Selectivity is very important in electrochemical reduction of CO2 (CO2RR) both scientifically and industrially. Recently, C2 selectivity has exceeded 80% on Cu-based catalyst using the flow cell, and ethylene and ethanol are the main two products1. Understanding the mechanism branching the ethylene and ethanol is the key to achieve high selectivity of CO2RR. In this work, we first used density functional theory (DFT) calculations to understand the reaction pathways of CO2RR to ethylene and ethanol. The reaction barriers and enthalpy changes are calculated for the elementary steps considered in the two pathways on Cu(100). Microkinetic modelling was used to evaluate the activity and selectivity of different products, including the CO, methanol, methane, ethylene, and ethanol. The selectivity trends at different applied potential from the microkinetic modelling are in agreement with the experiment results. Based on the DFT and micro-kinetic modelling results, we investigated two factors that could affect the ratio between ethylene and ethanol, namely CO coverage and surface doping. Using DFT calculation, we found that CO coverage could affect the relative energies of intermediates along ethylene and ethanol pathways, thus favoring one product over the other. With the decrease of CO coverage, the ethylene pathway becomes more favorable. Experiment results suggest the same trend and the highest ethylene selectivity is achieved with low CO partial pressure in CORR experiment. We also investigated the effect of surface doping and found Ag doping is favorable for ethanol.

Tuning selectivity of ethylene and ethanol in CO2RR using density functional theory and micro-kinetic modelling

2019 Fall National Meeting

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