CO2 electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt interface
18 May 2018-Science (American Association for the Advancement of Science)-Vol. 360, Iss: 6390, pp 783-787
TL;DR: A copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO2 to ethylene with 70% faradaic efficiency at a potential of −0.55 volts versus a reversible hydrogen electrode (RHE).
Abstract: Carbon dioxide (CO 2 ) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO 2 to ethylene with 70% faradaic efficiency at a potential of −0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO 2 reduction and carbon monoxide (CO)–CO coupling activation energy barriers; as a result, onset of ethylene evolution at −0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.
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TL;DR: In this paper, the authors present an approach for the herstellung of ethylen aus CO2 in an elektrochemischen hersteller. And this approach is based on the concept of Synthese-Struktur-Wirkungsbeziehungen.
Abstract: BMBF, 033RC004E, CO2Plus - Verbundvorhaben: eEthylen - Nutzung elektrischer Energie aus erneuerbaren Quellen zur elektrochemischen Herstellung von Ethylen aus CO2, Teilvorhaben 5: Charakterisierung und Testung fur Synthese-Struktur-Wirkungsbeziehungen
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TL;DR: In this paper , the authors proposed an efficient method for converting CO2 to biodegradable plastics via a systematic design of electrocatalysis, a chemical-biological interface, and microbes.
Abstract: •CO2 conversion via EMC2 intermediate•Soluble C2 intermediates play critical roles in the efficient integration•Systematic design enables continuous and rapid conversion of CO2 to bioproducts•EMC2 produces PHA with substantially improved productivity and product chain length The research uniquely addresses two daunting challenges our generation faces: global climate change and plastic waste accumulation. We demonstrated an efficient route for converting CO2 to biodegradable plastics via a systematic design of electrocatalysis, a chemical-biological interface, and microbes. The integration of chemical and biological conversions must overcome the intermediate incompatibility, the harsh chemical catalysis conditions, and the inefficient mass, energy, and electron transfers. This study overcomes these critical challenges by exploiting the soluble two-carbon molecules as intermediates from electrocatalytic CO2 reduction to bioconversion. These intermediates are better carriers for electrons and energy, facilitate mass transfer, and can readily enter primary metabolism as building blocks for bioproduction. Moreover, the systematic design achieved integrated, continuous, and rapid microbial biomass and PHA production from CO2 with record-level productivity. Integrating catalytic CO2 reduction with bioconversion could substantially advance carbon capture and utilization and mitigate climate change. However, the state-of-the-arts are limited by inefficient electron and mass transfers, unfavorable metabolic kinetics, and inadequate molecular building blocks. We overcome these barriers with the systematic design of electrocatalysis, a chemical-biological (chem-bio) interface, and microorganisms to enable efficient electro-microbial conversion with C2 (EMC2) intermediates. The soluble C2 intermediates can facilitate rapid mass transfer, readily enter primary metabolism, have less toxicity, carry more energy and electrons, and serve as better molecular building blocks for many microorganisms. The multi-tier chem-bio interface design delivered the EMC2 system to achieve 6 and 8 times increase of microbial biomass productivity compared to C1 intermediate and hydrogen-driven routes, respectively. The multi-module synthetic biology design produced medium-chain-length polyhydroxyalkanoates (PHAs), biodegradable polymers, representing much higher productivity and molecular chain length than the platforms based on C1 intermediates, hydrogen, or electrons. Integrating catalytic CO2 reduction with bioconversion could substantially advance carbon capture and utilization and mitigate climate change. However, the state-of-the-arts are limited by inefficient electron and mass transfers, unfavorable metabolic kinetics, and inadequate molecular building blocks. We overcome these barriers with the systematic design of electrocatalysis, a chemical-biological (chem-bio) interface, and microorganisms to enable efficient electro-microbial conversion with C2 (EMC2) intermediates. The soluble C2 intermediates can facilitate rapid mass transfer, readily enter primary metabolism, have less toxicity, carry more energy and electrons, and serve as better molecular building blocks for many microorganisms. The multi-tier chem-bio interface design delivered the EMC2 system to achieve 6 and 8 times increase of microbial biomass productivity compared to C1 intermediate and hydrogen-driven routes, respectively. The multi-module synthetic biology design produced medium-chain-length polyhydroxyalkanoates (PHAs), biodegradable polymers, representing much higher productivity and molecular chain length than the platforms based on C1 intermediates, hydrogen, or electrons. The synthesis of fuels, chemicals, and materials from CO2 is fundamental to human society.1Ort D.R. Merchant S.S. Alric J. Barkan A. Blankenship R.E. Bock R. Croce R. Hanson M.R. Hibberd J.M. Long S.P. et al.Redesigning photosynthesis to sustainably meet global food and bioenergy demand.Proc. Natl. Acad. Sci. USA. 2015; 112: 8529-8536https://doi.org/10.1073/pnas.1424031112Crossref PubMed Scopus (577) Google Scholar In the biosphere, plants, and algae convert CO2 through photosynthesis to macromolecules and diverse chemicals to sustain their own growth and feed other heterotrophic organisms. However, facing the increasing CO2 concentration caused by human activities, alternative CO2 conversion platforms were developed to mitigate the global climate change and manufacture valuable industrial products.2Hepburn C. Adlen E. Beddington J. Carter E.A. Fuss S. Mac Dowell N. Minx J.C. Smith P. Williams C.K. The technological and economic prospects for CO2 utilization and removal.Nature. 2019; 575: 87-97Crossref PubMed Scopus (755) Google Scholar Even though chemical synthesis has successfully converted CO2 into selective compounds (e.g., urea) at the commercial scale, the scope of diverse chemical compounds is still limited. Such challenge can be overcome via coupling electrochemical CO2 reduction with novel biological routes to produce macromolecules, polymers, and multi-carbon commodity chemicals, which leverages the diverse biosynthesis pathways while circumventing the low efficiencies in photosynthesis.3Zhang P. Dai S.Y. Yuan J.S. Producing the “molecules of life” from CO2 through hybrid catalytic relay.Chem. 2021; 7: 3200-3202https://doi.org/10.1016/j.chempr.2021.11.018Abstract Full Text Full Text PDF Scopus (4) Google Scholar,4Overa S. Feric T.G. Park A.-H.A. Jiao F. 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Integrated electromicrobial conversion of CO2 to higher alcohols.Science. 2012; 335: 1596https://doi.org/10.1126/science.1217643Crossref PubMed Scopus (520) Google Scholar The fundamental scientific barriers are therefore the identification and utilization of optimal electron carriers and carbon building blocks to enable microbial carbon fixation and bioproduction.6Claassens N.J. Sánchez-Andrea I. Sousa D.Z. Bar-Even A. Towards sustainable feedstocks: A guide to electron donors for microbial carbon fixation.Curr. Opin. Biotechnol. 2018; 50: 195-205https://doi.org/10.1016/j.copbio.2018.01.019Crossref PubMed Scopus (55) Google Scholar Earlier work has established that CO2 can be reduced to inorganic one-carbon (C1) intermediates such as CO or syngas at high Faradaic efficiency (FE) (route 1 in Figure 1A), which can be further fed to microorganisms for bioconversion.8Haas T. Krause R. Weber R. Demler M. Schmid G. Technical photosynthesis involving CO2 electrolysis and fermentation.Nat. Catal. 2018; 1: 32-39https://doi.org/10.1038/s41929-017-0005-1Crossref Scopus (351) Google Scholar Although the anaerobic CO-utilizers are energy efficient, the route is limited by the low gas-to-liquid transfer rate, the inadequate electron-carrying capacity of CO, limited strain choices and product profiles, and the often slower biomass growth and bioproduction rates than those of heterotrophic industrial microorganisms such as Pseudomonas putida (Figure 1A).9Abubackar H.N. Veiga M.C. Kennes C. Biological conversion of carbon monoxide: rich syngas or waste gases to bioethanol.Biofuels Bioprod. Bioref. 2011; 5: 93-114https://doi.org/10.1002/bbb.256Crossref Scopus (182) Google Scholar To overcome some of these challenges, prior work has established that CO2 can be electrocatalytically converted to soluble C1 electron carriers like formate for bioconversions (route 2A in Figure 1A). However, formate contains lower energy content than methanol and ethanol due to its chemical structure. C1 assimilation pathways like serine cycle can improve the formate utilization efficiency. The recently proposed synthetic reductive glycine pathway (rGlyP)10Bar-Even A. Formate assimilation: the metabolic architecture of natural and synthetic pathways.Biochemistry. 2016; 55: 3851-3863https://doi.org/10.1021/acs.biochem.6b00495Crossref PubMed Scopus (96) Google Scholar,11Claassens N.J. Bordanaba-Florit G. Cotton C.A.R. De Maria A. Finger-Bou M. Friedeheim L. Giner-Laguarda N. Munar-Palmer M. Newell W. Scarinci G. et al.Replacing the Calvin cycle with the reductive glycine pathway in Cupriavidus necator.Metab. Eng. 2020; 62: 30-41https://doi.org/10.1016/j.ymben.2020.08.004Crossref PubMed Scopus (56) Google Scholar,12Sánchez-Andrea I. Guedes I.A. Hornung B. Boeren S. Lawson C.E. Sousa D.Z. Bar-Even A. Claassens N.J. Stams A.J.M. The reductive glycine pathway allows autotrophic growth of Desulfovibrio desulfuricans.Nat. 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Catal. 2019; 2: 437-447https://doi.org/10.1038/s41929-019-0272-0Crossref Scopus (111) Google Scholar In particular, the relatively low energy content and limited electron capacity (Figure 1) make formate a less optimized substrate for aerobic fermentation. As compared to formate, methanol carries more electrons and energy content per carbon (route 2B in Figure 1A). However, the use of methanol as the electron carrier remains challenging. On one hand, the kinetics using NAD+ as the electron acceptor is often low due to the high redox potential of methanol oxidation.6Claassens N.J. Sánchez-Andrea I. Sousa D.Z. Bar-Even A. Towards sustainable feedstocks: A guide to electron donors for microbial carbon fixation.Curr. Opin. Biotechnol. 2018; 50: 195-205https://doi.org/10.1016/j.copbio.2018.01.019Crossref PubMed Scopus (55) Google Scholar On the hand, even though using quinone-dependent methanol dehydrogenase (MDH) can improve the kinetics, it lowers the overall energy efficiency due to the energy dissipation by quinones.14Claassens N.J. Cotton C.A.R. Kopljar D. Bar-Even A. Making quantitative sense of electromicrobial production.Nat. Catal. 2019; 2: 437-447https://doi.org/10.1038/s41929-019-0272-0Crossref Scopus (111) Google Scholar To overcome these challenges, an alternative route 2 is developed leveraging the cell-free system, where chemical catalysis is coupled with enzymatic catalysis to covert CO2 to starch.5Cai T. Sun H. Qiao J. Zhu L. Zhang F. Zhang J. Tang Z. Wei X. Yang J. Yuan Q. et al.Cell-free chemoenzymatic starch synthesis from carbon dioxide.Science. 2021; 373: 1523-1527https://doi.org/10.1126/science.abh4049Crossref PubMed Scopus (164) Google Scholar The chemo-enzymatic catalytic system advances the novel enzyme pathway design yet fails to achieve an integrated and continuous production. Moreover, the high temperature and harsh conditions in chemical catalysis are incompatible with biocatalysis, which leads to disjointed chemical and biological syntheses.3Zhang P. Dai S.Y. Yuan J.S. Producing the “molecules of life” from CO2 through hybrid catalytic relay.Chem. 2021; 7: 3200-3202https://doi.org/10.1016/j.chempr.2021.11.018Abstract Full Text Full Text PDF Scopus (4) Google Scholar,5Cai T. Sun H. Qiao J. Zhu L. Zhang F. Zhang J. Tang Z. Wei X. Yang J. Yuan Q. et al.Cell-free chemoenzymatic starch synthesis from carbon dioxide.Science. 2021; 373: 1523-1527https://doi.org/10.1126/science.abh4049Crossref PubMed Scopus (164) Google Scholar The enzyme catalysis steps by themselves are also separated, and the enzyme activity can only last for a few hours.5Cai T. Sun H. Qiao J. Zhu L. Zhang F. Zhang J. Tang Z. Wei X. Yang J. Yuan Q. et al.Cell-free chemoenzymatic starch synthesis from carbon dioxide.Science. 2021; 373: 1523-1527https://doi.org/10.1126/science.abh4049Crossref PubMed Scopus (164) Google Scholar Besides the catalytic CO2 reduction, another route relies on the direct or indirect usage of electrons from an electrode by microbes to reduce CO2 as the substrate in bioconversion (route 5 in Figure 1A). Even though studies have been carried to improve the energy efficiency in route 5, the process typically suffers from a limited electron transfer rate between the electrode and microorganism, and the products are often short-chain small molecules of limited applications, as the biochemical process often relies on the Wood-Ljungdahl pathway (W-L pathway).15Satanowski A. Bar-Even A. A one-carbon path for fixing CO2: C1 compounds, produced by chemical catalysis and upgraded via microbial fermentation, could become key intermediates in the valorization of CO2 into commodity chemicals.EMBO Rep. 2020; 21e50273https://doi.org/10.15252/embr.202050273Crossref PubMed Scopus (21) Google Scholar,16Anwer A.H. Khan N. Umar M.F. Rafatullah M. Khan M.Z. Electrodeposited hybrid biocathode-based CO2 reduction via microbial electro-catalysis to biofuels.Membranes. 2021; 11: 223https://doi.org/10.3390/membranes11030223Crossref PubMed Scopus (6) Google Scholar The system thus requires large surface area with low volumetric productivity and is limited to selective microorganisms such as chemolithotrophic, exoelectrogenic, and acetogenic microbes.17Prévoteau A. Carvajal-Arroyo J.M. Ganigué R. Rabaey K. Microbial electrosynthesis from CO2: forever a promise?.Curr. Opin. Biotechnol. 2020; 62: 48-57Crossref PubMed Scopus (173) Google Scholar Furthermore, another route (route 6, Figure 1A) to bypass the catalytic CO2 reduction utilizes electrochemically generated hydrogen as electron carrier to drive CO2 conversion in Ralstonia eutropha (also known as Cupriavidus necator).18Liu C. Colón B.C. Ziesack M. Silver P.A. Nocera D.G. Water splitting–biosynthetic system with CO2 reduction efficiencies exceeding photosynthesis.Science. 2016; 352: 1210-1213https://doi.org/10.1126/science.aaf5039Crossref PubMed Scopus (633) Google Scholar However, the carbon fixation rate, titer, and production efficiency of hydrogen-driven fermentation are fundamentally limited by the gas-to-liquid transfer rate, the slow hydrogen oxidation, Calvin-Benson cycle intermediate regeneration, and RuBisCo carbon fixation.6Claassens N.J. Sánchez-Andrea I. Sousa D.Z. Bar-Even A. Towards sustainable feedstocks: A guide to electron donors for microbial carbon fixation.Curr. Opin. Biotechnol. 2018; 50: 195-205https://doi.org/10.1016/j.copbio.2018.01.019Crossref PubMed Scopus (55) Google Scholar The choice of microbial species in route 6 is also limited due to the hydrogenotrophic growth.3Zhang P. Dai S.Y. Yuan J.S. Producing the “molecules of life” from CO2 through hybrid catalytic relay.Chem. 2021; 7: 3200-3202https://doi.org/10.1016/j.chempr.2021.11.018Abstract Full Text Full Text PDF Scopus (4) Google Scholar Recent advances in electrochemical CO2 reduction to C2 products using copper-based catalysts have opened new avenues to address the challenges in the previous chemical-biological (chem-bio) routes for CO2 fixation.19Dinh C.T. Burdyny T. Kibria M.G. Seifitokaldani A. Gabardo C.M. García de Arquer F.P. Kiani A. Edwards J.P. De Luna P. Bushuyev O.S. et al.CO2 electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt interface.Science. 2018; 360: 783-787https://doi.org/10.1126/science.aas9100Crossref PubMed Scopus (1228) Google Scholar,20Wang X. Wang Z. García de Arquer F.P. Dinh C.-T. Ozden A. Li Y.C. Nam D.-H. Li J. Liu Y.-S. Wicks J. et al.Efficient electrically powered CO2-to-ethanol via suppression of deoxygenation.Nat. Energy. 2020; 5: 478-486https://doi.org/10.1038/s41560-020-0607-8Crossref Scopus (252) Google Scholar,21Overa S. Ko B.H. Zhao Y. Jiao F. Electrochemical approaches for CO2 conversion to chemicals: a journey toward practical applications.Acc. Chem. Res. 2022; 55: 638-648https://doi.org/10.1021/acs.accounts.1c00674Crossref PubMed Scopus (45) Google Scholar,22Kuhl K.P. Cave E.R. Abram D.N. Jaramillo T.F. New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces.Energy Environ. Sci. 2012; 5: 7050-7059https://doi.org/10.1039/c2ee21234jCrossref Scopus (2046) Google Scholar,23Gu Z. Shen H. Chen Z. Yang Y. Yang C. Ji Y. Wang Y. Zhu C. Liu J. Li J. et al.Efficient electrocatalytic CO2 reduction to C2+ alcohols at defect-site-rich Cu Surface.Joule. 2021; 5: 429-440https://doi.org/10.1016/j.joule.2020.12.011Abstract Full Text Full Text PDF Scopus (102) Google Scholar Even though some C2 products like ethylene (route 3 in Figure 1A) are not amenable to bioconversion, others like ethanol (route 4A in Figure 1A) and acetate (route 4B in Figure 1A) can serve as substrates for broader bioconversion application.24Zhu Q. Sun X. Yang D. Ma J. Kang X. Zheng L. Zhang J. Wu Z. Han B. Carbon dioxide electroreduction to C2 products over copper-cuprous oxide derived from electrosynthesized copper complex.Nat. Commun. 2019; 10: 3851https://doi.org/10.1038/s41467-019-11599-7Crossref PubMed Scopus (217) Google Scholar Both compounds carry more energy and have better electron donation capacity than CO and formate.14Claassens N.J. Cotton C.A.R. Kopljar D. Bar-Even A. Making quantitative sense of electromicrobial production.Nat. Catal. 2019; 2: 437-447https://doi.org/10.1038/s41929-019-0272-0Crossref Scopus (111) Google Scholar The acetate and ethanol both can be converted to acetyl-CoA with two to three steps and enter primary metabolism rapidly to serve as energy sources and metabolic building blocks (route 4, Figure 1A). The fewer steps and favorable kinetics to convert C2 intermediates to acetyl-CoA empower these molecules to be better molecular building blocks for the synthesis of bioproducts with longer carbon chain. The metabolic kinetics of C2 intermediates could enable a new electro-microbial system with much faster conversion, more rapid cell growth, higher bioproduct yield and titer, broader species adaptation, and better biocompatibility than the current systems (routes 1, 2, 5, and 6 in Figure 1A; Table S2). Even though previous studies achieved multi-step microbial systems using C2 intermediates produced from bioconversion,25Hu P. Chakraborty S. Kumar A. Woolston B. Liu H. Emerson D. Stephanopoulos G. Integrated bioprocess for conversion of gaseous substrates to liquids.Proc. Natl. Acad. Sci. USA. 2016; 113: 3773-3778https://doi.org/10.1073/pnas.1516867113Crossref PubMed Scopus (125) Google Scholar,26Lehtinen T. Efimova E. Tremblay P.-L. Santala S. Zhang T. Santala V. Production of long chain alkyl esters from carbon dioxide and electricity by a two-stage bacterial process.Bioresour. Technol. 2017; 243: 30-36https://doi.org/10.1016/j.biortech.2017.06.073Crossref PubMed Scopus (35) Google Scholar,27Al Rowaihi I.S. Kick B. Grötzinger S.W. Burger C. Karan R. Weuster-Botz D. Eppinger J. Arold S.T. A two-stage biological gas to liquid transfer process to convert carbon dioxide into bioplastic.Bioresour. Technol. Rep. 2018; 1: 61-68https://doi.org/10.1016/j.biteb.2018.02.007Crossref Scopus (19) Google Scholar the direct electrocatalytic CO2 reduction to C2+ products allows us to maximize the benefits of electrocatalytic step for electron carrying, improve the system efficiency, and drastically increase bioproduction rate. Despite the potential, such integration between electrocatalysis and microbial conversion has not been achieved before. No study has established the scientific concept of such a new system, demonstrated feasibility, or overcame the challenges in the chem-bio interface to achieve integrated and continuous production. In this study, we have designed and implemented a novel route (route 4 in Figure 1A), namely electro-microbial conversion with C2 (EMC2) intermediates. EMC2 achieved seamless and systematic integration of electrocatalysis and bioconversion at chemical, cellular, and process levels, enabling continuous production. With this system, we have demonstrated the efficient electro-microbial CO2 conversion using a broadly adopted industrial microorganism, Pseudomonas putida. The innovative EMC2 platform achieved significantly improved cell biomass growth and bioproduct productivity as compared to other state-of-the-art routes (routes 1, 2, 5, and 6) and photosynthetic systems. The study highlighted the broad applicability of the EMC2 system in carbon fixation and conversion to macromolecule products. Even though acetate and ethanol are much better electron carriers and carbon intermediates than C1 compounds (Figure 1A), an efficient EMC2 system requires a four-tier design to achieve the integration of electrochemical CO2 reduction reaction (CO2RR) and the microbial conversion (Figure 1B). The first tier focuses on electrocatalysis, where the design and selection of electrolyzer, catalysts, and electrolytes need to ensure the efficient electrocatalytic CO2RR to C2 products under biocompatible conditions. The second tier is the design of a chem-bio interface to make sure that microbial conversion does not interfere with CO2RR (Figure 1B). The third tier is the design of an integrated EMC2 system to achieve efficient mass transfer of C2 products between electrocatalysis and fermentation (Figure 1B). The fourth tier is the microbial design to efficiently channel the C2 compounds to the tricarboxylic acid (TCA) cycle and to enhance the carbon flux toward target bioproducts (Figure 1B). The four-tier design will achieve complete and efficient electrotrophic microbial conversion of CO2, where ethanol and acetate will carry the electrons and carbon from electrocatalytic CO2RR to drive bioconversion. As the starting point to convert CO2 to C2 intermediates, electrocatalysis design is critical to generate sufficient C2 products for microbial conversion under bio-amicable conditions. These constraints require the integrated design and selection of electrolyzer, electrolytes, and catalysts (Figure 2A). First, a flow electrolyzer equipped with gas diffusion electrodes (GDEs) was selected for C2 production, considering the potentially high yield of C2 products (Figure 2A). We found that flow cells with GDE setting can achieve much higher current density and C2 product content than the conventional electrocatalysis with H-cell, as the CO2 feeding to GDE is not limited.21Overa S. Ko B.H. Zhao Y. Jiao F. Electrochemical approaches for CO2 conversion to chemicals: a journey toward practical applications.Acc. Chem. Res. 2022; 55: 638-648https://doi.org/10.1021/acs.accounts.1c00674Crossref PubMed Scopus (45) Google Scholar,28Lees E.W. Mowbray B.A.W. Parlane F.G.L. Berlinguette C.P. Gas diffusion electrodes and membranes for CO2 reduction electrolysers.Nat. Rev. Mater. 2022; 7: 55-64https://doi.org/10.1038/s41578-021-00356-2Crossref Scopus (105) Google Scholar Second, the selection of electrolytes is critical. When the flow electrolyzer is used for CO2RR, the whole chem-bio system will operate in a cascade mode with salt solution flows between the electrocatalysis and bioconversion. The same salt solution will serve as the catholyte for electrocatalysis and the media to support microbial growth. The electrolyte thus needs to be suited for both electrocatalysis and cell cultivation. Frequently used CO2RR electrolytes such as extreme alkaline solutions are not amenable to microorganism growth. Considering that the microbes need a neutral and stable pH environment, we investigated the CO2RR reaction in two solutions. The first one is the bicarbonate solution that contained mixed NaHCO3 and KHCO3 with Na/K ratio suitable for microbial growth and also was proven effective for CO2RR.29Ren S. Joulié D. Salvatore D. Torbensen K. Wang M. Robert M. Berlinguette C.P. Molecular electrocatalysts can mediate fast, selective CO2 reduction in a flow cell.Science. 2019; 365: 367-369https://doi.org/10.1126/science.aax4608Crossref PubMed Scopus (442) Google Scholar The second one is a “basal” solution mainly composed of phosphate buffer (NaH2PO4 + K2HPO4 + NaCl), which is widely used in fermentation, but not electrocatalysis. We have maintained both solutions at pH close to 7 to allow bioconversion integration, and the total ion concentrations in both solutions are kept the same to minimize the differences of resistance. To evaluate bioconversion compatibility, we first compared the microbial growth in the two electrolytes using ethanol as the primary carbon source. Although the pH of the bicarbonate solution was 7.2 (with CO2 and air bubbling), the cell growth of P. putida remained to be minimal after 72 h. While in the basal solution, the P. putida had shown significant growth within 24 h (Figure 2B). We therefore prioritized the basal solution as the electrolyte and compared the catalytic performances in both bicarbonate solution and basal solution to identify the best catalysts. Third, the design and configuration of catalysts are critical for C2 productivity, especially in biologically compatible conditions. We first investigated several typical CO2RR catalysts including CuO, Cu2O, and Cu–B (copper reduced by NaBH4), yet none of them achieved appreciable ethanol or C2 productivity when the basal solution was used as the electrolyte. These catalysts showed higher production of hydrogen, formate, and other C1 compounds (Figure S1). It is likely that these catalysts will undergo reduction and surface reconstruction in the electrocatalysis process. The strongly coordinating phosphate anions in the electrolyte could interact substantially with copper species in the catalysts and alternate their surface properties, which favor the generation of C1 products such as formate as well as hydrogen.30Zhao J. Sun L. Canepa S. Sun H. Yesibolati M.N. Sherburne M. Xu R. Sritharan T. Loo J.S.C. Ager III, J.W. et al.Phosphate tuned copper electrodeposition and promoted formic acid selectivity for carbon dioxide reduction.J. Mater. Chem. A. 2017; 5: 11905-11916https://doi.org/10.1039/C7TA01871ACrossref Google Scholar Based on these discoveries, we hypothesized that the metallic copper-based catalysts could maintain better catalytic properties under phosphate electrolyte, as metallic copper has more stable surface properties than the oxide-based or chemically pre-reduced copper catalysts.31Nitopi S. Bertheussen E. Scott S.B. Liu X. Engstfeld A.K. Horch S. Seger B. Stephens I.E.L. Chan K. Hahn C. et al.Progress and perspectives of electrochemical CO2 reduction on copper in aqueous electrolyte.Chem. Rev. 2019; 119: 7610-7672https://doi.org/10.1021/acs.chemrev.8b00705Crossref PubMed Scopus (1774) Google Scholar Besides the catalyst, another important consideration is the suitable configuration of the cathode in a flow cell to achieve sufficient gas diffusion. The sputtering method thus was adopted to direct deposit Cu catalysts on gas diffusion materials, as the method allows direct coating of a thin layer of metals on the substrates, forming a continuous and conductive layer. Moreover, the sputtering method enables the selection of various porous substrates as gas diffusion layers (GDLs), including both conductive and non-conductive ones, for building the GDE. Two Cu-based GDEs were designed by sputtering Cu on porous polytetrafluoroethylene film (PTFE film, the derived GDE catalyst is denoted as Cu/PTFE) and carbon paper (Sigracet 28 BC, the derived GDE catalyst is denoted as Cu/28BC), respectively. Scanning electronic microscope (SEM) images confirmed that the Cu layers were uniformly coated around the GDLs (Figures 2C and 2D). Although their morphologies vary due to the original substrates, powder X-ray diffraction (XRD) analysis showed that the ratios of Cu (111) to Cu (100) facets were the same on the two copper GDEs (Figure 2E), proving that the sputtering method is reliable and repeatable for fabricating catalytic electrodes. We then evaluated the CO2RR performances of these cathode designs in biocompatible phosphate electrolytes (basal solution) and electrocatalysis-favorable bicarbonate electrolytes. Figure 2F shows the FE for CO2RR products in the two electrolytes at the current densities ranging from 100 to 200 mA cm−2, which are comparable to industrial relevant current densities. In both electrolytes, Cu-based catalytic GDEs showed significant CO2 conversion to various C2 products. The main soluble C2 product was ethanol, while a small amount of acetate and 1-propanol was co-produced. Compared to the bicarbonate solution (left group, Figure 2F), the reaction in phosphate-based solution showed a higher FE of ethylene production but a lower concentration of the soluble C2 (middle group, Figure 2F). However, the total FE for soluble C2 products still reached around 15%, indicating that CO2RR in phosphate electrolytes could produce sufficient C2 intermediates for subsequent fermentation. Considering that P. putida grows much better in the basal solution (Figure 2B), the basal solution was selected as the primary electrolyte for CO2RR. With t
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TL;DR: In this paper, the microenvironment in the catalyst layer for CO2 electrolysis, including typical mass transport models for CO 2 reduction in H-type cells and GDE flow cells, the effect of a hydrophobic microenvironment on CO2 mass transport and catalytic performance, and the formation of a gas/liquid balance and solid-liquid-gas interfaces are discussed.
10 citations
TL;DR: In this article, a hybrid-catalyst that firmly anchors 2D-Cu metallic dots on F-doped CuxO nanoplates (CuxOF), synthesized by electrochemical-transformation under the same conditions as the targeted CO2RR, was reported.
Abstract: Copper-based catalysts are efficient for CO2 reduction affording commodity chemicals. However, Cu(I) active species are easily reduced to Cu(0) during the CO2RR, leading to a rapid decay of catalytic performance. Herein, we report a hybrid-catalyst that firmly anchors 2D-Cu metallic dots on F-doped CuxO nanoplates (CuxOF), synthesized by electrochemical-transformation under the same conditions as the targeted CO2RR. The as-prepared Cu/CuxOF hybrid showed unusual catalytic activity towards the CO2RR for CH3COO− generation, with a high FE of 27% at extremely low potentials. The combined experimental and theoretical results show that nanoscale hybridization engenders an effective s,p-d coupling in Cu/CuxOF, raising the d-band center of Cu and thus enhancing electroactivity and selectivity for the acetate formation. This work highlights the use of electronic interactions to bias a hybrid catalyst towards a particular pathway, which is critical for tuning the activity and selectivity of copper-based catalysts for the CO2RR.
10 citations
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TL;DR: A simple derivation of a simple GGA is presented, in which all parameters (other than those in LSD) are fundamental constants, and only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked.
Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif
146,533 citations
TL;DR: An efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set is presented and the application of Pulay's DIIS method to the iterative diagonalization of large matrices will be discussed.
Abstract: We present an efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrices will be discussed. Our approach is stable, reliable, and minimizes the number of order ${\mathit{N}}_{\mathrm{atoms}}^{3}$ operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special ``metric'' and a special ``preconditioning'' optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calculations. It will be shown that the number of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order ${\mathit{N}}_{\mathrm{atoms}}^{2}$ scaling is found for systems containing up to 1000 electrons. If we take into account that the number of k points can be decreased linearly with the system size, the overall scaling can approach ${\mathit{N}}_{\mathrm{atoms}}$. We have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable. \textcopyright{} 1996 The American Physical Society.
81,985 citations
TL;DR: In this paper, the formal relationship between US Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived and the Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional.
Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.
57,691 citations
TL;DR: An improved way of estimating the local tangent in the nudged elastic band method for finding minimum energy paths is presented, and examples given where a complementary method, the dimer method, is used to efficiently converge to the saddle point.
Abstract: An improved way of estimating the local tangent in the nudged elastic band method for finding minimum energy paths is presented. In systems where the force along the minimum energy path is large compared to the restoring force perpendicular to the path and when many images of the system are included in the elastic band, kinks can develop and prevent the band from converging to the minimum energy path. We show how the kinks arise and present an improved way of estimating the local tangent which solves the problem. The task of finding an accurate energy and configuration for the saddle point is also discussed and examples given where a complementary method, the dimer method, is used to efficiently converge to the saddle point. Both methods only require the first derivative of the energy and can, therefore, easily be applied in plane wave based density-functional theory calculations. Examples are given from studies of the exchange diffusion mechanism in a Si crystal, Al addimer formation on the Al(100) surfa...
6,825 citations
TL;DR: This paper describes how accurate off-lattice ascent paths can be represented with respect to the grid points, and maintains the efficient linear scaling of an earlier version of the algorithm, and eliminates a tendency for the Bader surfaces to be aligned along the grid directions.
Abstract: A computational method for partitioning a charge density grid into Bader volumes is presented which is efficient, robust, and scales linearly with the number of grid points. The partitioning algorithm follows the steepest ascent paths along the charge density gradient from grid point to grid point until a charge density maximum is reached. In this paper, we describe how accurate off-lattice ascent paths can be represented with respect to the grid points. This improvement maintains the efficient linear scaling of an earlier version of the algorithm, and eliminates a tendency for the Bader surfaces to be aligned along the grid directions. As the algorithm assigns grid points to charge density maxima, subsequent paths are terminated when they reach previously assigned grid points. It is this grid-based approach which gives the algorithm its efficiency, and allows for the analysis of the large grids generated from plane-wave-based density functional theory calculations.
5,417 citations