Reactions of carbon dioxide in biological systems are supported by a combination of nucleophilic and electrophilic interactions that influence product selectivity. The LUMO of CO2, strongly localized on the Cδ+ atom, is susceptible to nucleophilic addition, while the HOMO, localized on the Oδ- atoms, adds to electrophiles. Nature couples multiple electron and proton transfers to avoid high energy barriers from odd-electron intermediates. For example, formate dehydrogenases catalyze the reversible oxidation of formate to CO2 by direct hydride transfer from the C atom of formate to NAD+, where the hydride transfer is the rate-limiting step. The combination of these two strategies results in high energy-efficiency carbon fixation unrivaled by artificial systems – until now. Inspired by CO2-converting enzymes, a new family of five binary nickel phosphide compounds (NixPy) unlocks an efficient multi-proton, multi-electron pathway that selectively catalyzes formation of C3 and C4 products at exceptional energy efficiency (99%). These electro-catalysts are metallic compounds containing both Lewis-acidic and -basic sites that direct the mechanism to desired reaction intermediates. Formation of electron-rich surface hydrides at near-thermoneutral potentials below H2 formation gives selectivity to carbon products, while adsorption sites for CO2 direct intermediates to C-C bond coupling products. The sequential intermediates, formate then formaldehyde, undergo a series of exergonic aldol condensation reactions, selectively forming methylglyoxal and 2,3-furandiol products at record-breaking low overpotential (10 mV). This discovery opens a promising new avenue of research in CO2 conversion at ambient conditions. Supported by NSF-CBET/DOE-EERE and the Pray family fund.

Bioinspired heterogeneous electrocatalysts for CO2 reduction: Energy-efficient carbon-carbon coupling rivaling enzymes

256th National Meeting (2018)

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