Design and Analysis of Nonthermal Plasma Electrolytic Cells for Ammonia Synthesis

Abstract

Haber-Bosch production of ammonia, a fertilizer and energy-dense alternative fuel, accounts for 1.8 % of global fossil fuel demand and 1-2 % of global CO2 emissions. Nonthermal plasma-assisted ammonia synthesis is one solution that is able to counter these carbon emissions. The technology has been shown to be a viable and scalable ammonia production alternative to the Haber-Bosch process that also avoids expensive catalysts and minimizes the use of rare metal electrodes. The technology is able to cleanly produce ammonia at atmospheric pressures and ambient temperatures from just air and water without generating CO2 or harmful equivalents. This work developed two modular and portable designs for plasma-assisted ammonia synthesis and investigated their implementation on industrial farms as a way of producing ammonia directly in the places that need it. The two architectures utilized a piezoelectric direct discharge plasma and a glow discharge plasma. The design and fabrication processes for both apparatuses are detailed, and ammonia generation behavior in response to headspace gas concentration and run time is also reported. Without optimization of plasma operating parameters, the piezoelectric direct discharge device was already able to produce 10.5 µg of ammonia in 15 minutes, and the glow discharge electrolytic cell was able to produce 44.6 µg of ammonia in one hour. Samples collected were processed with an ammonia/ammonium assay using the o-phthalaldehyde method. Resulting fluorescence intensity measurements were then processed using statistical analysis techniques such as ANOVA, nested variance, and effects leverage. In the process, a number of useful observations regarding design improvements for subsequent plasma-assisted ammonia synthesis devices were made. The suggestions put forth in this research can be applied for better production efficacy and more consistent device operation during the research phase.