(IE&EE Student Achievement Award) Strategies for Sustainable Ethylene, Ethanol, and Acetate via Electrochemical CO₂ Reduction

There has been significant progress in the electrochemical reduction of CO 2 since the seminal work of Hori et al. in 1985 demonstrating hydrocarbon production at copper cathodes. The introduction of gas diffusion electrode (GDE) and membrane electrode assembly (MEA) flow cells have demonstrated progress to produce C 2 products (ethylene, ethanol and acetate) at current densities >150 mA cm -2 with Faradaic Efficiencies (FE) >50% at different types of Cu cathodes. Selectivity depends on several pathways and the intermediate binding strength of species like *CO, *CHO, *OCCO, and *OCCOH. Thus, there are opportunities to engineer or optimize product selectivity. The work advanced ethylene production through Cu-P 0.065 electrocatalyst (Cu δ+ = 0.13), achieving 52% FE at 150 mA cm -2 in 0.1 M KHCO 3 , and remarkably improving to 70% FE in weakly acidic conditions (pH 6) while maintaining 64% FE at 250 mA cm −2 . Electrolyte engineering demonstrated that larger alkali cations (Na + to Cs + ) effectively suppress hydrogen evolution from 31% to 4% while promoting C 2 formation (45% to 89% FE). K + concentration optimization (0.1-2M) further enhanced ethylene production, increasing FE from 42% to 65% at 4V while reducing HER from 48% to 20%. Mechanistic studies revealed K + and OH - species accumulation near the electrocatalyst surface promotes C-C coupling through K + and *OCCO intermediate interactions, while phosphorus doping enhances *CO generation and coupling. In terms of ethanol our work demonstrates that Cu-Sn 0.03 electrocatalyst (Cu δ+ = 0.27) can achieve 48% FE at 350 mA cm -2 under alkaline conditions. A breakthrough in product separation was achieved through a dual-layer membrane configuration incorporating CEM and AEM. This system, using 1M KOH (pH 14) inner layer and 1M KOH+H 3 PO 4 (pH 6) anolyte, reached 51.92% FE for ethanol with minimal anode crossover (<1.07% FE), enabling direct production of >8 wt% ethanol. Additionally, anion identity studies (PO 4 2- , SO 4 2- , and NO 4 - ) demonstrated consistent C 2 efficiencies (61-65%) at fixed pH. In terms of acetate production, we show Cu 2 Se electrocatalyst (Cu δ+ = 0.47), demonstrating 40% FE for acetate at 350 mA cm -2 . Notably, all electrocatalysts maintained exceptional stability over 250 hours with minimal degradation (0.02% FE loss/hour). These results show structure-function relationships of electrocatalysts in CO 2 reduction and high levels of ethylene, ethanol, and acetate production; however, several critical barriers related to operating (viz. Energy) cost and durability remain. We conclude with a review of the state of the art and the needs for commercialization.