Material property differences among components of solid oxide fuel cell (SOFC) lead to excessive stresses during cell fabrication and operation, among which functional gradient material electrodes have attracted attention for their ability to reduce residual and thermal stresses in SOFC. But so far, there is rare study on SOFC with functional gradient anode using numerical simulation of thermal stress. In this study, a multi-physics field coupling model of SOFC with complete structure was established by COMSOL Multiphysics 6.0. Based on multi-physics field coupling model and numerical simulation of the residual stresses and thermal stresses in SOFC, four different distribution curves were employed to characterize the component distribution of anode materials. The results show that the tensile stress of anode can be significantly reduced by using functional gradient material during fabrication at different temperatures, especially at room temperature. Compared with non-gradient distribution, the maximum tensile stress of the anode is reduced by 47.69% before reduction and 35.74% after reduction by using quadratic curve distribution. During the operation process, the heat generated by the electrochemical reaction and the convective heat transfer of gas leads to the temperature difference between inlet and outlet, resulting in significant stress concentration at inlet and outlet of the metal frame as well as at contact surface between rib and electrode. Functional gradient materials can significantly reduce the maximum stress on the anode, metal frame and electrolyte, which is particularly obvious when using quadratic curve distribution. Therefore, this research has potential theoretical significance and engineering value for designing and fabricating SOFCs.

Taking inspiration from the in-situ reduction technique employed for exsolved nano-metal as anodes in solid oxide fuel cells (SOFCs), this study utilized Sr₂V_0.1Co_0.9MoO₆, which was synthesized in an ambient air environment, with perovskites of other phases to co-fire with the electrolyte under atmospheric conditions for direct fabrication of a single cell. By this way, the procedure of subjecting the cell to harsh preparative conditions in a reducing/inert atmosphere to prevent its anodic oxidation can be circumvented. After preparation of the anode precursor on the electrolyte sheet, we adopted a simple process of in-situ reduction at 750 ℃ for 4 h on the fuel side to achieve formation of a pure phase Sr₂V_0.1Co_0.9MoO₆ (R-SVCMO) as anode. The results demonstrate a significant reduction in the activation energy of R-SVCMO, accompanied by an increase in conductivity from 2.7 to 21.6 S•cm^-1. Moreover, when employing R-SVCMO as anode in a single cell with H₂ and wet CH₄ as fuel gases, the maximum power density (P_max) at 850 ℃ can reach up to 862 and 514 mW·cm^-2, respectively, showcasing exceptional catalytic performance. The anodes before and after reduction exhibit average thermal expansion coefficient (TEC) of 1.15×10^-5 and 1.23×10^-5 K^-1, respectively, within the temperature range of 100-850 ℃, comparable to those observed in conventional SOFC electrolytes. Therefore, the reduction process does not induce any volumetric changes in the anode layer, significantly enhancing its structural stability. Meanwhile, degradation rate of only 0.13% is occurred. It is worth noting that this R-SVCMO synthesis method can result in remarkable long-term stability and high catalytic activity as an anode material. The obtained R-SVCMO can achieve a 60% catalytic efficiency for wet CH₄ and last for 1450 h. Based on this R-SVCMO, the single cell can maintain stability for 450 h at 0.7 V. In conclusion, this study demonstrates an effective way of employing an in-situ fuel reduction method to prepare a single cell with exceptional electrochemical performance and structural stability.

To solve the problem of large concentration polarization impedance of anode-supported direct carbon solid oxide fuel cell (DC-SOFC), tubular cone-shaped anode-supported segmented-in-series solid oxide fuel cell (SOFC) was prepared by an improved gel-casting method. By appropriately increasing content of the solvent, fluidity of the slurry and quality of the obtained product were improved. By increasing content of the pore-forming agent, the porosity of the anode was increased, reducing the diffusion resistance of gas. As-improved SOFC was fueled by hydrogen and operated at 800 ℃ with an open-circuit voltage of 1.05 V. The polarization impedance of the electrochemical impedance spectrum decreased while the maximum power density was 0.67 W•cm^-2 and the active area of the cathode was 2.2 cm². These SOFC electrochemical performances were significantly higher than that before improvement. Activated carbon loaded on the anode with 5% (in mass) K as catalyst was directedly used as the fuel of SOFCs. Using this anode-supported direct carbon, the DC-SOFC was prepared, showing an open circuit voltage of 1.030 V and a peak power density of 0.74 W•cm^-2 at 800 ℃. This DC-SOFC was discharged at a constant current of 400 mA, and its effective utilization rate of carbon fuel was 31% which was higher than that before improvement (17%). Four improved tubular cone-shaped single cells were connected in series to form a four-cell stack, showing a peak power of 8.0 W and a corresponding power density of 0.91 W•cm^-2 at 800 ℃, which was higher than that before improvement (4.1 W), exceeding the maximum of previous reported DC-SOFC, and displayed an effective utilization rate of 15% for carbon fuel.

Intermediate-temperature solid oxide fuel cells (IT-SOFCs), as the operating temperature decreases, require cathode materials with high catalytic activity. In this study, double perovskite Sr₂CoFeO_5+δ (SCF) was synthesized by Sol-Gel method, and effect of SCF cathode compounded with 20% (molar fraction) Sm₂O₃ doped CeO₂ (SDC) at different ratios on the electrode performance was elucidated. The SOFC single-cell performance was improved by optimized chemical expansion and area-specific resistance (ASR) from composite electrodes. Results show that, SCF cathode after annealing at 950 ℃ for 10 h exhibits good chemical compatibility with common electrolytes. For the composite of SCF and SDC at a mass ratio of 1 : 1, the average thermal expansion coefficient (TEC) can be significantly reduced from 2.44×10⁻⁵ K^-1 of pure SCF to 1.54×10⁻⁵ K^-1. ASR of SCF−xSDC (x=20, 30, 40, 50, x: mass percentage) composite cathodes are as low as 0.036, 0.034, 0.028 and 0.092 Ω·cm² at 800 ℃, respectively. The SCF−40SDC composite cathode displays the lowest ASR value among SCF−xSDC in the whole temperature range. Based on the 0.3 mm-thick La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ (LSGM) electrolyte, the maximum power density of SOFC using SCF−40SDC (757 mW·cm⁻²) as a cathode is higher than that of pure SCF (684 mW·cm⁻²). These results demonstrate that the SCF−40SDC composite cathode is a promising candidate for application in IT-SOFCs.

In order to fulfil the requirement of low area specific resistance and highly stable cathode contact material in planar type solid oxide fuel cell (SOFC) stack assembling, this work investigated the electrical property evolution of LaNi_0.6Fe_0.4O₃ (LNF) with manipulated particle size and its effect on SOFC electrochemical performance. The optimized pre-treatment strategies of LNF were obtained with decreasing ASR, improving SOFC single cell performance and thermal cycling stability. Results show that, the dry-pressed LNF-2 and the high-temperature sintering-pre-treated LNF-3 possess smaller area specific resistances of 0.074 and 0.076 Ω·cm², respectively, more stable particle sizes with shorter conditioning state and faster transfer into steady state after applying 1 A/cm² current load at 750 ℃. Specifically, the single cell with LNF-2 shows improved peak power density of 0.94 W/cm² compared to 0.66 W/cm² of LNF without treatment at 750 ℃. However, it exhibits significant performance degradation during thermal cycling, decreasing by 20%. In contrast, the peak power density of LNF-3 single cell decreases by only 4% after 20 thermal cycles. This work is expected to provide guideline and valued reference for reliable SOFC stack assembling and stable operation.

Oxygen reduction reaction (ORR) is an important electrochemical reaction process at the cathode of fuel cell, but its spontaneous reaction process is slow, and its catalysts, though efficient in catalyzing the ORR reaction, are facing problems of expensive price, complicated synthesis process, and polluting environment. Therefore, it is of great significance to explore the method of synthesizing a simple and environmentally friendly catalyst for the preparation of ORR catalysts. Fe-N co-doped mesoporous carbon substrate (Fe-N/MC) is a kind of non-precious metal catalysts for oxygen reduction reaction with great application value. In this work, mesoporous carbon substrate (MC_M) was obtained by high-temperature carbonization of small molecule precursors in a semi-closed system in a muffle furnace, and then Fe-N co-doped mesoporous carbon substrate (Fe-N/MC_MT) was prepared by mixing the obtained MC_M with iron salts in a tube furnace at a high temperature. This method only needs simple pyrolysis conditions, requiring no template agents and toxic substances such as NH₃ and HF. MC_M is beneficial to enhance the hydrophilicity and coordination ability of the mesoporous carbon substrate surface due to its high element contents of nitrogen and oxygen. Fe-N/MC_MT, prepared by MC_M and iron salts, contains abundant and catalytic ORR Fe-N_x active sites with onset potential and half-wave potential of 0.941 and 0.831 V(vs RHE), respectively, which are 34 and 16 mV more positive than those of commercial Pt/C catalyst, respectively. ORR can be divided into two-electron or four-electron type according to the reaction process, and the transfer electron numbers of Fe-N/MCMT and Pt/C are 3.77 and 3.91, respectively, indicating a four-electron reaction process.

The gas diffusion layer (GDL) is a critical component of proton exchange membrane fuel cells (PEMFCs) and accounts for 40%-50% of the fuel cell membrane's cost. Developing a low-cost and high-performance GDL is imperative to advance the commercialization of PEMFCs. In this study, we generated a flexible carbon cloth with high electrical conductivity and porosity from cellulose cloth at a low temperature (1500 ℃). The carbon cloth is composed of micron-sized carbon fibers with a porosity of up to 76.93%. Through catalytic graphitization of iron-based compounds, massive carbon nanotube clusters were formed in situ on the surface of carbon fibers, which effectively enhanced the electrical conductivity of the carbon cloth. The in-plane resistance was as low as 34 mΩ·cm while the through-plane resistance was 2.8 mΩ·cm under a pressure of 2 MPa, meeting the performance standard of commercial carbon cloth. Furthermore, the PEMFC with the prepared carbon cloth as GDLs exhibits a power density of 0.4 W·cm^-2 at current density of 0.7 A·cm^-2, exceeding the device with commercial carbon cloth (0.34 W·cm^-2 at 0.7 A·cm^-2). This study demonstrates that the prepared biomass-derived carbon cloth with low-cost and high- performance holds great potential for advanced GDLs for PEMFCs.

Ammonia with low cost, easily liquefied and high volumetric energy density is an attractive carbon-free fuel. Utilizing ammonia as anodic fuel, direct ammonia fuel cells are showing great interests to researchers. However, such amazing fuel cell device is limited by the sluggish anodic ammonia oxidation reaction. In this work, PtIr alloy aerogels with a three-dimensional porous network structure were prepared by nanoparticles (NPs) self-assembled under a simple and surfactant-free conditions. This structure provided a rich open interconnected proton transport channel and additional catalytically active sites which contributed to the dehydrogenation process of NH₃ molecules in ammonia electrocatalytic oxidation. An optimal AOR activity was achieved at the 80/20 molar ratio of Pt/Ir. Effects of NH₃ concentration and operating temperature on catalyst's ammonia oxidation performance were studied, which revealed that the AOR performance of Pt₈₀Ir₂₀ alloy aerogel was improved with the increase of ammonia concentration or operating temperature. For example, the mass specific activity, at 0.50 V of the Pt₈₀Ir₂₀ alloy aerogel, was estimated to be 44.03 A·g^-1, which was about 4 times as that of the ammonia concentration at 0.05 mol/L. In the case of operating temperature effect, the mass activity was estimated to be 148.73 A·g^-1, which was almost 12 times as that of the temperature rising (from 25 ℃) to 80 ℃. Encouragingly, the onset potential of the optimal Pt₈₀Ir₂₀ alloy aerogel catalyst displayed about 40 mV reduction during such a temperature change. Further calculations using the Arrhenius equation showed that its activation energy was reduced by about 9.43 kJ·mol^-1 as compared with commercial Pt/C. Moreover, its AOR stability was improved as evidenced by a loss of ~50.6% mass activity after 2000 potential cycles when compared with commercial Pt/C (~74.9%).

Intermediate-temperature solid oxide fuel cell (IT-SOFC) is promising for carbon neutrality, but its cathode is limited by the contradiction between thermal compatibility and catalytic activity. Herein, we propose a high-entropy double perovskite cathode material, GdBa(Fe_0.2Mn_0.2Co_0.2Ni_0.2Cu_0.2)₂O_5+δ (HE-GBO) with improved compatibility and activity, in view of the high-entropy strategy by multi-elemental coupling, which possesses double perovskite structure and excellent chemical compatibility with state-of-the-art Gd_0.1Ce_0.9O_2-δ (GDC). The polarization resistance (R_p) of the symmetrical cells with HE-GBO cathode is 1.68 Ω·cm² at 800 ℃, and the corresponding R_p of HE-GBO-GDC (mass ratio 7:3) composite cathode can be greatly reduced (0.23 Ω·cm² at 800 ℃) by introducing GDC. Dendritic microchannels anode-supported single cells with HE-GBO and HE-GBO-GDC cathodes realize maximum power densities of 972.12 and 1057.06 mW/cm² at 800 ℃, respectively, indicating that cell performance can be enhanced by high-entropy cathodes. The results demonstrate that high-entropy double perovskite cathode material HE-GBO has a high potantial to solve the conflict problem of thermal compatibility and catalytic activity in IT-SOFCs.

Direct ethanol fuel cell (DEFC) has been widely studied because of its advantages of easy fuel availability, green and high effiency. However, DEFC catalysts are still frustrated with low catalytic efficiency and poor catalyst stability, which restrict its rapid development. In this work, XC-72R carbon black-loaded Pt₁Co_x/C high-index crystalline nanocatalysts were prepared in one step by liquid-phase hydrothermal synthesis, using polyvinylpyrrolidone (PVP k-25) as dispersant and reducing agent, glycine as surface control agent and co-reducing agent, and modulating the molar ratio of Pt-Co metal precursors to achieve the in-situ growth of catalyst particles on carbon carriers. The exposed high index crystalline facets of the Pt₁Co_1/3/C nanocatalyst mainly consisted of (410), (510) and (610) crystalline facets. The growth pattern of the Pt₁Co_1/3/C nanocatalyst grains varied from 'sphere-like' to cubic, and eventually to concave with high index grain orientation. The Pt₁Co_1/3/C nanocatalyst with high index crystalline surface has the highest electrocatalytic activity with an electrochemically active surface area of 18.46 m²/g, a current density of 48.70 mA/cm² for the ethanol oxidation peak, a steady state current density of 8.29 mA/cm² and a potential of 0.610 V for the CO oxidation peak. This indicates that the defect atoms such as steps and kinks on the surface of the catalyst with high index crystal plane can increase the active sites, thus showing excellent electrocatalytic performance. This study may provide a theoretical basis for the development and industrial application of high index crystalline catalyst materials.