Simulating Solvated Electron Concentrations in Pure Water for Pulsed and Steady-State Atmospheric Pressure Plasmas

Solvated electrons produced by atmospheric pressure plasmas are a promising area of research for breaking down per- and poly-fluoroalkyl substances (PFAS) in water. We present simulation results predicting solvated electron concentration versus depth as a function of current density for pin-liquid discharges in nanosecond-pulsed and steady-state regimes. To conduct these simulations, we used a Python program (py-pde) to numerically solve the reaction-diffusion equation for the recombination of solvated electrons in water. For steady discharges, we predict that the integral of concentration with respect to depth, a parameter proportional to the signal from a total internal reflection absorption spectroscopy (TIRAS) apparatus [1], scales with the one-third power of current density. For pulsed discharges, we predict a transition from a nearly linear scaling domain to a one-third power scaling domain as current density increases, with an inflection point at current density j ≈ 10⁵ A/m². While these scaling relationships fit previous analytical predictions and measurements, our estimated signal is larger in all cases, ~4 times larger for j = 10⁴ A/m² [2]. We present these results and our progress on TIRAS measurements for both cases as the next steps toward resolving this discrepancy.

[1] Rumbach et al 2015 Nat. Commun. 6 7248

[2] Martin et al 2021 Plasma Sources Sci. Technol. 30 03LT01