(61b) Electrosynthesis of High-Purity Ethylene Using CO2 and H2O at Near Ambient Conditions

C₂H₄ is a hydrocarbon of extensive societal, environmental, and industrial importance. Therefore, synthesizing C₂H₄ sustainably via electrochemical CO₂ reduction reaction (CO2RR) is an attractive area to explore. Even though many existing CO2RR systems have reached industrially relevant current densities, almost all use a gas diffusion electrode (GDE)-based electrochemical system with a single-pass conversion of <10%. This leads to a lower concentration of C₂H₄ in the gaseous product stream that mainly comprises CO_2, which contributes significantly to the cost of post-CO2RR separation of products, rendering even processes with high CO2RR current densities unfit for scaling up. Here we develop an aqueous flow-through electrochemical cell to enhance the activity and selectivity of C₂H₄ on a 3D Cu mesh electrode by applying square wave oscillating potentials. We control the oxidation phase of the square-wave oscillating potential for in-situ generation of copper oxide, with some residual sub-surface oxide remaining in the cathodic phase. We hypothesize that the transient sub-surface oxide exerts a significant strain on the metallic copper surface during CO2RR, leading to enhanced C-C bond formation as predicted by DFT. A high C₂H₄ Faradaic efficiency (FE) of ~58%, unprecedented C₂H₄ current density of 306 mA/cm² in the aqueous cell, and gaseous C₂H₄ purity of ~52 wt% without CO₂ in the product stream is obtained. Integrating the 3D Cu mesh catalyst in a PV-electrolyzer yields a remarkable solar-to-carbon (STC) efficiency of ~10% with a solar-to-C₂H₄ efficiency of ~4%, almost double the current state-of-the-art solar-driven CO2RR systems. The novel electrochemical cell and catalysts offer several breakthroughs necessary for the sustainable manufacturing of C₂H₄.