Methanol synthesis in a temperature-controlled pulsed dielectric barrier discharge plasma reactor: Impact of electrode materials

Historically, methanol has been widely used as a valuable feedstock in the chemical industry. Recently its attractive properties as a low-carbon substitute fuel, especially in the maritime sector is increasingly gaining popularity. Conventional methanol production is heavily reliant on fossil fuels (99%) and thus negatively contributes towards climate change. In effect, a more sustainable synthesis process is required and this could be achieved through nonthermal plasma technology(NTP). NTP powered by renewable electricity coupled with carbon capture and utilization(CCU) for hydrogenation of CO
²
is one of the most promising methods for methanol production[1][2]. Recently, we demonstrated that the perennial problem of low methanol selectivity can be overcome through a unique gas mixture (H
2
, CO
2
, CO, and N
2
) with a dielectric barrier discharge(DBD) plasma[3]. In spite of this, the energy efficiency was still very low, as reported in other literature as well[4][5]. Therefore a much deeper study on the non-catalytic plasma system needs to be furthered to make the energy cost competitive. In this study, wefor the first time investigate the effect of electrode material(copper, stainless steel(SS), aluminum) on methanol synthesis using a temperature-controlled pulsed DBD plasma reactor. A digital oscilloscope was used for electrical characterization and a hyperspectral camera was employed to determine the optical emission spectra of plasma-activated species. Moreover, gas chromatography was used to analyze the outputs for conversion, selectivity, and methanol production rate calculations. Interestingly, our findings revealed that SS had the best methanol production rate (12% and 36% greater than Cu and Al respectively) despite having the lowest electrical conductivity. Moreover, SEM-EDX analysis on the electrodes provided critical information pointing towards plasma surface reactions that could promote or impede methanol synthesis. The aluminum electrode’s poor synthesis performance was attributed to significant oxide coating on its surface although it had a superior CO
²
and CO conversion rate.