Molecular tuning of CO<sub>2</sub>-to-ethylene conversion.
basic_science · Level V
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- Record sourced from PubMed, PMID 31747679.
- Also identified by DOI 10.1038/s41586-019-1782-2.
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Abstract
The electrocatalytic reduction of carbon dioxide, powered by renewable electricity, to produce valuable fuels and feedstocks provides a sustainable and carbon-neutral approach to the storage of energy produced by intermittent renewable sources<sup>1</sup>. However, the highly selective generation of economically desirable products such as ethylene from the carbon dioxide reduction reaction (CO<sub>2</sub>RR) remains a challenge<sup>2</sup>. Tuning the stabilities of intermediates to favour a desired reaction pathway can improve selectivity<sup>3-5</sup>, and this has recently been explored for the reaction on copper by controlling morphology<sup>6</sup>, grain boundaries<sup>7</sup>, facets<sup>8</sup>, oxidation state<sup>9</sup> and dopants<sup>10</sup>. Unfortunately, the Faradaic efficiency for ethylene is still low in neutral media (60 per cent at a partial current density of 7 milliamperes per square centimetre in the best catalyst reported so far<sup>9</sup>), resulting in a low energy efficiency. Here we present a molecular tuning strategy-the functionalization of the surface of electrocatalysts with organic molecules-that stabilizes intermediates for more selective CO<sub>2</sub>RR to ethylene. Using electrochemical, operando/in situ spectroscopic and computational studies, we investigate the influence of a library of molecules, derived by electro-dimerization of arylpyridiniums<sup>11</sup>, adsorbed on copper. We find that the adhered molecules improve the stabilization of an 'atop-bound' CO intermediate (that is, an intermediate bound to a single copper atom), thereby favouring further reduction to ethylene. As a result of this strategy, we report the CO<sub>2</sub>RR to ethylene with a Faradaic efficiency of 72 per cent at a partial current density of 230 milliamperes per square centimetre in a liquid-electrolyte flow cell in a neutral medium. We report stable ethylene electrosynthesis for 190 hours in a system based on a membrane-electrode assembly that provides a full-cell energy efficiency of 20 per cent. We anticipate that this may be generalized to enable molecular strategies to complement heterogeneous catalysts by stabilizing intermediates through local molecular tuning.