A record pace, the carbon dioxide is converted to ethylene!

An electrochemical gas reducing bottlenecks

Electrochemical renewable energy fixed drive gas, which was converted to value-added products, which is the conversion of CO to CO2 and hydrocarbons a compound of fuels and chemical feedstocks attractive way. The success of this approach will depend on the continuous improvement of energy efficiency to minimize operating costs and increase depending on the current density to minimize the cost of capital. This will require catalysts to proton coupled electron transfer step is performed by promoting adsorption, coupling and hydrogenation. In these reactions, both water-based electrolyte as a proton source and as the ionically conductive medium. However, these gases are limited solubility in water, when gas molecules collide with its environment or reaction, resulting in the gas diffusion restricted. In an alkaline aqueous environment, CO2 diffusion length may be as low as tens of nanometers. Because the mass transfer reasons, limiting the capacity of the catalyst in the aqueous phase of the battery, the current density in the range of tens of milliamps per square centimeter.

Design of the fuel cell catalyst layer

In the gas phase electrolysis cell, the catalyst layer is deposited on the hydrophobic gas diffusion layer, the diffusion of gaseous reactants only a short distance to reach the catalyst electrically active surface sites (FIG. 1A). Oxygen reduction reaction (ORR) shows that the fuel cell, the catalyst layer of the gas diffusion reactant mass transport become limiting step in the cathode. ORR in order to improve performance, the fuel cell catalyst layer is designed to be hydrophobic balance, to help drain the water and hydrophilic, in order to maintain a sufficient ionic conductivity. With different oxygen reduction reaction generated water, CO2 reduction reaction requires water as a proton source hydrocarbon production. Thus, the catalyst layer is hydrophilic, fully hydrated during the reaction. In this structure, CO2 The electrochemical reaction takes place at the interface reaction gassed (Figure 1B). When the gaseous reactants and the electrolyte coexist in electrically active sites of the catalyst quickly decays into the volume of the electrolyte, the high pH used in particular in the alkaline electrolyte. At high current densities, due to local generation of OH-, decay further increased. Most catalyst is contacted with an electrolyte, wherein the effectiveness of carbon dioxide by its solubility limit (pH 15 to <2 mM)。由于析氢是一种竞争性的反应,与CO2在相同的应用电位范围内的还原作用类似,催化剂暴露在CO2耗尽的电解液中的大部分表面积促进了不需要的H2生成(图1C)。

创纪录的速度,把二氧化碳转化为乙烯!

创纪录的速度,把二氧化碳转化为乙烯!
FIG. 1 (A) a schematic flow cell. The reaction gas passes through the electrolyte facing the gasBackside gas diffusion electrode catalyst feed. Anion exchange membrane (AEM) OH facilitate transfer from the cathode to the anode. GDL, the gas diffusion layer. (B) a hydrophobic carrier diffusion in the carrier gas [G] is deposited sodium salt (GDE). (C) gaseous reactants, water and ions and the active site coexistence determines the maximum volume of gas available current electrolysis. Limited the concentration of the reaction catalyst zone promotes reaction by-products, such as hydrogen evolution. (D) When the gas and electrolyte transport (water and ion source) decoupling, three phase reaction interface can be extended, so that all the electrons are involved in the desired electrochemical reaction.

at the University of Toronto in Canada David Sinton and Edward H. Sargent and other researchers have proposed [ 123] a mixed catalyst design, by decoupling gas, transporting electrons and ions of the CO2 and CO can be efficiently performed in vapor-phase electrolysis> cm 2-a current density of 1 a region to generate a plurality of carbon products [ 123] . to the research entitled \”CO2 electrolysis to multicarbon products at activities greater than 1 Acm -2 \” in the title, published in the top international journal \” Science [ 123] \”on. Here, the researchers used herein, a Ionomer layer , having hydrophobic and hydrophilic functions, it can be assembled into domains having different form, thereby facilitating transport gas and metal ions in the surface route: transport gas through the pendant hydrophobic domain of promoting extension causing gas diffusion, and absorption of water and ion transport is performed (FIG. 1D) by hydration of the hydrophilic domains. Thus, these three components (gaseous reactants, ions and electrons) together are in interfacial reaction catalytically active sites, increases the length of the submicron range from a few microns. Catalyst 3D: ionomer planar heterojunction 创纪录的速度,把二氧化碳转化为乙烯!

Researchers trying to enhance the transmission system through an experimental design. ResearchersAttention to perfluorosulfonic acid (a PFSA) ion, which combination of hydrophobic and hydrophilic function and ion transport. Provided that they are controlled assembled into different layered hydrophobic and hydrophilic domains, will provide different routes facilitate gas transport, water and a hydrophilic domain facilitates ion transfer (FIG. 2A) by a hydrophobic domain. PFSA ion, such as the Nafion,-SO3-containing (hydrophilic) and -CF2 (hydrophobic) group. Nafion membrane material and the binder is catalyst a widely used fuel cell, has a strong structure – functional dependency. In a polar solvent. PFSA colloid-forming ions in a solvent exposed hydrophilic group -SO3-. When PFSA ion solution is coated on the surface of the metal catalyst, researchers expect -SO3- preferentially exposed polycrystalline metal surface hydrophilic, hydrophobic electrolyte to provide a continuous permeate channel (FIG. 2B) by -CF2 hydrophobic region.

FIG. 2 (A) is deposited on the hydrophobic polytetrafluoroethylene fiber support metal catalysts FIG. A layer evenly covering the flat metal ionomer layer. (B) perfluorinated ionomers, such as the Nafion, respectively exhibit different hydrophilic and hydrophobic properties imparted by -SO3- and -CF2 function.

创纪录的速度,把二氧化碳转化为乙烯! Researchers designed a new catalyst, with gas – separating the electrolyte beyond the two-dimensional transmission catalyst. Ideally, such a reaction catalyst to maximize the three-phase interface on a three-dimensional configuration, it is possible to efficiently run in a higher current region.
Researchers in the PTFE / Cu / ionomer (CIPH) of the gas diffusion layer supports the 3D Catalyst Preparation: ionomer bulk heterojunction (CIBH), which is made of copper nano-particles and mixing and injection molding the PFSA so formed with a metal ionomer morphology and 3D permeation path
(Figure 3A). Shows a cross-sectional SEM image of the catalyst in different layers CIBH (FIG. 3B). High-resolution TEM images using cryosections and energy dispersive X-ray spectroscopy elemental FIG obtained was further revealed a continuous and Cu nanoparticles (FIG. 3, C and D) from the present domain ionomer. Mer schematic metal catalyst from the heterojunction

FIG. 3 (A) polytetrafluoroethylene carrier. (B) CIBH catalyst is a cross-sectional SEM. (C and D) low shearCIBH sheet (C) and TEM image reveals CIBH nanotopography (D) of the elements Cu and C in FIG.

创纪录的速度,把二氧化碳转化为乙烯!
a record rate of catalysis

Researchers first by adjusting the deposition conditions, and Cu: blending ratio of ionomer to optimize CIBH morphology was found that the mass ratio of 4 : 3:00 is the best. With this ratio, the electrolytic solution in 7 M KOH and 50 cm3 min-1 CO2 flow rate, researchers have explored the effects of the thickness of the catalyst layer. In the active catalyst CIBH expected CO2RR current increases as catalyst loading increases, the length of the ionomer phase until gas permeation path reaches a diffusion length of the gaseous reactants. With increased catalyst loading and the respective thickness observed CO2RR total current monotonously increases, when the load is 3.33 mg cm-2 (5.7 μm thick) is more than 1 A cm-2, when the load reaches a higher saturated, current density 1.32 A cm-2 , and the energy efficiency drop (FIG. 3E). In 7 M KOH electrolyte solution, the best products at different CIBH catalyst showed that the current density distribution, from 0.2 to 1.5 A cm-2, H2 generation rate was maintained at 10% or less.

at the highest current operating conditions, the catalyst ethylene optimized for maximum yield of 65 to 75% , in the case where the cathode of the energy efficiency of 46.3%, the peak bias current density was 1.34 A cm- 2 (FIG. 3F). In thin flow cell for an optimal CIBH catalyst (no reference electrode, the smallest catholyte channels ≈ 3 mm, water is oxidized at the anode nickel foam), at 1.1 A cm-2 and no iR under compensation, on energy efficiency of the whole cell C2 + products is estimated at 20% (FIG. 3G). Current density portion FIG. 3 (E) Total CO2RR reaction, the energy efficiency of the cathode maximum C2 + and C2H4. Of 6 mm for the thickness exceeds CIBH, prior to the energy efficiency of the cathode drop, the total current CO2R saturated cm-2 at 1.3 A. Each sample was run and the operating conditions for at least 30 minutes. Electric highest score (F) eight kinds of catalyst Cu CIBHFlow configuration performance statistics. Performance (G) in the best catalyst CIBH a thin flow cell catholyte 3mm wide channel is comprised of.

创纪录的速度,把二氧化碳转化为乙烯!
Summary

from this study demonstrated the gas – ion – electron transport limitations catalyst design principles. CIBH catalyst at a desired operating current industrial applications, the electrochemical production of hydrocarbons renewables paved the way, as the solid oxide cell implemented as synthesis gas. Original link: https: //science.sciencemag.org/content/367/6478/661

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