Mustapha Bello

Article

Highly Selective Electrolytic Reduction of CO2 to Ethylene

Monsuru Olatunji Dauda, Mustapha Bello, John Hendershot, Nkechi Kingsley, Ignace Agbadan, Junghyun Park, Soundarzo Tasnim, Omotolani Oduyebo, Anthony Christian Engler, Craig Plaisance, John C Flake

ACS Applied Energy Materials

DOI: https://pubs.acs.org/doi/full/10.1021/acsaem.5c01866

Abstract

We investigate the reduction of CO2 to ethylene across buffered anolyte pH values 4 to 14 using a copper–phosphorus (Cu–P) electrocatalyst in a zero-gap membrane electrode assembly. Electrochemical CO2 reduction 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–2 and 51% FE at 500 mA cm–2, including a 51% single-pass CO2 conversion 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 C2 products), 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 C2 product selectivity through manipulation of the CO coverage and local proton activity.