Research background
Fuel Cells (Fuel Cells) is an efficient and pollution-free energy power system, it is stored in hydrogen, methanol, ethanol, formic acid and other fuels with air or oxygen and other oxidants react and convert chemical energy into electrical energy a conversion device. A fuel cell is a device that continuously converts chemical energy into electrical energy through a REDOX reaction that takes place at the anode and cathode. The difference between a fuel cell and a conventional battery is that it needs to continuously input fuel and oxidizer into the battery when it works, and as long as it is continuously supplied, the fuel cell will continue to provide electrical energy. Fuel cell is a new energy technology that directly converts chemical energy of fuel into electric energy, which is environmentally friendly and efficient. Because of its high energy conversion efficiency, low impact on the environment, fuel diversification and many other advantages, it has been widely concerned. It is called the fourth generation of energy conversion power generation technology after hydropower, thermal power and nuclear power.
A fuel cell usually consists of an anode (fuel electrode), a cathode (air or oxygen electrode), and an electrolyte that conducts ions. When the fuel cell is working, the gas fuel or organic liquid fuel is continuously passed to the anode, and the air or oxygen is passed to the cathode, the gas or organic liquid fuel is oxidized in the anode, the lost electrons flow through the external circuit to the cathode, and the reduction reaction with air or oxygen in the cathode to produce water. The electrolyte diaphragm acts as an ion conductive separator between the fuel for oxidation at the anode and the air or oxygen for reduction at the cathode.
Canonical study
The research of fuel cell materials mainly focuses on catalyst and catalyst support materials. The research of catalysts includes precious metal catalysts, transition metal catalysts, metal/metal oxide-inorganic doped catalysts, etc. Fuel cell catalyst carrier plays an important role in reducing the amount of precious metal catalyst and improving the catalytic activity of catalyst.
1. Precious metal catalyst: Pt material has become the most commonly used fuel cell catalyst layer material because of its good molecular adsorption dissociation behavior. The high price of Pt is a great obstacle to the large-scale commercialization of fuel cells, so the development of low platinum and non-platinum catalysts has become the trend of future development. There are two metal platinum-based catalysts and three metal platinum-based catalysts based on Pt which have been studied.
2. Composite catalyst: transition metal-oxygen (sulfur, nitrogen, etc.) -carbon catalyst, which has high conductivity and corrosion resistance.
3. Carrier materials: mainly carbon materials and non-carbon materials. Carbon materials mainly include carbon black, carbon nanotubes and graphene. Non-carbon-based materials include titanium dioxide, tungsten trioxide, cerium dioxide, zirconia, indium oxide, alumina and conductive polymers.
4. Supported catalyst: It plays a crucial role in reducing the amount of precious metal catalyst and improving the catalytic activity of the catalyst. The carrier can interact with the metal nanoparticles to improve the catalytic activity of the catalyst by modifying the electronic state on the catalyst surface.
Equipment recommendation
The performance of fuel cell materials is tested using the EC701F fuel cell analysis system, which mainly measures current or potential changes. The use of AES-4TH to control the environment of the test system can avoid the interference of the external environment (temperature, humidity, etc.) to the system, and provide a controllable and stable environment for the study of low temperature, medium temperature and high temperature fuel cell testing, and improve the repeatability of measurement.
1. Measuring equipment
EC701F fuel cell analysis system: provides current-potential analysis, potential-time analysis, impedance analysis, etc. The equipment has stable performance and high measurement accuracy. It can be tested with three electric levels or two electrodes.
2. Consumables and accessories
Electrode accessories, rotating disk electrode, rotating ring electrode, advanced sealed electrolytic cell, etc.
Typical result
Cyclic voltammetry (CV) is a commonly used electrochemical research method. This method controls the electrode potential at different rates and repeatedly scans with triangular waveform over time, and records the current-potential curve. According to the curve shape, the reversible degree of electrode reaction, the possibility of intermediate phase boundary adsorption or new phase formation can be judged. It is commonly used to measure electrode reaction parameters and judge its control steps and reaction mechanism.
Linear scanning (LSV) : A method to measure the linear change of current density in response to applied voltage is one of the main methods to test catalyst performance. Because the scanning rate is relatively slow, the peak potential and other parameters can be obtained from the linear scanning curve to characterize the performance of the catalyst. To study the distribution of current density on the surface of the electrode and reduce or eliminate the influence of the diffusion layer, electrochemical researchers have developed a high-speed rotating electrode - rotating disk electrode (RDE) by comparing various electrodes and stirring methods. When the electrode rotates, the control steps of the electrode can be changed by changing the rotational speed and different limiting diffusion currents can be obtained. As an important parameter for the study of electrochemical dynamics, the process mechanism of some complex catalytic reactions and information such as corrosion and passivation potential of metal materials can be calculated by using the limiting current. A rotating disk electrode or a rotating ring electrode is used to test the changes of current density and voltage at different speeds, and the Koutrcky-Levich curve of the rotating disk electrode under different potential conditions is obtained, so as to evaluate the ORR catalytic performance of the material.
i-t test: It is an important method to measure the change of current density over time at a certain potential. The measurement curve can evaluate the activity and stability of the catalyst, which is very important for the investigation of the practical application performance of the catalyst. In the oxidation process, the magnitude and attenuation of the oxidation current can be seen from the level and change rate of the curve, so as to infer the stability of the catalyst in the oxidation process.
Ac impedance testing (EIS) : The AC impedance method is a method of electrochemical testing by using a small amplitude of AC voltage or current to disturb the electrode. From the obtained AC impedance data, the impedance characteristics and kinetic properties of the electrode structure in the electrochemical process can be analyzed according to the equivalent circuit of the electrode, such as the equivalent series capacitance, charge transfer resistance, etc., and the corresponding electrode reaction parameters can be calculated.
XRD: mainly analyzes the types and crystal types of elements in the catalyst, and calculates the average particle size and lattice constant of the electrocatalyst.
XPS: The characteristic binding energy of electrons in atoms is used for surface composition analysis, chemical state analysis and in-depth analysis of elemental composition of the sample.
Scanning electron microscope (SEM) : It is a kind of microscopic morphology observation instrument between transmission electron microscope and optical microscope measurement scale, which can directly use the material properties of the surface materials of the sample for microscopic imaging, mainly used for the surface morphology characterization of the sample.
Transmission electron microscopy (TEM) : mainly used to observe the morphology, particle size and dispersion of catalyst particles, is a more commonly used means of microscopic characterization.
N2 adsorption and desorption: The specific surface area and pore size distribution of the catalyst were obtained.
reference
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J.J. Wang, P. Tian, K.X. Li, B.C. Ge, D. Liu, Y. Liu, T.T. Yang, R. Ren, The Excellent Performance of Nest-like Oxygen-deficient Cu1.5Mn1.5O4 Applied in Activated Carbon Air-cathode Microbial Fuel Cell, Bioresource Technol., 2016, 222, 107-113.
Y.X. Lu, S.F. Du, R.S. Wilckens, One-dimensional Nanostructured Electrocatalysts for Polymer Electrolyte Membrane Fuel Cells-A Review, Appl. Cata. B: Environ., 2016, 199, 292-314.
S. Ratsoa, I. Kruusenberg, A. Sarapuua, P. Rauwel, R. Saar, Enhanced Oxygen Reduction Reaction Activity of Iron-containing Nitrogen-doped Carbon Nanotubes for Alkaline Direct Methanol Fuel Cell Application, J. Power Sources, 2016, 332, 129-138.
