Latest ArticlesAn appropriate amount of carbon nanotubes can be added into cement-based materials to obtain the unique conductive properties (i.e., self-sensing and intelligence of cement-based material). The electrical conductivity of carbon nanotube cement-based composites is affected and restricted by some factors such as physical field and material composition. Some recent works on influencing factors on electrical conductive properties of carbon nanotubes-reinforced cement based composite materials were reviewed. For the electrical indicators such as resistivity and current of composites, the mechanism of the physical field influencing the conductive properties of composites was analyzed. The effect of material component on the conductive mechanism of carbon nanotube cement-based composites was discussed. The problems to be further investigated were proposed, and the future research and trends of the conductive properties of carbon nanotube cement-based composite materials were prospected.
Admixtures play an important role in concrete engineering. The performance of admixtures is highly dependent on their releasing behavior. With the introduction of controlled release technology, the efficiency of admixtures is improved and the adverse effects caused by premature release is reduced, which are beneficial to the quality control of concrete. This review summarized the concept and classification of controlled release technologies and introduced recent work on controlled release technology in the field of concrete admixtures. The controlled release mechanism of concrete admixtures is also represented based on passive and active responses.
Concrete cracks will affect the building appearance and the structural safety. A novel type of concrete microbial self-healing material with the unique mineralization metabolic mechanism of bio-mineralizing bacteria can be used to repair concrete cracks intelligently and obtain the self-awareness and self-healing of concrete materials. This novel concrete microbial self-healing material can replace the conventional concrete with some disadvantages like poor repairing effect, high cost and even heavy environmental pressure. Recent development on the overall evolution, frontier hotspots and applications of this environment-friendly material by CiteSpace and knowledge map technology was represented.
In this report, the applications for National Natural Science Foundation of China programs on inorganic nonmetallic materials in 2020 were summarized and statistically analyzed. A pilot classified evaluation measure according to the scientific attributes of individual project was introduced in the evaluation process and the new-methodology-based trial results were revealed and objectively interpreted.
The crystal defects structure, thermal expansion coefficients, electrical transport property, redox cycling stability, and electrochemical performance of Sr2FeMo0.6Mg0.25Al0.15O6(SFMMA) double perovskite material as a high-performance anode for solid oxide fuel cells (SOFCs) were investigated. The SFMMA has a tetragonal structure of I 4/m at room temperature, but transforms into a cubic structure of at 400℃. The real structure of SFMMA should be in the form of Sr2(Fe0.75Mg0.25)(Mo0.6Fe0.25Al0.15)·O6-δ, generating a plenty amount of anti-site defects FeB' and -FeB-O-FeB'-bonds formed in the crystal lattice, which are beneficial to the formation of oxygen vacancies and migration of oxygen ions. The thermal expansion coefficients of SFMMA anode are 13.0×10-6 K-1 and 17.6×10-6 K-1 at 25-400℃ and 400-900℃, respectively. The electrical conductivity of SFMMA is greater than 35 S/cm in the operating temperature range of 600-900℃. The SFMMA anode shows a fast oxygen surface exchange kinetic and an excellent redox cycling stability. The area specific resistances of SFMMA/La0.4Ce0.6O2(LDC)/La0.8Sr0.2Ga0.8Mg0.2O3(LSGM)/LDC/SFMMA symmetrical half-cell are 0.096, 0.142, 0.239 Ω·cm2 and 0.447 Ω·cm2 at 900, 850, 800℃ and 750℃ in wet H2(3% H2O, 50 mL/min), respectively. The electrolyte supported single cell with the configuration of SFMMA/LDC/LSGM (300 μm)/PrBa0.5Sr0.5Co1.5Fe0.5O5+δ can deliver a maximum power density of 886 mW·cm-2 at 850℃.
La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) anode structure, electrochemical performance and operating stability are characterized using CO-CO2 mixed as fuel. Results show that, the ABO3 perovskite structure of LSCFN is reduced to A2BO4 Ruddlesden-popper structure in CO fuel. While, the addition of CO2 can shift the structure of LSCFN back to single perovskite, and inhibit coking effectively. The maximum output power density of single cell using pure CO fuel is 0.6 W/cm2 at 850℃. And the cell operates for more than 100 hours when using CO∶CO2 mixed gas as fuel in molar ratio of 5∶1.
Al2O3-SiO2-CaO-based sealing material was developed. The properties of high-temperature crystallization/softening, thermal behavior and interfacial bonding of the sealing material were observed in situ. The results show that the sealing material begins to soften at 850℃, spheroidizes at 900-1 000℃ and keeps amorphous at <1 100℃. In addition, the sealing material has a slight mass loss according to the thermal analysis, and it is bonded with the interconnect and the cell tightly, which is conducive to the application in solid oxide fuel cell (SOFC) stack. Two 5-cell solid oxide fuel cell (SOFC) stacks were assembled by the sealing material. The cycling and stability performance of SOFC stacks were tested. The results indicate that the open circuit voltage (OCV) of the stack reaches 6.0 V, showing an average OCV of 1.2 V for single cells. The stack 1 is operated under cycling conditions, showing no degradation before and after cycling. The stack 2 is operated under stability conditions, exhibiting no degradation for 300 h operation.
Effects of temperature, fuel composition and flow rate on the performance of an anode-supported cell and a stack were studied. The results show that in the complex impedance spectrum, the activation energy corresponding to high frequency arc is the highest; that of the Ohmic loss is lower, which indicates that not only the ionic conductivity resistance, but also the surface resistance and possible contact resistance are included. With dry hydrogen as fuel, the results show that the activation polarization near the open circuit voltage is large and the activation energy is very small, which indicates that the rate control step of the activation polarization is not a charge transfer process, but a surface diffusion process. For simulated reforming gas fuels, the results show the activation polarization is small, but the open circuit voltage is lower, so that the performance is worse than that of hydrogen fuel. With the increase of the stack current, the temperature of the fuel exhaust gas increases, showing obvious thermal effect.
A cobalt-free double-perovskite cathode SmBaFeNiO5+δ (SBFN) was synthesized by a modified sol-gel process, and SmBaFeNiO5+δ-Sm0.2Ce0.8O1.9 (SBFN-SDC) composite cathodes were applied to reduce the thermal expansion coefficient (TEC) and improve the electrochemical performance. The average TEC of SBFN is 14.1×10-6K-1 in air at 30-900℃, while the SBFN-SDC15 (the mass ratio is 85∶15) composite cathode shows the lowest average TEC of 12.0×10-6K-1. The maximum conductivity of SBFN is 48 S/cm at 425℃. The polarization resistance (Rp) of SBFN is 0.386 Ω·cm2 at 700℃ on SDC electrolyte. Introducing SDC to SBFN can increase the electrochemical catalytic activity of the cathode materials. SBFN-SDC10 (the mass ratio is 90∶10) composite cathode has the lowest Rp, which is 0.224 Ω·cm2 at 700℃. The maximum power densities of Ni-SDC|SDC|SBFN and Ni-SDC|SDC|SBFN-SDC10 single cells are 367.6 mW/cm2 and 507.8 mW/cm2 at 800℃, respectively.
The response of a large area single cell and a kW class stack against step current change, hot start-up and thermal cycling (cold start-up) were systematically investigated when the current change, gas composition, flow rate and operating temperature were fixed. The results show that the voltage and power of the stack can quickly track the corresponding current changes in the small current area. The on-off of current test results show that SOFC stack is sufficiently tolerant, and a certain amount of on-off of current test cannot cause the significant degradation of the stack performance. However, the thermal cycling will lead to stress release and changes in contact resistance, thus result in the degradation of the stack performance. The more than 5 heat cycles can ease the stress release to a modest way.
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