Department of Energy Engineering (Energy Engineering)

81 Figure 4-3 (a) Nyquist plots and (b) Arrhenius plots of the polarization resistance for the single cell. GBSCF–YSZ/YSZ/YSZ–PBM) using humidified H2 as fuel: without catalyst and with Ni-, Ni-Cu, Ni-Co and Ni-Fe catalysts. Schematic illustrations of the microstructure of the yellow inset box in the SEM image are presented.

Introduction

Motivation and Research objective

Global Energy Issue
Change of Energy Resources

Among the various clean and renewable energy systems, the hydrogen energy system has recently emerged because it is the most abundant element in the universe (75% of the universe) and efficient resources with the highest energy density (32 kWh kg-1). The hydrogen energy system is operated by utilizing the electrochemical reactions between hydrogen, oxygen and water.

Figure 1-2 The strategy of the Paris Climate Accord to realize zero carbon footprint

Energy Circulation

Energy conversion: Solid oxide fuel cells (SOFCs)

Overview
Operating principle of SOFCs
Challenges of SOFCs
Theoretical Background

Energy Storage: Metal-air Batteries (MABs)

Overview
Operating principle of MABs
Theoretical background

Energy Reuse: Solid oxide electrolysis cell (SOECs)

Overview
Operating principle
Advantages and Challenges
Theoretical Background

The electrochemical efficiency can be derived from the product of the thermodynamic efficiency (𝜀𝑇), the voltage efficiency (𝜀𝑉) and the current efficiency (𝜀𝐽). 𝜀𝐽 is the ratio of the actual power produced to the available power from complete electrochemical fuel conversion.

Figure 1-6 Operation principle of solid oxide fuel cells

Nanocatalyst

Catalyst
Nanostructured materials
Infiltration

Overview
Theoretical background
Factors of infiltration to control the morphology of nanomaterials

Materials

Simple Perovskite (ABO 3 )
Layered Perovskite (AA’B 2 O 5 )
Ruddlesden-popper (A n+1 B n O 3n+1 )
Spinel (AB 2 O 4 )

Briefly, the principle of infiltration is the capillary phenomenon caused by fluid cohesion and adhesion between the tube and the fluid. For infiltration, the dry pore of the scaffold acts as a tube, and in this way, the capillary phenomenon occurs with the cohesion of the precursor solution and the adhesion between the scaffold wall and the precursor solution [40,68,69]. 𝑉 = 𝐴 𝑆 √𝑡 Equation 1-57, where S is the absorbance of the precursor solution, A is the cross-sectional area of the scaffold, and t is the time, respectively.

𝐴= 𝑆 √𝑡 Equation 1-58 Since the wetted length (x) is dependent on the porosity (f) ─the fraction of the volume occupied by voids─, the value x is written as follows. As a result, for the HF treatment, they found significant increases in the surface areas even after calcination of the treated scaffold. It is well known that the ionic radii of the component ions play important factors in determining the crystal structure, which is called "tolerance factor t".

This can be used as a measure of the deviation of the ABO3 perovskite structure from the ideal cubic symmetry. Cations (usually metals) occupy 1/8 of the tetrahedral site and 1/2 of the octahedral site, and there are 32 O ions in the unit cell. It is also interesting because they can each contain voids as a regular part of the crystal.[90–92].

Figure 1-17 Schematics of infiltration process

Introduction
Experimental
Results and Discussions
Conclusion

As a means of increasing the electrochemical properties of the cathode material in this study, the doping of alkaline elements in the A sites is also considered. The surface areas of LSNO oxide were quantified using Brunauer–Emmett–Teller (BET) isotherms (Belsorp-max) to clarify the SEM results. Meanwhile, it has been reported that the nanocomposite has higher electrical conductivity with equal concentration of the conducting phase in the solid due to the formation of particles in the YSZ porous walls [25,29].

In this context, the electrical conductivity of LNO nanocomposite is reasonable, although it has a relatively lower value than bulk LNO. The active area of the fuel cell electrode where the reaction took place is related to the length of TPB and 2PB. The SEM images clarify that LSNO oxide particles are synthesized at the nanoscale by infiltration, which means an increase in electrochemically active sites.

The adsorption and desorption isotherms of the YSZ scaffold (a) are type II, indicating that the YSZ scaffold is a non-microporous material. An electrolyte-supported single cell (LSNO-YSZ/YSZ/Ce-Pd-YSZ) based on a ∼120 μm YSZ electrolyte was fabricated to measure the electrochemical performance of the LNO-YSZ cathode. Since the active sites for ORR are connected to the entire surface of the cathode (2PB+TPB), the smaller particle size, indicating larger surface area, confirmed by SEM seems to have a positive effect on the electrochemical performance.

Table 2-1. Abbreviation and composition of La 4-x Sr x Ni 3 O 10- 

Energy Conversion: Nanostructured Double Perovskite Cathode with Low

Introduction
Experimental

Preparation of porous scaffold
Characterization of infiltrated cathode
Electrical and electrochemical testing

Structural characteristics of the GBSCF–YSZ composite
Characteristics of GBSCF–YSZ composite depending on sintering temperature
Electrochemical properties of the optimized cathode GY700

Conclusions

The microstructures of the GBSCF sintered at 650, 700, and 750 oC were examined using scanning electron microscopy (SEM) (Nova SEM). The areas of the YSZ scaffold and GBSCF sintered at 700 oC were quantified using Brunauer–. Structural features of the GBSCF-YSZ composite In situ XRD patterns In situ XRD patterns.

For compositional analysis, energy dispersive spectroscopy (EDS) was performed for compositional analysis of GBSCF infiltrated into the YSZ scaffold (GBSCF-YSZ composite) sintered at 700 oC for 4 h. A cross-sectional view of the GBSCF-YSZ composite provides more information about the realistic structure of GBSCF particles infiltrated in YSZ. For the GBSCF-YSZ composite, nanosized GBSCF particles cover the surface of the porous YSZ scaffold, showing an increase in particle size with increased sintering temperature.

In this regard, the optimized microstructure of GBSCF-YSZ sintered at 700 oC is expected to improve the electrochemical properties of the cathode as the microstructure resembles the ideal model explained above. The destruction of the villus-like structure and the agglomeration of particles sintered at 800 oC (Figure 3-2 c and f) decrease the electrochemically active surface area. A GdBa0.5Sr0.5CoFeO5+–yttria-stabilized zirconia (GBSCF–YSZ) composite was prepared by infiltration of the YSZ scaffold, giving rise to an optimized cathode microstructure that reduces the cathode polarization resistance (Rp).

Figure 3-1 a) XRD patterns obtained through in situ annealing of an as-prepared sample in the range 550–900 o C

Energy Conversion: Tailoring Ni-based catalyst by alloying with transition

Introduction
Experimental

Solution preparation and infiltration process
Preparation of porous scaffold
Characterization and electrochemical testing of single cell
Density Functional Theory (DFT) calculation

Structural characteristics of the anode side
Electrochemical properties of the single cell
Carbon tolerance test

Conclusions

Here, both experimental and theoretical aspects of Ni-based alloy catalysts for direct hydrogen utilization are reported to consolidate the results. The PBM oxide microstructure was evaluated using scanning electron microscopy (SEM) (Nova SEM). The XRD patterns of the anode with different Ni-M catalysts (M = Ni, Co, Cu and Fe) are shown in Figs.

The peaks of the samples were therefore attributed to the formation of the Ni-M catalysts (M = Ni, Co, Cu and Fe) without any unwanted reactions between catalysts and the PBMO anode. The presence of the infiltrated PBMO layer on the porous YSZ scaffold is confirmed in Figure 4-2b. Electrochemical properties of the single cell Area specific resistance under H2 fuel Area specific resistance under H2 fuel.

The OCV of a single cell is close to the theoretical Nernst potential in the temperature range 550-700 oC. The trend shows that the activation energy for hydrogen dissociation is one of the critical factors for the electrochemical performance of fuel cells. To evaluate the tolerance of Ni and Ni-M alloy catalysts (M = Co, Cu and Fe) to carbon deposition, the prepared cells were exposed to wet and dry C3H8 at 700 oC for 8 h.

Figure 4-1 (a) X-ray diffraction patterns (XRD) patterns of Pr 0.5 Ba 0.5 MnO 3-  and

Energy Storage: Strategy for Enhancing Interfacial Effect of Bifunctional

Introduction
Experimental

Material Synthesis
Characterization
Rotating Ring-Disk Electrode (RRDE)
Hybrid Li-air Battery

Significance of morphology: Control of the wettability of precursor solution
Optimization of the Co 3 O 4 layer thickness: Control of the Co 3 O 4 concentration
Structural properties of Opt-NSC@Co 3 O 4 : TEM, XRD
Electrochemical properties of Opt-NSC@Co 3 O 4 : XPS
The catalytic activity of Opt-NSC@Co3O4: RRDE & hybrid Li-air battery

Conclusions

-e) Scanning transmission electron microscopy (STEM) images and (f-h) schematics below for NSC, W-NSC@Co3O4 and E-NSC@Co3O4. Co3O4, NSC@Co3O4 takes full advantage of the interfacial effect and therefore shows the best ORR performance. Transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS) were performed to confirm the structural properties of Opt-NSC@Co3O4.

To compare the catalytic activity of Opt-NSC@Co3O4 (20 wt.% Co3O4 infiltrated NSC), the RRDE measurement was performed in 0.1 M KOH. Thus, higher OER performance of Opt-NSC@Co3O4 than the NSC+Co3O4 blend can be expected due to the interfacial effect (i.e. strain effect and ligand effect). Furthermore, the limiting current density of Opt-NSC@Co3O4 is very similar to that of Pt/C and higher than them.

The discharge voltage of Opt-NSC@Co3O4 is slightly lower than that of Pt/C and Pt/C+IrO2. These results confirm the superior catalytic activity and stability of Opt-NSC@Co3O4 for both ORR and OER. In TEM, the strain effect on Opt-NSC@Co3O4 was recognized by the change in d-spacing values between the bulk region and the interface of Co3O4 and NSC.

Table 5-1 Abbreviation of chemical compositions

Introduction
Experimental

Preparation of air electrodes
Characterization and electrochemical measurements on a half cell
Preparation and assembly of seawater batteries

Conclusions

PPy/C and carbon felt were used as benchmarked materials to distinguish the peaks of bf-PPy+Co3O4@CF. The detailed surface morphology of bf-PPy+Co3O4@CF was observed and identified by high-resolution (HR) transmission electron microscopy (TEM) images and fast-Fourier transform (FFT) patterns. Apparent cathodic peaks attributed to the typical oxygen reduction reaction (ORR) are observed in O2-saturated state for both bi-Pt/C+IrO2 and bf-PPy+Co3O4@CF.

Cathodic currents, however, bf-PPy+Co3O4@CF shows better performance than bi-Pt/C+IrO2 with strongly increasing CV peaks related to electrochemical kinetics. Cathodic and anodic CV profiles for bf-PPy+Co3O4@CF were further investigated under seawater, which is the actual operating condition of a seawater battery. The anodic CV scan of bf-PPy+Co3O4@CF measured under seawater is presented in Figure 6-3d.

In addition, the cathode potential and anode potential (denoted as Ecathode and Eanode) for binder included Pt/C+IrO2 and bf-PPy+Co3O4@CF electrode are shown in Figure 6-4c and 4d. Without the use of binder materials (e.g., Nafion, PVdF, PTFE), the bf-PPy+Co3O4@CF air electrode shows stable cyclic performance for 300 hours. Cathode and anode potential during the cycling test for (c) bi-Pt/C+IrO2 and (d) bf-PPy+Co3O4@CF.

Figure 6-1 Schematic illustration of the synthetic strategy for binder free catalyst via infiltration technique

Energy Reuse: Self-Transforming Configuration Based on Atmospheric-

Introduction
Experimental

Preparation of the transforming cell
Measurements
Data availability

Conclusions

As expected, with the derived electrode materials, the transformer cell shows competitive electrochemical performance and promising stability compared to other symmetrical cells reported in the literature. The operating conditions of the transformer cell were determined by performing in situ X-ray diffraction (XRD) under hydrogen with a pre-sintered Pr0.5Ba0.5Mn0.85Co0.15O3- (PBMCo)-LSGM electrode. These microstructural features of a cell with nanostructured electrodes and a thin electrolyte layer are expected to exhibit high electrochemical performance of self-transformation cells.

For the electrochemical analysis, the impedance spectra (Fig. S4) of the transforming cells were measured at 700, 750 and 800 oC. The fitted lines were in good agreement with the Nyquist plots based on the equivalent circuit in the inset of Fig. Even the small amount of H2O was applied, the transforming cell shows the reasonable electrochemical performance of -0.42 A cm-2 for 3 vol.% H2O and -0.62 A cm-2 for.

To take full advantage of both asymmetric and symmetric configurations, the transformation cell was designed by applying the atmospheric-adaptive material Pr0.5Ba0.5Mn0.85Co0.15O3- (PBMCo) to the electrodes. For reversible cycle testing, the transforming cell maintains the constant voltages for 30 hours at +/- 0.2 A cm-2 under 10 vol. These results indicate that the transforming cell is a promising system for solid oxide cells as both fuel cells and electrolytic cells.