Journal of Mechanical Engineering (Dec 2019)
Study of the Influence of Operating Conditions on High Pressure Electrolyzer Efficiency
Abstract
The high pressure of the gases being generated (hydrogen and oxygen) makes it possible to increase the efficiency of the electrochemical generator. Energy components of the process of liquid electrolyte decomposition under pressure are described. Dependencies of reducing energy costs per cell during the electrolysis of water under pressure at different temperatures are presented. It has been established that with increasing pressure, the processes of electrode depolarization by dissolved gases increase, however, their quantitative value and influence on the current efficiency depend on the design of electrolyzers, adopted electrolyte circulation scheme, and conditions for the penetration of the dissolved hydrogen into the anode space and of oxygen into the cathode. The pressure increase of the electrochemical process of producing hydrogen and oxygen is accompanied by an increase in their solubility in the electrolyte, which may be accompanied by the anode and cathode depolarization by dissolved gases. The transition of the electrolysis equipment to the operation from atmospheric pressure to the operation from pressures of the order of 0.1−4.0 MPa is most effective. The decrease in the voltage of electrochemical reactions is due to the processes of electrode depolarization, dissolved gases, as well as a decrease in gas filling due to a decrease in the size of gas bubbles. With increasing pressure, the value of the electrode potential increases, which should lead to an increase in the cell voltage, but the opposite is observed. This can be explained by a decrease in voltage loss during electrolysis. We conducted a comparative analysis of the existing technologies for the electrolysis of hydrogen and oxygen. To correctly compare the energy efficiency of a membrane-free technology for producing high-pressure hydrogen and oxygen as well as existing industrial electrolyic technologies, the energy costs for electrolytic hydrogen production by an industrial method and its subsequent compression should be summarized.
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