The Chemical Composition of Species Formed in a Water Anode under the Action of a Direct Current Electric Discharge: Comparison with Liquid Cathode—Experiment and Simulation

The kinetics of the formation of hydrogen peroxide (H 2 O 2 ), nitrite ( NO_2^ - ) and nitrate ions ( NO_3^ - ), pH changes in an aqueous liquid anode under the action of a direct current discharge of atmospheric pressure in air were studied. To describe the obtained results and analyze them, a 0-D model of the discharge system was used, which consisted of two submodels. One of them described the discharge, and the other—the solution. The sub-model of the discharge in air was based on the self-consistent solution of the Boltzmann equation, the equations of vibrational kinetics for the ground states of N 2 , O 2 , H 2 , H 2 O, NO molecules, and the equations of chemical kinetics. The electric field strengths, gas and vibrational temperatures required for these calculations were measured experimentally. Based on these calculations, the fluxes of various species arriving at the surface of the solution from the plasma were determined. Solution reactions included 28 components and 119 reactions between them. The results of calculations of the concentrations of NO_2^ - , NO_3^ - , and pH agree with the experiment within the limits of the latter’s accuracy. The data obtained for both calculations and experiments are compared with those previously obtained for a discharge with a liquid cathode at the same discharge parameters. It was found that the concentration of H 2 O 2 in the liquid cathode is two orders of magnitude higher, and the concentration of NO_2^ - ions is two orders of magnitude lower than in the liquid anode. And the concentrations of NO_3^ - ions are close. The action of the discharge on the liquid anode leads to higher pH values compared to the liquid cathode. The differences in concentrations are due to the fact that in a liquid cathode, an essential role in the initiation of chemical reactions is played by the bombardment of the solution surface by positive ions accelerated in the cathode voltage drop. In a liquid anode, this factor is absent. But the reactions associated with electrons coming from the gas phase, which are solvated in solution, become significant. The data obtained explain the different chemical activity of anodic and cathodic solutions in relation to the reduction of some strong inorganic oxidants and the preparation of insoluble metal hydroxo compounds.