Search

A noble-metal-free bifunctional electrocatalyst with outstanding activity and stability is of great importance for the development of rechargeable zinc-air batteries (ZABs). Herein, we employed a facile strategy to fabricate nitrogen-doped NiCo 2 O 4 nanostructures on carbon paper as a binder-free air cathode for rechargeable ZABs. An optimized process of nitrogen plasma treatment has enhanced the electrical conductivity of the metal oxide and induced abundant active sites into the crystal structures, resulting in enhanced electrocatalytic activities toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Notably, mild plasma treatment leads to efficient N doping while the morphology and specific surface area of the catalyst both remain unchanged. The air cathode with NiCo 2 O 4 doped with nitrogen in 2 min plasma treatment and integrated into a zinc-air battery with liquid electrolyte provided a small charge-discharge voltage gap and distinguished cycling stability superior to the air cathode with noble-metal catalyst counterparts. Furthermore, the solid-state zinc-air battery with this material displays excellent stability with just a small increase of the charge-discharge voltage gap over 20 h of operation. This work illustrates the promising potential of plasma treatment in the fabrication of high-performance catalysts. • N-doped NiCo 2 O 4 was prepared by hydrothermal method and N 2 plasma treatment. • Mild plasma treatment leads to efficient N doping in NiCo 2 O 4. • NiCo 2 O 4 with N 2 plasma treatment of 2 min exhibits excellent OER/ORR performances. • N–NiCo 2 O 4 -2 min worked as a binder-free air cathode in Zn-air batteries. [ABSTRACT FROM AUTHOR]

Abstract: The choice of the cathode material is crucial for every bio-cathode microbial fuel cell (MFC) setup. The commonly used biocathode materials, Graphite felt (GF), carbon paper (CP) and stainless steel mesh (SSM) were compared and evaluated in terms of current density, power density, and polarization. The maximum current density and power density of the MFC with GF-biocathode achieved 350 mA m−2 and 109.5 mW m−2, which were higher than that of the MFC with CP-biocathode (210 mA m−2 and 32.7 mW m−2) and the MFC with SSM-biocathode (18 mA m−2 and 3.1 mW m−2). The polarization indicated that the biocathode was the limiting factor for the three MFC reactors. Moreover, cyclic voltammetry (CV) showed that the microorganisms on the biocathode played a major role in oxygen reduction reaction (ORR) for GF- and CP-biocathode but SSM-biocathode. Electrochemical impedance spectroscopy suggested that GF biocathode performed better catalytic activity toward ORR than that of CP- and SSM-biocathode, also supported by CV test. Additionally, the MFC with GF-biocathode had the highest Coulombic Efficiency. The results of this study demonstrated GF was the most suitable biocathode for MFCs application among the three types of materials when using anaerobic sludge as inoculums. [Copyright &y& Elsevier]

In Lithium-air cathode, graphene containing materials have been reported as ideal cathode materials due to their large theoretical specific surface area, chemical stability, high electrical conductivity and charge capacity. In this study; three free-standing flexible graphene cathodes were produced with different thickness by vacuum filtration technique. For preparation of the graphene electrodes, graphene oxide (GO) papers were chemically reduced. Surface morphology of the produced graphene cathodes were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) was conducted to understand elemental composition of the GO paper. X-ray diffraction (XRD) technique and Raman spectroscopy were carried out to investigate the structure of the GO paper electrode. Moreover, specific surface area and porosity distribution of the GO paper was performed using Brunauer–Emmett–Teller (BET) method from N 2 adsorption and desorption isotherms and the pore size were calculated using the Barrett–Joyner–Halenda (BJH) algorithm on the desorption branch. Electrochemical performance of the free-standing graphene electrodes were assessed in ECC-Air test cell from 1.5 V to 4.5 V at a constant current density. [ABSTRACT FROM AUTHOR]

It is important to consider the synergy of heterostructures to improve the slow kinetics of water dissociation in the alkaline hydrogen evolution reaction (HER). Herein, we report a simple method to design a heterohierarchical CoMo catalyst. The CoMo catalyst was prepared by simple one-pot electrodeposition on carbon paper (CP). The CoMo/CP catalyst was optimized for the alkaline HER by controlling the electrodeposition bath conditions, potential, and time. The optimized catalyst shows the heterohierarchical structure containing the electrically conductive metallic Co in the bulk and Mo-incorporated Co containing Mo4+ at the surface. It exhibited a lower HER overpotential of 0.11 V at −20 mA/cm2 compared to those of the others owing to the synergetic effect of the between the Co and Mo incorporated Co. The results highlight the advantages of the simple method developed herein for the design of heterohierarchical catalysts. [Display omitted] • A heterohierarchical CoMo catalyst is fabricated on carbon paper. • The optimized CoMo/CP shows a low HER overpotential of 0.11 V at −20 mA/cm2. • A facile method is proposed to design the heterostructured catalyst. [ABSTRACT FROM AUTHOR]

To reduce the fabrication cost of proton exchange membrane water electrolyzers (PEMWEs), low-loading platinum-based cathodes were fabricated through constant potential (−1.1 V SCE) electrodeposition of Co, galvanic displacement with Pt in K 2 PtCl 4 + NaCl solution, and subsequent chemical (immersion in 0.5 M H 2 SO 4 for 5 min) or electrochemical dealloying (2000 potential cycles at −0.2 to −0.5 V SCE in 0.5 M H 2 SO 4) processes. These simple electrochemical steps produced a bimodal structure of layered Pt/Co/carbon paper (CP) and particulate Pt/CP catalysts on a porous transport layer of carbon fiber. Heat treatment of Co deposits (500 °C for 2 h, H 2 /Ar atmosphere) prior to Pt displacement was found to strongly affect the stability of Co and the electronic structures of subsequently placed Pt, resulting in high activity (an overpotential of 18.4 mV at −10 mA cm−2) and durability (∼6000 potential cycles) of the electrochemically dealloyed catalyst in hydrogen evolution reaction. A single cell with this catalyst at low cathode Pt loading of 18.4 μg cm−2 further demonstrated excellent performance of 2.39 A cm−2 @ 1.9 V. The cathode Pt mass activity is superior to previous works on other low Pt electrode fabrication methods using pulse electrodeposition or self-terminated electrodeposition, providing a new lower limit of precious metal usage for PEMWE. [Display omitted] • Bimodal-structured Pt catalysts were fabricated by displacement of Co deposits. • Heat treatment of Co deposits prior to displacement enhanced H 2 evolution activity. • 18.4mV overpotential at −10 mA cm−2 and 6000 cycles durability were achieved. • 2.39 A cm−2 at 1.9 V of PEMWE was achieved with 18.4 μg cm−2 Pt loading. [ABSTRACT FROM AUTHOR]

This study reports a unique flow-through electrode design for hydrogen production in alkaline water electrolysis. This paper investigates a variety of electrodeposition coatings on the 3D-printed electrodes, including nickel, nickel-copper, and nickel-iron. The catalytic activity and properties of the electrodes are examined through electrochemical measurements involving linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and surface morphology analysis. An experimental setup is also developed to measure hydrogen production and evaluate the efficiency of the designed electrodes. The study finds the flow-through electrodes coated with nickel-copper and nickel-iron achieve the current densities of 54 mA/cm2 and 45 mA/cm2, respectively. The activation overpotentials for the nickel-copper coated electrode are reported as 539 mV, and 408 mV for the nickel-iron coated electrode, both at a current density of 10 mA/cm2. The highest production rate is obtained within the first 15 minutes, 0.273 μg/s for the Ni-Cu flow-through electrode and 0.255 μg/s for the Ni-Fe flow-through electrode. The study further shows that flow-through electrodes produce hydrogen with an efficiency approximately 74% higher than traditional electrodes, suggesting a potentially better design for better hydrogen production in industrial applications. • This study reports a new flow-through electrode design for hydrogen production. • The electrodes are fabricated using 3D-printing and coated using electrodeposition. • The performance is evaluated using electrochemical and hydrogen measurements. • The study finds that flow-through electrodes perform better than traditional. • The flow-through electrodes consume less energy with the same or higher production. [ABSTRACT FROM AUTHOR]

Achieving low cost at high performance is difficult for direct ammonia microfluidic fuel cell (DAMFC) as a portable clean energy conversion device. In this work, a DAMFC with Ni nanoparticles anode and catalyst-free cathode is proposed to realize low cost and high performance of the fuel cell at room temperature. Due to the uniform distribution and spherical geometry of the Ni nano-catalyst, the Ni anode prepared by cyclic voltammetry owns excellent activity of ammonia oxidation. Meanwhile, sodium persulfate having strong oxidizing properties is selected as the oxidant, resulting in catalyst-free carbon paper by cyclic voltammetry treatment directly used as the cathode to greatly reduce the cost of the DAMFC. By optimizing the electrodeposition conditions of Ni electrode and the operating conditions of fuel cell, the DAMFC achieves optimal performance. The maximum power density is 8.43 mW cm−2 and the limiting current density is 78.58 mA cm−2, which is higher than that of most previously reported low-temperature ammonia fuel cells. Moreover, the fuel cell has good stability. Therefore, it proves that a DAMFC with Ni nanoparticles anode and catalyst-free cathode is an effective method to realize low cost and high performance of the ammonia fuel cell at room temperature. [Display omitted] • A low-cost and high-performance ammonia microfluidic fuel cell is proposed. • The spherical nickel nanoparticle catalyst with uniform dispersion is prepared. • Sodium persulfate with strong oxidizing property is selected as oxidant. • The effect of reactant concentration on cell performance is discussed. • The introduction of sodium persulfate removes noble-metal catalyst and improves cell performance. [ABSTRACT FROM AUTHOR]

In this paper, the mechanism of proton exchange membrane fuel cell (PEMFC) cathode cycling is discussed and the high potential suppression control problem for fuel cell vehicles is investigated by using cathode cycling. Firstly, a rigorous single-cell experimental investigation is performed to reveal the impact mechanism of cathode recirculation on the internal polarization processes of PEMFC. Results show that an increase in the recirculation ratio leads to an increase in the polarization impedance in the low and medium frequency regions but decreases the ohmic impedance. Consequently, when the recirculation ratio increases to 1, the voltage drop rates are 2.2%, 3%, 4.6%, 5.8%, and 7% as the current density varies from 0 to 0.2 A/cm2, respectively, and the ohmic impedance decreases by 28.1%. On the basis, the optimal control scheme for high potential suppression based on cathode circulation in vehicular PEMFC system is proposed. The performance comparison of different control method is carried out on a software-in-the-loop testing platform. The results show that, for the same control objective, the model predictive control (T-S MPC) method is 55.5% and 16.7% lower than the proportional integral (PI) controller and the Takagi-Sugeno linear quadratic Gaussian (T-S LQG) in terms of controller input cost. On the contrary, the cumulative error of voltage tracking is reduced by 62% and 30.4% and the voltage response against disturbances is improved by 9.7% and 42.8%. Overall, the T-S MPC achieves the optimal control effect with less control effort. • An insight into the mechanism of cathode recirculation affecting PEMFC performance. • Cathode recirculation reduces ORR reaction rate and oxygen diffusion rate. • The T-S MPC provides optimal closed-loop control of high potential suppression. [ABSTRACT FROM AUTHOR]

Improving the commercial fuel cell system efficiency is critical to reducing hydrogen consumption and improving the operational economy. This paper studies the power consumption pattern of the air supply subsystem, the most power-consuming auxiliary components, aiming to improve the system's efficiency. A method was proposed to get the extremum of the system net power by optimizing the oxygen excess ratio and cathode pressure. Mathematical models describing the fuel cell stack and air supply subsystem power characteristics were developed based on the mechanism analysis and estimation of unknown parameters. Then, a system net power model for energy efficiency optimization was developed. The operating conditions for optimal efficiency at a specific current density can be obtained by numerical calculation. To verify the method's effectiveness, a series of experiments were conducted, and the results show that the proposed method can maximize system net power output at various current density conditions. Compared with the conventional oxygen excess rate based one-dimensional optimization, the two-dimensional method can improve system efficiency by 2.06%, offering a good application prospect. • A mathematical model describing the fuel cell stack and air supply subsystem power characteristics was developed. • An energy efficiency optimization method based on the oxygen excess ratio and cathode pressure is proposed. • The operating conditions for optimal efficiency can be obtained by numerical calculation. • Maximum efficiency improvement of 2.06% can be achieved compared with One-dimensional optimization. [ABSTRACT FROM AUTHOR]

The paper aims to examine the possibility of improving the manufacturing process for MCFC cathodes. using noble, semi-precious, and rare earth metals sourced from waste electric and electronic equipment (WEEE). As MCFC components are not particularly sensitive to ceramic and metal impurities. The addition of noble metals recovered from WEEE as catalysts are economically justifiable. The reported experimental research revealed the positive impact of MCFC cathode fabricated with 20% recycled electronic scrap. Especially the cell with powder marked as 4/1 enjoyed much better performance operating at 550 °C than the reference cell. During the operation at a temperature of 650 °C, the cell with powder marked as 4/1 has almost the same performance as the reference cell, i.e., 1.01 V OCV and power density of 0.13 A/cm2. The cell with cathode with 4/2 powder has the worst performance – current density of 0.09 A/cm2 and OCV of 0.97 V. [Display omitted] • Rare earth elements separated by positive charge contains less cerium than separated by negative charge. • The maximum current densities and Open Circuit Values are similar as reference case for maximum gas flows. • The maximum current densities and Oper Circuit Voltages are better with additives for lower operational temperature. [ABSTRACT FROM AUTHOR]

As a Ruddlesden-Popper (RP) phase solid oxide fuel cell (SOFC) cathode material, Pr 2 NiO 4+δ (PNO) is a critical challenge for SOFC commercialization due to the lack of oxygen vacancies and insufficient redox reaction (ORR) activity. In this paper, various concentrations of La 0.6 Sr 0.4 CoO 3-δ (LSC) nanoparticles are coated on the surface of PNO by an impregnation method, and the ORR kinetics of PNO is found to be improved by constructing a composite cathode with heterointerfaces. The formation of the heterointerface effectively enhances the transfer of interstitial oxygen in the PNO and the oxygen vacancies in LSC, which can promote the conduction of O2− in the cathode and thus improves the ORR activity of the material. When the impregnation concentration of LSC reached C LSC = 0.2 mol L−1, the ORR activity can reach the highest level. At 700 °C, the area-specific resistance of PNO-LSC reaches 0.024 Ω cm2, which is 83.4% lower than that of PNO (0.145 Ω cm2). And the peak power density of PNO-LSC reaches 0.618 W cm−2, which is 1.89 times larger than that of PNO (0.327 W cm−2). Therefore, the construction of composite cathodes with heterointerfaces via impregnation provides an alternative strategy for enhancing the ORR activity of the cathode materials in SOFC. [Display omitted] • Pr 2 NiO 4+δ -La 0.6 Sr 0.4 COO 3-δ cathode is prepared by impregnation method. • The heterointerface promotes the ORR activity of the cathode. • Pr 2 NiO 4+δ -La 0.6 Sr 0.4 COO 3-δ has excellent ORR activity. [ABSTRACT FROM AUTHOR]

Abstract: Microbial electrolysis cell (MEC) provides a sustainable way for hydrogen production from organic matters, but it still suffers from the lack of efficient and cost-effective cathode catalyst. In this work carbon paper coated with Pd nanoparticles was prepared using electrochemical deposition method and used as the cathodic catalyst in an MEC to facilitate hydrogen production. The electrode coated with Pd nanoparticles showed a lower overpotential than the carbon paper cathode coated with Pt black. The coulombic efficiency, cathodic and hydrogen recoveries of the MEC with the Pd nanoparticles as catalyst were slightly higher than those with a Pt cathode, while the Pd loading was one order of magnitude less than Pt. Thus, the catalytic efficiency normalized by mass of the Pd nanoparticles was about fifty times higher than that of the Pt black catalyst. These results demonstrate that utilization of the cathode with Pd nanoparticles could greatly reduce the costs of the cathodic catalysts when maintaining the MEC system performance. [Copyright &y& Elsevier]

Hexaphenanthrene iron, cobalt and ruthenium(II) macrobicyclic complexes, the molecules of which have been designed for their efficient immobilization on carbon materials, such as activated carbon (AC), reduced graphene oxide (RGO) and carbon paper (CP), were tested as the cathode electro(pre)catalysts for hydrogen production in a PEM MEA water electrolysis cell. They were found to possess the good performances of hydrogen production. The use of the suitable carbon materials of a high surface area, AC and RGO, as the substrates for their efficient immobilization, as well as the addition of Nafion® as a polymer electrolyte, allowed to substantially increase an electrocatalytic activity of the corresponding clathrochelate-containing CP-based cathodes. Chemical design of the above metal-encapsulating cage molecules allowed a substantial decrease in a consumption of these metals by using their adsorbed monolayers. The high adsorptive capacities of the suitable carbon materials resulted in a substantial increase in a surface concentration of their electrocatalytically active centers, and, therefore, in that of an electrocatalytic activity of the obtained hybrid clathrochelate-containing carbon-based cathode materials. • Co, Ru and Fe clathrochelates were obtained and immobilized on carbon materials. • Clathrochelate-based electrocatalysts were implemented in a water electrolysis. • Hexaphenanthrene complexes are efficient catalysts of hydrogen evolution reaction. • They were physisorbed on carbon paper used as cathode of an electrolyser. • Best performances were observed with cobalt(II) clathrochelate-based cathode. [ABSTRACT FROM AUTHOR]

The paper investigates the influence of the La 0.6 Sr 0.4 CoO 3-δ -Gd 0.1 Ce 0.9 O 1.95 (LSC-GDC) composite cathode interlayer on the operation of solid oxide fuel cells (SOFCs). Thin composite layers with the different GDC content are obtained by the reactive magnetron sputtering. The impact of the high-temperature annealing on the LSC-GDC phase composition is studied by the X-ray diffraction instrument using additionally a synchrotron radiation. The NiO-YSZ anodes with the YSZ electrolyte thin film and GDC barrier layer are used for the SOFC fabrication. The current-voltage curves and impedance spectra of SOFCs are obtained in the temperature range of 700–800°С. It is shown that not annealed composite layers with ∼50 vol% GDC content possess the most efficient electrochemical activity. The maximum power density of the SOFC with the LSC-GDC interlayer is 1322, 1041 and 796 mW/cm2 at 800, 750 and 700 °C, respectively, which is 20–35% higher than that of the cell without cathode interlayer. • Anode-supported SOFCs with LSC-GDC composite cathode interlayer were fabricated. • LSC-GDC with ∼50 vol% GDC possess the highest electrochemical activity. • Not annealed LSC-GDC layers are more efficient. • The cell performance was increased by deposition of LSC-GDC interlayer. [ABSTRACT FROM AUTHOR]

In this paper, a new carbon support with a large number of mesoporous-structures is selected to prepare Pt/C catalysts. Transmission electron microscope (TEM) results show that the Pt/3# catalyst presents a sponge-like morphology, Pt particles are not only evenly distributed on the surface of carbon support, but also the smaller Pt particles are deposited in the mesoporous inside the support. The average diameter of Pt particles is only 2.8 nm. The membrane electrode assembly (MEA) based on Pt/3# catalyst also shows excellent performance. In conclusion, the 3# support is an idea carbon support for PEMFC, which helps to improve the oxygen reduction reaction (ORR) activity of the catalyst. Based on the "internal-Pt" structure of the support mesoporous, the efficient three-phase boundaries (TPBs) are construct to avoid the poisoning effect of ionomer on the nano-metal particles, reduce the activation impedance and oxygen mass transfer impedance, and improve the reaction efficiency. • The utilization efficiency of nano metal particles is significantly improved by the new support. • MEA based on new support also shows excellent performance. • Smaller Pt particles occupy part of the original mesoporous space of the support. • The "internal Pt" structure catalyst as PEMFC cathode can build efficient three-phase boundary. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells are perspective electrochemical devices for hydrogen energy applications and require long time performance. The paper studies the influence of the processes of particles coarsening and cation interdiffusion on the degradation kinetics of the LSM–YSZ cathode material catalytic activity as related to the interaction processes with oxygen from the gas phase. The exchange kinetics with the gas phase oxygen was studied by the oxygen isotope exchange method with the gas phase equilibration at the temperature of 850 °С and Po 2 = 10 −2 atm. The samples were exposed for 1000 h. The coefficient of gas phase and surface oxygen exchange was found to decrease at the exposure. The paper discusses the physical reasons, which lead to the oxygen surface exchange coefficient decrease in LSM–YSZ electrodes and degradation of the polarization conductivity measured by electrochemical impedance spectroscopy. [ABSTRACT FROM AUTHOR]

It is a big challenge to develop composite materials with high catalytic activity and stability in a fast and simple way in the field of solid oxide fuel cells (SOFCs). In this paper, Pr 2 CuO 4 -Pr 6 O 11 composites are prepared by a novel one-pot synthesis method. The temperature dependent phase evolution of the composite material is studied, and the oxygen reduction reaction (ORR) properties are characterized in detail by electrochemical impedance spectroscopy combining with the distribution of relaxation time analysis. The decoration of Pr 6 O 11 effectively inhibits the coarsening of Pr 2 CuO 4 particles, enlarging the specific surface area and thereby promoting the oxygen adsorption capability of the composite cathode. Compared to Pr 2 CuO 4 , the polarization resistance of Pr 2 CuO 4 -20%Pr 6 O 11 is 0.07 Ω cm2 at 700 °C, and the power (current) density reachs to 0.97 W cm−2 (1.62 A cm−2) at 0.6 V for the anode supported fuel cell. This result proves that one-pot synthesis method is an effective strategy to design cathode materials with high activity, and Pr 2 CuO 4 -20%Pr 6 O 11 is potential cathode material for SOFC. • Pr 6 O 11 decorated Pr 2 CuO 4 heterogeneous structure is realized by one-pot synthesis strategy. • 20PPCO cathode exhibits the ASR of 0.07 Ω cm2 and the PPD of 1.07W.cm−2 at 700 °C. • The reaction rate limiting step is identified as oxygen dissociation process. [ABSTRACT FROM AUTHOR]

This paper describes a lumped dynamic model for a high pressure PEM water electrolyzer. Since the electrolyzer under analysis is characterized by unbalanced pressure configuration with high cathodic working pressure, the model focuses on the cathode side to adequately predict the electrolyzer performance, analyzing and highlighting the importance of the cathodic activation overpotential term. The model is calibrated using experimental data from a 5.6 kW PEM water electrolyzer stack. A very good fit can be observed between the model and the experimental data, not only at different temperatures, but also at different pressures. It is found that the rise of temperature affects mainly the ohmic overpotential, while increasing the cathode pressure leads to an increment in the cathode activation overpotential that is not negligible for the electrolyzer performance. By rising the operating current, the cathode activation overpotential becomes 63% of that of the anode (at 70 bar, 1.2 A/cm2 and 50 °C). • Dynamic model of PEM electrolyzer stack with unbalance pressure configuration. • Model calibrated with experimental data from a 5.6 kW PEM water electrolyzer stack. • Modeling of pressure influence on the activation overpotential term. • Non negligible contribution of cathodic activation overpotential at high pressure. • Voltage increase when increasing pressure mainly due to activation overpotential. [ABSTRACT FROM AUTHOR]

Developing cathodes capable of working at intermediate temperatures (IT) is key to improving solid oxide fuel cells' (SOFC) durability, ease of operation, and manufacturing cost reduction. BaFeO 3-δ (BFO)-based perovskites are ideal candidates because of their fast kinetics, which is due to the mixed conduction of oxygen vacancies and electron-holes. Thus, maximizing their oxygen vacancy and hole concentration can further enhance oxygen reduction reaction (ORR) catalysis. This work proposes to achieve this by generating A-site deficiency, which introduces negative charges into the perovskite crystal. The paper presents a computational and experimental analysis of this strategy on BFO-based cathodes, using (Ba 0.95 La 0.05) 1-x FeO 3-δ as a case study. A-site deficiency increases the concentration of oxygen vacancies and holes, improving ORR catalysis. In addition, it eases oxygen surface exchange by hindering Ba segregation. As a result, A-site deficiency improves the overall electrochemical properties of BFO-based cathodes, providing a simple and effective method to enhance their performance. • A-site deficiency generates oxygen vacancies and electron holes in BaFeO 3-δ. • Oxygen vacancies boost the ionic conductivity. • Electron holes increase the electronic conductivity. • A-site deficient BaFeO 3-δ -based materials also show reduced Ba surface segregation. • A-site deficiency has an overall beneficial effect on the cathode performance. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cell (SOFC) is known for its higher efficiency compared to the other types of fuel cells. Even so, the application of SOFC is hindered by the operational temperature of 800 °C–1000 °C. Lowering the operational temperature below 1000 °C of SOFC becomes the major concern to allow wider applications as well as to increase the durability of the system. Improving the electrochemical performance for SOFC requires further improvement on the main components of SOFC including the air/oxygen electrode namely, the cathode. The manganite, cobaltite, ferro-cobaltite, and ferrite-based materials are known to be used as SOFC cathode, alongside new candidates such as lithiated-based material. Nonetheless, the key challenges for SOFC cathode are to find a suitable material with high electrocatalytic property at lower operational temperature of 400 °C–800 °C. This review paper provides brief information that covered as-mentioned cathode categories, taking into account the microstructural modifications performed via composite, doping, infiltration technique, and synthesis method. Finally, electrolyte-layer free fuel cell (EFFC) is introduced as a new type of SOFC that use natural resources in the fuel cells as a process to reduce its cost. • Developing new cathode material to solve existing problem in solid oxide fuel cells. • Modifying the microstructure improves the electrical efficiency at low temperature. • Understanding the mechanism of oxygen reduction reaction for the rational design. • Electrolyte layer free fuel cells can reduce the cost of cells manufacturing. [ABSTRACT FROM AUTHOR]

The cobalt/iron-containing perovskites are the most promising cathodes for the intermediate-temperature solid oxide fuel cell (IT-SOFC). However, these cathodes are generally not directly applied on the currently available commercial yttria-stabilized zirconia (YSZ) electrolyte due to the issues of over-firing, harmful reaction and thermal incompatibility. BaCo 0.4 Fe 0.4 Zr 0.1 Y 0.1 O 3-δ (BCFZY) which contains both zirconium and yttrium ions can theoretically be more compatible with the YSZ electrolyte. This paper focuses on the surficial and interfacial properties of BCFZY directly prepared with YSZ under different conditions. The surface of BCFZY by the glycine-nitrate process (GNP) can form the nanoparticles in contrast to that by solid-state reaction (SSR). The peak power density of the cell with BCFZY-GNP cathode directly on YSZ electrolyte can reach 1250 mW cm−2 at 750 °C, which is hardly achieved on the reported traditional cobalt/iron-containing cathodes. It is proved that BCFZY-GNP cathode fired at 900 °C can show more distinct nanoparticles with extensive specific surface area and better BCFZY|YSZ interface, which can promote both oxygen exchange and ion incorporation processes. • The BaCo 0.4 Fe 0.4 Zr 0.1 Y 0.1 O 3-δ (BCFZY) can form nanoparticles to extend surface area. • BCFZY cathode shows a well-connected interface when directly applied on YSZ. • BCFZY cathode fired at 900 °C shows both low surficial and interfacial resistances. • The single cell exhibits the excellent performance of 1250 mW cm−2 at 750 °C. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells (SOFCs) have the potential to replace conventional thermal power plants due to their high efficiency and low emission. As the activation loss of the cathode usually limits the SOFC performance, the development of high-performance and durable cathode materials has received extensive attention in the past few decades. It is therefore essential to keep track of the research progress to identify significant research gaps and future directions. In this study, we retrieved the bibliometric data of 1101 cutting-edge research articles focused on cathode development for SOFCs and conducted a scientometric review. Even though significant research in cathode development for intermediate to low temperature SOFCs started in the 1990s, significant growth in the research output appeared in the year 2000 and remarkably continued till 2010 before exhibiting a sinusoidal pattern. Overall, there is a record of average decadal progress in this research area. We found that only a small percentage of countries in the world (i.e., about 29%) are involved in the research for the development of intermediate to low temperature SOFC cathodes. A highlight of core assessment criteria for cathode developments is presented with a summary of the most recent articles (i.e., including those in 2021). This paper can help early-stage researchers, journal outlets, governments, funding authorities, and investors understand the current progress in this area and how close researchers are to a breakthrough that could lead to the commercialization of this emerging technology. • Solid oxide fuel cell (SOFC) cathode development over the past 30 years. • Participation of countries in the world in SOFC cathode development is analyzed. • The Asian countries are the most active in SOFC cathode research. • Future development of SOFC cathode is discussed. [ABSTRACT FROM AUTHOR]

The energy density of a flexible all-solid-state supercapacitor (ASC) requires new electrode material with special structure and morphology as a prerequisite for its secured improvement. In this paper, a new morphological exploration of chicken nuggets-like core/shell NiCo 2 O 4 /MnO 2 (NCM) nanosheet arrays on Ni foam was employed. The application of this special morphology aims to greatly improve the electrochemical performance of the cathode electrode. Additionally, Buckwheat Biochar (BBC) is utilized as the anode while the PVA/KOH thin film is prepared as the separator. The chicken nuggets-like core/shell NCM nanosheet arrays were obtained by a two-step hydrothermal method. A series of characterization methods were carried out to further support the core/shell's well-designed structure and precise composition. The tests exhibited excellent specific capacitance of 593.3 F g−1 at 5 mA cm−2 and outstanding cycling stability with a retention of 90% after 10000 cycles. Furthermore, the assembled NCM//BBC ASC device indicated a high specific capacitance (239 F g−1 at the current density of 5 mA cm−2), this is in due part of the unique architecture of NCM nanosheet arrays and interconnected special porous structure of the BBC and the thin film PVA/KOH. Hence, the assembled ASC device exhibited high energy density (an energy density of 58 Wh·kg−1 at 3263 W kg−1) and remarkable cycling stability. A flexible sandwich-structured ASC using buckwheat biochar (BBC) as an anode, NCM nanosheet arrays as a cathode, PVA/KOH thin film as separator was assembled. The device has high power/energy density and has great potential in green and renewable energy storage. [Display omitted] • Chicken nuggets-like core/shell NCM nanosheet arrays on Ni foam has been prepared as the cathode. • BBC is performed as the anode. • PVA/KOH thin film is prepared as separator. • The assembled ASC device exhibits high energy density and remarkable cycling stability. [ABSTRACT FROM AUTHOR]

Electrode materials having a combined heterostructure morphology can boost the electrochemical performance of energy conversion and storage applications. In this paper, we prepared three-dimensional (3D) porous NiCo 2 O 4 dodecahedron nanosheets (NCO) from a metal–organic framework template (ZIF-67) and incorporated them with two-dimensional (2D) multilayer graphene nanosheets (GNS) through a simple and rapid ultrasonication process. The combination of these 3D/2D nanostructures created effective interfaces between the NCO and GNS components that enhanced the intrinsic electronic properties and increased the number of active catalytic sites on the NCO@GNS surfaces. Accordingly, the NCO@GNS electrocatalyst displayed superior kinetics for both the oxygen reduction and evolution reactions in both aqueous and non-aqueous electrolytes and could be fabricated into an air-cathode for Li–O 2 battery applications. The NCO@GNS air-cathode delivered a specific storage capacity (7201 mA h g−1) higher than those of the NCO and commercial carbon black electrodes. We tested the durability of the Li–O 2 battery featuring the NCO@GNS cathode in a new PAT-cell configuration; it exhibited long-term cyclability for 200 cycles with a limited capacity of 500 mA h g−1 at a current density of 100 mA g−1. This cathode design featuring meso- and micropores shortened the pathways for Li+ ion diffusion and ensured rapid electron and oxygen transfer, thereby increasing the lifetime of its corresponding Li–O 2 battery. [Display omitted] • NiCo 2 O 4 @GNS based Li–O 2 battery cathode is prepared by ultrasonication method. • The cathode demonstrated enhanced bifunctional OER/ORR activities in Li–O 2 batteries. • The durability of the Li–O 2 battery featuring NCO@GNS cathode in a PAT-cell pattern. • A high specific capacity of 7201 mAh g−1 with stability of 200 cycles is achieved. [ABSTRACT FROM AUTHOR]

Humidity of proton exchange membrane fuel cell, a critical underlying variable that affects stack efficiency and durability, is quite challenging to be well controlled due to the measuring difficulty and multiple couplings with other variables. For precise humidity description and control, this paper utilizes the internal water content as the feedback signal, whose dynamic model is developed by taking into account various auxiliary couplings. Based on the mechanistic model, the dynamic responses of the internal water content are exhibited and analyzed by manipulating the external current, air compressor voltage and humidifier electrical power, respectively. It is shown that the internal water content is able to better describe the real humidity environment, in contrast with the conventional method using cathode inlet relative humidity. Furthermore, a combined feed-forward and feedback control structure is proposed to maintain the internal humidity as close to the desired as possible. Simulation results show that the proposed control method is able to maintain the fuel cell operating within the safe and efficient region, and the humidification power consumption can be reduced because of the precise and less conservative description on the internal humidity. • A control-oriented model is developed to fully describe the humidity dynamics. • The soft sensing of the water content of cathode is used as the feedback signal. • New control structure is developed to maintain the relative humidity at 100%. • The proposed control strategy prevents flooding and reduces humidification power. [ABSTRACT FROM AUTHOR]

Traditional dense microporous layers (MPLs) are suitable for low-temperature proton exchange membrane fuel cells (PEMFCs), but they greatly hinder mass transport in high-temperature PEMFCs. Here, we report a novel cathode MPL based on reticulated polyaniline nanowires that were grown on carbon paper via in-situ electropolymerization. The maximum power density of the high-temperature PEMFC based on the new MPL was 476 mW/cm2, which was 36% higher than that based on a conventional MPL. Oxygen gain tests and electrochemical impedance spectroscopy showed that the new MPL accelerated oxygen transfer due to its unique pore size distribution, which ultimately improved the performance of the HT-PEMFC. Image 1 • Reticulated polyaniline nanowires are used as a new microporous layer (MPL). • The novel MPL accelerates oxygen transfer due to its unique pore size distribution. • The peak power density of HT-PEMFC based on the new MPL is 476 mW/cm2. • The peak power density of HT-PEMFC based on traditional MPL is 350 mW/cm2. • The performance improvement of HT-PEMFC is evidenced by EIS and oxygen gain tests. [ABSTRACT FROM AUTHOR]

Core–shell catalyst has been attracting attention as a low-Pt catalyst for PEFC cathode. However, its mass production method has not yet been established. In this paper, a novel method suitable for continuous production of low-platinum catalyst layer for PEFC is proposed. Catalyst layer of carbon-supported Pd@Pt core–shell catalyst (Pd@Pt/C) is fabricated by using Cu underpotential deposition (UPD) followed by surface-limited redox replacement (SLRR) directly to the porous catalyst layer made of Pd core (Pd/C). The distribution of Pt corresponded well with that of Pd throughout the catalyst layer, indicating that the core–shell reaction occurs in the entire catalyst layer. Pd@Pt/C shows 1.8 times higher mass activity than Pt/C, which is comparable to Pd@Pt/C prepared by conventional microgram-scale method. • A novel method for mass production of catalyst layer for PEFC electrode was proposed. • Core-shell reaction was used directly to the catalyst layer made of core material. • Pd@Pt was made by Cu underpotential deposition and surface-limited redox replacement. • Pd core was sufficiently covered by Pt shell in the entire catalyst layer. • The mass activity of Pd@Pt/C was 1.8 times higher than that of conventional Pt/C. [ABSTRACT FROM AUTHOR]

The oxygen transport resistance in the cathode catalyst layer (CL) of polymer electrolyte fuel cells (PEFCs) has been reported to be significantly higher than expected, especially when the platinum (Pt) loading is low and/or the degree of CL degradation is severe. In this paper, the oxygen transport resistance behavior in the cathode CL is numerically analyzed under various CL design and operating conditions. Particular emphasis is placed on the aged CL wherein Pt particle growth and active Pt surface area loss are observed. For this study, a previously developed micro-scale catalyst model is improved upon to account for Pt particle size. The new model includes calculations of catalyst activity and electrochemically active surface areas, as well as various transport resistances through the ionomer and liquid films. After coupling the micro-scale CL model with a three-dimensional PEFC model, multi-scale simulations are carried out under various PEFC catalyst designs (varying Pt loading, ionomer fraction, oxygen permeation rate through the ionomer film) and operating conditions (drying or flooding of the electrode, high or lower current density). The simulation results agree well with experimental oxygen transport resistance data and further indicate that CL design with low Pt loading is more susceptible to degradation. Providing extensive multi-dimensional contours of species concentration, temperature, and current density inside the PEFC, this study provides a comprehensive understanding of oxygen transport resistance in the cathode CL in different PEFC situations. • A microscale catalyst layer model is newly developed and coupled with a three-dimensional macroscale fuel cell model. • The oxygen transport behavior inside the microstructure of cathode catalyst layer is analyzed. • Improvement of oxygen diffusivity in the ionomer film is critical under low Pt loading conditions. • Thick CL or using bare carbon particles helps to reduce the oxygen transport resistance. [ABSTRACT FROM AUTHOR]

This paper experimentally explores the spatiotemporal distribution and variation characteristics of temperature in an open cathode proton exchange membrane fuel cell stack based on thermal imager and thermocouples inserted in the cathode flow channels. The temperature distribution and evolution during the dynamic process are analyzed in detail. Besides, the effects of air flow rate and load current on the thermal characteristics of the stack are also investigated. The results show that during the start-up, the hot spot first sprouts in the central area and then spreads rapidly to the surrounding area. During the shutdown, the central and lower regions are first cooled, followed by the hydrogen inlet region, and finally the endplates. The temperature during the load stepwise increase is inconsistent with that during the load stepwise decrease, showing a temperature drift phenomenon. Moreover, there is a time lag in the response of temperature and voltage to changes in current. • Temperature distribution and evolution during dynamic process are analyzed. • Air flow rate significantly affect thermal response and temperature uniformity. • There is temperature drift during load stepwise increase and decrease. • There is a time lag between temperature and voltage when the load changes. [ABSTRACT FROM AUTHOR]

In this paper, we have shown that an increase in the pressure of oxygen on the cathode side in HT-PEM fuel cells leads first to an increase and then a decrease in the potential of the cell and again at even higher pressures to an increase. The most likely explanation for this peculiar phenomenon is a competition between oxygen and phosphoric acid on the surface of the platinum catalyst in the three phase boundary. An increase in the oxygen pressure will in this way remove phosphoric acid from the platinum giving more space for oxygen but at higher pressure creating mass transport problems due to lack of phosphoric acid whereas at even higher pressures oxygen can orient itself in a different way on the platinum surface giving more space to the acid. • High concentrations of O 2 on the cathode side can create mass transport problems. • Even higher concentrations of O 2 can reduce the transport problems. • Competition is possible between O 2 and H 3 PO 4 at the three phase boundary. • Oxygen seems to reorient itself at high pressures. [ABSTRACT FROM AUTHOR]

Abstract: This paper evaluated the oxygen reduction reaction (ORR) in a microbial fuel cell (MFC) system by using chemically and physically activated electrospun carbon nanofibers (ACNFs) in an MFC and comparing their performance with that of plain carbon paper. The chemical and physical activation was carried out by KOH reagents and CO2 gas to increase the electrode surface area and the catalytic activity. As a result, it was found that the MFC with the chemically activated carbon nanofibers (ACNFs) exhibited better catalytic activity than that of the physically activated ACNFs. Chemically ACNFs with 8 M KOH were found to be one of the most promising candidates for the ORR and could generate up to 3.17 times more power than that of the carbon paper. The ACNFs with 8 M KOH exhibited 78% more power generation than that of the physically activated ACNFs and exhibited 16% more power generation than the chemically activated ACNFs with 4 M KOH. The power per cost of ACNFs with 8 M KOH is 2.65 times greater than that of the traditionally used platinum cathode. Thus, ACNFs are a good alternative catalyst to Pt for MFCs. [Copyright &y& Elsevier]

Abstract Development of efficient, earth-abundant and low-cost electrocatalyst for effective water electrolysis is highly demanding for production of sustainable hydrogen energy. In this paper, we report the cost-effective synthetic protocol for porous NiO hollow spheres in large scale through a simple spray drying strategy, using aqueous nickel ammonium carbonate complex solution, followed by calcination. The synthesized NiO hollow spheres calcined at 300 °C (NiO-300) are porous, made of nanoparticles in size range of 10–16 nm with a size range of 2.5–4 μm and total surface area of 120 m2/g. The NiO-300 exhibited excellent bifunctional electrocatalytic water splitting characteristic, both OER, and HER, in basic solution. NiO-300 modified glassy carbon electrode showed superior water electrolysis kinetics and to achieve 10 mA cm−2 current density, it required 370 mV overpotential for OER and 424 mV overpotential for HER in 1 M KOH. It is also worked well with cost-effective plastic chip electrode. An assembled two-electrode system by pairing NiO modified plastic chip electrode as both anode and cathode in a 1.0 M KOH electrolyte for overall water splitting exhibit clear bubble formation at 1.6 V potential. Graphical abstract Image 1 Highlights • Synthesis of porous NiO hollow spheres by spray drying followed by calcination. • Showed efficient bifunctional electrocatalytic behaviour for Overall Water-Splitting. • Reaches 10 mA/cm−2 current density at a overpotential of 370 mV in 1 M KOH for OER. • 424 mV overpotential in required to achieve 10 mA cm−2 current density 1 M KOH for HER. • Exhibit clear bubble formation at 1.6 V potential in an assembled two-electrode system. [ABSTRACT FROM AUTHOR]

Abstract: The paper was aimed at investigating PEMFC ageing upon current cycling: periods of operation under nominal conditions (540 mA cm−2) were followed by periods at low current density (120 or 20 mA cm−2), the two phases of the cycles being hour-long periods. The progressive ageing of the MEA in the single 25 cm2 FC was followed by monitoring the cell voltage, impedance spectroscopy at the end of the various test periods, and by analysis of the water fractions collected. Ageing at 120 mA cm−2 was shown to be of reduced intensity as confirmed by the weak increase in the various resistances of the equivalent cell circuit, whereas repeated operation at 20 mA cm−2 resulted in far more severe degradation. This was confirmed by the significance of Pt dissolution from the cathode and recrystallisation in the bulk of the perfluorinated sulfonate polymer, as revealed by TEM photographs of the MEA after the long-term tests. Besides, the loss of sulfur from the membrane was shown to depend little on the ageing procedure, whereas the loss of fluorine was four times larger at 20 mA cm−2 than at 120 mA cm−2: the high cathode potential allowed by the lower current density might change the decomposition mechanism of the polymer chain, as discussed in the paper. [ABSTRACT FROM AUTHOR]

Abstract: Simulation is an important method for engineers to probe the detailed transportation and reaction information inside fuel cells and guide their designs without large amount of experiments. Although many papers discussing fuel cell flow fields design could be found in documents, relative positions of the ribs and channels in the anode and cathode flow field plates haven''t been paid attention to surprisingly. In this paper, simulation results were given to explain the influences of relative positions of the ribs and channels in the anode and cathode flow field plates on the proton exchange membrane fuel cell (PEMFC) performances. It is interesting that the influence differs with several factors and the information will be helpful for fuel cell design. [Copyright &y& Elsevier]

Abstract In this paper, the electrochemical performance of nanostructured LaNi 0.6 Fe 0.4 O 3-δ (LNF) infiltrated La 2 NiO 4+δ (LNO) material was evaluated as a potential cathode for BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ (BZCY)-based proton-conducting solid oxide fuel cell (H-SOFC). The performance of LNO backbone cathodes with different loading amounts of LNF infiltrated phase were investigated, and electrochemical studies implied that the single cell with about 31 wt% LNF infiltrated cathode exhibited the lowest polarization resistance of 0.027 Ω cm2 and the highest maximum power density of 969 mWcm−2 at 700 °C, which were encouraging compared with that in previous reports of cobalt-free cathodes for H-SOFCs. This work demonstrated that the infiltrated LNF-LNO cathode had a great potential for H-SOFC and the optimization of the loading amount of LNF nanoparticles on LNO was critical for the fuel cell performance. Highlights • Nanostructured LNF infiltrated cathode was studied for H-SOFC for first time. • The influence of LNF amounts on the performance was systematically analyzed. • 31 wt% LNF was the optimal infiltration for LNO scaffold. • Outstanding fuel cell performance and low polarization resistance were obtained. [ABSTRACT FROM AUTHOR]

Abstract In this paper, effects of Ce substitution of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) on the crystal structure have been investigated by XRD Rietveld refinement and results show that Ce doping at La-sites leads to lattice expansion without changing centrosymmetric cubic space group of LSCF. The electrochemical results suggest that the electrocatalytic activity of LSCF cathodes is enhanced by Ce doping. The values of oxygen surface exchange coefficient of LSCF, LCSCF03, LCSCF06, measured by electrical conductivity relaxation (ECR) method, are 5.6 × 10−4 cm s−1, 1.0 × 10−3 cm s−1, 3 × 10−3 cm s−1 at 750 °C respectively, implying that oxygen surface exchange coefficients are increased by Ce doping compared with that of LSCF. The enhancement of electrochemical performance of LSCF cathodes can be ascribed to the increase of the concentration of oxygen vacancies obtained from the thermogravimetric results, which results in faster kinetics of oxygen transport by Ce doping. Highlights • The electrochemical performance was significantly enhanced by Ce doping. • The reason of the enhanced electrochemical catalytic activities was revealed. • Oxygen surface exchange properties of the cathodes were characterized by ECR method. [ABSTRACT FROM AUTHOR]

In this paper, selected layered cuprates with La 2-x (Sr,Ba) x CuO 4-δ formula are evaluated as candidate cathode materials for Solid Oxide Fuel Cells. Two synthesis routes, a typical solid state reaction and a sol-gel method yield well-crystallized La 1.5 Sr 0.5 CuO 4-δ , La 1.6 Ba 0.4 CuO 4-δ and La 1.5 Sr 0.3 Ba 0.2 CuO 4-δ materials having tetragonal I 4/ mmm space group, but differing in morphology of the powder. Fine powders obtained using sol-gel route seem to be more suitable for preparation of the porous cathode layers having good adhesion on the solid electrolyte, but powders obtained after the solid state route can be also successfully utilized. Investigations of structural and transport properties, the oxygen nonstoichiometry and its change with temperature, thermal expansion, as well as chemical and thermal stability are systematically performed, to evaluate and compare basic physicochemical properties of the oxides. At room temperature the average valence state of copper is found to be in 2.2–2.35 range, indicating oxygen deficiency in all of the compounds, which further increases with temperature. The conducted high-temperature X-ray diffraction tests reveal moderate, but anisotropic thermal expansion of La 2-x (Sr,Ba) x CuO 4-δ , with higher expansion at temperatures above 400 °C occurring along a- axis, due to the oxygen release. However, the corresponding chemical expansion effect is small and the materials possess moderate thermal expansion in the whole studied temperature range. All compounds show relatively high electrical conductivity at the elevated temperatures, related to the Cu 2+ /Cu 3+ charge transfer, with the highest values recorded for La 1.5 Sr 0.5 CuO 4-δ . Comprehensive studies of chemical stability of the selected La 1.5 Sr 0.5 CuO 4-δ material with La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3-δ solid electrolyte revealed complex behavior, with stability being dependent apart from temperature, also on morphology of the powders. A model describing such behavior is presented. While it is possible to minimize reactivity and characterize electrochemical properties of the La 1.5 Sr 0.5 CuO 4-δ -based cathode layer, usage of the buffer layer is indispensable to maintain full stability. It is shown that mutual chemical compatibility of La 1.5 Sr 0.5 CuO 4-δ and commonly used La 0.4 Ce 0.6 O 2-δ buffer layer material is excellent, with no reactivity even at 1000 °C for prolonged time. Laboratory-scale fuel cell with the La 1.5 Sr 0.5 CuO 4-δ cathode sintered at the optimized temperature is able to deliver 0.16 W cm −2 at 800 °C while fueled with wet hydrogen. [ABSTRACT FROM AUTHOR]

Different types of self-supported SOFCs (i.e., anode-supported, cathode-supported and electrolyte-supported SOFCs) have been compared in literature mostly from technical point of view. In this study, the mentioned types of SOFCs are compared from technical and economic points of view simultaneously. In this regard, “maximum power density” and “material cost of PEN layer” are taken as objective functions. These functions are evaluated through numerical modeling and based on available cost data, respectively. The results illustrate that the cathode-supported SOFC is the optimal choice when power density is regarded alone. On the other hand, the electrolyte-supported SOFC is observed to be the optimal option when the material cost of PEN is considered as the only objective function. However, the anode-supported SOFC makes the best trade-off between the two objective functions when they are simultaneously taken into consideration. The results also indicate that the electrolyte-supported SOFC leads to a symmetrical and most uniform current density distribution as compared to the electrode-supported ones in which peak local current densities tend toward non-supporting side. The paper discusses in detail the reasoning for the mentioned observations. [ABSTRACT FROM AUTHOR]

The research dealing with performance enhancement by Sm 0.5 Sr 0.5 CoO 3−δ (SSC) fibrous cathode with embedded Sm 0.2 Ce 0.8 O 1.9 (SDC) particles has been reported by our previous study. In this paper, in order to assess the feasibility and reliability of this fibrous SSC-SDC cathode as a practical cathode, we conducted the short-term stability test using a half-cell under cathodic polarization treatment to identify the degradation phenomena only at the cathode. The polarization treatment was conducted under the current density of 500 mA/cm 2 . The stability test was carried out at 700 °C in air under the condition of open circuit. After the measurement, the resistance associated with charge transfer and surface catalytic reaction were increased by 159 and 77%, respectively. The reasons for this degradation can be considered common approaches of perovskites cathode materials such as grain growth and Sr-enrichment. Fortunately, the fibers maintain their original shape, porosity and interfacial adhesion to electrolyte. [ABSTRACT FROM AUTHOR]

In this paper, a facile hydrothermal synthetic strategy was developed for MoS 2 nanoflowers with enlarged interlayer spacing on the carbon cloth (CC) as a high efficiency cathode electrode for hydrogen evolution reaction (HER) under wide pH condition. It was observed that the loading amount of MoS 2 has a major impact on the HER performance, where the optimized MoS 2 /CC exhibited a low onset potential of 94 mV and a small Tafel slope of 50 mV dec −1 in strong acid solution (pH = 0). The improved HER performance can be contributed to the enlarged interlayer spacing, abundant defects and more exposed active sites in the small size MoS 2 nanosheets as revealed by XRD and HRTEM. Meanwhile, it also exhibited relatively good performance for HER under basic and neutral conditions with the overpotentials of 188 (pH = 14) and 230 (pH = 7) mV to achieve current density of 10 mA cm −2 and the Tafel slopes of 52 and 84 mV dec −1 , respectively. [ABSTRACT FROM AUTHOR]

The present paper investigates the performance of a solid oxide fuel cell based on proton-conducting electrolyte (SOFC-H + ) using one-dimensional steady-state model. The analysis covers a detailed electro-chemical model for H 2 and NH 3 fuels. The direct internal reforming of NH 3 is examined, and the effects of some operating parameters (e.g. temperature, pressure, fuel utilization and oxidant utilization) on the reversible cell potential are investigated. In addition, the overpotentials (including activation, ohmic and concentration) are calculated to study the irreversible behavior of the SOFC-H + with some actual data operating conditions and material properties taken from the literature. In addition, effects of some operation and structural parameters on cell performance were examined. The present results indicate that the activation and the ohmic losses are considerable. The concentration overpotential at the anode side is negligible due to the fact that H 2 O is produced at the cathode side. The maximum power density is calculated as 3212 and 3113 W/m 2 at 1073 K and 1 atm for the fuels of H 2 and NH 3 . The results further show that H 2 provides better performance than NH 3 at the same partial pressure. Moreover, NH 3 is an excellent hydrogen carrier which is a potential candidate for SOFC-H + due to its high hydrogen content and considerable cell performance. [ABSTRACT FROM AUTHOR]

In this paper, we report a highly active and robust three-dimensional (3D) Cu foam@MoS x electrode for electrocatalytic hydrogen evolution reaction (HER) prepared by a simple and controllable electrochemical deposition method. Highly conductive Cu foam scaffold with exposed 3D frameworks can not only ensure an intimate interface for facilitate a fast electron transfer but also render the deposited amorphous MoS x with abundant exposed active sites and large contact area for electrolyte diffusion. As a result, the optimized Cu foam@MoS x electrode exhibits high activity for electrocatalytic H 2 evolution in 0.5 M H 2 SO 4 , the required overpotentials to reach current densities of 10 and 100 mA cm −2 are 200 and 250 mV, respectively. Moreover, the Cu foam@MoS x electrode shows no obvious deactivation after 2000 potential cycling and also retains its outstanding electrocatalytic activity after 10 h bulk electrolysis for H 2 evolution due to the robust adhesion of MoS x . This work provides a new strategy to the development of highly active HER electrocatalyst by integrating high-surface-area and conductive substrate and the favorable surface structures of active components. [ABSTRACT FROM AUTHOR]

Fuel cells are devices that convert hydrogen into electric power using electrochemical reactions. It is an essential to understand the underlying dynamic behaviour of proton exchange membrane (PEM) fuel cells and optimize their performance. In this paper, the analysis of activation, ohmic and mass transport voltage drop is viewed. Different operating parameters such as the exchange current density, the transfer coefficient, electrolyte thickness, cell useful area and temperature effect on the voltage-current density curve are simulated. The results show that the voltage drops decrease the voltage and efficiency of the cell. Activation voltage drop reduces the voltage of about 0.2 V, ohmic voltage drop up to 0.8 V and mass transport to nearly to 1 V in high current densities. In addition, high pressures of hydrogen, oxygen and water lead to an increasing of the cell output power. Moreover, the temperature affects the performance of the cell that is reduced in low operating temperature conditions. [ABSTRACT FROM AUTHOR]

In this paper, critical role of infiltrated nanoparticles (NPs) on the electrocatalytic activity of cathodes of solid oxide fuel cells (SOFCs) for O 2 reduction reaction is studied on well-defined and microstructurally clean Pt electrodes using infiltrated La 0.8 Sr 0.2 CoO 3 (LSC), La 0.8 Sr 0.2 Co 0.5 Mn 0.5 O 3 (LSCM), and La 0.8 Sr 0.2 MnO 3 (LSM) NPs. The promotion factor, f p , as defined as the ratio of electrode polarization resistance, R E of the electrode prepared by the conventional method to that of the infiltrated electrode measured under identical conditions, is close to unit for the 0.2 mg cm −2 NPs infiltrated Pt electrodes, indicating that the promotion effect of infiltrated perovskite NPs on the electrocatalytic activity of Pt electrodes is very small or negligible under open circuit conditions. However, under dc bias of 100 mV, f p is 35, 18 and 7 for the infiltrated LSC-Pt, LSCM-Pt and LSM-Pt electrodes, respectively. The electrode activity is significantly promoted by the presence of the NPs under cathodic polarization conditions. The electrochemical activity of Pt electrodes with infiltrated NPs depends strongly on the nature of the infiltrated materials with the order of LSC > LSCM > LSM. The higher oxygen surface exchange rate as well as faster oxygen transportation kinetics of the B-site Co-rich perovskite oxides is responsible to the better catalytic activity of the infiltrated Pt cathodes. [ABSTRACT FROM AUTHOR]

In a planar solid oxide fuel cell (SOFC) stack, a number of individual cells are stacked together to increase the voltage and power output. At both the cathode– and anode–interconnect interfaces, electrical contact layers are applied between the interconnect and electrodes during cell fabrication process or stack assembly to increase the electrode-interconnect contact area and to compensate for dimensional tolerance variation of the contacting components, thus minimizing ohmic contact resistance throughout the stack. As such, electrical contact is an essential component in SOFC stacks. In this paper, we review the cathode-side electrical contact design and contact materials for application in SOFC stacks. Following an introduction of the function and working principles of electrical contact, the material requirements for cathode-side contact layer in SOFC stacks are outlined. The current materials for the cathode–interconnect contact are thoroughly reviewed, including noble metals, conductive ceramics (e.g. perovskites and spinels), composites, and other more complex structures. Several potential directions for cathode–interconnect contact material research and development are also highlighted. [ABSTRACT FROM AUTHOR]

Real-time water management is a major ongoing challenge for PEM fuel cell technologies. Given the inherently distributed nature of the system, local conditions can change significantly from cell-to-cell. To compensate for this variance, a control-oriented PEM fuel cell model that is capable of capturing localized differences in operating conditions in real time is needed. To fulfill this need, the authors previously investigated the use of multiple, equally sized control volumes (CVs) to represent the cathode channel. This modification to the modeling architecture greatly improved the accuracy over a one CV model, which was incapable of capturing the stack vapor dynamics. However, because the relative humidity distribution in the stack is non-linear, equally sized CVs do not optimize the additional information gained from the multiple cathode CV approach. In this paper, an algorithm to optimally size CVs based on an analytical solution of the relative humidity profile in the cathode channel is presented. The analytical solution was found based on the vapor mass conservation equation in the cathode. This conservation equation includes consideration of electro-osmotic drag, concentration gradient based diffusion, vapor generation, and bulk fluid flow. The solution was validated by correcting the one CV model to match experimental data using the result of the analysis. After applying the analytical adjustment strategy to the one CV model, the dewpoint temperature predicted by the augmented one CV model was in good agreement with experimental results. The solution also revealed a coefficient that relates the current, flow rate, and membrane diffusion in a single term. This coefficient could be used for control decisions to avoid flooding issues in the stack. Furthermore, using the analytical RH profile equation, CVs can be optimally, unevenly sized to improve the modeling of local operating conditions. [ABSTRACT FROM AUTHOR]

Transfer (crossover) leaks initiated by the chemical deterioration of the PEM and the resulting performance degradation has been previously identified as one the primary life-limiting factors in fuel cells. The leaks result in reduced oxygen levels in affected cells, where a secondary factor intimately related to this is high hydrogen emissions in the cathode exhaust when some cells operate in fully-oxygen-starved conditions. This paper builds on previous work that developed a unified fuel cell model that predicts cell voltage behavior under driving (normal) and driven (oxygen-starved) conditions, where this latest analysis now explicitly includes hydrogen pumping and emissions release when operating under oxygen-depleted conditions. In addition to considering diffusion effects and electrochemical effects, the model tracks the evolution of hydrogen in the cell cathode when no oxygen remains to generate water. The voltage response of the model under normal (non-starved) conditions is first validated for steady-state and transient (current step-change) conditions against previously published experiments, and then the model is used to simulate the cell voltage and stack hydrogen emissions behavior measured from three different commercially available fuel cell stacks. In the first fuel cell stack, a 9-cell commercial short stack, only one cell was fully oxygen-starved. Excellent agreement is seen between the measured and simulated hydrogen release concentrations (where air injection was used downstream of the stack to ensure adequate oxygen levels for measurement with a catalytic hydrogen sensor and to condense water vapor in the exhaust), where the role of hydrogen pumping is seen to contribute significantly to the release behavior. The first fuel cell stack is then used transiently in comparison with testing performed where the hydrogen injection level in the cell is changed quickly, where the model gives good agreement with the measured emission response and cell voltage behavior. Further comparisons with test data from a second and third 10-cell commercial short stack models operated with stack inlet hydrogen injection show good agreement with measured emissions onset versus current, where the observed threshold of starvation and emissions occurs a few percent sooner in the third model than the simulation, but the overall behavior is well predicted. [ABSTRACT FROM AUTHOR]

The PEM fuel cell has been widely used in the area of transportation and power station. The surface area of a fuel cell is enlarged to provide high enough power but the problem of analysis of internal water content behavior follows tightly. Many scholars have investigated the mathematical models of a small fuel cell and validated them through experiment. Besides, the introduction of AC impedance technique helps find relationship between water content and membrane resistance. Based on their research, an approach is put forward in this paper to model and analyze the internal water content behavior in a fuel cell of large surface area. For large surface area, three special cases are studied according to the actual operating states at cathode outlet. The first case applies to a fuel cell with no saturated water vapor at both outlets while in the second and third case, the fuel cell is divided into an electrochemical reaction zone and no reaction zone owing to emerging liquid water. The indicators of model are the water content profile inside membrane and the total membrane resistance. The simulation results show that the net water transfer coefficient has significant influence on the performance of the membrane and the constituents of anode side are easy to be varied. In addition, when the fuel cell is operated in counter-flow mode with emerging liquid water, the only back diffusion of water from cathode to anode helps improve the state of the membrane. [ABSTRACT FROM AUTHOR]

This paper investigates the start-up or warm-up process of a high-temperature proton exchange membrane fuel cell (HT-PEMFC) from room temperature to a desired temperature of ∼180 °C. The heating strategy considered in this study involves an initial heating of the HT-PEMFC by a process referred to as inlet gas heating to a temperature above 100 °C. After the fuel cell reaches above 100 °C, a voltage is applied, where electrochemical reaction heating is expected to contribute to the heating process. Thus, a numerical transient non-isothermal three-dimensional model is derived to mimic the start-up process. Operational parameters such as anode inlet temperature, cathode inlet temperature, applied voltage and voltage application temperature are varied and their effects on the maximum temperature in the membrane electrode assembly (MEA) and temperature difference in the MEA are studied. Firstly, the distribution of temperature along the channel length indicates an increase of temperature during gas heating and as the voltage is applied at the voltage application temperature, the temperature increases at the centre of the MEA due to exothermic reactions. The two-dimensional temperature distribution indicates a temperature difference between the centre of the MEA and the regions below the bipolar plate where the temperature is relatively lower. Considering the whole start-up process with respect to time, the temperature difference exists throughout the process. This will be the key focus in the parametric study. The parametric study indicates that the inlet gas temperatures, applied voltage and the voltage application temperature affect the maximum temperature in the MEA and most importantly, the temperature difference in the MEA. This can cause thermal stresses to build-up if the increase rate of temperature difference is excessive. Setting the applied voltage high (thus, lower current density) is necessary to reduce the increase rate of temperature difference. [ABSTRACT FROM AUTHOR]