Atomic Layer Deposition Of ZrO2 Research Articles

Ultrathin ZrO2 thickness control on TiO2/ZrO2 core/shell nanoparticles using ZrO2 atomic layer deposition and etching

Atomic layer deposition (ALD) and atomic layer etching (ALE) techniques were used to control the ZrO2 shell thickness on TiO2/ZrO2 core/shell nanoparticles. ALD and ALE were performed at 200 °C while the nanoparticles were agitated using a rotary reactor. To increase the ZrO2 shell thickness, ZrO2 ALD films were deposited using sequential exposures of tetrakis(dimethylamino) zirconium and H2O. Ex situ analysis using transmission electron microscopy (TEM) observed the growth of the ZrO2 shells. The ZrO2 ALD led to more spherical ZrO2 shells on the crystalline and irregular TiO2 cores. The ZrO2 ALD on the nanoparticles had a growth rate of 0.9 ± 0.1 Å/cycle. Tunable ZrO2 coatings were observed with thicknesses ranging from 5.9 to 27.1 nm after 240 ZrO2 ALD cycles. To demonstrate the decrease in the ZrO2 shell thickness, the ZrO2 film was then etched using sequential hydrogen fluoride (HF) and TiCl4 exposures. Quadrupole mass spectrometry experiments performed in a separate reactor identified the volatile products during ZrO2 ALE. H2O was monitored during HF exposures, and ZrCl4 etch products and TiFxCly ligand-exchange products were observed during TiCl4 exposures. Ex situ TEM studies revealed that the ZrO2 shells remained spherical during ZrO2 ALE. The ZrO2 ALE on the nanoparticles had an etch rate of 6.5 ± 0.2 Å/cycle. Tunable ZrO2 coatings were produced from 27.1 down to 7.6 nm using 30 ZrO2 ALE cycles. This study demonstrated that ZrO2 ALD and ZrO2 ALE can control the thickness of ZrO2 shells on TiO2/ZrO2 core/shell nanoparticles without inducing nanoparticle agglomeration.

Novel deuterated cyclopentadienyl zirconium/hafnium precursors for atomic layer deposition of high-performance ZrO2/HfO2 thin films

The need to improve the electrical properties of ZrO2 and HfO2 thin films deposited by atomic layer deposition (ALD), which is widely used in the field of microelectronics, is growing. Attempts to improve precursor stability unavoidably lead to reduced reactivity and diminished utility. Therefore, we synthesized and developed two new ALD precursors by introducing deuterium, which simultaneously exhibit enhanced thermal stability and enhanced reactivity as a result of the introduction of deuterium. For the substitution of deuterium for hydrogen in the precursors responsible for the enhanced thermal stability, we experimentally and theoretically demonstrated that thermal stability and reactivity can be simultaneously enhanced by reducing the bonding dissociation energy of ligands that have not undergone deuterium substitution. This observation led to the development of ZrO2 and HfO2 ALD processes that result in no impurities within the thin films and minimal substrate damage even at a very high deposition temperature of 400 °C. In particular, the improvement in crystallinity through ultra-high-temperature ALD deposition resulted in excellent electrical properties in a metal–insulator–metal capacitor in which the film was incorporated; the capacitor demonstrated a dielectric constant of 37.9 and leakage current of 3.52 × 10−9 A cm−2, without the need for a subsequent annealing process.

Investigation of intermediates formation in the CO2 hydrogenation to methanol reaction over Ni5Ga3-ZrO2-SBA-15 materials prepared via ZrO2 atomic layer deposition

The production of methanol through CO2 hydrogenation holds great promise for efficient CO2 utilization. The development of catalysts that exclusively favor the formate route is desirable as this enhances methanol selectivity and avoids CO formation. Here, the synthesis of two groups of Ni5Ga3-ZrO2-SBA-15 based materials was studied through the atomic layer deposition (ALD) of ZrO2. The first group was prepared applying ZrO2 ALD over a Ni5Ga3/SBA-15 material and the second group was prepared doing ZrO2 ALD over a mesoporous silica, Santa Barbara Amorphous (SBA-15), followed by impregnation with Ni5Ga3. Some characterization techniques were employed to assess the effectiveness of the ZrO2 ALD on both groups. Interestingly, it was observed that ZrO2 deposition was less effective over the Ni5Ga3/SBA-15 sample compared to its deposition over pure SBA-15, and through XPS analysis was noticed that ZrO2 is probably covering part of the Ni5Ga3 alloys. Furthermore, in situ DRIFTS analysis was performed during reaction conditions and revealed that ZrO2 deposition facilitated the formation of formate and methoxy intermediates in both material groups. The increase in the ZrO2 ALD cycles increased the formate and methoxy bands and decreased CO-related bands. After 6 cycles, only the ZrSBANG_6 catalyst exclusively followed the formate route, as only formate and methoxy bands were present.

Electronic properties of ZrO2 films fabricated via atomic layer deposition on 4H-SiC and Si substrates

Being an important semiconductor material for high power applications, silicon carbide (SiC) faces the problems while used as a gate oxygen layer in traditional Si MOS devices. In view of this, an innovative approach was adopted in the present work to replace the conventional SiO2 with a high-k material (ZrO2) as the gate oxygen layer to investigate its effect on the electrical characteristics of the devices. In particular ZrO2 films were deposited on Si and SiC substrates by atomic layer deposition (ALD), and Al was used as the electrode. The atomic force microscopy (AFM) microregion scan revealed a highly flat surface with Rq < 1 nm after the ALD growth of ZrO2 layer. The sample surface analysis via x-ray photoelectron spectroscopy (XPS) suggested the presence of a small amount of ZrOx components. According to the electron energy loss spectrum (EELS), the band gap width (Eg) of this ALD ZrO2 dielectric was 5.45 eV, which met the requirements for high-quality 4H-SiC-related MOS devices. The electrical properties of the samples were then studied, and the maximum breakdown voltage of the Al/ZrO2/SiC/Al MOS structure was obtained to be 23 V, i.e., nearly twice that of the Si substrate. As for the oxide layer, the interface defect density (Dit) near the conduction band of the Al/ZrO2/SiC/Al MOS structure was only 1012 eV−1 cm−2 orders of magnitude. The Neff value (the movable charge) of the structure was also controlled at 1012 cm−2. Therefore, the overall performance of the ZrO2/SiC structure in terms of electrical properties exceeded that of the ZrO2/Si structure and previously reported counterparts. In this respect, the ZrO2/SiC MOS capacitor structure has great research potential.

Towards modeling of ZrO2 atomic layer deposition at reactor scale based on experimental kinetic approximation

In this study, the growth kinetics of ZrO2 via the atomic layer deposition (ALD) using a mixed alkylamido-cyclopentadienyl zirconium precursor are proposed based on experimental data to evaluate the film growth behavior using reactor-scale simulation. In the ALD process, the hydroxyl concentration on the targeted surface govern the saturated growth per cycle values. However, we found that the bulkiness of remaining ligands on adsorbed species hinders the adsorption of Cp-Zr molecules.Considering this phenomenon, we proposed a kinetic model by calculating the energetic terms to quantify the “steric hindrance effect” of the first elementary surface reaction of CpZr(N(CH3)2)3 precursor (Cp-Zr), which enables the film growth prediction with the reactor-scale computational fluid dynamic (CFD) model.According to the experimental ALD process, the film growth was found to be influenced by the steric hindrance factor, especially at the temperature range from 150 °C to 250 °C, but the hindrance effect decreases with increasing temperature and disappears at 300 °C. The effective activation energy of the adsorption of Cp-Zr molecules on Si substrate was estimated to be 0.175 eV. Further understanding of the kinetic of ZrO2 deposition in this study is estimated to contribute to the optimization of the high-k metal oxides ALD deposition processes.

Simultaneous Performance and Stability Enhancement in Intermediate Temperature Solid Oxide Fuel Cells by Powder-Atomic Layer Deposited LSCF@ZrO2 Cathodes.

Employing porous structures is essential in high-performance electrochemical energy devices. However, obtaining uniform functional coatings on high-tortuosity structures can be challenging, even with specialized processes such as atomic layer deposition (ALD). Herein, a novel method for achieving a porous composite electrode for solid oxide fuel cells by coating La0.6 Sr0.4 Co0.2 Fe0.8 O3 -δ (LSCF) powders with ZrO2 using a powder ALD process is presented. Unlike conventional ALD, powder ALD can be used to fabricate extremely uniform coatings on porous electrodes with a thickness of tens of micrometers. The powder ALD ZrO2 coating is found to effectively suppress chemical degradation of the LSCF electrodes. The cell with the powder ALD coated cathode shows a 2.2 times higher maximum power density and 60% lower thermal degradation in activation resistance than the bare LSCF cathode cell at 700-750 °C. The result demonstrated in this study is expected to have significant implications for high-performance and durable electrodes in energy conversion/storage devices.

Resolving the Heat Generated from ZrO2 Atomic Layer Deposition Surface Reactions.

In situ pyroelectric calorimetry and spectroscopic ellipsometry were used to investigate surface reactions in atomic layer deposition (ALD) of zirconium oxide (ZrO2 ). Calibrated and time-resolved in situ ALD calorimetry provides new insights into the thermodynamics and kinetics of saturating surface reactions for tetrakis(dimethylamino)zirconium(IV) (TDMAZr) and water. The net ALD reaction heat ranged from 0.197 mJ cm-2 at 76 °C to 0.155 mJ cm-2 at 158 °C, corresponding to an average of 4.0 eV/Zr at all temperatures. A temperature dependence for reaction kinetics was not resolved over the range investigated. The temperature dependence of net reaction heat and distribution among metalorganic and oxygen source exposure is attributed to factors including growth rate, equilibrium surface hydroxylation, and the extent of the reaction. ZrO2 -forming surface reactions were investigated computationally using DFT methods to better understand the influence of surface hydration on reaction thermodynamics.

Ultra-thin ZrO2 overcoating on CuO-ZnO-Al2O3 catalyst by atomic layer deposition for improved catalytic performance of CO2 hydrogenation to dimethyl ether

An ultra-thin overcoating of zirconium oxide (ZrO2) film on CuO-ZnO-Al2O3 (CZA) catalysts by atomic layer deposition (ALD) was proved to enhance the catalytic performance of CZA/HZSM-5 (H form of Zeolite Socony Mobil-5) bifunctional catalysts for hydrogenation of CO2 to dimethyl ether (DME). Under optimal reaction conditions (i.e. 240 °C and 2.8 MPa), the yield of product DME increased from 17.22% for the bare CZA/HZSM-5 catalysts, to 18.40% for the CZA catalyst after 5 cycles of ZrO2 ALD with HZSM-5 catalyst. All the catalysts modified by ZrO2 ALD displayed significantly improved catalytic stability of hydrogenation of CO2 to DME reaction, compared to that of CZA/HZSM-5 bifunctional catalysts. The loss of DME yield in 100 h of reaction was greatly mitigated from 6.20% (loss of absolute value) to 3.01% for the CZA catalyst with 20 cycles of ZrO2 ALD overcoating. Characterizations including hydrogen temperature programmed reduction, x-ray powder diffraction, and x-ray photoelectron spectroscopy revealed that there was strong interaction between Cu active centers and ZrO2.

Three-Dimensional Metal-Insulator-Metal Decoupling Capacitors with Optimized ZrO2 ALD Properties for Improved Electrical and Reliability Parameters

Embedded three-dimensional (3-D) metal-insulator-metal (MIM) decoupling capacitors with high-κ dielectric films of high capacitance and long-life time are increasingly needed on integrated chips. Towards achieving better electrical performance, there is a need for investigation into the influence of the variation in atomic layer deposition (ALD) parameters used for thin high-κ dielectric films (10 nm) made of Al2O3-doped ZrO2. This variation should always be related to the structural uniformity, the electrical characteristics, and the electrical reliability of the capacitors. This paper discusses the influence of different Zr precursor pulse times per ALD cycle and deposition temperatures (283 °C/556 K and 303 °C/576 K) with respect to the capacitance density (C-V), voltage linearity and leakage current density (I-V). Moreover, the dielectric breakdown and TDDB characteristics are evaluated under a wide range of temperatures (223-423 K).

Reaction mechanism of atomic layer deposition of zirconium oxide using zirconium precursors bearing amino ligands and water.

As a unique nanofabrication technology, atomic layer deposition (ALD) has been widely used for the preparation of various materials in the fields of microelectronics, energy and catalysis. As a high-κ gate dielectric to replace SiO2, zirconium oxide (ZrO2) has been prepared through the ALD method for microelectronic devices. In this work, through density functional theory calculations, the possible reaction pathways of ZrO2 ALD using tetrakis(dimethylamino)zirconium (TDMAZ) and water as the precursors were explored. The whole ZrO2 ALD reaction could be divided into two sequential reactions, TDMAZ and H2O reactions. In the TDMAZ reaction on the hydroxylated surface, the dimethylamino group of TDMAZ could be directly eliminated by substitution and ligand exchange reactions with the hydroxyl group on the surface to form dimethylamine (HN(CH3)2). In the H2O reaction with the aminated surface, the reaction process is much more complex than the TDMAZ reaction. These reactions mainly include ligand exchange reactions between the dimethylamino group of TDMAZ and H2O and coupling reactions for the formation of the bridged products and the by-product of H2O or HN(CH3)2. These insights into surface reaction mechanism of ZrO2 ALD can provide theoretical guidance for the precursor design and improving ALD preparation of other oxides and zirconium compounds, which are based ALD reaction mechanism.

Structure and Electrical Properties of Zirconium-Aluminum-Oxide Films Engineered by Atomic Layer Deposition

Thin films containing either multilayer ZrO2:Al2O3 structures or ZrO2 deposited on ZrxAlyOz buffer layers were characterized. The films were grown by atomic layer deposition (ALD) at 300 °C from ZrCl4, Al(CH3)3, and H2O. The multilayer ZrO2:Al2O3 structures were grown repeating different combinations of ZrO2 and Al2O3 ALD cycles while the ZrxAlyOz layers were obtained in a novel process using ALD cycles based on successive adsorption of ZrCl4 and Al(CH3)3, followed by surface reaction with H2O. The films were grown on TiN electrodes, and supplied with Ti top electrodes, whereby ZrxAlyOz films were exploited as thin buffer layers between TiN and ZrO2. The as-deposited ZrO2 films and ZrO2:Al2O3 structures with sufficiently low concentrations of Al2O3 were crystallized in the form of cubic or tetragonal ZrO2 polymorph possessing relative permittivities reaching 35. Notably, multilayered ZrO2:Al2O3 films could exhibit resistive switching behavior with ratios between low- and high-resistive-state current values, extending up to five orders of magnitude. Implications of multilevel switching were recorded. In the double-layered ZrxAlyOz-ZrO2 stacks, the ON/OFF current ratios remained below 40, but the endurance could become extended over 3000 cycles. Remarkably, instabilities, when detected in endurance behavior expressed by reduction in an ON/OFF current ratio could be compensated and the current values restored by real time readjustment of the programming voltage amplitude.

Engineering metal-oxide interface by depositing ZrO2 overcoating on Ni/Al2O3 for dry reforming of methane

Zirconium oxide (ZrO2) was deposited onto Ni/Al2O3 catalyst as overcoating by atomic layer deposition (ALD) for dry reforming of methane (DRM). High-temperature heating during H2-reduction could transform the ALD-prepared ZrO2 thin film to tetragonal phase and crack the encapsulating layer on Ni sites, which constructed a beneficial Ni-ZrOx interface. Interfacial surface oxygen vacancies on ZrO2 overcoating were induced by the partial reduction of ZrO2 surface during high-temperature H2 reduction, with the assistance of Ni. During DRM, the interfacial oxygen vacancies enhanced CO2 activation by dissociating CO2 and releasing active O, thereby limiting carbon formation. For DRM at 700 °C and 800 °C, Ni/Al2O3 with 5 cycles of ZrO2 ALD overcoating enhanced both activity and stability significantly. For a 100-h DRM test at 600 °C, no deactivation was observed for the Ni/Al2O3 catalyst with 10 cycles of ZrO2 ALD overcoating, as compared to 59% relative activity loss of Ni/Al2O3.

Formation of mononuclear N,O-chelate zirconium complexes by direct insertion of epoxide into tetrakis(dimethylamido)zirconium: highly promising approach for developing an ALD precursor of ZrO2 thin films.

A zirconium complex containing an N,O-chelate and alkylamide ligand has great potential for application in atomic layer deposition (ALD). However, the synthesis of this mononuclear Zr complex remains a major challenge because of the highly electrophilic nature and rich coordination of the Zr(IV) atom. Herein, a nonclassical and highly effective route for synthesizing the mononuclear N,O-chelate Zr complex was envisaged and verified using rationally designed reactions, involving the ring-opening insertion of epoxide into tetrakis(dimethylamido)zirconium(IV) (TDMAZ) at room temperature. To the best of our knowledge, very few studies in which mononuclear Zr complexes comprising alkylamide in combination with aminoalkoxide are structurally characterized. This method is extremely simple, atom economical, and easily scalable. Importantly, the produced precursor complex enables ALD of ZrO2 at a satisfactory growth rate (0.93 Å per cycle), close to that of the commercial ALD precursor CpZr(NMe2)3 (0.9 Å per cycle).

On the corrosion, stress corrosion and cytocompatibility performances of ALD TiO2 and ZrO2 coated magnesium alloys

Magnesium alloys are increasingly studied as materials for temporary implants. However, their high corrosion rate and susceptibility to corrosion-assisted cracking phenomena, such as stress corrosion cracking (SCC), continue to prevent their mainstream use. Recently, coatings have been considered to provide an effective solution to these issues and researchers have focused their attention on Atomic Layer Deposition (ALD). ALD stands out as a coating technology due to the outstanding film conformality and density achievable, and has shown encouraging preliminary results in terms of reduced corrosion rate and reduced SCC susceptibility. Here, we contribute to the ongoing interest in ALD-coated Mg alloys, providing a comprehensive characterisation of the effect of 100 nm thick ALD TiO2 and ZrO2 coatings on the corrosion behaviour and SCC susceptibility of AZ31 alloy. Moreover, we also investigate the effect of these coatings on the induced biological response. Our results suggest that the ALD coatings can improve the corrosion and SCC resistance of the Mg alloy, with the ZrO2 ALD coating showing the best improvements. We suggest that the different corrosion behaviours are the cause of the cytocompatibility results (only the ZrO2 ALD coating was found to meet the demands for cellular applications). Finally, we leverage on considerations about the coatings’ wettability, electrochemical stability and surface integrity to justify the different results.

Order of magnitude enhancement of inherently selective atomic layer deposition of zirconia on silicon without deposition on copper: The role of precursor

Zirconia atomic layer deposition (ALD) using zirconium 2-methyl 2-butoxide (ZMB) and ethanol is reported for the first time. The process selectively deposits a uniform ZrO2 film on silicon with a high deposition rate (∼2 Å/cycle), without any deposition on copper at a relatively low temperature (200 °C) and up to at least 200 cycles. This is the largest thickness of inherently surface selective ZrO2 ALD ever reported (∼400 Å) and is at least 10 times more selective than that achieved using a similar deposition process but with a different precursor, tris(dimethylamino)cyclopentadienyl Zirconium (ZyALD™). The selectively deposited ZrO2 films were characterized using spectral ellipsometry, X-ray photoelectron spectroscopy, extended X-ray absorption fine structure spectroscopy (EXAFS), atomic force microscopy and energy dispersive spectroscopy obtained during scanning electron microscopy and scanning transmission electron microscopy. Surface characterization techniques employed here confirmed the chemical nature and topography of the deposited ZrO2, whereas EXAFS showed the ZrO2 to be amorphous on silicon having local bonding structure similar to that of ZrO2 deposited with ZyALD™ precursor.

On the evaluation of ALD TiO2, ZrO2 and HfO2 coatings on corrosion and cytotoxicity performances

Magnesium alloys have been widely studied as materials for temporary implants, but their use has been limited by their corrosion rate. Recently, coatings have been proven to provide an effective barrier. Though only little explored in the field, Atomic Layer Deposition (ALD) stands out as a coating technology due to the outstanding film conformality and density achievable. Here, we provide first insights into the corrosion behavior and the induced biological response of 100 nm thick ALD TiO 2 , HfO 2 and ZrO 2 coatings on AZ31 alloy by means of potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), hydrogen evolution and MTS colorimetric assay with L929 cells. All three coatings improve the corrosion behavior and cytotoxicity of the alloy. Particularly, HfO 2 coatings were characterized by the highest corrosion resistance and cell viability, slightly higher than those of ZrO 2 coatings. TiO 2 was characterized by the lowest corrosion improvements and, though generally considered a biocompatible coating, was found to not meet the demands for cellular applications (it was characterized by grade 3 cytotoxicity after 5 days of culture). These results reveal a strong link between biocompatibility and corrosion resistance and entail the need of taking the latter into consideration in the choice of a biocompatible coating to protect degradable Mg-based alloys.

Mechanism for growth initiation on aminosilane-functionalized SiO2 during area-selective atomic layer deposition of ZrO2

The mechanism for growth initiation on the nongrowth surface during area-selective atomic layer deposition (ALD) processes is not well understood. In this study, we examine the ALD of ZrO2 on a SiO2 surface functionalized with alkylated-aminosilane inhibitors delivered from the vapor phase. ZrO2 films were deposited by ALD using tetrakis(ethylmethylamino)zirconium(IV) with H2O as the coreactant. In situ surface infrared spectroscopy shows that aminosilane inhibitors react with almost all the surface —SiOH groups on the SiO2 surface by forming Si—O—Si bonds. In situ four-wavelength ellipsometry shows that no ZrO2 growth occurs on the functionalized SiO2 during the first few ALD cycles, but growth eventually initiates after a few ALD cycles. We speculate that after repeated exposure of the functionalized SiO2 surface to Zr precursors, in the absence of surface —SiOH groups, growth initiates due to either reaction of the precursors with strained Si—O—Si bonds or through a strongly physisorbed state. These reaction pathways are usually not relevant in ALD reactions on the unprotected —SiOH-terminated SiO2 surface due to a higher activation energy barrier, but become relevant on the passivated surface as a result of repeated precursor exposure. Thus, this study highlights the importance of steric blocking of these higher activation energy barrier reaction pathways.

Optimization of substrate-selective atomic layer deposition of zirconia on electroplated copper using ethanol as both precursor reactant and surface pre-deposition treatment

Recent developments on the further optimization of the selective atomic layer deposition (ALD) of zirconium oxide (ZrO2) onto silicon over electroplated copper are reported with tris(dimethylamino)cyclopentadienyl zirconium as the zirconium precursor and ethanol as both oxygen source for precursor and pretreatment of copper surface to reduce surface oxides. A comparison between the electroplated (EP) and e-beam deposited (EB) copper before ALD using high-resolution X-ray photoelectron spectroscopy (XPS) showed EP Cu having more oxides on the surface and unexpectedly the EP Cu was found to have higher selectivity of ALD. In addition, a comparison of deposition of zirconia on silicon over EP and EB copper substrates for 70 ALD cycles show experimental conditions can impact the degree of selective deposition with the electroplated copper. With further optimization of the substrate pretreatment and ALD process parameters, both XPS survey analysis and ellipsometry showed ALD selectivity was enhanced up to 100 cycles on electroplated copper samples which is higher than ever previously reported forming an amorphous ZrO2 film of ~ 3 nm thickness on silicon and no deposition on copper. Lack of crystallinity of the ALD ZrO2 films is manifested by X-ray absorption fine structure and grazing incidence X-ray diffraction. Atomic force microscopy and scanning electron microscopy performed on the samples indicated no significant changes of the roughness and topography on the samples before and after ZrO2 ALD. Both thermodynamic calculations and experimental data presented here show that ALD selectivity is mainly dictated by the balance of the total amounts of oxygen and carbon in the reactor along with the ALD conditions and reactor design. These studies show pre-deposition ethanol exposure of the substrate, deposition/adsorption of reduction byproducts formed, and the total oxygen and carbon in the ALD reactor are important contributors to whether ALD selectivity can be significantly enhanced or even achieved at all.

The Effect of Atomic Layer Deposition of ZrO2 on the Cathode on the Performance of Molten Carbonate Fuel Cell

Molten carbonate fuel cell (MCFC) is a high-temperature fuel cell for power plants. Since MCFC is operated at approximately 650 °C, the lifetime of the MCFC is limited by the thermal degradation of MCFC components. To reduce thermal degradation, the lower temperature for long-term operation is suggested. However, the electrochemical reaction on the cathode becomes slower at the lower operational temperature. To improve the performance for the long-term operation of MCFC, a ZrO2 coated cathode was fabricated by atomic layer deposition. The cell using the ZrO2 coated cathode showed a high voltage of 0.867 V at a temperature of 600 °C and a current density of 150 mA/cm2. The charge transfer resistance is also reduced dramatically at that same time. It can be confirmed that the high cell performance is presented when the electron-rich environment of NiO by ZrO2 coating improved the performance of the cell. Also, the cell using the ZrO2 coated cathode kept a stable performance over 2,000 h due to the prevention of NiO sintering by the uniform ZrO2 coating layer.

Atomic Layer Deposited Zirconia Overcoats as On-Board Strontium Getters for Improved Solid Oxide Fuel Cell Nano-Composite Cathode Durability

In order to improve the electrochemical performance of Solid Oxide Fuel Cells (SOFCs), nano-composite cathodes (NCCs), which are fabricated by adding nano-sized mixed ionic and electronic conducting (MIEC) catalysts into backbones of partially-sintered micro-sized ionic conducting particles via precursor solution infiltration, have been intensively studied.1,2 Despite the reduced operating temperatures, poor long-term stability has still been observed for these high-performance NCCs.3 As a low-temperature, nano-sized thin-film deposition method, atomic layer deposition (ALD) has been shown to help stabilize SOFC cathodes.4 Therefore, in this work ZrO2 overcoats of various thicknesses were deposited onto 12 vol% La0.6Sr0.4Co0.8Fe0.2O3-x (LSCF) - Gd0.1Ce0.9O2 (GDC) NCCs using ALD. The initial 400oC-700oC electrochemical performance long-term 650oC degradation behavior were studied with electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the microstructure of NCCs with different ZrO2 thicknesses, while X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were conducted to investigate aging-induced compositional changes.Figure 1 shows that no significant change in initial polarization resistance (RP ) was observed for LSCF-GDC NCCs with 1-10 nm ZrO2 ALD overcoats between 400oC and 700oC. However, as shown in Figure 2, while no significant ohmic resistance (R0) degradation happened for any of the LSCF-GDC NCCs, different RP aging behavior was observed for cells with different ZrO2 thicknesses. Specifically, the 650oC RP degradation rate dropped from ~45%/khrs for uncoated LSCF-GDC NCCs, to ~28%/khrs, ~18%/khrs, and ~12%/khrs for NCCs with 1, 2, and 5 nm of ZrO2 overcoat, respectively, indicating improved durability. With 10 nm ZrO2 overcoat, however, the RP degradation rate increased to ~87%/khrs. SEM analyses showed no evidence of LSCF particle coarsening for any of the cells, while XPS showed less inactive Sr species on the LSCF surface for ZrO2-coated cells after aging, compared with uncoated ones. As discussed in our recent paper on the subject,5 this reduced inactive Sr species, together with the SrZrO3 phase observed from detailed XRD analyses for ZrO2 coated LSCF pellets after aging, suggested that the ZrO2 overcoats act as Sr getters and react with inactive Sr species on the LSCF surface during aging. This reaction cleans up the LSCF surface and leads to better RP stability. For 10 nm overcoats, too much SrZrO3 starts to accumulate on the LSCF surface during aging, causing the observed increase in the RP degradation rate. References T. E. Burye and J. D. Nicholas, J. Power Sources, 300, 402–412 (2015).T. E. Burye and J. D. Nicholas, J. Power Sources, 276, 54–61 (2014).M. Shah, P. W. Voorhees, and S. A. Barnett, Solid State Ionics, 187, 64–67 (2011).Y. Gong et al., Nano Lett., 13, 4340–4345 (2013).Y. Zhang, Y. Wen, K. Huang and J. D. Nicholas, ACS Applied Energy Materials, 3, 4057 (2020). Figure 1