Enhanced Molecular CO2 Electroreduction Enabled by a Flexible Hydrophilic Channel for Relay Proton Shuttling

Surface Ligand Modification on Ultrathin Ni(OH)2 Nanosheets Enabling Enhanced Alkaline Ethanol Oxidation Kinetics

The ethanol oxidation reaction (EOR) is an economical pathway in many electrochemical systems for clean energy, such as ethanol fuel cells and the anodic reaction in hydrogen generation. Noble metals, such as platinum, are benchmark catalysts for EOR owing to their superb electrochemical capability. To improve sustainability and product selectivity, nickel (Ni)-based electrocatalysts are considered promising alternatives to noble-metal EOR. Although Ni-based electrocatalysts are relieved from intermediate poisoning, their performances are largely limited by their relatively high onset potential. Therefore, the EOR usually competes with the oxygen evolution reaction (OER) at working potentials, resulting in a low EOR efficiency. Here, we demonstrate a strategy to modify the surface ligands on ultrathin Ni(OH)2 nanosheets, which substantially improved their catalytic properties for the alkaline EOR. Chemisorbed octadecylamine ligands could create an alcoholophilic layer at the nanosheet surface to promote alcohol diffusion and adsorption, resulting in outstanding EOR activity and selectivity over the OER at higher potential. These non-noble-metal-based 2D electrocatalysts and surface ligand engineering showcase a promising strategy for achieving high-efficiency electrocatalysis of EOR in many practical electrochemical processes.

Proton Transfer Dynamics-Mediated CO2 Electroreduction

Electrochemical CO₂ reduction reaction (CO₂ RR) is crucial to addressing environmental crises and producing chemicals. Proton activation and transfer are essential in CO₂ RR. To date, few research reviews have focused on this process and its effect on catalytic performance. Recent studies have demonstrated ways to improve CO₂ RR by regulating proton transfer dynamics. This Concept highlights the use of regulating proton transfer dynamics to enhance CO₂ RR for the target product and discusses modulation strategies for proton transfer dynamics and operative mechanisms in typical systems, including single-atom catalysts, molecular catalysts, metal heterointerfaces, and organic-ligand modified metal catalysts. Characterization methods for proton transfer dynamics during CO₂ RR are also discussed, providing powerful tools for the hydrogen-involving electrochemical study. This Concept offers new insights into the CO₂ RR mechanism and guides the design of efficient CO₂ RR systems.

Outer-coordination sphere in multi-H+/multi-e-molecular electrocatalysis

Electrocatalysis is an indispensable technique for small-molecule transformations, which are essential for the sustainability of society. Electrocatalysis utilizes electricity as an energy source for chemical reactions. Hydrogen is considered the “fuel for the future,” and designing electrocatalysts for hydrogen production has thus become critical. Furthermore, fuel cells are promising energy solutions that require robust electrocatalysts for key fuel cell reactions such as the interconversion of oxygen to water. Concerns regarding the rising concentration of atmospheric carbon dioxide have prompted the search for CO₂ conversion methods. One promising approach is the electrochemical conversion of CO₂ into commodity chemicals and/or liquid fuels, but such chemistry is highly energy demanding because of the thermodynamic stability of CO₂. All of the above-mentioned electrocatalytic processes rely on the selective input of multiple protons (H⁺) and electrons (e^–) to yield the desired products. Biological enzymes evolved in nature to perform such redox catalysis and have inspired the design of catalysts at the molecular and atomic levels. While it is synthetically challenging to mimic the exact biological environment, incorporating functional outer coordination spheres into molecular catalysts has shown promise for advancing multi-H⁺ and multi-e^– electrocatalysis. From this Perspective, herein, catalysts with outer coordination sphere(s) are selected as the inspiration for developing new catalysts, particularly for the reductive conversion of H⁺, O₂, and CO₂, which are highly relevant to sustainability. The recent progress in electrocatalysis and opportunities to explore beyond the second coordination sphere are also emphasized.

Hydrodechlorination of Dichloromethane by a Metal-Free Triazole-Porphyrin Electrocatalyst: Demonstration of Main-Group Element Electrocatalysis*

In this work, the electrocatalytic reduction of dichloromethane (CH₂ Cl₂ ) into hydrocarbons involving a main group element-based molecular triazole-porphyrin electrocatalyst H2PorT8 is reported. This catalyst converted CH₂ Cl₂ in acetonitrile to various hydrocarbons (methane, ethane, and ethylene) with a Faradaic efficiency of 70 % and current density of -13 mA cm^-2 at a potential of -2.2 V vs. Fc/Fc⁺ using water as a proton source. The findings of this study and its mechanistic interpretations demonstrated that H2PorT8 was an efficient and stable catalyst for the hydrodechlorination of CH₂ Cl₂ and that main group catalysts could be potentially used for exploring new catalytic reaction mechanisms.

Effects of Appended Poly(ethylene glycol) on Electrochemical CO2 Reduction by an Iron Porphyrin Complex

Electrochemical carbon dioxide (CO₂) reduction is a sustainable approach for transforming atmospheric CO₂ into chemical feedstocks and fuels. To overcome the kinetic barriers of electrocatalytic CO₂ reduction, catalysts with high selectivity, activity, and stability are needed. Here, we report an iron porphyrin complex, FePEGP, with a poly(ethylene glycol) unit in the second coordination sphere, as a highly selective and active electrocatalyst for the electrochemical reduction of CO₂ to carbon monoxide (CO). Controlled-potential electrolysis using FePEGP showed a Faradaic efficiency of 98% and a current density of -7.8 mA/cm² at -2.2 V versus Fc/Fc⁺ in acetonitrile using water as the proton source. The maximum turnover frequency was calculated to be 1.4 × 10⁵ s^-1 using foot-of-the-wave analysis. Distinct from most other catalysts, the kinetic isotope effect (KIE) study revealed that the protonation step of the Fe-CO₂ adduct is not involved in the rate-limiting step. This model shows that the PEG unit as the secondary coordination sphere enhances the catalytic kinetics and thus is an effective design for electrocatalytic CO₂ reduction.

Enhanced Electrocatalytic Activity of a Zinc Porphyrin for CO2 Reduction: Cooperative Effects of Triazole Units in the Second Coordination Sphere

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.