Advancements in Nitric Oxide Emission Control With a Perovskite Based Membrane via High Frequency Electric Potential Oscillations
Authors: Willsey Aliza M. , Welles Thomas S. , Ahn Jeongmin 
Published: September 2022

Increased concerns over climate change, limited fossil fuel resources, emissions, and poor air quality has created a greater need for sustainable energy systems. The need for increased sustainable energy systems has created largely two cooperative movements: 1) technologies that are considered renewable or more environmentally friendly and 2) higher efficiency. The automotive industry has long been a target for increasing efficiency and decreasing environmentally harmful emissions. The combustion of hydrocarbon fuels results in harmful and reactive incomplete combustion byproducts. Fully electric and hybrid powertrains are increasing in commonality but have not yet fully penetrated the market. Many automobile manufacturers are still producing vehicles which rely solely on the internal combustion engine and hydrocarbon-based fuels.

Currently, manufacturers utilize a combination of three-way catalytic converters and nitrogen oxide traps to rid the exhaust flow of harmful combustion emissions. Catalytic converters use expensive precious platinum group metals (PGM) to simultaneously react unwanted hydrocarbon, carbon monoxide, and nitrogen oxides into less harmful, complete products of combustion, such as nitrogen, carbon dioxide, and water vapor. However, the performance of these devices is highly dependent upon the equivalence ratio of the exhaust. Three-way catalysts require that the exhaust remain at stoichiometric conditions for optimal performance. Prolonged fuel lean engine operation renders the PGM catalyst incapable of reacting nitrogen oxide emissions. Nitrogen oxide, and more specifically nitric oxide (NO), emissions are of significant concern, as such emissions directly contribute to increased smog, acid rain, climate change, and respiratory inflammation within the population. Lean nitrogen oxide traps (LNTs) are incorporated into the exhaust system to temporarily capture excess nitrogen oxide emissions. However, the zeolite-based materials used in LNTs have a finite limit on nitrogen oxide storage capacity. Once nitrogen oxide capacity is reached, the engine must enter a fuel rich combustion condition or additional reactants must be injected directly into the exhaust system to regenerate the LNT’s function. Therefore, current exhaust treatment measures introduce significant complexity into the exhaust system and significant constraints on engine operation.

As such, this work investigates the potential for new exhaust treatment materials, capable of maintaining performance across all conditions. Specifically, this work investigates the NO reduction potential of a multilayered ceramic electrochemical catalytic membrane. Prior work has demonstrated that the natural electric potential oscillation, which develops across such a membrane, significantly reduces NO emissions. The ceramic membrane, consisting of two dissimilar metal electrodes, sandwiching a dielectric layer, is able to achieve an NO reduction in excess of 2X that of a traditional PGM three-way catalytic converter [1]. Here, the possibility for externally inducing a low magnitude (&lt; 500 mVpp), high frequency (&gt; 1kHz) electric potential oscillation across the reacting membrane and increasing the conversion of NO into diatomic nitrogen and oxygen is investigated. Electric potential oscillation at the surface generates an altered electrochemical reaction pathway. During the breakdown of NO, N2O is recorded as an intermediate species without the introduction of NH3. This result diverges from traditional theory, which predicts the formation of NO2. This work further explores the relation between externally applied electric potential oscillation, N2O formation, and reduction of NO.