Volume 2, 2024

Tunable product selectivity on demand: a mechanism-guided Lewis acid co-catalyst for CO2 electroreduction to ethylene glycol

Abstract

Bioinspired nickel phosphide electrocatalysts can produce more complex multi-carbon products than natural photosynthetic enzymes but controlling C-product selectivity and suppressing H2 evolution remain open challenges. Here, we report a significant shift in the CO2RR product distribution on Ni2P in the presence of boric acid/borate, a soluble Lewis acid/base co-catalyst. Using Ni2P without a co-catalyst, CO2 reduction produces a mixture of methyl glyoxal (C3) > 2,3-furnadiol (C4) and formic acid (C1) with 100% Faradaic efficiency for carbon products. Addition of boric acid/borate shifts product selectivity to ethylene glycol (EG) with an 85% CO2-Faradaic efficiency (at 10 mM, 0 V vs. RHE), with the balance being the aforementioned C1, C3 and C4 products. The mechanism of EG formation is proposed to occur by the co-catalyst activating a reaction between surface *hydride and *glycolaldehyde on Ni2P, while suppressing the aldol C–C coupling reaction that forms the C3 and C4 products. The formation of an intermediate borate-EG-diester, [(OCH2CHO)2B], is detected by 11B-NMR, which hydrolyzes to release the EG product. Extended electrolysis of boric acid modifies the surface of Ni2P by forming *BO3–Ni2P, as shown by XPS. CO2 electro-reduction on *BO3–Ni2P in the absence of free boric acid produces exclusively ethylene oxide (EO), which slowly hydrolyzes to EG in the bicarbonate electrolyte. The combined Faradaic efficiencies for CO2RR products EO + EG with free boric acid as the co-catalyst and *BO3–Ni2P as the cathode reaches 88% (at 0 V vs. RHE), a record carbon selectivity. This work illustrates the feasibility of using Lewis acid/base co-catalysts to change the established chemical reaction mechanism of an electrocatalyst to form a new, chemically predictable, more valuable product in high yield.

Graphical abstract: Tunable product selectivity on demand: a mechanism-guided Lewis acid co-catalyst for CO2 electroreduction to ethylene glycol

Supplementary files

Article information

Article type
Paper
Submitted
27 sep. 2023
Accepted
21 des. 2023
First published
26 jan. 2024
This article is Open Access
Creative Commons BY license

EES. Catal., 2024,2, 823-833

Tunable product selectivity on demand: a mechanism-guided Lewis acid co-catalyst for CO2 electroreduction to ethylene glycol

Y. Li, K. U. D. Calvinho, M. Dhiman, A. B. Laursen, H. Gu, D. Santorelli, Z. Clifford and G. C. Dismukes, EES. Catal., 2024, 2, 823 DOI: 10.1039/D3EY00237C

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