PtGd/Gd2O3 alloy/metal oxide composite catalyst for methanol oxidation reaction

Pt-transition metal alloys are frequently used to improve the catalytic activity for methanol oxidation reaction. However, the severe dealloying strongly limits the applications of Pt-based alloy in fuel cells. Recently, Pt-rare earth metal alloys are considered to be the promising catalysts for electrocatalytic application in fuel cells. Metal oxide as the co-catalytic component of composite catalyst, is also applied to regulate the electronic structure and strengthen resistance to CO poisoning. In this work, we utilized hydrogen reduction method to prepare PtGd/Gd₂O₃ composite catalyst. X-ray diffraction result illustrates that both Gd₂O₃ and PtGd alloy co-exist in PtGd/Gd₂O₃ material. X-ray photoelectron spectroscopy data confirms that the main valence states of Pt and Gd are metal form in the PtGd/Gd₂O₃ catalyst and emerges obvious transfer of element binding energy. Transmission electron microscopy data presents that composite PtGd/Gd₂O₃ particles are uniformly dispersed on the carbon power with a typical core-shell structure. And upon the increase of Gd precursor in reduction process, the metal oxide layer becomes more thicker for PtGd/Gd₂O₃ composite material. Because of the synergistic contributions given by the Pt–Gd bimetals and alloy-metal oxide between PtGd alloy and Gd₂O₃ oxide, the PtGd/Gd₂O₃ composite catalysts exhibit superior catalytic performance toward methanol oxidation reaction. Specifically, the mass activity of Pt₁Gd₁/Gd₂O₃ is about 1.9 times that of commercial Pt/C; besides this, the optimal specific activity of Pt₁Gd₂/Gd₂O₃ is almost 4 times that of commercial Pt/C. More importantly, the Pt₁Gd₁/Gd₂O₃ emerged a 20.9% degradation after 8000 cycles test, while commercial Pt/C showed a 61.7% degradation. And this work provides an important insight for rare earth elements investigation on the electrocatalysis application in fuel cells.     

Ni-Sm2O3 cermet anodes for intermediate-temperature solid oxide fuel cells with stabilized zirconia electrolytes

Ni-LnO_x cermets (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd), in which LnO_x is not an oxygen ion conductor, have shown high performance as the anodes for low-temperature solid oxide fuel cells (SOFCs) with doped ceria electrolytes. In this work, Ni-Sm₂O₃ cermets are primarily investigated as the anodes for intermediate-temperature SOFCs with scandia stabilized zirconia (ScSZ) electrolytes. The electrochemical performances of the Ni-Sm₂O₃ anodes are characterized using single cells with ScSZ electrolytes and LSM-YSB composite cathodes. The Ni-Sm₂O₃ anodes exhibit relatively lower performance, compared with that reported Ni-SDC (samaria doped ceria) and Ni-YSZ (yttria stabilized zirconia) anodes, the state-of-the-art electrodes for SOFCs based on zirconia electrolytes. The relatively low performance is possibly due to the solid-state reaction between Sm₂O₃ and ScSZ in fuel cell fabrication processes. By depositing a thin interlayer between the Ni-Sm₂O₃ anode and the ScSZ electrolyte, the performance is substantially improved. Single cells with a Ni-SDC interlayer show stable open circuit voltage, generate peak power density of 410 mW cm⁻² at 700 °C, and the interfacial polarization is about 0.7 Ω cm².     

The effect of Fe2O3 sintering aid on Gd0.1Ce0.9O1.95 diffusion barrier layer and solid oxide fuel cell performance

Solid oxide fuel cells (SOFCs) with the Gd_0.1Ce_0.9O_1.95 (GDC) diffusion barrier layer require the densification of GDC to improve the performance of the cells. In this work, the addition of 0.5 mol% Fe₂O₃ in GDC diffusion barrier layer as sintering aid is studied. The symmetrical cell and the fuel cell are fabricated by hot-pressing, co-sintering and screen-printing technologies. It is found that the addition of Fe₂O₃ can make GDC barrier layer denser at a reduced sintering temperature of 1250 °C and prevent diffusion of Sr to form ionic insulating interface between YSZ (Y₂O₃ stabilized ZrO₂) and La_0.6Sr_0.4Co_0.8Fe_0.2O_3-δ (LSCF). The fuel cell based on the GDC-Fe₂O₃ barrier layer achieves better maximum power density of 0.89 W cm⁻² at 800 °C than that of 0.68 W cm⁻² without Fe₂O₃ addition. No obvious degradation was observed on fuel cell based on the GDC-Fe₂O₃ diffusion barrier layer after a stability test at 750 °C for 100 h under 0.75 V and the thermal cycling between 750 and 400 °C. The results indicate that the addition of Fe₂O₃ sintering aid in GDC diffusion barrier layer can promote the densification of GDC and exhibit good long-term stability and thermal cycle stability.     

Fabrication of ultrafine Gd2O3 nanoparticles/carbon aerogel composite as immobilization host for cathode for lithium‐sulfur batteries

Carbon aerogel (CA), possessing abundant pore structures and excellent electrical conductivity, have been utilized as conductive sulfur hosts for lithium‐sulfur (Li‐S) batteries. However, a serious shuttle effect resulted from polysulfide ions has not been effectively suppressed yet due to the weak absorption nature of CA, resulting in rapid decay of capacity as the cycle number increases. Herein, ultrafine (~3 nm) gadolinium oxide (Gd₂O₃) nanoparticles (with upper redox potential of ~ 1.58 V versus Li⁺/Li) are uniformly in‐situ integrated with CA through directly sol‐gel polymerization and high‐temperature carbonization. The Gd₂O₃ modified CA composites (named as Gdx‐CA, where x means molar ratio of Gd₂O₃ nanoparticles to carbon) are incorporated with S. Then, the products (S/Gdx‐CA) are acted as sulfur host materials for Li‐S batteries. The results demonstrate that adding ultrafine Gd₂O₃ nanoparticles can dramatically improve the electrochemical properties of the composite cathodes. The S/Gd2‐CA electrode (loading with 58.9 wt% of S) possesses the best electrochemical properties, including a high initial capacity of 1210 mAh g^?1 and a relatively high capacity of 555 mAh g^?1 after 50 cycles at 0.1 C. It is noteworthy that the performance of long‐term cycle (350 cycles) for the S/Gd2‐CA (317 mAh g^?1 after 100 cycles and 233 mAh g^?1 after 350 cycles at 1 C) is improved significantly than that of S/CA (150 mAh g^?1 after 150 cycles at 1 C). Overall, the enhancement of electrochemical performances can be due to the strong polar nature of the ultrafine Gd₂O₃ nanoparticles, which provide strong adsorption sites to immobilize S and polysulfide. Furthermore, the Gd₂O₃ nanoparticles present a catalytic effect. Our research suggests that adding Gd₂O₃ nanoparticles into S/CA composite cathode is an effective and novelty method for improving the electrochemical performances of Li‐S batteries.     

Fabrication and evaluation of solid-oxide fuel cell anodes employing reaction-sintered yttria-stabilized zirconia

This paper reports on the fabrication and performance of solid-oxide fuel cell (SOFC) anodes utilizing yttria reaction-sintered zirconia (YRSZ). Through the reaction-sintering process, the technical-grade YSZ commonly used in the Ni-YSZ anode cermet is replaced with lower-cost ZrO₂ and Y₂O₃ materials. When sintered in the presence of nickel oxide, ZrO₂ and Y₂O₃ form cubic-phase YSZ at temperatures characteristic of SOFC processing (1400-1550 °C). Reaction sintering enables the formation of YSZ during cell fabrication, reducing SOFC anode raw-materials cost and the number of SOFC-fabrication processes. This paper reports the results of a broad range of characterization and performance measurements to evaluate the YRSZ material, including (1) crystal structure, (2) morphology, (3) pore-size distribution, (4) electronic resistivity, (5) fracture strength, (6) gas transport and catalytic activity, and (7) electrochemical performance. Material properties and performance are found to be comparable to or better than equivalent materials fabricated by conventional processes.     

Conceptual design of long-cycle boron-free small modular pressurized water reactor with control rod operation

This paper presents a new conceptual design of soluble-boron-free small modular pressurized water reactor (SMPWR) core with the following singular features: long operation cycle, axially heterogeneous adjuster control rods, and ring-type burnable absorbers (R-BAs) coated on the outside of cladding materials. The core loads 37 Westinghouse-type 17 × 17 fuel assemblies (FAs) of active fuel height 200 cm and produces 180 MW of nominal thermal power during a cycle length of 1555 effective full power days (EFPDs). Three types of burnable absorbers (BAs) are used to address the excess reactivity and obtain a long cycle: 2 w/o and 8 w/o enriched Gd₂O₃ integral-type BA (IBA), natural gadolinium R-BA, and 80 w/o enriched ¹⁰B Al₂O₃/B₄C wet annular burnable absorber (WABA). Two types of 200 cm long axially heterogeneous adjuster control rods are used to control the reactivity and the offset in axial power distribution. The first rod type adopts HfB₂ with 80 w/o enriched ¹⁰B for the bottom 140 cm and stainless steel for the top 60 cm. The second rod type uses HfB₂ (natural boron) for the bottom 100 cm and HfB₂ (80 w/o enriched ¹⁰B) for the top 100 cm. A detailed safety parameter analysis is conducted to verify the imposed design limits, namely, axial shape index of less than ±0.4, 3D power peaking factor of smaller than 5.09, required shutdown margin of greater than 3000 pcm, and negative isothermal temperature coefficient during the entire reactor operation. It is successfully demonstrated that the proposed novel SMPWR design satisfies all the design limits and the target cycle length of 1500 EFPDs.     

Enhancing Ni anode performance via Gd2O3 addition in molten carbonate-type direct carbon fuel cell

Recently, there is a consensus that a limited performance in direct carbon fuel cell (DCFC) using molten carbonate electrolyte is caused by the limited triple phase boundaries (TPB) formation. In order to solve this problem, we added Gd₂O_3, a well-known lanthanide oxide material for the improvement of wettability in the Ni anode. As a result, it was clearly shown that the voltage drop level and charge transfer resistance was decreased, and therefore the peak power density was increased by almost two times that of solely Ni anode to reach up to 106.7 mW/cm² with carbon black and 114.1 mW/cm² with actual coal fuel. The increased wettability led to the improvement of triple phase boundary (TPB) formation and consequently the enhancement of DCFC performance. While the wettability was increased with oxide content in Ni anode, the proportion of Ni at the surface of anode and the electronic conductivity was gradually decreased. With this reason, the peak power density showed the volcano type change with the amount of Gd₂O₃ addition. Finally, it was revealed that the optimum composition for the anode was Ni:Gd₂O₃ = 1:5 in weight ratio.     

Ni–YSZ-supported tubular solid oxide fuel cells with GDC interlayer between YSZ electrolyte and LSCF cathode

Highly sinterable gadolinia doped ceria (GDC) powders are prepared by carbonate coprecipitation and applied to the GDC interlayer in Ni–YSZ (yttria stabilized zirconia)-supported tubular solid oxide fuel cell in order to prevent the reaction between YSZ electrolyte and LSCF (La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ) cathode materials. The formation of highly resistive phase at the YSZ/LSCF interface was effectively blocked by the low-temperature densification of GDC interlayer using carbonate-derived active GDC powders and the suppression of Sr diffusion toward YSZ electrolyte via GDC interlayer by tuning the heat-treatment temperature for cathode fabrication. The power density of the cell with the configuration of Ni–YSZ/YSZ/GDC/LSCF–GDC/LSCF was as high as 906 mW cm⁻², which was 2.0 times higher than that (455 mW cm⁻²) of the cell with the configuration of Ni–YSZ/YSZ/LSM(La_0.8Sr_0.2MnO_3−δ)–YSZ/LSM at 750 °C.     

Sintering behavior of BaCe0.7Zr0.1Y0.2O3-δ electrolyte at 1150 °C with the utilization of CuO and Bi2O3 as sintering aids and its electrical performance

BaCe_0.7Zr_0.1Y_0.2O_3-δ (BCZY) is one of the promising electrolytic candidate for solid oxide fuel cell (SOFC) due to its good proton conductivity and better stability. Herein, the effect of dual sintering aids such as CuO-Bi₂O₃ upon the sinterability at low temperature, improved electrochemical properties, and thermo-chemical changes about proton-conducting BaCe_0.7Zr_0.1Y_0.2O_3-δ electrolyte were investigated in detail. FESEM micrographs and shrinkage curves revealed significant improvement in sinterability and densifications of BCZY electrolyte. The dense pellets were sintered with CuO-Bi₂O₃ (2–3 mol %) as sintering aids at a temperature of 1150 °C for 5 h. The perfectly uniform distribution of sintering aids increased the linear shrinkage of BCZY from 5% till 19–21%. The crystallite size and grain growth within the structure was enhanced due to the formation of the melting phase of Bi₂O₃ and Cu²⁺ incorporation in the perovskite structure. The elevated and improved electrochemical measurement for BCZY with 2 mol% of CuO-Bi₂O₃ as sintering aid categorized it well suited for solid oxide fuel cells.     

Structure and conductivity of yttria-stabilized zirconia co-doped with Gd2O3: A combined experimental and molecular dynamics study

Yttria-stabilized zirconia (YSZ) samples co-doped with Gd₂O₃ in the range 0-4 mol% were prepared and their ionic conductivities were investigated as a function of Gd₂O₃ concentration by impedance spectroscopy. Bulk conductivity of 8 mol% YSZ electrolyte at temperatures <726 K was enhanced by Gd₂O₃ co-doping up to levels of 2 mol%, while the total conductivity maxima was achieved at a composition of 2 mol% at temperatures not over than 623 K. Based on analyses of results from both molecular dynamics calculation and experimental investigation, the achievement of higher ordered cubic symmetry is suggested as an explanation for the enhanced conductivity at a relatively low temperature arising from co-doping YSZ with Gd₂O₃.     

The effects of polarisation on the performance of the Ba2Co9O14–Ce0.8Gd0.2O2-δ composite electrode for fuel cells and electrolysers

The potential of the [BaCoO₃]_n [BaCo₈O₁₁] family as a cathode for solid oxide fuel cells (SOFCs) or as an anode for solid oxide electrolyser cells (SOECs) is investigated via structural, microstructural and electrochemical characterisation. The crystallographic structure of the n = 1 member compound, Ba₂Co₉O₁₄ (BCO), exhibits rhombohedral symmetry and presents a microstructure consisting of large platelets. Overall, the electrochemical performance of the Ba₂Co₉O₁₄/Ce_0.8Gd_0.2O_2-δ (BCO/CGO-20) composite electrode is found to be enhanced under cathodic polarisation, while becoming impaired under anodic polarisation. The latter behaviour may result from the high local oxygen partial pressures upon increasing the applied anodic polarisation that lead to a depletion of oxygen vacancies at the electrode/electrolyte interface, thus, decreasing the ionic conductivity as well as electrocatalytic activity of this interface. This work, therefore, provides the first electrochemical analysis of the performance of BCO-based electrodes under applied polarisation conditions for SOFC and SOEC applications, and highlights the higher potential of this compound as a cathode material for intermediate-temperature solid oxide fuel cells.     

Ta-doped PrBaFe2O5+δ double perovskite as a high-performance electrode material for symmetrical solid oxide fuel cells

Symmetrical solid oxide fuel cells (S-SOFCs) have received considerable attention due to fewer preparation steps in recent years. The PrBaFe₂O_5+δ (PBF) is a candidate material due to good catalytic activity and electrochemical stability. In this work, Ta-substituted PBF materials (PrBaFe_2-xTa_xO_5+δ, denoted as PBFTx, x = 0, 0.1, 0.2, 0.3) are prepared and evaluated as symmetrical electrodes on GDC(Gd_0.1Ce_0.9O_2-δ)-YSZ(yttria-stabilized zirconia)-GDC three-layer electrolyte. The PrBaFe_1.8Ta_0.2O_5+δ (PBFT0.2) symmetrical cell presents the lowest polarization resistance, and the value is 0.171 Ω cm² and 0.503 Ω cm² in air and hydrogen atmosphere at 800 °C, respectively. In addition, the PBFT0.2 cell shows a peak power density of 234 mW/cm² using humidified hydrogen as fuel gas and air as oxidant at 800 °C, which is enhanced by 68% compared with that of PBF (138 mW/cm²). The results indicate that the strategy of Ta doping can improve the electrochemical performance of PBF and PBFT0.2 is a potential electrode for S-SOFCs.     

An ultra-fast fabrication technique for anode support solid oxide fuel cells by microwave

An effective and facile technique has been developed for high temperature anode-electrolyte co-sintering of anode support solid oxide fuel cells by using microwave activated sparking plasma. A high sintering temperature of 1600 °C can be achieved in a few minutes time by discharging effect. Anode support substrate pellet is uniaxially pressed, and then dip-coated with a 10 μm yttria stabilized zirconia electrolyte layer. After the microwave co-sintering, La_0.8Sr_0.2MnO_x cathode is screen-printed onto electrolyte and sintered by conventional thermal method. The cell has stably operated in 3% humidified hydrogen for more than 130 h.     

High sintering activity Cu-Gd co-doped CeO2 electrolyte for solid oxide fuel cells

Nano-sized Ce_0.79Gd_0.2Cu_0.01O_2−δ electrolyte powder was synthesized by the polyvinyl alcohol assisted combustion method, and then characterized by crystalline structure, powder morphology, sintering micro-structure and electrical properties. The results demonstrate that the as-synthesized Ce_0.79Gd_0.2Cu_0.01O_2−δ was well crystalline with cubic fluorite structure, and exhibited a porous foamy morphology composed of gas cavities and fine crystals ranging from 30 to 50 nm. After sintering at 1100 °C, the as-prepared pellets exhibited a dense and moderate-grained micro-structure with 95.54% relative density, suggesting that the synthesized Ce_0.79Gd_0.2Cu_0.01O_2−δ powder had high sintering activity. The powders made by this method are expected to offer potential application in intermediate-to-low temperature solid-oxide fuel cells, due to its very low densification sintering temperature (1100 °C), as well as high conductivity of 0.026 S cm⁻¹ at 600 °C and good mechanical performance with three-point flexural strength value of 148.15 ± 2.42 MPa.     

A novel Chinese parasol leaf biochar fuelled direct carbon solid oxide fuel cell for high performance electricity generation

A direct carbon solid oxide fuel cell is a new technology for clean and efficient utilization of carbon resources to generate electricity, with the advantages of high power generation efficiency and wide available fuel flexibility. Biomass, in virtue of large specific surface area, numerous oxygen-containing functional groups which can promote the electrooxidation of carbon, and low ash content which can increase the cell stability, reveals promising feasibility as a fuel for direct carbon fuel cells. Here we report a high-performance direct carbon fuel cell utilizing Chinese parasol leaf biochar as fuel, among which Ag–Gd_0.1Ce_0.9O_2-δ and Al₂O₃ doped yttria-stabilized zirconia are employed as symmetrical electrodes and electrolyte materials, respectively. The cell with pure leaf biochar fuel gives a maximum power density of 249 mW cm^?2 and an open circuit voltage (OCV) of 1.008 V at 850 °C while an improved performance of 272 mW cm^?2 and OCV of 1.01 V are achieved for the cell fuelled by Fe catalyst-loaded leaf biochar. The above results demonstrate that Chinese parasol leaf biochar can be applied as a potential fuel for high performance direct carbon solid oxide fuel cells.     

Methanol steam reforming over PdZn/ZnAl2O4/Al2O3 in a catalytic membrane reactor: An experimental and modelling study

A catalytic membrane reactor equipped with Pd–Ag metallic membranes and loaded with PdZn/ZnAl₂O₄/Al₂O₃ catalytic pellets was tested for the methanol steam reforming reaction (S/C = 1) aimed at producing a pure hydrogen stream for PEM fuel cell feeding. The catalyst was prepared in two steps. First, commercial γ-Al₂O₃ pellets were impregnated with ZnCl₂ and calcined at 700 °C to obtain a ZnAl₂O₄ shell, and subsequently impregnated with PdCl₂ and reduced at 600 °C to obtain PdZn alloy nanoparticles. The catalyst was tested both in a conventional packed bed reactor and in a catalytic membrane reactor. A 3D CFD non-isothermal model with mass transfer limitations was developed and validated with experimental data. The reactions of methanol steam reforming, reverse water-gas shift and methanation were modeled under different pressure, temperature and feed load values. The model was used to study and simulate the CMR under different operation conditions.     

Reactive Spray Deposition Technology - An one-step deposition technique for Solid Oxide Fuel Cell barrier layers

In order to reduce the cost of the manufacturing of Solid Oxide Fuel Cells (SOFC), and to enable metal supported cell fabrication, a new fabrication method called Reactive Spray Deposition Technology (RSDT) for direct deposition of the material onto ceramic or metal support for low temperature SOFC is currently being developed. The present work describes the effect on the performance of a SOFC when a Gd_0.2Ce_0.8O_1.9 (GDC) layer has been introduced as diffusion barrier layer between the yttria stabilized zirconia (YSZ) electrolyte and the La_0.6Sr_0.4CoO_3−δ (LSC) cathode. The dense, thin and fully crystalline GDC films were directly applied by RSDT, without any post-deposition heating or sintering step. The quality of the film and performance of the cell prepared by RSDT was compared to a GDC blocking layer deposited by screen printing (SP) and then sintered. The observed ohmic resistance of the ASC with a GDC layer deposited by RSDT is 0.24 Ω cm², which is close to the expected theoretical value of 0.17 Ω cm² for a 5-μm thick 8 mol% yttria YSZ (8YSZ) electrolyte at 873 K.     

Low-temperature preparation of dense (Gd,Ce)O2−δ–Gd2O3 composite buffer layer by aerosol deposition for YSZ electrolyte-based SOFC

The (Gd_0.1Ce_0.9)O_2−δ (GDC)–Gd₂O₃ composite buffer layer was fabricated on yttria stabilized zirconia (YSZ) electrolyte by aerosol deposition for usage as diffusion barrier layer between YSZ and (La_0.6Sr_0.4)(Co_0.2Fe_0.8)O_3−δ (LSCF)–GDC composite cathode. The deposited composite buffer layer was quite dense in nature and effectively prevented the formation of SrZrO₃ and La₂Zr₂O₇ interlayer with low conductivity at the interfaces. The cell's I–V performance was enhanced with an increase in the GDC content in the composite buffer layer. The cell containing composite buffer layer showed maximum power density of up to 1.74 W/cm² at 750 °C, which was ∼30% higher than that of the cell containing GDC buffer layer prepared using conventional process.     

Electrochemical stability of La0.6Sr0.4Co0.2Fe0.8O3−δ-infiltrated YSZ oxygen electrode for reversible solid oxide fuel cells

La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF)-YSZ (yttria stabilized zirconia) oxygen electrodes were developed by an infiltration process for reversible solid oxide fuel cells (RSOFCs). Electrochemical performance of the LSCF-YSZ composite oxygen electrode was investigated in both fuel cell and steam electrolysis modes. Galvanostatic polarization operated at ±600 mA cm⁻² and 750 °C showed that the cell has a voltage degradation rate of 3.4% and 4.9% for fuel cell mode and steam electrolysis mode, respectively. Post-test SEM (scanning electronic microscopy) analysis of the electrodes indicates that the agglomeration of infiltrated LSCF particles is possibly responsible for the performance degradation of the cell.     

On a variation of the kinetics of hydrogen oxidation on Ni–BaCe(Y,Gd)O3 anode for proton ceramic fuel cells

The electrochemical behaviour of Ni-based anodes for H⁺ solid oxide fuel cells (SOFCs) with a composition consisting of Ni–BaCe_0.89Gd_0.1Cu_0.01O_3–δ and Ni–BaCe_0.8Y_0.2O_3–δ was studied. Ni–BaCe_0.8Y_0.2O_3–δ exhibited poorer performance in comparison with Ni–BaCe_0.89Gd_0.1Cu_0.01O_3–δ, which was explained by the formation of the BaY₂NiO₅ phase at the electrode–electrolyte interface during electrode sintering. It was found that the hydrogen oxidation rate on the Ni–BaCe_0.89Gd_0.1Cu_0.01O_3–δ anode in the temperature range of 700–900 °C was determined by the rate of the three stages. It was shown that the electrode reaction mechanism did not change in this temperature range. At the temperature of 600 °C, the reaction mechanism became more complicated, most likely due to the influence of increased protonic conductivity in the electrolyte. The nature of the probable rate-determining stages of hydrogen oxidation is suggested.