Hydrogen and sulfuric acid production by electrolysis with anodic depolarization by sulfurous anhydride

Abstract

Practical aspects of improving the efficiency of water electrolysis with anodic depolarization by sulfurous anhydride in an electrolyzer with a solid polymeric electrolyte are discussed. Methods of reducing energy outlays for the production of hydrogen, for example, by altering the organization of the feed of sulfurous anhydride to the reaction zone, are proposed and implemented. This made it possible to remove restraints on the mass transfer of SO 2 , and reduce the overvoltage of the anodic reaction. An electrolyzer is developed and fabricated for the corresponding process with an overall effective electrode area of 12.25 cm 2 . A so-called mixed loop for the feed of sulfurous anhydride, which makes it possible to achieve the following energy characteristics of the electrolysis process is implemented: a cell voltage of 1 V at a current density of 2000 A/m 2 . The yield of hydrogen with respect to the current was 95%, and the energy outlays for the production of 1 m 3 of hydrogen were 2.5 kWh, which amounted to half that for traditional electrolysis. No irreversible degradation of the properties of the electrolyzer was observed during longevity tests over a period of 180 h.Electrolysis with electrooxidation (anodic depolarization) by sulfurous anhydride is the low-temperature stage of the dual-stage thermoelectrochemical cycle of hydrogen and oxygen production using the heat of high-temperature gas-cooled reactors, which was proposed by the Westinghouse Electric Company (United States) in the mid 1970s [1][2][3]. In addition to the electrolysis of water with anodic depolarization by sulfurous anhydride, the closed cycle includes processes involving the concentration of the sulfuric acid that forms on the anode of the electrolyzer, and thermal decomposition of the sulfuric acid with the production of sulfurous anhydride, water, and oxygen.For a hydrogen-oxygen electrolyzer, the equilibrium difference of the potentials (the minimum voltage at which the electrolysis of water begins) is 1.23 V at 25°C, while the actual voltage U at industrial current densities (i = 2000 A/m 2 ) is of the order of 2.2 V. The voltage increases as a result of polarization of the electrodes, and an increase in ohmic losses in the electrolyzer and its current-conducting parts. Moreover, overvoltage of the anode is a basic component of the total overvoltage; depolarization of the anode, for example, by sulfurous anhydride, is therefore one of the most promising means of lowering the electrolysis voltage. Thus, the equilibrium difference in electrolysis potentials with anodic depolarization by the anhydride SO 2 is all of 0.47 V. The possibility of a significant reduction in energy outlays for the production of hydrogen is therefore a basic advantage of this process.Research trending toward the development of electrolyzers for implementation of the above-indicated scheme for the production of hydrogen was being actively conducted in Russia at the outset of the 1970s; this was associated with the development of designs for high-temperature ...

Membrane electrolysis—History, current status and perspective

“…In this approach the electrolysis step can also be accomplished utilizing a PEM electrolyzer similar to that used for water electrolysis [118,119] have proven to be stable in this system, but other polymeric membranes have also been studied [120]. However, the PBI membrane has been identified as the best option from the point of view of a combination of performance and minimized SO2 cross-over, with a 27% increase in current density.…”