Hydrogen energy is the clean energy that drives the transformation from traditional fossil energy to green energy. Its energy density is 3 times that of oil and 4.5 times that of coal! It is the disruptive technology direction of the future energy revolution. The hydrogen fuel cell is the key carrier to realize the conversion of hydrogen energy into electric energy, and countries around the world attach great importance to the development of hydrogen fuel cell technology. This has put forward higher requirements on materials, process technology, and characterization means of hydrogen energy and hydrogen fuel cell industry chain. Gas adsorption technology is one of the important methods for material surface characterization, and plays a crucial role in the utilization of hydrogen energy mainly in hydrogen fuel cells.
Application of gas adsorption technology for characterization in the hydrogen production industry
How to produce hydrogen is the first step in harnessing hydrogen energy. Hydrogen production from electrolytic water with high purity grade, low impurity gas, and easy to combine with renewable energy sources is considered as the most promising green hydrogen energy supply in the future .
In order to improve the efficiency of hydrogen production from electrolytic water, the development and utilization of high-performance HER electrode catalysts is a proven way.
Porous carbon materials represented by graphene have excellent physicochemical properties, such as rich pore structure, large specific surface area, high electrical conductivity, and good electrochemical stability, which bring new opportunities for the construction of efficient composite catalytic systems. The hydrogen precipitation capacity is enhanced by means of co-catalyst loading or heteroatom doping .
In addition, a large number of studies have shown that the catalytic activity of HER electrode catalysts depends largely on the number of active sites exposed on their surfaces, and the more active sites exposed, the better their corresponding catalytic performance. The larger specific surface area of porous carbon material, when used as a carrier, will to a certain extent expose more active sites to the active material and accelerate the reaction of hydrogen production.
The following are examples of the characterization of graphene materials using CIQTEK V-Sorb X800 series specific surface and pore size analyzer. From Figure 1, it can be seen that the surface area of graphene prepared by different processes has a large difference of 516.7 m2/g and 88.64 m2/g, respectively. Researchers can use the results of the specific surface area test to make a judgment of the basic catalytic activity, which can provide a corresponding reference for the preparation of composite catalysts.
Fig. 1 Test results of the specific surface area of graphene synthesized by different processes
In addition, many researchers have improved the electrocatalytic activity of hydrogen production from electrolytic water by combining transition metal phosphides, such as cobalt phosphide, with carbon materials with a high specific surface area. As shown in Figure 2, by loading cobalt phosphide on porous carbon materials, the specific surface area of carbon/cobalt phosphide composites can be concluded as high as 195.44 m2/g by BET test results. The high specific surface area can provide more active sites in contact with the electrolyte, and at the same time, due to the moderate oxygen/hydrogen adsorption and dissociation energy, it will then exhibit excellent electrocatalytic activity.
Fig. 2 Specific surface area test results of carbon/cobalt phosphide composites
Application of gas adsorption technology for characterization in the hydrogen fuel cell industry
The hydrogen fuel cell is a power generation device that uses hydrogen as fuel and converts the chemical energy in the fuel directly into electricity through an electrochemical reaction, which has the advantages of high energy conversion efficiency, zero-emission, and no noise.
Current research in hydrogen fuel cells focuses on the attack of technologies such as proton exchange membranes, electrocatalysts, and bipolar plates. In a hydrogen fuel cell, an ideal proton exchange membrane (PEM) completely separates the hydrogen-filled chamber from the oxygen-filled combustion chamber, allowing only protons to pass through alone. The current commonly used hydrogen fuel cell proton exchange membrane isolation is not good enough, which can partially mix the hydrogen fuel with the oxidizer and thus impair the electrochemical performance of the hydrogen fuel cell.
In recent years, the study of PEMs formed by the composite of porous MOF and polymers has received much attention, in which the MOF framework structure can be modified by some compounds that facilitate proton conduction, and then the formed MOF-based materials are further made into polymer-based hybrid membranes. The high specific surface area of MOF can also accommodate more proton carriers, which provides an opportunity to increase the proton conductivity of the composite membranes opportunities. In addition, the rich pore structure of MOF facilitates the construction of hydrogen bonding networks in its pores as an effective pathway for proton transport, which in turn increases the mobility of active protons .
Figure 3 shows an example of the characterization of MOF composites using GSI's self-developed V-Sorb X800 series specific surface and pore size analyzer.
Fig. 3 (a) BET test results; (b) N2 adsorption-desorption isotherm
Figure 3(a) demonstrates the BET of MOF composites at 1242.58 m2/g. Figure 3(b) N2 adsorption-desorption isotherms are close to the class I isotherms, indicating a more abundant microporous structure. Combined with the analysis of the pore size distribution diagram, Figure 4(a) shows that there is no obvious trend of concentrated distribution in the BJH-pore size distribution diagram, indicating that there is basically no concentrated mesoporous pore size distribution. In Fig. 4(b), the SF-pore size distribution shows that there is a concentrated distribution of micropores near 0.57 nm, indicating that the most available pore size is 0.57 nm.
Fig. 4 (a) BJH-adsorption-pore size distribution; (b) SF-adsorption-pore size distribution
In addition, in the stack of hydrogen fuel cells, the process of hydrogen oxidation reaction and oxygen reduction reaction at the electrode is mainly controlled by the catalyst. The catalyst is the main factor affecting the activation polarization of hydrogen fuel cells and is considered a key material for hydrogen fuel cells, which determines the overall performance and economy of the use of hydrogen fuel cell vehicles . Platinum is one of the most commonly used catalysts for fuel cells, but the higher cost limits its large-scale use. The same porous carbon material represented by graphene can also be used as an electrocatalyst carrier for hydrogen fuel cells. Loaded with non-platinum catalysts on its surface, its catalytic efficiency for hydrogen production can meet or exceed that of conventional platinum-based catalysts, helping to scale up the application of hydrogen fuel cells.
CIQTEK Automatic BET Surface Area & Porosimetry Analyzer CIQTEK EASY-V Series
CIQTEK Automatic BET Surface Area & Porosimetry Analyzer CIQTEK EASY-V Series adopts the static volume method testing principle, with a fully automated operation, humanized operation interface, and easy to learn.
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