Catalyseur hétérogène bio-inspiré pour la réduction électrochimique du CO2

Au cours des dernières décennies, dans le contexte du réchauffement climatique, l'utilisation accrue de combustibles fossiles a incité à développer de nouvelles sources d'énergie propre et durable. L'une des méthodes durables de stockage et de conversion de l'énergie consiste à réduire le CO2 en produits à haute valeur ajoutée. La valorisation du CO2 par réduction électrochimique attire l'attention en raison de sa facilité d'adaptation et d'utilisation avec différents types d'énergies renouvelables. L'objectif principal de la recherche sur la réduction électrochimique du CO2 est la conception d'un électrocatalyseur capable de réduire le CO2 en produits thermodynamiquement stables, de manière efficace et sélective, en s'inspirant de processus naturels. De plus, pour une durabilité à long terme, nous nous concentrons sur le développement d'un électrocatalyseur hétérogène. Récemment, les matériaux contenant un métal coordonné à une porphyrine ressemblant à des anneaux dans une structure en carbone (M-N-C), ont une importance particulière pour la réaction de réduction du dioxyde de carbone (CO2RR) en raison de leur faible coût, de leurs surfaces ajustables et de leur activité électrocatalytique. Cependant, il reste encore des défis à relever pour l’application au niveau industriel, tels que la faible densité de courant, le surpotentiel élevé. Le premier chapitre abordera certains de ces défis en couplant les catalyseurs à base de carbone poreux dopés avec des métaux et de l'azote sur des supports de carbone nanostructurés. Nous étudierons ensuite l’effet des supports carbonés nanostructurés sur l’activité et la sélectivité de la réduction électrochimique du CO2. Dans le deuxième chapitre, en raison de la forte demande de produits multicarbonés issus de la réduction électronique du CO2 sur le marché, la recherche a porté sur un nouveau catalyseur à base de cuivre afin d’obtenir un produit multicarboné efficace et sélectif. À cet égard, nous avons introduit la synthèse, la caractérisation structurale et morphologique (in situ et ex situ) d'un matériau carboné dopé au cuivre-azote (Cu-N-C). Le matériau présente des sites de CuN4 isolés bien définis intégrés dans une matrice de carbone et réalise la formation sélective d'éthanol à partir de l’électroréduction du CO2 avec un rendement faradique allant jusqu'à 55% (0,1 M CsHCO3, −1.2V vs. RHE, expérience de recyclage en phase gazeuse). Enfin, afin d’augmenter les sites actifs de surface, de nouveaux matériaux analogues M-N-C ont été étudiés. Dans ce chapitre, la synthèse, la caractérisation et l’activité CO2RR d’un nouveau matériau à base de Cu - polyphtalocyanine de cuivre sur nanotube de carbon (CNT) (CuPolyPc @ CNT) - ont été introduites. Une réduction efficace et sélective du CO2 en CO avec une stabilité à long terme a été démontrée.Over the past decades, in the context of global warming the increase in usage of fossil fuels urges to develop new sources of clean and sustainable energy. One of the longitudinal method of energy storage and conversion is the reduction of CO2 into high-value added products. CO2 valorization via electrochemical reduction at electrode is drawing attention due to its easy adaptation and utilization with different type of renewable energy. The main research aim into the electrochemical reduction of CO2 is the design of electrocatalyst that can reduce CO2 to thermodynamically stable products both efficiently and selectively by taking inspiration from keystone of natural process. Moreover, for long term durability, we focus on developing heterogeneous electrocatalyst. Recently, materials containing of a metal coordinated to a porphyrin like ring places in carbon framework (M-N-C), come into prominence for carbon dioxide reduction reaction (CO2RR) because of their low cost, tunable surface areas, and electrocatalytic activity. However there are still remained challenges approaching to the application towards industrial level such as low current density, high overpotenyial.The first chapter will address some of these challenges by coupling the metal- and nitrogen- doped porous carbon-based catalysts on nanostructured carbon supports. Then, we investigate the effect of nanostructured carbon supports on activity and selectivity for electrochemical CO2 reduction. In the second chapter, due to the high market demand of multicarbon products from CO2 electroreduction, the research focused on to new copper-based catalyst to have efficient and selective multicarbon product. In this regard, we introduced the synthesis, structural and morphological characterization (in-situ and ex-situ) of a copper-nitrogen-doped carbon material (Cu-N-C). The material is presenting well-defined isolated CuN4 sites integrated in a carbon matrix and demonstrating selective ethanol formation from CO2 electroreduction with Faradaic yield of up to 55% (0.1 M CsHCO3 , −1.2V vs. RHE, gas-phase recycling experiment).Lastly, in order to increase surface active sites, new analogous M-N-C material was studied. In this chapter, the synthesis, characterization and CO2RR activity of novel Cu based material- copper polyphthalocyanine on multi-walled carbon nanotube (CNT) (CuPolyPc@CNT)- was introduced. Active and selective CO2 reduction to CO with long term stability were disclosed

Benchmarking of oxygen evolution catalysts on porous nickel supports

Active and inexpensive oxygen evolution reaction (OER) electrocatalysts are needed for energy-efficient electrolysis applications. Objective comparison between OER catalysts has been blurred by the use of different supports and methods to evaluate performance. Here, we selected nine highly active transition-metal-based catalysts and described their synthesis, using a porous nickel foam and a new Ni-based dendritic material as the supports. We designed a standardized protocol to characterize and compare the catalysts in terms of structure, activity, density of active sites, and stability. NiFeSe- and CoFeSe-derived oxides showed the highest activities on our dendritic support, with low overpotentials of η100 ≈ 247 mV at 100 mA cm–2 in 1 M KOH. Stability evaluation showed no surface leaching for 8 h of electrolysis. This work highlights the most active anode materials and provides an easy way to increase the geometric current density of a catalyst by tuning the porosity of its support

FeNC catalysts for CO 2 electroreduction to CO: effect of nanostructured carbon supports

International audienceCO2 electroreduction to CO is an attractive strategy for using CO2 as a feedstock for the production of organic chemicals. However, there is still a need to develop catalysts based on non-noble metals since the best catalytic systems for that specific reaction are based on silver and gold, in particular when high current densities are required. Iron- and nitrogen-doped carbon materials (FeNC) have recently emerged as cheap, stable and active alternatives, however with still limited current densities. Here we report that both the current density and the selectivity of FeNC-based cathodes can be significantly improved by mixing FeNC with carbon materials such as carbon nanotubes (CNT) or carbon nanofibers (CNF). More specifically, we show that a cathode based on a FeNC–CNF composite material shows ca. a twice higher jCO/jH2 ratio and up to twice higher jCO value over a broad potential range. The FeNC–CNF electrode compares well with Ag and Au electrodes with a very high selectivity for CO production (FY for CO of almost 90%) and current densities above 10 mA cm−2 at −0.7 V vs. RHE

Electrochemical CO2 Reduction to Ethanol with Copper-Based Catalysts

Electrochemical CO2 reduction presents a sustainable route to storage of intermittent renewable energy. Ethanol is an important target product, which is used as a fuel additive and as a chemical feedstock. However, electrochemical ethanol production is challenging, as it involves the transfer of multiple electrons and protons alongside C–C bond formation. To date, the most commonly employed and effective catalysts are copper-based materials. This Review presents and categorizes the most efficient and selective Cu-based electrocatalysts, which are divided into three main groups: oxide-derived copper, bimetallics, and copper- and nitrogen-doped carbon materials. Only a few other specific examples fall outside this classification. The catalytic performance of these materials for ethanol production in aqueous conditions is discussed in terms of current density, overpotential, and faradaic efficiency. A critical evaluation of the factors that contribute to high performance is provided to aid the design of more efficient catalysts for selective ethanol formation

Molecular Inhibition for Selective CO2 Conversion

Electrochemical CO2 reduction presents a sustainable route to the production of chemicals and fuels. Achieving a narrow product distribution with copper catalysts is challenging and conventional material modifications offer limited control over selectivity. Here, we show that the mild cathodic potentials required to reach high currents in an alkaline gas-fed flow cell permits retention of a surface-bound thiol (4-mercaptopyridine), enabling molecule-directed selective formate generation at high reaction rates. Combined experimental and computational results showed that formate production is favoured due to the inhibition of a CO producing pathway caused by destabilising interactions with the anchored molecule. The immobilisation of molecules to inhibit specific carbon-based products therefore offers a novel approach to rationally tune the selectivity of heterogeneous catalysts

Carbon‐Nanotube‐Supported Copper Polyphthalocyanine for Efficient and Selective Electrocatalytic CO 2 Reduction to CO

International audienceElectroreduction of CO2 to CO is one of the simplest ways to valorise CO2 as a source of carbon. Herein, a cheap, robust, Cu-based hybrid catalyst consisting of a polymer of Cu phthalocyanine coated on carbon nanotubes, which proved to be selective for CO production (80 % faradaic yield) at relatively low overpotentials, was developed. Polymerisation of Cu phthalocyanine was shown to have a drastic effect on the selectivity of the reaction because molecular Cu phthalocyanine was instead selective for proton reduction under the same conditions. Although the material only showed isolated Cu sites in phthalocyanine-like CuN4 coordination, in situ and operando X-ray absorption spectroscopy showed that, under operating conditions, the Cu atoms were fully converted to Cu nanoparticles, which were likely the catalytically active species. Interestingly, this restructuring of the metal sites was reversible

Electroreduction of CO 2 on Single-Site Copper-Nitrogen-Doped Carbon Material: Selective Formation of Ethanol and Reversible Restructuration of the Metal Sites

International audienceIt is generally believed that CO2 electroreduction to multi‐carbon products such as ethanol or ethylene may be catalyzed with significant yield only on metallic copper surfaces, implying large ensembles of copper atoms. Here, we report on an inexpensive Cu‐N‐C material prepared via a simple pyrolytic route that exclusively feature single copper atoms with a CuN4 coordination environment, atomically dispersed in a nitrogen‐doped conductive carbon matrix. This material achieves aqueous CO2 electroreduction to ethanol at a Faradaic yield of 55 % under optimized conditions (electrolyte: 0.1 m CsHCO3, potential: −1.2 V vs. RHE and gas‐phase recycling set up), as well as CO electroreduction to C2‐products (ethanol and ethylene) with a Faradaic yield of 80 %. During electrolysis the isolated sites transiently convert into metallic copper nanoparticles, as shown by operando XAS analysis, which are likely to be the catalytically active species. Remarkably, this process is reversible and the initial material is recovered intact after electrolysis

Low-cost high-efficiency system for solar-driven conversion of CO2 to hydrocarbons

Conversion of carbon dioxide into hydrocarbons using solar energy is an attractive strategy for storing such a renewable source of energy into the form of chemical energy (a fuel). This can be achieved in a system coupling a photovoltaic (PV) cell to an electrochemical cell (EC) for CO2 reduction. To be beneficial and applicable, such a system should use low-cost and easily processable photovoltaic cells and display minimal energy losses associated with the catalysts at the anode and cathode and with the electrolyzer device. In this work, we have considered all of these parameters altogether to set up a reference PV–EC system for CO2 reduction to hydrocarbons. By using the same original and efficient Cu-based catalysts at both electrodes of the electrolyzer, and by minimizing all possible energy losses associated with the electrolyzer device, we have achieved CO2 reduction to ethylene and ethane with a 21% energy efficiency. Coupled with a state-of-the-art, low-cost perovskite photovoltaic minimodule, this system reaches a 2.3% solar-to-hydrocarbon efficiency, setting a benchmark for an inexpensive all–earth-abundant PV–EC system.ISSN:0027-8424ISSN:1091-649