Three-Dimensional Inkjet Printed Solid Oxide Electrochemical Reactors. I. Yttria-Stabilized Zirconia Electrolyte. Electrochim. Acta 2016, 213, 324–331. [Google Scholar] [CrossRef] [Green Version]
  26. Salari, F.; Badihi Najafabadi, A.; Ghatee, M.; Golmohammad, M. Hybrid Additive Manufacturing of the Modified Electrolyte-Electrode Surface of Planar Solid Oxide Fuel Cells. Int. J. Appl. Ceram. Technol. 2020, 17, 1554–1561. [Google Scholar] [CrossRef]
  27. Okabe, T.; Kim, Y.; Jiao, Z.; Shikazono, N.; Taniguchi, J. Fabrication Process for Micropatterned Ceramics via UV-Nanoimprint Lithography Using UV-Curable Binder. Jpn. J. Appl. Phys. 2018, 57, 106501. [Google Scholar] [CrossRef]
  28. Akama, R.; Okabe, T.; Sato, K.; Inaba, Y.; Shikazono, N.; Sciazko, A.; Taniguchi, J. Fabrication of a Micropatterned Composite Electrode for Solid Oxide Fuel Cells via Ultraviolet Nanoimprint Lithography. Microelectron. Eng. 2020, 225, 111277. [Google Scholar] [CrossRef]
  29. Masciandaro, S.; Torrell, M.; Leone, P.; Tarancón, A. Three-Dimensional Printed Yttria-Stabilized Zirconia Self-Supported Electrolytes for Solid Oxide Fuel Cell Applications. J. Eur. Ceram. Soc. 2019, 39, 9–16. [Google Scholar] [CrossRef] [Green Version]
  30. Pesce, A.; Hornés, A.; Núñez, M.; Morata, A.; Torrell, M.; Tarancón, A. 3D Printing the next Generation of Enhanced Solid Oxide Fuel and Electrolysis Cells. J. Mater. Chem. A 2020, 8, 16926–16932. [Google Scholar] [CrossRef]
  31. Merino, R.I.; Laguna-Bercero, M.A.; Lahoz, R.; Larrea, Á.; Oliete, P.B.; Orera, A.; Peña, J.I.; Sanjuán, M.L.; Sola, D. Laser Processing of Ceramic Materials for Electrochemical and High Temperature Energy Applications. Boletín Soc. Española Cerámica Vidr. 2021, 61, S19–S39. [Google Scholar] [CrossRef]
  32. Cebollero, J.A.; Lahoz, R.; Laguna-Bercero, M.A.; Larrea, A. Tailoring the Electrode-Electrolyte Interface of Solid Oxide Fuel Cells (SOFC) by Laser Micro-Patterning to Improve Their Electrochemical Performance. J. Power Sources 2017, 360, 336–344. [Google Scholar] [CrossRef]
  33. Cebollero, J.A.; Laguna-Bercero, M.A.; Lahoz, R.; Silva, J.; Moreno, R.; Larrea, A. Optimization of Laser-Patterned YSZ-LSM Composite Cathode-Electrolyte Interfaces for Solid Oxide Fuel Cells. J. Eur. Ceram. Soc. 2019, 39, 3466–3474. [Google Scholar] [CrossRef] [Green Version]
  34. Cebollero, J.A.; Lahoz, R.; Laguna-Bercero, M.A.; Peña, J.I.; Larrea, A.; Orera, V.M. Characterization of Laser-Processed Thin Ceramic Membranes for Electrolyte-Supported Solid Oxide Fuel Cells. Int. J. Hydrogen Energy 2017, 42, 13939–13948. [Google Scholar] [CrossRef]
  35. Cai, G.; Zhang, Y.; Dai, H.; He, S.; Ge, L.; Chen, H.; Guo, L. Modification of Electrode/Electrolyte Interface by Laser Micro-Processing for Solid Oxide Fuel Cell. Mater. Lett. 2017, 195, 232–235. [Google Scholar] [CrossRef]
  36. Konno, A.; Iwai, H.; Saito, M.; Yoshida, H. A Corrugated Mesoscale Structure on Electrode–Electrolyte Interface for Enhancing Cell Performance in Anode-Supported SOFC. J. Power Sources 2011, 196, 7442–7449. [Google Scholar] [CrossRef]
  37. Seo, H.; Kishimoto, M.; Nakagawa, T.; Iwai, H.; Yoshida, H. Mechanism of Improved Electrochemical Performance of Anode-Supported Solid Oxide Fuel Cells by Mesostructural Modification of Electrode–Electrolyte Interface. J. Power Sources 2021, 506, 230107. [Google Scholar] [CrossRef]
  38. Liu, P.; Fan, S.; Liu, Y.; Han, X.; Jin, Z. Three-Dimensional Modeling of Anode-Supported Planar SOFC with Corrugated Electrolyte. J. Electrochem. Soc. 2021, 168, 104501. [Google Scholar] [CrossRef]
  39. Zhang, Y.; Cai, G.; Gu, Y.; Ge, L.; Zheng, Y.; Chen, H.; Guo, L. Modifying the Electrode-Electrolyte Interface of Anode Supported Solid Oxide Fuel Cells (SOFCs) by Laser-Machining. Energy Convers. Manag. 2018, 171, 1030–1037. [Google Scholar] [CrossRef]
  40. Gurauskis, J.; Sola, D.; Peña, J.I.; Orera, V.M. Laser Drilling of Ni–YSZ Cermets. J. Eur. Ceram. Soc. 2008, 28, 2673–2680. [Google Scholar] [CrossRef]
  41. Gu, D.; Shi, N.; Yu, F.; Zheng, Y.; Chen, H.; Guo, L. Asymmetric Anode Substrate Fabricated by Phase Inversion Process and Its Interface Modification for Solid Oxide Fuel Cells. J. Alloys Compd. 2018, 742, 20–28. [Google Scholar] [CrossRef]
  42. Samant, A.N.; Dahotre, N.B. Laser Machining of Structural Ceramics—A Review. J. Eur. Ceram. Soc. 2009, 29, 969–993. [Google Scholar] [CrossRef]
  43. Gautam, G.D.; Pandey, A.K. Pulsed Nd:YAG Laser Beam Drilling: A Review. Opt. Laser Technol. 2018, 100, 183–215. [Google Scholar] [CrossRef]
  44. Liang, L.; Yuan, J.; Lin, G. Effect of the Scanning Speed on the Microgroove Formation Regime in Nanosecond-Pulsed Laser Scanning Ablation of Cermet. Int. J. Adv. Manuf. Technol. 2020, 107, 97–107. [Google Scholar] [CrossRef]
  45. Tsibidis, G.D.; Mansour, D.; Stratakis, E. Damage Threshold Evaluation of Thin Metallic Films Exposed to Femtosecond Laser Pulses: The Role of Material Thickness. Opt. Laser Technol. 2022, 156, 108484. [Google Scholar] [CrossRef]
  46. Mutlu, M.; Kacar, E.; Akman, E.; Akkan, C.K.; Demir, P.; Demir, A. Effects of The Laser Wavelength on Drilling Process of Ceramic Using Nd:YAG Laser. JLMN J. Laser Micro/Nanoeng. 2009, 4, 84–88. [Google Scholar] [CrossRef]
  47. Hejjaji, A.; Singh, D.; Kubher, S.; Kalyanasundaram, D.; Gururaja, S. Machining damage in FRPs: Laser versus conventional drilling. Compos. A: Appl. Sci. Manuf. 2016, 82, 42–52. [Google Scholar] [CrossRef]
  48. Solati, A.; Hamedi, M.; Safarabadi, M. Comprehensive Investigation of Surface Quality and Mechanical Properties in CO 2 Laser Drilling of GFRP Composites. Int. J. Adv. Manuf. Technol. 2019, 102, 791–808. [Google Scholar] [CrossRef]
  49. Sola, D.; Gurauskis, J.; Peña, J.I.; Orera, V.M. Cold Laser Machining of Nickel-Yttrium Stabilised Zirconia Cermets: Composition Dependence. Mater. Res. Bull. 2009, 44, 1910–1915. [Google Scholar] [CrossRef]
  50. Malbakhova, I.; Bagishev, A.; Vorobyev, A.; Borisenko, T.; Logutenko, O.; Titkov, A. Fabrication of NiO/YSZ-Based Anodes for Solid Oxide Fuel Cells by Hybrid 3D Inkjet Printing and Laser Treatment. Ceramics 2022, 5, 1115–1127. [Google Scholar] [CrossRef]
  51. Roitero, E.; Lasserre, F.; Anglada, M.; Mücklich, F.; Jiménez-Piqué, E. A Parametric Study of Laser Interference Surface Patterning of Dental Zirconia: Effects of Laser Parameters on Topography and Surface Quality. Dent. Mater. 2017, 33, e28–e38. [Google Scholar] [CrossRef] [Green Version]
  52. Roitero, E.; Lasserre, F.; Roa, J.J.; Anglada, M.; Mücklich, F.; Jiménez-Piqué, E. Nanosecond-Laser Patterning of 3Y-TZP: Damage and Microstructural Changes. J. Eur. Ceram. Soc. 2017, 37, 4876–4887. [Google Scholar] [CrossRef]
  53. Roitero, E.; Anglada, M.; Mücklich, F.; Jiménez-Piqué, E. Mechanical Reliability of Dental Grade Zirconia after Laser Patterning. J. Mech. Behav. Biomed. Mater. 2018, 86, 257–263. [Google Scholar] [CrossRef] [Green Version]
  54. Morales, M.; García-González, S.; Rieux, J.; Jiménez-Piqué, E. Nanosecond Pulsed Laser Surface Modification of Yttria Doped Zirconia for Solid Oxide Fuel Cell Applications: Damage and Microstructural Changes. J. Eur. Ceram. Soc. 2023, 43, 3396–3403. [Google Scholar] [CrossRef]
  55. Alenazey, F.; Alyousef, Y.; Brancaccio, E.; Montinaro, D. Parameters Affecting CO2 Production in a Planar Anode Supported SOFC Based System. Int. J. Hydrogen Energy 2015, 40, 642–651. [Google Scholar] [CrossRef]
  56. Alenazey, F.; Alyousef, Y.; Almisned, O.; Almutairi, G.; Ghouse, M.; Montinaro, D.; Ghigliazza, F. Production of Synthesis Gas (H2 and CO) by High-Temperature Co-Electrolysis of H2O and CO2. Int. J. Hydrogen Energy 2015, 40, 10274–10280. [Google Scholar] [CrossRef]
  57. Oliver, W.C.; Pharr, G.M. Measurement of Hardness and Elastic Modulus by Instrumented Indentation: Advances in Understanding and Refinements to Methodology. J. Mater. Res. 2004, 19, 3–20. [Google Scholar] [CrossRef]
  58. Marquardt, T.; Hollmann, J.; Gimpel, T.; Schade, W.; Kabelac, S. Femtosecond Laser-Induced Surface Modification of the Electrolyte in Solid Oxide Electrolysis Cells. Energies 2020, 13, 6562. [Google Scholar] [CrossRef]
  59. Zhu, W.; Nakashima, S.; Marin, E.; Gu, H.; Pezzotti, G. Microscopic Mapping of Dopant Content and Its Link to the Structural and Thermal Stability of Yttria-Stabilized Zirconia Polycrystals. J. Mater. Sci. 2020, 55, 524–534. [Google Scholar] [CrossRef]
  60. Parmigiani, F.; Depero, L.E.; Sangaletti, L.; Samoggia, G. An XPS Study of Yttria-Stabilised Zirconia Single Crystals. J. Electron Spectros. Relat. Phenomena 1993, 63, 1–10. [Google Scholar] [CrossRef]
  61. Lu, Q.H.; Huang, R.; Wang, L.S.; Wu, Z.G.; Li, C.; Luo, Q.; Zuo, S.Y.; Li, J.; Peng, D.L.; Han, G.L.; et al. Thermal Annealing and Magnetic Anisotropy of NiFe Thin Films on N+-Si for Spintronic Device Applications. J. Magn. Magn. Mater. 2015, 394, 253–259. [Google Scholar] [CrossRef]
  62. Kalita, C.; Sarkar, R.D.; Verma, V.; Bharadwaj, S.K.; Kalita, M.C.; Boruah, P.K.; Das, M.R.; Saikia, P. Bayesian Modeling Coherenced Green Synthesis of NiO Nanoparticles Using Camellia Sinensis for Efficient Antimicrobial Activity. Bionanoscience 2021, 11, 825–837. [Google Scholar] [CrossRef]
  63. Cabello, A.; Gayán, P.; García-Labiano, F.; De Diego, L.F.; Abad, A.; Izquierdo, M.T.; Adánez, J. Relevance of the Catalytic Activity on the Performance of a NiO/CaAl2O4 Oxygen Carrier in a CLC Process. Appl. Catal. B Environ. 2014, 147, 980–987. [Google Scholar] [CrossRef]
  64. Grosvenor, A.P.; Biesinger, M.C.; Smart, R.S.C.; McIntyre, N.S. New Interpretations of XPS Spectra of Nickel Metal and Oxides. Surf. Sci. 2006, 600, 1771–1779. [Google Scholar] [CrossRef]
  65. Ji, S.; Kim, S.K.; Choi, S.H.; Byun, J.S.; Kim, D.K.; Lee, H.J.; Choi, H.M.; Song, W.; Myung, S.; Suk, J.; et al. Yttria-Stabilized Zirconia Nanoparticles Carbon Nanotube Composite as a Polysulfide-Capturing Lithium-Sulfur Battery Separator. ACS Appl. Energy Mater. 2022, 5, 12196–12205. [Google Scholar] [CrossRef]
  66. Luo, S.; Li, X.; Wang, M.; Zhang, X.; Gao, W.; Su, S.; Liu, G.; Luo, M. Long-term electrocatalytic N2 fixation by MOF-derived Y-stabilized ZrO2: An insight into deactivation mechanism. J. Mater. Chem. A. 2020, 8, 5647–5654. [Google Scholar] [CrossRef]
  67. Roa, J.J.; Ruiz-Morales, J.C.; Canales-Vazquez, J.; Morales, M.; Capdevila, X.G.; Nuñez, P.; Segarra, M. Mechanical characterisation at nanometric scale of a new design of SOFCs. Fuel Cells 2011, 11, 124–130. [Google Scholar] [CrossRef]
  68. Xiang, Z.; Fenghui, W.; Jianye, H.; Tiejun, L. Determining the mechanical properties of solid oxide fuel cell by an improved work of indentation approach. J. Power Sources 2012, 201, 231–235. [Google Scholar] [CrossRef]
Crystals 13 01016 g001 550
Figure 1. Sketch of laser equipment and optical composing the experimental setup at our laboratory.
Figure 1. Sketch of laser equipment and optical composing the experimental setup at our laboratory.
Crystals 13 01016 g001
Crystals 13 01016 g002 550
Figure 2. (a) Scheme of the profile for a laser track on a sample, indicating that Hv corresponds to the height valley; Hp, the pile-up height; Ht, the total height of track; Wv, the laser width; Wp, the pile-up width; and Wt, the total width of track. Topographic profiles of the laser tracks, recorded perpendicularly to the laser trench, varying: (b) the laser beam energy density at 1.0 kHz, and (c) the frequency at 4.3 J/cm2.
Figure 2. (a) Scheme of the profile for a laser track on a sample, indicating that Hv corresponds to the height valley; Hp, the pile-up height; Ht, the total height of track; Wv, the laser width; Wp, the pile-up width; and Wt, the total width of track. Topographic profiles of the laser tracks, recorded perpendicularly to the laser trench, varying: (b) the laser beam energy density at 1.0 kHz, and (c) the frequency at 4.3 J/cm2.
Crystals 13 01016 g002
Crystals 13 01016 g003 550
Figure 3. Topographic profiles for laser machined surfaces obtained at 1.0 kHz frequency and a laser energy density of: (a) 2.9 J/cm2, (b) 3.6 J/cm2, (c) 4.3 J/cm2, and (d) 5.1 J/cm2.
Figure 3. Topographic profiles for laser machined surfaces obtained at 1.0 kHz frequency and a laser energy density of: (a) 2.9 J/cm2, (b) 3.6 J/cm2, (c) 4.3 J/cm2, and (d) 5.1 J/cm2.
Crystals 13 01016 g003
Crystals 13 01016 g004 550
Figure 4. Topographic profiles for laser machined surfaces obtained at a laser energy density of 4.3 J/cm2 and a frequency of: (a) 0.4 kHz, (b) 0.6 kHz, (c) 1.0 kHz, and (d) 2.0 kHz.
Figure 4. Topographic profiles for laser machined surfaces obtained at a laser energy density of 4.3 J/cm2 and a frequency of: (a) 0.4 kHz, (b) 0.6 kHz, (c) 1.0 kHz, and (d) 2.0 kHz.
Crystals 13 01016 g004
Crystals 13 01016 g005 550
Figure 5. FESEM surface images of: (a) three laser tracks fabricated at 4.3 J/cm2 and 1.0 kHz, (b,c) the valley region, and (d,e) the pile-up region; and (f–h) blank NiO–YSZ.
Figure 5. FESEM surface images of: (a) three laser tracks fabricated at 4.3 J/cm2 and 1.0 kHz, (b,c) the valley region, and (d,e) the pile-up region; and (f–h) blank NiO–YSZ.
Crystals 13 01016 g005
Crystals 13 01016 g006 550
Figure 6. FESEM images of laser tracks fabricated at 4.3 J/cm2 and 1.0 kHz, showing surface porosity (in highlighted in blue) corresponding to: (a–d) the valley region, and (e–h) the pile-up region; and (i–l) blank for NiO–YSZ and Ni–YSZ.
Figure 6. FESEM images of laser tracks fabricated at 4.3 J/cm2 and 1.0 kHz, showing surface porosity (in highlighted in blue) corresponding to: (a–d) the valley region, and (e–h) the pile-up region; and (i–l) blank for NiO–YSZ and Ni–YSZ.
Crystals 13 01016 g006
Crystals 13 01016 g007 550
Figure 7. FIB-FESEM images of the cross-section corresponding to: (a,b) a laser machined surface at 4.3 J/cm2 and 1.0 kHz, and (c) a blank surface (unmachined).
Figure 7. FIB-FESEM images of the cross-section corresponding to: (a,b) a laser machined surface at 4.3 J/cm2 and 1.0 kHz, and (c) a blank surface (unmachined).
Crystals 13 01016 g007
Crystals 13 01016 g008 550
Figure 8. (a) XRD spectra of the blank and laser machined NiO–YSZ at 4.3 J/cm2 and 1.0 kHz, and (b) zoom graph of XRD spectra within the 26–34° region. Diffraction peaks of the monoclinic phase are indicated with “m”.
Figure 8. (a) XRD spectra of the blank and laser machined NiO–YSZ at 4.3 J/cm2 and 1.0 kHz, and (b) zoom graph of XRD spectra within the 26–34° region. Diffraction peaks of the monoclinic phase are indicated with “m”.
Crystals 13 01016 g008
Crystals 13 01016 g009 550
Figure 9. (a) FESEM image, and (b) Raman spectra of the laser machined surface at the points marked with numbers. Raman peaks of the monoclinic and tetragonal phases are indicated with “m” and “t”.
Figure 9. (a) FESEM image, and (b) Raman spectra of the laser machined surface at the points marked with numbers. Raman peaks of the monoclinic and tetragonal phases are indicated with “m” and “t”.
Crystals 13 01016 g009
Crystals 13 01016 g010 550
Figure 10. XPS spectra of: (a) Zr, (b) Y, (c) Ni, and (d) O, for the blank and laser-treated NiO–YSZ surfaces at 4.3 J/cm2 and 1.0 kHz.
Figure 10. XPS spectra of: (a) Zr, (b) Y, (c) Ni, and (d) O, for the blank and laser-treated NiO–YSZ surfaces at 4.3 J/cm2 and 1.0 kHz.
Crystals 13 01016 g010
Crystals 13 01016 g011 550
Figure 11. (a) Elastic Modulus and (b) Hardness as a function of the indentation depth, testing on the valley of the laser-track, pile-up (laser-tracked peripheral surface), and blank surface.
Figure 11. (a) Elastic Modulus and (b) Hardness as a function of the indentation depth, testing on the valley of the laser-track, pile-up (laser-tracked peripheral surface), and blank surface.
Crystals 13 01016 g011
Table
Table 1. Values of Hv the height valley; Hp, the pile-up height; Ht, the total height of track; Wv, the laser width; Wp, the pile-up width; and Wt, the total width of track for each energy density and frequency of the laser machined surfaces.
Table 1. Values of Hv the height valley; Hp, the pile-up height; Ht, the total height of track; Wv, the laser width; Wp, the pile-up width; and Wt, the total width of track for each energy density and frequency of the laser machined surfaces.
Energy Density
(J/cm2)		Frequency
(kHz)		Hv (µm)Hp (µm)Ht (µm)Wv (µm)Wp (µm)Wt (µm)
2.91.00.72 ± 0.070.27 ± 0.080.91 ± 0.1213.2 ± 0.54.1 ± 0.320.8 ± 1.2
4.30.40.67 ± 0.070.23 ± 0.070.87 ± 0.1411.5 ± 0.43.8 ± 0.318.5 ± 1.1
4.30.60.81 ± 0.090.36 ± 0.081.05 ± 0.1515.3 ± 0.74.4 ± 0.224.1 ± 1.2
3.61.01.12 ± 0.110.41 ± 0.101.31 ± 0.1815.1 ± 0.85.8 ± 0.826.7 ± 2.2
4.31.01.48 ± 0.130.45 ± 0.111.86 ± 0.2116.4 ± 0.96.1 ± 0.928.6 ± 2.6
4.32.01.71 ± 0.180.59 ± 0.122.08 ± 0.2818.7 ± 0.88.2 ± 1.135.1 ± 2.8
5.11.02.82 ± 0.260.86 ± 0.133.38 ± 0.3819.3 ± 0.98.9 ± 1.237.1 ± 2.7
Table
Table 2. Values of surface roughness (Ra) at the laser machined surfaces recorded parallel to the laser trench in the valley region.
Table 2. Values of surface roughness (Ra) at the laser machined surfaces recorded parallel to the laser trench in the valley region.
Energy Density (J/cm2)Frequency (kHz) Ra at Valley (µm)
2.91.00.16 ± 0.03
4.30.40.14 ± 0.03
4.30.60.15 ± 0.02
3.61.00.17 ± 0.02
4.31.00.18 ± 0.03
4.32.00.28 ± 0.08
5.11.00.31 ± 0.09
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Morales, M.; García-González, S.; Plch, M.; Montinaro, D.; Jiménez-Piqué, E. Laser Machining of Nickel Oxide–Yttria Stabilized Zirconia Composite for Surface Modification in Solid Oxide Fuel Cells. Crystals 2023, 13, 1016. https://doi.org/10.3390/cryst13071016

AMA Style

Morales M, García-González S, Plch M, Montinaro D, Jiménez-Piqué E. Laser Machining of Nickel Oxide–Yttria Stabilized Zirconia Composite for Surface Modification in Solid Oxide Fuel Cells. Crystals. 2023; 13(7):1016. https://doi.org/10.3390/cryst13071016

Chicago/Turabian Style

Morales, Miguel, Sandra García-González, Michaela Plch, Dario Montinaro, and Emilio Jiménez-Piqué. 2023. "Laser Machining of Nickel Oxide–Yttria Stabilized Zirconia Composite for Surface Modification in Solid Oxide Fuel Cells" Crystals 13, no. 7: 1016. https://doi.org/10.3390/cryst13071016

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop