Introduction of Disruptive Gas Flow Via Fluidic Oscillation to Improve Solid Oxide Cell Performance

An increased focus on renewable technologies is necessary to meet the level of carbon emission reduction required to achieve the 2°C scenario (2DS). Carbon containing materials are at the root of most industrial value chains and currently 90% of organic chemicals are made from fossil fuels and 5-10% of global crude oil demand is for the manufacture of chemicals. By providing a process to convert waste CO₂ into high value CO we can take steps towards the goal of reducing emissions and provide an important link between various sectors to turn waste materials into new products, improving resource efficiencies, and reducing negative environmental factors. This presents a significant opportunity to leverage CO₂ as a feedstock while supporting global goals in green energy, manufacturing, etc.

Solid oxide cells (SOCs) provide an effective mode of simultaneously reducing CO₂ and separating O₂, however, over 80% of the cost to co-electrolyse CO₂ and H₂O comes from electrical input necessary to drive a SOEC. While changes in cell geometry and composition have been used to improve performance, energy inputs need to be reduced to increase overall device efficiency for widespread commercialisation to be realised.

In this work we focus on the use of oscillating the gas flow into an SOC to create a highly efficient energy conversion device to facilitate the reduction of CO₂ to CO. Fluidic oscillation is known to cause disruptive flow which promotes turbulence in small flow fields, thereby increasing the overall efficiency – key to furthering their commercialisation.

Fluidic oscillators are one of a variety of fluidic switching devices developed in the field of microfluidics. A single gas supply inlet guides an incoming gas flow into a destabilising microfluidic feature, generating the necessary disruption that results in jet diversion between two identical channels. This switching results in a pulsed flow in each of the outlet channels, alternating between full forward flow, and very slight backflow. The flow in the forward regime bears similarity to laminar flow, whereas the slight backflow regime more closely resembles turbulence. This effect can be observed even in extremely small channel diameters and causes a disruptive effect which interrupts the formation of a boundary layer of stagnant gas flow along flow field chamber walls. While conventional oscillators require high flow rates on the order of 50-80 L/min, for this particular work we are utilising a novel fluidic oscillator capable of producing an oscillatory flow at low onset flow rates of as low as 50 ml/min, which is necessary for operation with lab scale SOCs.

Experimental results show improved performance with the addition of oscillating gas flow and no other changes to cell geometry, materials composition, or gas composition. The magnitude of improvement in polarization resistance was dependent on operating conditions, the reasons for which will be discussed in the paper.