Study On Humidity Factor And Performance Of Solid Oxide Electrolysis Cells For Hydrogen Production From Seawater

To promote cleaner shipping and reduce environmental pollution at sea,the main power plant of ships is gradually changing from a heavy oil-based power plant to a clean energy source.Electric propulsion of ships has improved environmental pollution to some extent.New hydrogen fuel cell ships have become the mainstream direction of the development of the shipbuilding industry.The green hydrogen produced by the electrolysis of water is very friendly to the environment and helps to reduce pollution of the marine environment.Solid oxide electrolysis is a new energy storage technology that can efficiently convert electrical energy into chemical energy.Effectively absorb the electrical energy converted from wind and photovoltaic power generation.At present,the reserves of seawater on the Earth are very abundant.Due to the existence of many impurities and other elemental ions in seawater,other electrolysis cells have a significant loss of life during the electrolysis of seawater.The solid oxide electrolysis cells technology,on the other hand,reduces the impact on the electrolysis cells due to the high-temperature operating environment where seawater enters the cells in the form of steam and small amounts of ions from seawater enter the cells.This thesis uses solid oxide electrolysis cells technology to study the technology of direct electrolysis of seawater from the East China Sea.（1）The high-temperature operating environment can increase the electrical conductivity of the electrode material of the solid oxide electrolysis cells and improve the energy efficiency of the solid oxide electrolysis cells.The factors affecting the performance of the solid oxide electrolysis cells in a seawater operating environment were investigated by varying the ratio of water steam passing into the seawater of the electrolysis cells.The results show that the high humidity environment favors higher hydrogen production,but also aggravates the degradation of the electrolysis cells,which operate at 67%seawater steam ratio and 62%seawater steam ratio with smaller degradation rates.Later,a current density of300 m A/cm² was used to electrolyze seawater at 67%and 62%seawater steam ratio for 1000hours.During the electrolysis,the hydrogen production of the cell was maintained at 137m L/min,and the long-term degradation rates of the electrolysis cells were 129 m V kh^-1 and48 m V kh^-1,respectively.the fuel electrode of the cell induced by the addition of humidity was changes were analyzed,and the distribution and area share of Ni particles in the cell cross-section were compared using Image-J software,and it was found that the fuel electrode degraded severely under high water vapor volume,which aggravated the agglomeration and loss of Ni particles in the electrolysis cells.（2）The changes in microstructure captured by electrochemical impedance spectroscopy,DRT technique,and scanning electron microscopy were used to analyze the causes concerning the degradation of the solid oxide electrolysis cells.The impedance peak corresponding to the reaction with the fuel electrode on the impedance DRT plot increases significantly in the case of increasing humidity during long-term operation.The energy spectrum of the electrolysis cells was photographed to analyze the deposition of seawater ions on the cell surface after 1000 hours of seawater electrolysis and to investigate the changes in the mechanical properties of ceramic materials due to the long-term electrolysis effect of seawater.The mathematical and electrochemical models of the solid oxide electrolysis cells were established using mathematical principles,and the temperature field distribution,stress field distribution,and gas distribution at different locations in the flow channel of the solid oxide electrolysis cells used in the experimental part were analyzed.（3）Based on the above study,to explore the homogenization of the physical field distribution of the cell under different conditions to reduce the condition that the electrolysis cells are subjected to increased local thermal stresses that make the cells fail.The distribution of temperature and stress fields is analyzed by varying the airflow distribution of the air electrode of the solid oxide electrolysis cells and modeling the serpentine,transverse,and longitudinal flow channels.The results show that when the flow channel structure is in the form of a longitudinal flow channel,the temperature field of the electrolysis cells is more uniformly distributed and the stress difference is smaller at this point,and the longitudinal flow channel reduces the concentrated distribution of the thermal stress of the air electrode of the electrolysis cells.To investigate the influence of electrode porosity on the temperature field of electrolysis cells,different porosities were set for calculation and the distribution pattern of the temperature field was summarized.The changes in the physical field of the electrolysis cells with different inlet mass flow rates are analyzed to guide the experiments.