Mustapha Bello

Article

ELECTROCHEMICAL REDUCTION OF CO IN MEMBRANE ELECTRODE ASSEMBLY CELLS AT COPPER-BASED ELECTROCATALYST

Bello, Mustapha O.,

LSU Doctoral Dissertations. 6836.

DOI: https://repository.lsu.edu/gradschool_dissertations/6836/

Abstract

The electrochemical reduction of carbon monoxide (CO) represents a promising pathway for sustainable chemical production, offering advantages over direct CO₂ reduction, including enhanced selectivity and improved energy efficiency. This dissertation investigates CO electroreduction using copper-based electrocatalysts in zero-gap membrane electrode assembly configurations, evaluating anolyte pH effects, CO surface coverage, and chalcogenide catalyst modifications for product selectivity toward C₂⁺ chemicals. The research achieves unprecedented acetate selectivity of 90% Faradaic efficiency at 300 mA cm⁻² using phosphate-buffered neutral anolytes (pH 8) with copper nanoparticle electrocatalyst, representing the highest acetate selectivity reported for CO electroreduction at industrially relevant current densities. pH studies across pH 8-14 reveal optimal operating conditions at mildly alkaline pH, where acetate formation is maximized while hydrogen evolution is minimized, with the buffering capacity maximizing CO activation to acetate and minimizing HER. The phosphate buffer system provides surface interactions that stabilize the acetyl reaction pathway beyond simple pH control. Chalcogenide modification of copper electrocatalysts enables performance enhancement by suppressing hydrogen evolution. Copper selenide (Cu₂Se) achieves 74.6% acetate selectivity at 350 mA cm⁻², representing an 85% enhancement compared to CO₂ reduction systems, reducing hydrogen production from 38.3% to 8.8% and achieving total carbon selectivity of 91.2%. Copper telluride (Cu₂Te) demonstrates enhanced ethanol production (28.7%) while maintaining acetate as the primary product (60.9%), achieving 90.3% total C₂ efficiency. Mechanistic investigations through CO/CO₂ co-feeding experiments reveal that CO concentrations as low as 10% influence product selectivity, shifting distributions from acetate-dominant to ethylene-dominant products through coverage-dependent intermediate binding effects. The proposed mechanism involves weakened binding of hydrogenated intermediates at higher CO surface coverage, promoting acetyl formation through desorption of ketene intermediates. Linear sweep voltammetry studies confirm CO reduction occurs at lower overpotentials (-0.22 V vs. RHE) compared to CO₂ reduction (-0.83 V vs. RHE). Comparative analysis with CO₂ reduction reveals advantages of CO as feedstock, including simplified product distributions (2-3 major products versus 7-8 from CO₂), enhanced energy efficiency (4.2 vs. 7.5 kWh/kg acetate), and stability with less than 3% variation over 48 hours. This work establishes design principles for electrocatalyst development and demonstrates pathways toward commercial viability for electricity-driven chemical manufacturing.