Multiphase modeling of the DC plasma–water interface: application to hydrogen peroxide generation with experimental validation

Abstract

Here, we present a one-dimensional, time-dependent multi-physics model of the plasma-liquid interface that encompasses both the plasma and liquid phases using the MOOSE-based drift-diffusion-reaction software, Zapdos-Crane. The model was applied to an experimental configuration comprised of a direct-current powered argon plasma formed at the surface of an aqueous, ionically conductive solution. In this system, one of the reactions that occurs is the formation of hydroxide radicals, which subsequently produce hydrogen peroxide. We studied potential mechanisms for hydrogen peroxide production with the plasma operated as either the cathode or anode. Experiments were performed in support of modeling to characterize the plasma and measure the aqueous hydrogen peroxide, and both modeling and experimental results show that its production is substantially higher during anodic operation. In the case of the cathodic plasma, the simulations predict that solvated electrons degrade aqueous hydrogen peroxide, and in support, adding nitrate, a known electron scavenger, to the electrolyte during cathodic operation is shown to increase the production of aqueous hydrogen peroxide by an order of magnitude in experiments.

Rate, Efficiency, and Mechanisms of Electrochemical Perfluorooctanoic Acid Degradation with Boron-Doped Diamond and Plasma Electrodes

“…In the presence of a 100 mM concentration of the solvated electron scavenging NaNO 3 , the plasma electrode showed a minor increase in X D , whereas the BDD electrode showed only a negligible change in the efficiency. While NaNO 3 could be mass transfer limited due to the adverse electric fields for the NO 3 – anion near the plasma–liquid interface, 100 mM has been previously shown to be sufficient to quench the majority of the solvated electrons. ,, The absence of a clear decrease in degradation performance for either scavenger suggests that PFOA degradation with the plasma electrode is not radical-mediated.…”

“…In eq , I is the current, μ e is the electron mobility, | V a | is the mean potential in the anode sheath, d a is the width of the anode sheath, k B is Boltzmann’s constant, and T e is the mean electron temperature in the anode sheath. μ e can be calculated from known relationships, and | V a | and T e are estimated from a recent multiphase simulation of the plasma–liquid interface beneath a DC plasma cathode, allowing the calculation of C e as a function of current (see Supplementary Information). Eq allows determination of the intrinsic rate constant, , from the data presented in Figure .…”

“…− anion near the plasma−liquid interface, 100 mM has been previously shown to be sufficient to quench majority of the solvated electrons. 64,70,75 The absence of a decrease in degradation performance for either scavenger suggests that PFOA degradation with the plasma electrode is not radicalmediated.…”

“…Eq 11 shows that reaction rate increases with increasing TDS, due to a decrease in b, and increases with C e , which is proportional to current. 75 Furthermore, the rate expression is pseudo first-order since C e and b do not change during degradation. This observation yields a definition for k r,1 in eq 5:…”

Plasma-Induced Selective Propylene Epoxidation Using Water as the Oxygen Source

“…Depending on the energy of the free electrons (1–10 eV), the formation of the OH· proceeds via a water excitation reaction (H 2 O (g) + e – (g) → H 2 O* (g) + e – (g) ; H 2 O* (g) + H 2 O (g) → H· (g) + OH· (g) + H 2 O (g) ), a dissociative attachment of a free electron to water (H 2 O (g) + e – (g) → H – (g) + OH· (g) ), or via a direct ionization of water (H 2 O (g) + e – (g) → H· (g) + OH· (g) + e – (g) ) . It is generally agreed that H 2 O 2(g) is formed readily through the recombination of two OH· (g) . , The generated peroxide rapidly dissolves into the liquid phase (H 2 O 2(g) → H 2 O 2(aq) ). Alternatively, H 2 O 2(aq) can be also formed by the recombination of two dissolved OH· (aq) , which originates from the dissolution of the gas-phase OH· (g) or dissociation of H 2 O (l) at the plasma–water interface .…”