Immobilization of a Molecular Re Complex on MOF‐derived Hierarchical Porous Carbon for CO₂ Electroreduction in Water/Ionic Liquid Electrolyte

Abstract

The development of molecular catalysts for CO2 electroreduction within electrolyzers requests their immobilization on the electrodes. While a variety of methods have been explored for the heterogenization of homogeneous complexes, a novel approach using a hierarchical porous carbon material, derived from a metal–organic framework, is reported as a support for the well‐known molecular catalyst [Re(bpy)(CO)3Cl] (bpy=2,2’‐bipyridine). This cathodic hybrid material, named Re@HPC (HPC=hierarchical porous carbon), has been tested for CO2 electroreduction using a mixture of an ionic liquid (1‐ethyl‐3‐methylimidazolium tetrafluoroborate, EMIM) and water as the electrolyte. Interestingly, it catalyzes the conversion of CO2 into a mixture of carbon monoxide and formic acid, with a selectivity that depends on the applied potential. The present study thus reveals that Re@HPC is a remarkable catalyst, enjoying excellent activity (turnover numbers for CO2 reduction of 7835 after 2 h at −1.95 V vs. Fc/Fc+ with a current density of 6 mA cm−2) and good stability. These results emphasize the advantages of integrating molecular catalysts onto such porous carbon materials for developing novel, stable and efficient, catalysts for CO2 reduction.

From NiMoO4 to γ-NiOOH: Detecting the Active Catalyst Phase by Time Resolved in Situ and Operando Raman Spectroscopy

“… 4 , 12 − 14 Not only is splitting water photochemically, electrochemically, or photoelectrochemically of high interest for hydrogen generation, but a similar approach can also be utilized for the reduction of carbon dioxide to different chemicals (carbon monoxide, methane, or smaller organic molecules) or the reduction of nitrogen to form ammonia in a carbon neutral process. 12 , 15 − 21 The formation of hydrogen, carbon monoxide, methane, organic molecules, or ammonia from N 2 is done via reduction of their starting products and is thus taking place at the cathode of the electrochemical cell. The reaction at the anode is instead oxidation of water or hydroxide ions to molecular dioxygen.…”

“…A transition to renewable fossil free or carbon neutral fuels is therefore highly desired and urgent. − Rising effort is made to store renewable energy in chemical bonds where hydrogen, with its high gravimetric energy density, is a very promising energy carrier. − Unfortunately, most of the hydrogen utilized today is produced by steam re-forming from methane, in which methane is transformed at high temperatures to hydrogen with an accompanying release of carbon dioxide. , An interesting and carbon neutral method to generate hydrogen is sustainable water electrolysis, in which water is split into molecular oxygen and hydrogen with the use of renewable electricity . By powering of this process with solar or wind energy, the obtained hydrogen is carbon dioxide neutral and fully renewable, neglecting the carbon footprint of the manufactured wind, solar, and electrolysis devices. ,− Not only is splitting water photochemically, electrochemically, or photoelectrochemically of high interest for hydrogen generation, but a similar approach can also be utilized for the reduction of carbon dioxide to different chemicals (carbon monoxide, methane, or smaller organic molecules) or the reduction of nitrogen to form ammonia in a carbon neutral process. ,− The formation of hydrogen, carbon monoxide, methane, organic molecules, or ammonia from N 2 is done via reduction of their starting products and is thus taking place at the cathode of the electrochemical cell. The reaction at the anode is instead oxidation of water or hydroxide ions to molecular dioxygen.…”

Synthesis of FeNiCo Ternary Hydroxides through Green Grinding Method with Metal‐Organic Frameworks as Precursors for Oxygen Evolution Reaction

“…These resultant MOF‐derived materials have also attracted extensive attention because they could add diverse functional components or increase more active sites while preserving the original structure of MOFs [6–9] . To date, the popular methods employed to prepare MOF‐derivatives include high‐temperature pyrolysis, [10] chemical vapor deposition (CVD), [11] ion exchange, [12] etching, [13] and electrochemical redox [14] . Despite tremendous progress, most of these preparation processes generally require high temperatures or large amounts of solvents, triggering high energy costs and heavy contamination.…”

Heterogenised Molecular Catalysts for Sustainable Electrochemical CO2 Reduction

“…The method of immobilisation also influences the performance and efficiency of the system. Different strategies are described in the literature, such as grafting via covalent bonding, [24–26] immobilisation via weak interactions and physical adsorption, [27–29] and integration of the molecular complexes into the porous support structure [17, 30–32] . Each strategy has its own merits and drawbacks.…”

“… Summary of the most relevant work presented in this review for each support considered: a) from “Immobilisation of a molecular Re complex on MOF‐derived hierarchical porous carbon for CO 2 electroreduction in water/ionic liquid electrolyte” . Reproduced with permission, Copyright 2020, Wiley‐VCH [17] . b) From “Electrocatalytic CO 2 reduction with a ruthenium catalyst in solution and on nanocrystalline TiO 2 ”.…”