| dc.description.abstract | This work aims at analysing the energy efficiency of a high pressure, high temperature water electrolysis by current-voltage diagram.
Four different kinds of reaction mechanisms,namely,1. reversible voltage, 2. activation polarization, 3. ohmic polarization,and 4. concentration polarization,are investigated in details.。
The results of each different reaction mechanisms are: 1. Reversible voltage: The higher the temperature and pressure are, the lower its potential is. 2.Activation polarization: The higher the temperature is, the lower its potential is. However,the influence of pressure can be neglected. 3. Ohmic polarization: it can be divided into electrode resistance and bubble resistance . Between them, the electrode resistance overpotential
rises with temperature, but is not effected by pressure. The bubble resistance overpotential increases as temperature rises,and drops as the pressure rises.However, as the current density is smaller than 1A/cm2, the bubble resistance overpotential is very small and can be neglected.4. Concentration polarization: As temperature gets higher, the concentration overpotential decreases, and the influence of pressure can be neglected.
The whole electric energy consumption at 500bar/370oC, compared with that at 1bar/80oC, is saved about 17%. If the consumption of compressing the gas from 1bar to 500bar is considered, then the water electrolysis at 500bar/370oC saves about 22% of the electric energy.
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