Many metal coordination compounds catalyze CO2 electroreduction to CO, but cobalt phthalocyanine hybridized with conductive carbon such as carbon nanotubes is currently the only one that can generate ...methanol. The underlying structure–reactivity correlation and reaction mechanism desperately demand elucidation. Here we report the first in situ X‐ray absorption spectroscopy characterization, combined with ex situ spectroscopic and electrocatalytic measurements, to study CoPc‐catalyzed CO2 reduction to methanol. Molecular dispersion of CoPc on CNT surfaces, as evidenced by the observed electronic interaction between the two, is crucial to fast electron transfer to the active sites and multi‐electron CO2 reduction. CO, the key intermediate in the CO2‐to‐methanol pathway, is found to be labile on the active site, which necessitates a high local concentration in the microenvironment to compete with CO2 for active sites and promote methanol production. A comparison of the electrocatalytic performance of structurally related porphyrins indicates that the bridging aza‐N atoms of the Pc macrocycle are critical components of the CoPc active site that produces methanol. In situ X‐ray absorption spectroscopy identifies the active site as Co(I) and supports an increasingly non‐centrosymmetric Co coordination environment at negative applied potential, likely due to the formation of a Co−CO adduct during the catalysis.
Electrocatalytic and spectroscopic characterizations of cobalt phthalocyanine on carbon nanotubes (CoPc/CNT) and its catalyst analogs are reported. The results help us understand the nature of the active site for the electrochemical CO2 reduction to methanol.
Hybrid electrodes with improved O2 tolerance and capability of CO2 conversion into liquid products in the presence of O2 are presented. Aniline molecules are introduced into the pore structure of a ...polymer of intrinsic microporosity to expand its gas separation functionality beyond pure physical sieving. The chemical interaction between the acidic CO2 molecule and the basic amino group of aniline renders enhanced CO2 separation from O2. Loaded with a cobalt phthalocyanine‐based cathode catalyst, the hybrid electrode achieves a CO Faradaic efficiency of 71 % with 10 % O2 in the CO2 feed gas. The electrode can still produce CO at an O2/CO2 ratio as high as 9:1. Switching to a Sn‐based catalyst, for the first time O2‐tolerant CO2 electroreduction to liquid products is realized, generating formate with nearly 100 % selectivity and a current density of 56.7 mA cm−2 in the presence of 5 % O2.
An aniline‐infiltrated polymer‐of‐intrinsic‐microporosity (PIM) membrane is reported for direct valorization of CO2 from its mixture with O2. The acid–base interaction between CO2 and aniline enhances CO2/O2 separation, enabling catalytic electrodes capable of producing CO from a feed gas with an O2/CO2 ratio as high as 9:1 and of reducing CO2 selectively to formate in the presence of O2.
Fe3GeTe2 have proven to be of greatly intrigue. However, the underlying mechanism behind the varying Curie temperature (Tc) values remains a puzzle. This study explores the atomic structure of ...Fe3GeTe2 crystals exhibiting Tc values of 160, 210, and 230 K. The elemental mapping reveals a Fe‐intercalation on the interstitial sites within the van der Waals gap of the high‐Tc (210 and 230 K) samples, which are observed to have an exchange bias effect by electrical transport measurements, while Fe intercalation or the bias effect is absent in the low‐Tc (160 K) samples. First‐principles calculations further suggest that the Fe‐intercalation layer may be responsible for the local antiferromagnetic coupling that gives rise to the exchange bias effect, and that the interlayer exchange paths greatly contribute to the enhancement of Tc. This discovery of the Fe‐intercalation layer elucidates the mechanism behind the hidden antiferromagnetic ordering that underlies the enhancement of Tc in Fe3GeTe2.
The Fe intercalation on the interstitial sites in high Curie temperature (Tc) Fe3GeTe2 may be responsible for the local antiferromagnetic coupling that gives rise to the exchange bias effect, and that the interlayer exchange paths greatly contribute to the enhancement of Tc.
Many metal coordination compounds catalyze CO
electroreduction to CO, but cobalt phthalocyanine hybridized with conductive carbon such as carbon nanotubes is currently the only one that can generate ...methanol. The underlying structure-reactivity correlation and reaction mechanism desperately demand elucidation. Here we report the first in situ X-ray absorption spectroscopy characterization, combined with ex situ spectroscopic and electrocatalytic measurements, to study CoPc-catalyzed CO
reduction to methanol. Molecular dispersion of CoPc on CNT surfaces, as evidenced by the observed electronic interaction between the two, is crucial to fast electron transfer to the active sites and multi-electron CO
reduction. CO, the key intermediate in the CO
-to-methanol pathway, is found to be labile on the active site, which necessitates a high local concentration in the microenvironment to compete with CO
for active sites and promote methanol production. A comparison of the electrocatalytic performance of structurally related porphyrins indicates that the bridging aza-N atoms of the Pc macrocycle are critical components of the CoPc active site that produces methanol. In situ X-ray absorption spectroscopy identifies the active site as Co(I) and supports an increasingly non-centrosymmetric Co coordination environment at negative applied potential, likely due to the formation of a Co-CO adduct during the catalysis.
The control of the second coordination sphere in a coordination complex plays an important role in improving catalytic efficiency. Herein, we report a zinc porphyrin complex ZnPor8T with multiple ...flexible triazole units comprising the second coordination sphere, as an electrocatalyst for the highly selective electrochemical reduction of carbon dioxide (CO2) to carbon monoxide (CO). This electrocatalyst converted CO2 to CO with a Faradaic efficiency of 99 % and a current density of −6.2 mA cm−2 at −2.4 V vs. Fc/Fc+ in N,N‐dimethylformamide using water as the proton source. Structure‐function relationship studies were carried out on ZnPor8T analogs containing different numbers of triazole units and distinct triazole geometries; these unveiled that the triazole units function cooperatively to stabilize the CO2‐catalyst adduct in order to facilitate intramolecular proton transfer. Our findings demonstrate that incorporating triazole units that function in a cooperative manner is a versatile strategy to enhance the activity of electrocatalytic CO2 conversion.
A set of zinc porphyrin electrocatalysts with flexible triazole units as the second coordination spheres is prepared for cooperative‐effect studies. The electrocatalyst with a triazole bundle displays efficient CO2‐to‐CO conversion with a Faradaic efficiency of 99 % and a current density of −6.2 mA cm−2 at −2.4 V vs. Fc/Fc+.
Dramatic enhancement of electrochemical CO2 conversion to CO, catalyzed by Ni(cyclam)(PF6)2 is observed on mercury/gold electrodes. We find that Hg provides favorable noncovalent dispersive ...interactions with the cyclam ligand. As a result, the Hg surface destabilizes the poisoned CO-bound form of the catalyst, leading to enhanced reaction kinetics. These findings are particularly relevant to the design of ligands that improve the electrocatalytic performance of transition-metal complexes on interaction with metallic surfaces under cell operating conditions.
The production of CO from the CO
reduction reaction (CO
RR) is of great interest in the renewable energy storage and conversion, the neutral carbon emission, and carbon recycle utilization. Silver ...(Ag) is one of the catalytic metals that are active for electrochemical CO
reduction into CO, but the catalysis requires a large overpotential to achieve higher selectivity. Constructing a metal-oxide interface could be an effective strategy to boost both activity and selectivity of the catalysis. Herein, density functional theory (DFT) calculations were first conducted to reveal the chemical insights of the catalytic performance on the interface between metal oxide and Ag(111) (MO
/Ag(111)). The results show that the *COOH intermediates can be more stabilized on the surfaces of MO
/Ag(111) than pure Ag(111). The hydrogen evolution reaction on MO
/Ag(111) can be suppressed due to the significantly higher Gibbs free energy for hydrogen adsorption (Δ
*), thereby enhancing the selectivity toward CO
RR. A series of MO
/Ag composites with the unique interface based on the DFT results were then introduced though a two-step approach. The as-obtained MO
/Ag catalysts boosted both the CO activity and selectivity at a relatively positive potential range, especially in the case of MnO
/Ag. The reduction current density on the MnO
/Ag catalyst can reach 4.3 mA cm
at -0.7 V (vs RHE), which is 21.5 times higher than that on pure Ag, and the overpotential of CO
to CO (390 mV) possesses is much lower than that on pure Ag NPs (690 mV). This study proposes an effective design strategy to construct a metal-oxide interface for CO
RR based on the synergistic effect between metals and MO
.
Electrochemical reduction of CO2 (CO2R) by Cu metal holds promise to convert CO2 to valuable C2+ chemicals at scale using electricity and water but suffers from poor selectivity. Coating of metal ...electrodes with small organic molecules or polymers has been shown to effectively enhance catalytic performance but remains underexplored. Herein, facile modification of Cu surfaces by a polyaromatic layer was found to boost both selectivity and activity toward C2+ products. Using phenyldiazonium or diphenyliodonium salts to graft an organic layer onto the surface of Cu foil electrodes resulted in up to 75% Faradaic efficiency (FE) for C2+ at neutral pH. Modified electrodes have electrochemical active surface areas and proton diffusion coefficients similar to those of bare Cu. High CO2R performance was maintained in a gas diffusion electrode, with a pH ≈ 1 electrolyte (1 M H3PO4, 1 M KCl; −100 mA/cm2), producing 65% FE for C2+ over 5 h, with no delamination.
Abstract
Electrocatalysts that start a reaction as molecules do not always end the reaction as molecules, and even when they do, they might not be molecules during catalysis. In this Perspective, we ...discuss knowledge learned from the study of Cu‐based molecularly structured electrocatalysts––including metal coordination complexes, metal‐organic frameworks, single‐atom catalysts, and polymeric materials––that restructure under electrochemical CO
2
reduction reactions. Recent reports are summarized with an emphasis on the nature and significance of post‐mortem and in situ characterization for the proper identification of active sites. We demonstrate that molecular and material structures determine whether electrocatalysts restructure and how they restructure, that understanding of restructuring processes can help us identify active sites for catalysis, and that this knowledge can be leveraged to design precatalysts that generate highly active catalysts under reaction conditions. In addition, we provide recommended practices for studying the integrity of heterogeneous molecular catalysts during and after CO
2
reduction reactions.
Key Points
Heterogeneous molecular Cu catalysts have been observed to restructure to metallic Cu clusters under reaction conditions.
Dynamic or reversible restructuring confounds identification of real active sites.
Both ex situ and in situ techniques are recommended for robust catalyst characterization.
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