Solid oxide fuel cells are all concerned about the advantages of all solid state, no noise, no pollution and high energy conversion efficiency. The high temperature fuel cell working in the temperature range of 8001000e is called high temperature fuel cell, which has fast electrode reaction speed, low battery internal resistance and comprehensive efficiency High advantages, but high temperature work has a great impact on materials, equipment and battery life. The medium temperature fuel cell, which works in the temperature range of 500800e, not only has the advantages of a high temperature fuel cell, but also overcomes its shortcomings, and has been widely valued by people. There are many options for the electrolyte of medium temperature fuel cells. Among them, rare earth or alkaline earth doped cerium oxide is one of the research hotspots, while Gd or Sm doped cerium oxide solid solution ceramics have the best electrochemical performance and become the material of choice. 1. The anode is made of nickel-electrolyte cermet composite material, and the selection of the corresponding cathode material is currently the subject of research. Studies have shown that Sm as a fuel cell cathode exhibits very good electrochemical performance. The sol-gel method is favored by its simple process, low operating temperature, uniform product composition distribution, especially the small grains of the resulting product. Among people who favor medium-temperature ceramic fuel cells that are electrolytes, ISHIHARA et al. Have studied fuel cells that use Sm as the cathode. Good results have been obtained with Ce as the electrolyte and Sm prepared by the sol-gel method as the cathode material. Composite cermet is used as anode material to study the output performance of cerium oxide-based medium temperature fuel cell with Sm material as cathode.
1 Experiment Weigh SmO (all analytically pure) according to stoichiometric ratio (molar ratio 1B1B2), dissolve in deionized water after mixing, then add appropriate amount of citric acid solution (concentration 1mol / L), adjust the pH of the solution with ammonia water Value (pH = 2), evaporate in an electric thermostatic water bath to obtain a gel (T = 80e), and then put it in a drying oven to further remove water to form a dry gel (T = 130e). When the xerogel is heated to about 300e in the air, a self-propagating combustion reaction occurs to obtain fluffy nano powder. The nano powder is calcined at a higher temperature to obtain the desired powder. The phase of the obtained powder was analyzed by Rigaku-D / max-CA X-ray diffractometer on 800 transmission electron microscope to observe the powder morphology and particle size.
The microstructure of the sintered ceramic sheet was observed under dry pressure by pressing the prepared nano-powder to a size of pan to obtain the best sintering process.
For the electrolyte, the compound of nickel oxide and electrolyte (volume ratio 1B1) is the anode for the cathode. The three-in-one green body is made by the dry pressing method and sintered at the optimal sintering temperature of 1100e for 4 hours to make a battery sheet. Put the battery in the tube furnace, connect an external variable resistor, connect the anode with hydrogen and the cathode with air, adjust the furnace temperature, measure the working voltage between the yin and yang and the current through the load resistance by voltammetry, test the battery Output power.
2 Results and discussion 211 powder characterization X-ray diffraction pattern of the powder obtained after firing for 5 hours. It can be seen that the Sm crystal phase is formed in the sample calcined at 700e, but the crystal is not fully developed, and also contains heterophases such as Sm and Co oxides; the spectrum after calcination at 900e only has a single phase diffraction of Sm Peak, from the peak shape, we can see that the crystal is well developed, and there is no other miscellaneous phase; the spectrum after calcination at 1100e is basically the same as that at 900e. It can be seen that 900e can be used as the calcination temperature to obtain the desired powder.
Select 2H from Figure 1 after removing the instrument width, take the arithmetic average of the calculation results of each diffraction peak. The results are shown in Table 1.
The calcination temperature / e crystal grains have been fully formed at 900e, but the grain size has not changed much after calcination at 1100e. This provides an important reference for further research on the sintering properties of the powder.
Morphology (TEM), the particle size of the powder is about 50100nm, most of which are nearly spherical polyhedrons, and the size is relatively uniform. Comparison with the XRD analysis results in Table 1 shows that there is agglomeration.
The atomic percentage content of each element in the product obtained after (after removing O), using surface scanning, take the average value of several micro area scanning results, listed in Table 2. As can be seen from the table, SmBSrBCo is about 1B1B2 , Which is consistent with the XRD analysis results.
Synthesis of medium temperature fuel cell cathode material Sm and application of powder morphology (TEM) The results of the raw material ratio energy spectrometer during element synthesis The sintering performance of ceramics The powder obtained after roasting 900e for 5h is made by dry pressing The plain blanks were sintered at 900e, 1100e, and 1300e for 4 hours. The changes in size, shrinkage, and relative density of the sample after sintering are shown in Table 3.
It can be seen from the table that the 1100e sintering shrinkage rate is much higher than the 900e sintering shrinkage rate, and the relative density has also increased by nearly 50%. As mentioned above, the grain size does not change much at these two temperatures, which shows that even at 1100e, the sample is still It is in the shrinking stage of densification. The shrinkage of the sintered sample at 1300e is not much different from that of 1100e, and the relative density is only less than 10% higher than that at 1100e.
SEM observations were made on the microstructures of the products at three sintering temperatures. It can be seen that the microstructure of the sintered at 900e is loose, the sample sintered at 1100e is relatively dense, and the average particle size is about 1Lm. grow up. Therefore, 1100e sintering is more suitable.
The output performance of the 213 single cell is based on the above research results of the sintering performance of the nano-powder, taking into account the properties of the electrolyte material and the anode material, the three-in-one type green body is sintered at 1100e to make a battery sheet, and test the output performance of the battery.
As the temperature rises, the open circuit voltage rises linearly, slowly rising within 350380e, and then rises linearly again. When the temperature is higher than 420e, the open circuit voltage does not change much with the increase of temperature. When the temperature is low, the electromotive force of the single fuel cell is the anode side and the cathode side.
In the formula: F is Faraday's constant; n is the number of electrons transferred in the oxidation-reduction reaction; R is the universal gas constant; T is the absolute temperature, K; p is the partial pressure of the gas, Pa.
When the partial pressure of oxygen on both sides of the electrode is constant, it can be seen from equation (2) that the open circuit voltage increases linearly with increasing temperature, and the internal resistance of the battery is large when the temperature is low, so the open circuit voltage is lower than 350e, and The open circuit voltage increases linearly with increasing temperature.
The morphology after sintering (SEM), but in the temperature range of 350380e, the open circuit voltage changes slowly with temperature. This is because the nickel oxide in the anode begins to be reduced to metal nickel by hydrogen, which causes the internal resistance of the battery to drop to 380e. , It is likely that the restoration has been completed, so the open circuit voltage has increased again in the interval of 380420e.
In the temperature range of 420600e, the open circuit voltage is maintained at 110111V. This is because after the temperature rises, the activity of oxygen ions in the electrolyte is greatly enhanced, and the catalytic activity of the electrode is improved. At this time, the electromotive force of the battery is determined by the following formula Middle: G is the change of the free energy of the battery reaction, and the meanings of other symbols are the same as in formula (2).
After the temperature reaches a certain range, the entire fuel cell system is in a dynamic equilibrium state, the internal resistance of the battery no longer changes, and the open circuit voltage tends to be stable.
At the same operating temperature, the output power increases with the increase of the operating current, but this increase is not continuous. When a certain operating current is reached, the output power reaches the maximum value, and then the output power gradually decreases with the increase of the operating current At the same time, it can also be seen that when the operating current is the same, as the operating temperature increases, the output power of the battery increases, but when the operating temperature is within the range of 550600e, the output power increases slowly. Among them, when working under 600e, when corresponding to the maximum output power density 2, the working voltage is 016V.
As the temperature rises, the activity of oxygen ions in the electrolyte is greatly enhanced, and the catalytic activity and conductivity of the electrode will also be improved, which is conducive to reducing the internal resistance of the battery and reducing the polarization of the electrode, so that the output performance of the battery 3 conclusions are obtained 1) Sm nano powder can be prepared by the sol-gel method, and the initial powder after the burning of the dry gel is roasted at 900e to obtain Sm single-phase powder with a grain size of about 20nm; 2) using dry The best sintering temperature of the Sm green body obtained by pressing is 1100e. If the sintering temperature is too low, the product is loose, and if it is too high, grain growth in the sample will occur, which is undesirable.
The synthesis and application of the medium temperature fuel cell cathode material Sm is an electrolyte, the combination of nickel oxide and electrolyte (volume ratio 1B1) is the anode, and Sm is the cathode. The manufactured hydrogen-oxygen fuel cell operates at 600e and its maximum power density reaches 260mW / cm2, the current density is 2, and the operating voltage is 016V. The power density obtained is higher than the literature at the same temperature, doped LaGaO as the electrolyte value; and with Ce as the electrolyte, but with another calcium The power density of a single cell with titanium oxide La as the cathode at 700e is quite high.
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