The limited selectivity of existing CO2 reduction catalysts and rising levels of CO2 in the atmosphere necessitate the identification of specific structure–reactivity relationships to inform catalyst ...development. Herein, we develop a predictive framework to tune the selectivity of CO2 reduction on Cu by examining a series of polymeric and molecular modifiers. We find that protic species enhance selectivity for H2, hydrophilic species enhance formic acid formation, and cationic hydrophobic species enhance CO selectivity. ReaxFF reactive molecular dynamics simulations indicate that the hydrophilic/hydrophobic modifiers influence the formation of surface hydrides, which yield formic acid or H2. These observations offer insights into how these modifiers influence catalytic behavior at the non-precious Cu surface and may aid in the future implementation of organic structures in CO2 reduction devices.
Dinickel bisphenoxyiminato complexes based on highly substituted p- and m-terphenyl backbones were synthesized, and the corresponding atropisomers were isolated. In the presence of a phosphine ...scavenger, Ni(COD)2, the phosphine-ligated syn-dinickel complexes copolymerized α-olefins and ethylene in the presence of amines to afford 0.2–1.3% α-olefin incorporation and copolymerized amino olefins and ethylene with a similar range of incorporation (0.1–0.8%). The present rigid catalysts provide a bimetallic strategy for insertion polymerization of polar monomers without masking of the heteroatom group. The effects of the catalyst structure on the reactivity were studied by comparisons of the syn and anti atropisomers and the p- and m-terphenyl systems.
We elucidate the role of subsurface oxygen on the production of C2 products from CO2 reduction over Cu electrocatalysts using the newly developed grand canonical potential kinetics density functional ...theory method, which predicts that the rate of C2 production on pure Cu with no O is ∼500 times slower than H2 evolution. In contrast, starting with Cu2O, the rate of C2 production is >5,000 times faster than pure Cu(111) and comparable to H2 production. To validate these predictions experimentally, we combined time-dependent product detection with multiple characterization techniques to show that ethylene production decreases substantially with time and that a sufficiently prolonged reaction time (up to 20 h) leads only to H2 evolution with ethylene production ∼1,000 times slower, in agreement with theory. This result shows that maintaining substantial subsurface oxygen is essential for long-term C2 production with Cu catalysts.
Using our company’s CO2 electrolysers as a model, we describe the challenges involved in incorporating nanomaterial catalysts into industrial-scale electrolysers and suggest ways to more efficiently ...realize the performance improvements of academic-scale novel nanomaterials at industrial scales.
Using 31P nuclear magnetic resonance (NMR) spectroscopy, we monitor the competition between tri-n-butylphosphine (Bu3P) and various amine and phosphine ligands for the surface of chloride terminated ...CdSe nanocrystals. Distinct 31P NMR signals for free and bound phosphine ligands allow the surface ligand coverage to be measured in phosphine solution. Ligands with a small steric profile achieve higher surface coverages (Bu3P = 0.5 nm–2, Me2P-n-octyl = 2.0 nm–2, NH2Bu = >3 nm–2) and have greater relative binding affinity for the nanocrystal (binding affinity: Me3P > Me2P–n-octyl ∼ Me2P–n-octadecyl > Et3P > Bu3P). Among phosphines, only Bu3P and Me2P–n-octyl support a colloidal dispersion, allowing a relative surface binding affinity (K rel) to be estimated in that case (K rel = 3.1). The affinity of the amine ligands is measured by the extent to which they displace Bu3P from the nanocrystals (K rel: H2NBu ∼ N-n-butylimidazole > 4-ethylpyridine > Bu3P ∼ HNBu2 > Me2NBu > Bu3N). The affinity for the CdSe surface is greatest among soft, basic donors and depends on the number of each ligand that bind. Sterically unencumbered ligands such as imidazole, pyridine, and n-alkylamines can therefore outcompete stronger donors such as alkylphosphines. The influence of repulsive interactions between ligands on the binding affinity is a consequence of the high atom density of binary semiconductor surfaces. The observed behavior is distinct from the self-assembly of straight-chain surfactants on gold and silver where the ligands are commensurate with the underlying lattice and attractive interactions between aliphatic chains strengthen the binding.
We report the discovery of a quaternary ammonium surface additive for CO2 reduction on Ag surfaces that changes the Faradaic efficiency for CO from 25% on Ag foil to 97%, while increasing the current ...density for CO production by a factor of 9 from 0.14 to 1.21 mA/cm2 and reducing the current density for H2 production by a factor of 440 from 0.44 to 0.001 mA/cm2. Using ReaxFF reactive molecular dynamics, we find that the surface additive with the highest selectivity, dihexadecyldimethylammonium bromide, promotes substantial population of CO2 near the Ag surface along with sufficient H2O to activate the CO2. While a critical number of water molecules is required in the reduction of CO2 to CO, the trend in selectivity strongly correlates with the availability of CO2 molecules. We demonstrate that the ordering of the cationic modifiers plays a significant role around the active site, thus determining reaction selectivity. The dramatic improvement by addition of a simple surface additive suggests an additional strategy in electrocatalysis.
Electrochemical CO2 reduction (CO2R) is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent ...progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO2R technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application of data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle.
The limited selectivity of existing CO
reduction catalysts and rising levels of CO
in the atmosphere necessitate the identification of specific structure-reactivity relationships to inform catalyst ...development. Herein, we develop a predictive framework to tune the selectivity of CO
reduction on Cu by examining a series of polymeric and molecular modifiers. We find that protic species enhance selectivity for H
, hydrophilic species enhance formic acid formation, and cationic hydrophobic species enhance CO selectivity. ReaxFF reactive molecular dynamics simulations indicate that the hydrophilic/hydrophobic modifiers influence the formation of surface hydrides, which yield formic acid or H
. These observations offer insights into how these modifiers influence catalytic behavior at the non-precious Cu surface and may aid in the future implementation of organic structures in CO
reduction devices.
Confinement of metal centers is a powerful tool to manipulate reactivity and tune selectivity in chemical transformations. While aluminum as a foil is inactive for carbon dioxide reduction and shows ...high selectivity for the hydrogen evolution reaction, here we show that aluminum confined in a metal–organic framework (MOF), MIL-53(Al), suppresses hydrogen evolution reaction activity and enhances carbon dioxide reduction. This aluminum MOF can produce up to 40% faradaic efficiency for carbon monoxide and formic acid. This study demonstrates that the unique reaction environment created by the MOF enables changes in reaction selectivity and can impart atypical catalytic capabilities to metals.
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