Electrolyte Effects on CO<sub>2</sub> Electrochemical Reduction to CO

Marcandalli, Giulia; Monteiro, Mariana C. O.; Goyal, Akansha; Koper, Marc T. M.

doi:10.1021/acs.accounts.2c00080

Cited by 222 publications

(159 citation statements)

References 78 publications

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“…To understand the product selectivity of a manganese polypyridyl catalyst between CO, H 2 , and HCO 2 H is challenging as it is dependent upon not only the ligand structure but also the applied potential, electrolyte solvent, p K a of the proton source used (or generated in situ), and mass-transfer diffusion rates of both CO 2 and the proton source . Prior heterogeneous studies by Reuillard et al.…”

Section: Resultsmentioning

confidence: 99%

Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO₂ Reduction by Manganese Bipyridyl Complexes

et al. 2022

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This study aims to provide a greater insight into the balance between steric (bpy vs (Ph)2bpy vs mes2bpy ligands) and Lewis basic ((Ph)2bpy vs (MeOPh)2bpy vs (MeSPh)2bpy ligands) influence on the efficiencies of the protonation-first vs reduction-first CO2 reduction mechanisms with [MnI(R2bpy)(CO)3(CH3CN)]+ precatalysts, and on their respective transition-state geometries/energies for rate-determining C–OH bond cleavage toward CO evolution. The presence of only modest steric bulk at the 6,6′-diphenyl-2,2′-bipyridyl ((Ph)2bpy) ligand has here allowed unique insight into the mechanism of catalyst activation and CO2 binding by navigating a perfect medium between the nonsterically encumbered bpy-based and the highly sterically encumbered mes2bpy-based precatalysts. Cyclic voltammetry conducted in CO2-saturated electrolyte for the (Ph)2bpy-based precatalyst [2-CH 3 CN] + confirms that CO2 binding occurs at the two-electron-reduced activated catalyst [2] – in the absence of an excess proton source, in contrast to prior assumptions that all manganese catalysts require a strong acid for CO2 binding. This observation is supported by computed free energies of the parent–child reaction for [Mn–Mn] 0 dimer formation, where increased steric hindrance relative to the bpy-based precatalyst correlates with favorable CO2 binding. A critical balance must be adhered to, however, as the absence of steric bulk in the bpy-based precatalyst [1-CH 3 CN] + maintains a lower overpotential than [2-CH 3 CN] + at the protonation-first pathway with comparable kinetic performance, whereas an ∼2-fold greater TOFmax is observed at its reduction-first pathway with an almost identical overpotential as [2-CH 3 CN] + . Notably, excessive steric bulk in the mes2bpy-based precatalyst [3-CH 3 CN] + results in increased activation free energies of the C–OH bond cleavage transition states for both the protonation-first and the reduction-first pathways relative to both [1-CH 3 CN] + and [2-CH 3 CN] + . In fact, [3-CH 3 CN] + requires a 1 V window beyond its onset potential to reach its peak catalytic current, which is in contrast to the narrower (<0.30 V) potential response window of the remaining catalysts here studied. Voltammetry recorded under 1 atm of CO2 with 2.8 M (5%) H2O establishes [2-CH 3 CN] + to have the lowest overpotential (η = 0.75 V) in the series here studied, attributed to its ability to lie “on the fence” when providing sufficient steric bulk to hinder (but not prevent) [Mn–Mn] 0 dimerization, while simultaneously having a limited steric impact on the free energy of activation for the rate-determining C–OH bond cleavage transition state. While the methoxyphenyl bpy-based precatalyst [4-CH 3 CN] + possesses an increased steric presence relative to [2-CH 3 CN] +, this is offset by its capacity to stabilize the C–OH bond cleavage transition states of both the protonation-first and the reduction-first pathways by facilitating second coordination sphere H-bonding stabilization.

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Section: Resultsmentioning

confidence: 99%

Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO₂ Reduction by Manganese Bipyridyl Complexes

et al. 2022

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“…DFT). [24][25][26]46 Thus, to date there has remained a disconnect between the sub-elds of mechanistic investigation and practical cell development. Our results highlight the importance of quantifying (and ideally controlling) the movement of cations from anolyte to MEA cathodes.…”

Section: Resultsmentioning

confidence: 99%

“…(iii) tuning the local electric eld. [24][25][26] An experimental-theoretical study by Resasco et al highlighted the essential role of cations in facilitating the C-C coupling step, and hence enhancing the selectivity towards C 2+ products. 50 They reported higher C 2+ production rates in the presence of heavier alkali cations attributing to their higher concentration (due to more compact hydrated radius) compared to the lighter ones in the outer Helmholtz plane.…”

Section: Resultsmentioning

confidence: 99%

“…A few recent review articles provide summaries of work in this area and present a range of possible hypotheses regarding the effects of alkali cations. [24][25][26] Various theories exist, suggesting cations may contribute to buffering of local pH, stabilization of key reaction intermediates, and/or modulating local electric elds at the catalyst surface. A pair of recent studies showed that e cient CO 2 ER using acidic catholytes is possible by intentionally concentrating K + ions at the cathode, 27,28 while Monteiro et al observed an absence of CO 2 ER activity in solutions devoid of metal cations.…”

Section: Introductionmentioning

confidence: 99%

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Unintended cation crossover influences CO2 reduction activity in Cu-based zero-gap electrolysers

El‐Nagar

Flora

Gupta

et al. 2022

Preprint

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Gas-diffusion anion exchange membrane electrode assemblies enable CO2 reduction at industrially relevant rates, yet their long-term operational stability is often limited by the formation of solid precipitates in the cathode pores. This is a consequence of unintended cation crossover from the anolyte, and a detailed understanding of the factors enabling this crossover is lacking. Here we show that the anolyte concentration governs the flux of cation migration through the membrane, and this substantially influences the behaviors of copper catalysts in catholyte-free CO2 electrolysers. Systematic variation of the anolyte ionic strength (using aqueous KOH or KHCO3) correlated with drastic changes in the observed product selectivity – most notably, below a threshold ionic strength, Cu catalysts produced predominantly CO, in contrast to the mixture of C2+ products typically observed on Cu. Cation (K+) quantification at the zero-gap cathode revealed that the magnitude of K+ crossover depends on the anolyte concentration, but becomes significant only above the aforementioned threshold which closely correlates with the onset of C2+ product formation, suggesting cations play a key role in C-C coupling reaction pathways. Operando X-ray absorption spectroscopy and quasi in situ X-ray photoelectron spectroscopy were used to study how the catalyst is affected by operation conditions. Cu surface speciation was found to show a strong dependence on the anolyte concentration, wherein dilute anolytes or pure H2O resulted in a mixture of Cu+ and Cu0 surface species, while concentrated anolytes led to exclusively Cu0 under similar testing conditions. Overall, our results show that even in catholyte-free cells, cation effects (including unintentional ones) can significantly influence reaction pathways, which must be considered in future development of catalysts and devices.

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“…Recent study has reported that the electrolyte cation affects the activity of CO2 reduction reaction in the following order: Li + <Na + <K + <Cs + . 119 The roles of electrolyte cation in modulating the structure, conductivity and stability of POMs are rarely reported.…”

Section: Discussionmentioning

confidence: 99%

Polyoxometalate-based nanostructures for electrocatalytic and photocatalytic CO ₂ reduction

Zang¹,

Wang²

2022

Polyoxometalates

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Electro/photo-catalytic CO2 reduction to value-added chemicals and fuels is being actively studied as a promising pathway for renewable energy storage and climate change mitigation. Since the inert molecular properties and the competing hydrogen generation reaction, the development of high-performance electrocatalysts with high Faradaic efficiency and product selectivity but low overpotential is in urgent need. Polyoxometalate (POM) is a class of polynuclear metal oxide clusters with precise atomic structure, thus providing ideal research platform to reveal the relationship between macroscopic properties and microstructure. Moreover, the highly tunable redox properties and the abundant transition-metal atom composition ensure thriving research for POM-based nanostructures towards CO2 reduction. In this review, we firstly introduce the specific roles of POM in electro/photo-catalytic CO2 reduction. The recent advances in POM-based nanostructures ranging from single cluster, assemblies, organic-inorganic hybrids, to derivatives are systematically summarized. Particularly, the structure-performance relationship of POM-based nanostructures is discussed at the atomic and molecular level. Finally, the challenges and opportunities in the design of high-efficiency POM-based nanostructures are proposed for inspiring the development of electro/photo-catalytic CO2 reduction field.

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Electrolyte Effects on CO₂ Electrochemical Reduction to CO

Cited by 222 publications

References 78 publications

Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO₂ Reduction by Manganese Bipyridyl Complexes

Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO₂ Reduction by Manganese Bipyridyl Complexes

Unintended cation crossover influences CO2 reduction activity in Cu-based zero-gap electrolysers

Polyoxometalate-based nanostructures for electrocatalytic and photocatalytic CO ₂ reduction

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Electrolyte Effects on CO2 Electrochemical Reduction to CO

Cited by 222 publications

References 78 publications

Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO2 Reduction by Manganese Bipyridyl Complexes

Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO2 Reduction by Manganese Bipyridyl Complexes

Unintended cation crossover influences CO2 reduction activity in Cu-based zero-gap electrolysers

Polyoxometalate-based nanostructures for electrocatalytic and photocatalytic CO 2 reduction

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Product

Resources

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Electrolyte Effects on CO₂ Electrochemical Reduction to CO

Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO₂ Reduction by Manganese Bipyridyl Complexes

Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO₂ Reduction by Manganese Bipyridyl Complexes

Polyoxometalate-based nanostructures for electrocatalytic and photocatalytic CO ₂ reduction