Highly Selective Electrolytic Reduction of CO2to Ethylene

Document Type

Article

Publication Date

1-1-2025

Abstract

We investigate the reduction of CO2to ethylene across buffered anolyte pH values 4 to 14 using a copper–phosphorus (Cu–P) electrocatalyst in a zero-gap membrane electrode assembly. Electrochemical CO2reduction using alkaline electrolytes typically shows limited carbon efficiencies and single-pass efficiencies, while acidic conditions typically favor the hydrogen evolution reaction. Results from this work show that weakly phosphate-buffered acidic anolytes (pH 6) maximize ethylene production with a 73% FE at 300 mA cm–2and 51% FE at 500 mA cm–2, including a 51% single-pass CO2conversion efficiency for over 400 h of continuous operation. We propose a mechanism based on pH-dependent CO coverage that controls the selectivity at the *HCCOH intermediate. Low CO coverage at pH 6 favors hydroxide elimination to *CCH, yielding ethylene (98% of C2products), while high coverage at pH 14 promotes hydrogenation to ethanol (44% of C2). The HER mechanism transitions from H2O-mediated at pH 14 to phosphate-mediated (H2PO4–/HPO42–) at weakly acidic pH, minimizing HER competition at pH 6. This mechanistic understanding enables controlled C2product selectivity through manipulation of the CO coverage and local proton activity.

Publication Source (Journal or Book title)

ACS Applied Energy Materials

First Page

13607

Last Page

13619

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