Rare-earth doped metal oxide nanocomposites were become very unique and tend to show abundant performance in all types of fields such as electrochemical, photocatalytic, and biological. Gadolinium and Samarium co-doped ceria i.e., Ce1−xGd1−yO2−δ-Ce1−x Sm−yO2−δ [x = 0.2, y = 0.8] nanocomposite was synthesized by co-precipitation method for various applications. The formation of fluorite cubic crystal structure was observed and functional group analysis was revealed by XRD and FTIR correspondingly. SEM with EDAX was revealed the morphological and chemical composition analysis of the prepared nanocomposite. Impedance studies were completed at particular conditions and proved as a suitable electrolyte for low temperature solid oxide fuel cell (LT-SOFC) applications.
SOFCs are unresolved alternates to established power sources; however, they undergo few technical issues like larger temperature processes (1000 °C), which diminish them from commercialization. Presently, uncountable works have been assigned to enlarge a low or transitional temperature SOFCs functioning at 500–800 °C. Due to reducing the operating temperature can detain the dilapidation of components and enlarge the variety of appropriate material assembly; it also attends to improve cell sturdiness and lessen the system expense. Therefore, innovative materials with upright functioning conditions like chemically, mechanically, and compatible also level of conductance have to be recognized and industrialized principally for purpose in LT or ITSOFCs [1, 2]. The price reduction, immediate operation, and greater robustness of IT-SOFCs ought to create them well matched with purposes such as remote power production; uninterruptible power supplies (UPS), and auxiliary power units (APU).
Several metal oxide nanocomposites have wide purposes such as gas and chemical sensors, wastewater remediation, and biological activity. With respect to ecological remediation, nanomaterials have prevalent and become capable material owing to their tapered bandgap, economically cheap, non-toxicity, thermally, and chemically stable [3, 4]. YDC and SDC were propositioned as possible materials as anode for IT-SOFCs due to their typical mixed ionic-electronic conductive nature [5, 6]. It was found that combined metal oxides might demonstrate exceptional elevated electronic, ionic conductivity, and catalytic activity, consecutively, which could maintain to accomplish raised power production [7,8,9,10]. Present literature on nanotechnology exposes that numerous nanoparticles (NPs) with CeO2, NiO, CGO, CYO have been broadly utilized in biological applications [11,12,13,14]. Metal oxide NPs fascinated numerous young scientists due to their noticeable unusual physical, chemical properties, and non-toxic feature. The metal oxide NPs are also eminent in the tradition of pharmaceutical and regenerative medication technologies [15,16,17].
Amongst numerous metal oxide NPs, cerium oxide (CeO2) NPs are creatures widely employed owing to their lesser bandgap, chemical stability, and electrochemical action [1, 2]. Such impending properties correlated with the CeO2 with rare earth dopants defended the use of nanocomposites in dissimilar fields resembling sensing applications, solid oxide fuel cells, photocatalytic, and biological activities [18,19,20]. Plentiful ways have been executed such as ultra-sonication, ball milling, microwave, sol–gel, mechanical alloying and chemical-precipitation, etc. for the preparation of nanocomposite materials from the mixed metal oxide precursors. [21,22,23,24]. From above all well-known methods, the chemical-precipitation process is used as a competent technique for the production of nanomaterials, owing to effortlessness. This move toward is extra operative for yielding homogeneity, particularly sample without impurities, tiny particle size, and a short period of time [25,26,27].
Ceria with rare earth metal oxides combination is of considerable attention for potential applications in SOFCs due to their change in morphology and outstanding ionic conductivity [16, 17]. Recently, nanocomposite materials have been used as electrolyte materials for LTSOFC. A comparative study with single-doping electrolytes (SDC, YSZ) and multi doping or nanocomposite electrolyte encompass lots of interface sections amid the two constituent phases [26, 27]. Here, rare earth based ceria doped nanocomposite was synthesized thoroughly using surfactant (C-TAB) as described in previous literature [28, 29]. It contrasts with the design of Sm doped-CGO nanocomposite using wet chemical synthesis using CTAB surfactant. The prepared composite was investigated to know structural, morphological and electrochemical performance.
Materials and methodology
The starting chemicals consumed in this process were the analytical grade without any additional purification. The cerium nitrate hexahydrate, gadolinium oxide, samarium oxide, and C-TAB were used as a precursor material and sodium hydroxide, nitric acid, and ethanol employed as a precipitating agent. The experiment involved in the synthesis of aqueous solutions as accounted previously .
Principally, NaOH was blended with CTAB and then Ce(NO3)3, Gd(NO3)3, and Sm(NO3)3 solutions were accordingly included. They subjected to stirring for two–three hours at room temperature (RT) with pH > 9 [30, 31]. The resulting precipitate (Ce(OH)4 + Gd(OH)3 + Sm(OH)3 with C-TAB) was separated by filtration using filter paper, washed and dehydrated at 50–100 °C for two–three hours and left for overnight. The acquired material was calcined for 2 h at various temperatures till 750 °C. The method of preparation was followed as reported in earlier work and it was shown in Fig. 1 .
The subsequent steps involved in the production of nanocomposite throughout the experiment can be written and was shown below:
The thermal behaviour of the synthesized precursor sample was examined by Perkin Elmer TGA 7 under N2 atmosphere at 10 °C/min of heating rate. The powder XRD measurements were done via a Shimadzu XRD 6000 X-ray diffractometer. Functional group analysis was carried out by the FTIR spectrometer (Bruker IFS 66 V). The size of the particles for prepared samples was investigated using Malvern Particle Size Analyzer. The morphological study of samples was done using the JEOL Model JSM-6360 SEM. The bulk conductivity was estimated using impedance analysis.
Results and discussion
The synthesized precursor sample [Ce(OH)4 + Gd(OH)3 + Sm(OH)3with CTAB] with an initial mass of 13–14 mg was situated in pt crucible and proceed for investigation as reported earlier and the thermogram as shown in the Fig. 2.
From the above TGA spectrum, it was found that the weight loss initiates to show from the beginning stage itself. The nanocomposite (thermal decomposition) can be distributed into 4 distinct regions as elucidated in the previous research report [5, 32] and also the weight loss change observed for the precursor material obtained from the TGA data signified in Tables 1 and 2 correspondingly.
The XRD pattern of the calcined nanocomposite reveals the creation of fluorite cubic well crystallined single-phase as shown in Fig. 3 [19, 33,34,35]. There is no secondary phase were scrutinized in the XRD pattern of prepared sample and the crystallographic planes monitored at 2 theta values of 28.8°, 33.3°, 47.7°, 56.5°, 59.3°, 69.6°, 76.8°, 79.2° and 88.5° shown the intensity peaks with following h k l values respectively (1 1 1), (2 0 0), (2 2 0), (3 1 1), (2 2 2), (4 0 0), (3 3 1), (4 2 0) and (4 2 2). All these values are in good agreement with the customary JCPDS card No: 81-0792 and indicated that the CeO2 phase is pure . And also there were few more crystallographic planes observed at 2 theta values of 79.2° and 88.5° shown the intensity of peaks with following h k l values respectively (4 2 0) and (4 2 2). These peaks were represented with the dot symbol and it revealed that the presence of Sm-doped ceria and they were well matched with the literature. The calculated d-spacing values for S-CGO nanocomposite were also matched with the earlier research reports. The crystallographic parameters were calculated and displayed in Table 3.
Particle size characteristics
S-CGO nanocomposite was exposed to study particle size analysis followed by 0.30 g of material sonicated in 30 mL deionized water for around 15 min, and the plot was shown in Fig. 5.
From this analysis, it is revealed that the size of particles is in the range of 180.2–243.1 nm. The data obtained from particle size analysis (Table 5). Due to calcination at high-temperature, the presence of bigger particles (> 200 nm) appeared in the sample .
SEM and EDAX studies
The SEM and EDAX pictures obtained on S-CGO are displayed in Fig. 6a, b and SEM photograph has taken at 35,000 resolutions. The surface morphology of prepared nanocomposite revealed the shape and size of the particle and pore. From Fig. 6a, it noticed that the grain size is in the range from 40 to 70 nm. Due to calcination at high temperatures, there is the presence of a few bigger particles in the samples [26, 43,44,45]. It is a recognized reality that the complement of the CTAB surfactant diminishes the opportunity of tremendous agglomeration to attain superior nanocomposite. The EDAX exposed the occurrence of Ce (44.65%), Gd (5.72%), Sm (3.31%), and O (46.32%) as shown in Fig. 6b. No additional peaks were shown in the spectrum signifying the absence of chemical impurities in the sample [25,26,27].
Employing hydraulic pressure pelletizer, pellets (compacts) from the synthesized nanocomposite with the thickness (2 mm) and diameter (10 mm) were equipped by operating pressure (1.2 ton). Ahead of the impedance capacities to get an extremely densified state, the sample was annealed at 750 °C for 3 h to decrease the pores . The prepared compacts were employed as working electrodes. The ac impedance tests were examined at customary circumstances and temperatures equal to RT, 300, 400, 500, and 600 °C. By submitting the 2RQR corresponding circuit (Fig. 7), ZVIEW software was used to fit the measurement data. The impedance plots acquired at diverse temperatures are designated in Fig. 8a–e.
The outcomes are employed for estimating the conductivity values and they are demonstrated in Table 6. It pursues that nanocomposite exhibits superior conductivity values at elevated temperatures (400–600 °C) [7, 46, 47].
The activation energy of the prepared sample has been computed dealing with Eq. 1 via the Arrhenius linear fit connection.
Table 7 summarizes the computed activation energies values. Finally, when the conductivity amplifies, the activation energy also increases up.
Using Arrhenius data, it was expected that the ionic conductivity of doped ceria electrolyte materials is stimulated not alone by the concentration and the lattice strain, but also by the allocation of oxygen vacancy levels . From this, it was revealed that partial replacement of Gadolinium with CeO2 could lead to two reverse consequences. Firstly, it is the containment of the organization of the oxygen vacancy levels and which could cause a reduction in the activation energy of conduction and growth in the ionic conductivity . Secondly, it is the deviance of the lattice constant from pure ceria and which might cause to enlarge in the activation energy (conductivity) and the reduction (ionic conductivity) . Consequently, the electrolyte with greater ionic conductivity and poorer activation energy ought to be with a suitable dopant level.
In this study, Ce1-xGd1-yO2-δ-Ce1-xSm-yO2-δ [x = 0.8, y = 0.2] nanocomposite was productively synthesized by co-precipitation route. TGA pattern reveals the approach to acquire phase pure nanocomposite powder. The XRD spectrum exhibits a crystalline structure whereas SEM/EDAX studies prove the sphere-shaped morphology of the S-CGO nanocomposite with particle size differing from 40 to 70 nm and the chemical composition present in the prepared sample as per the requirement without any impurities respectively. The typical peaks of the FTIR spectrum express the occurrence of the M–O bond in the material. The determined conductivity of the sintered sample proposes that it could be proficiently employed as an electrolyte substance in LT-SOFC systems.
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Kannan, K., Radhika, D., Nesaraj, A.S. et al. A simple chemical precipitation of ceria based (Sm doped-CGO) nanocomposite: structural and electrolytic behaviour for LT-SOFCs. SN Appl. Sci. 2, 1220 (2020). https://doi.org/10.1007/s42452-020-3035-2
- Chemical precipitation