1. The electrochemical reaction involves two processes: interfacial charge transfer reaction and mass transfer reaction, and the overall speed is limited by the slowest step reaction.
2. During the stationary test, the use of conventionally sized millimeter-scale electrodes (except microelectrodes, such as 10 μm diameter electrodes) is often limited by mass transfer and can affect the kinetics of faster electrochemical reactions.
3. In order to enhance mass transfer, RDE and RRDE technologies have been gradually developed since the 1940s. The current density is evenly distributed, and the time to achieve stable current is short, which has become a very economical stationary measuring technology.
4. For RDE, the hydrodynamic boundary thickness L is controlled by the electrode velocity and is related to the viscosity coefficient of the electrolyte. For aqueous solution, 1600 rpm, the boundary thickness is about 280 μm.
5. WhenBefore the RDE rotates, the thickness of the mass transfer diffusion layer decreases with the increase of rotation speed. At 1600 rpm, under the conventional acid-base electrode solution, the thickness of the diffusion layer is about 12 μm, which is less than the typical 100 μm diffusion layer thickness in the static solution by 1 order of magnitude or so.
6. In the ORR test, the half wave is the potential corresponding to half of the limit diffusion current density, which can be obtained by taking data in a certain voltage range (0.4-1 V RHE) and fitting the curve to the sigmoidal function. Catalyst activity can be judged qualitatively, but catalyst load and rotational speed have some influence on it.
7. Pt catalysts are tested for ORR. Generally 0.9 V RHE activity is selected. ), this may also be related to the loading capacity, the deterioration of the catalytic converter performance after not standing for a long timean (preferably not more than half a year), and testing techniques (such as ink film production), impurities, etc.
8. Commercial Pt/C, via HUPD or CO solution test, ECSA should be higher than 70 m2/g. At 0.1 M perchloric acid, 0.9 V RHE, the surface specific activity should be greater than 0.2 mA/cm2 and the mass specific activity greater than 0.15 mA/µg.
9. RRDE tests the H2O2 yield. In the initial phase of the measurement, due to the surface oxidation of Pt, there will be a background current that decreases with time. It can be prepolarized with high potential for a period of time to eliminate background current.
10. If you want to test whether the H2O2 yield is less than 1%, you must use the CI power interruption method to test. This method can eliminate background current interference and can measure ultra-low H2O2 yields, such as 0.01%.
11. The RDE speed must be appropriate to ensure laminar flow. If the speed llower than 100 rpm, the natural convection will be relatively large. If the speed is too high, turbulent flow can occur. literature is generally 400-2500 rpm, which is appropriate.
12. Nafion has two side effects, the first is sulfonate anionIt will be adsorbed on the surface of platinum, and the second will wrap the catalyst and hinder the mass transfer of oxygen.
13. RDE technology also has limitations. Due to technical limitations, it often cannot exceed 10,000 rpm. Compared with microelectrodes, the mass transfer capacity is still limited. For a microelectrode with a radius of 10 µm, the mass transfer rate is equal to 2485 rpm, and for a microelectrode with a radius of 1 µm, the mass transfer rate is equal to 248500 rpm. This is hard for RDE to do.
14. In the actual process of PEMFC, the mass transfer is based on gas convection, which is about 3 orders of magnitudefaster than RDE.
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