G. Schmid, M. Fleischer, K. Wiesner, R. Krause CT NTF COS November 04, 2014 Electrochemical Reduction of CO2 Restricted © Siemens AG 2014. All rights reserved Power to Value Compound based Energy Storage CO2ToValue Overcapacity of Renewable Electricity CO2 from fossil-fired power plants + Electrocatalysis Synthetic fuels or chemical feedstock Methane (CH4) Market Price 81 €/t Market Volume > 2400 Mt/y Page 2 Oct. 13, 2014 Ethylene (C2H4) 1000 €/t 141 Mt/y Corporate Technology Formic acid (HCOOH) 0.7 Mt/y Carbon monoxide (CO) 650 €/t (+ H2 Naphtha) > 210 000 Mt/y Restricted © Siemens AG 2014. All rights reserved Remarks: Power-to-Gas The Ideas behind CO2-to-Value CO2ToValue Stromspeicherung Fossile gas ~ 81€/t Verstromung H2 difficult to store Heat of combustion + 286 kJ H2 + ½ O2 → H2O CH4 + 3 O2 → 2 H2O + CO2 + 890 kJ Combustion stability of the net 2% max. H2 addition/perfect mixing 2.9% (price increase for customer) (not 8% as technical feasible) Energy storage with H2 reduction is very attractive from energetic considerations, but low attractive from economic considerations What can we do with electrochemistry to overcome such problems Page 3 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved Complexity Analysis Direct catalytic reduction of CO2 CO2ToValue CO2+ 2H2O C2H4 + 3/2O2 Electrolyte Vision Photocatalysis • diluted CO2 (350 ppm) • Protons from water • Electrons from oxygen • presence of O2 (air) • all energy from photons • enrichment, separation, collection in one unit • distributed and not stationary • autarkic Page 4 Oct. 13, 2014 Simplification • conc. CO2 (20 – 100 %) (up to 50000 t/day/plant) • H2 as such • inert (no competitive back - reaction) • energy from photons & electro-assistance • stationary • separation of products & educts can be solved (process flow) Corporate Technology Photo catalytic Reaction Center • all on one micro particle very complex • CO2-reduction catalyst • H2O/CO2-oxidation catalyst • (add O2 non-sensitivity) • photo-sensitizer dye • catalysts for consecutive reactions @ high temp. • Keys energy-level alignment yield CH4, CH3OH, C2H4 Electro assisted Photocatalysis & electro catalysis • published photo anodes & cathodes relay on photo assistance • reduction & oxidation catalyst separated • electrolyte determines products & yield • highest projected efficiency • Intermediate business case ? CO2- Electrolyzer (I) Energy Storage Carbon Capture (E) Restricted © Siemens AG 2014. All rights reserved CO2-Electrolyser – basic principle CO2ToValue Possible Products Electrolyzer Carbon dioxide (CO2) Ethylene (C2H4) Separated by • 34,032 million tons carbon dioxide (CO2) were emitted for energetic usage in 2011 Carbon monoxide (CO) post combustion carbon capture process Methane (CH4) • F.e. Germany’s biggest power station Niederaussem emitted 26 million tons in 2011 Formic acid (HCOOH) Renewable electricity • Excess energy of 10 TWh can be expected Page 5 Oct. 13, 2014 • High Faradic Efficiencies Current Eff. > 90% • Low power consumption System Eff. > 50% • High turnover rates current densities > 0.3A/cm² • Long lifetime > 4000h Corporate Technology Methanol (CH3OH) Ethanol (C2H5OH) Depending on catalyst Restricted © Siemens AG 2014. All rights reserved CO2 reduction on metal electrodes in aqueous CO2ToValue [1] Y. Hori, Electrochemical CO2 reduction on metal electrodes, in: C. Vayenas, et al. (Eds.), Modern Aspects of Electrochemistry, Springer, New York, 2008, pp. 89–189. • CO2 can be reduced at metal electrodes in aqueous solution • Copper leads to a variety of different hydrocarbons • For some metals hydrogen evolution is dominating in aqueous media Page 6 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved Electrochemical Conversion of CO2 Basic Considerations - economic CO2ToValue Ethylene: Single Step Process - 1 electrochemical Anode 2 + CO2 2 Cathode 3 H2O + aequeous electrolyte Copper electrode O2 C2H4 Ethylene ~ 1000€/t CO: Three Step Process - 2 electrochemical + 1 thermal Anode Cathode ½ CO2 Different electrolytes and electrodes Fischer-Tropsch Verfahren + O2 CO Zn: Methanol Fe: Hydrocarbons ½ H2O Page 7 Different electrolytes Oct. 13, 2014 Corporate Technology and electrodes + i.e. Naphtha (~ 650 €/t) O2 H2 Restricted © Siemens AG 2014. All rights reserved Electrochemical Conversion of CO2 Basic Considerations - Efficiency CO2ToValue Goal for 2015 Higher current density Target Efficiency improvement • Efficiency improvement • Higher current density for unchanged product composition • Lab-scale product feasibility demonstrated, but not on an industrial-relevant level Page 8 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved Topic of Current Development Build up of “high pressure” setup (30 bar) • The increased pressure leads to an increased concentration of CO2 • But also the decreased volume of the reduction products will help to increase current densities Electrode development • Development of a catalyst system of (binary/ternary) electrode & electrolyte system with a stable product composition & long lifetime Page 9 Oct. 13, 2014 Corporate Technology CO2ToValue Ionic liquids as electrolyte • IL’s seems to be an ideal alternative to water as electrolyte • Higher solubility of CO2 compared to water • Reduction of over potentials (catalytic activity) • Suppression of H2-evolution Gas diffusion Electrodes • High concentration of gaseous CO2 at the three-phase interface (gas/solution/solid) should help to increase selectivity of ethylene Restricted © Siemens AG 2014. All rights reserved CO2ToValue Electrochemical Reduction of CO2 to CO Page 10 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved Flow Cell-Setup - Overview CO2ToValue Siemens flow cell setup Anolyte cycle Catholyte cycle Product exit Gas Separation O2 exit Gas Separation Anode Cathode CO2-Saturation CO2 Peristaltic pump • No gasses in the electrolytic chamber (catholyte will be saturated with CO2 before) • Pressurized system up to several bars M. Alvarez-Guerra, S. Quintanilla, and A. Irabien, Chemical Engineering Journal 207, 278 - 284 (2012). • Peristaltic pump to control Catholyte flow Page 11 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved Medium Pressure CO2-Electrolysis CO2ToValue Setup of our current “1 bar” setup Picture of the cell Gas separation Gas/Electrolyte outlet Gas inlet Electrolyte outlet IEM Gas-Diffusion-Electrode Full SYSTEM includes pumps, gas separation etc. Gas Diffusion Electrode for high current densities Page 12 Oct. 13, 2014 CO2 (g) (g) (l) (s) 3-phase reaction center (l) Gas inlet Porous Agmembrane Corporate Technology Electrolyte inlet Restricted © Siemens AG 2014. All rights reserved How to increase system efficiency? O2 A N O D E H+ H2O / CO2 C A T H O D E Reduction of over potential • By choice of hydrogen ion activity (pH) and salt anion / cation of anolyte and catholyte 1.5 1.0 E0 [V vs. SHE] H2, C2H4 CO, CH4 CO2ToValue E0=-1.31V 0.5 0.0 Reduction Oxidation -0.5 -1.0 Utotal = Uanode + Uelectrolyte + Unafion + Ucathode Reduction of IR-drop over electrolyte at high current densities • Reduced distance between electrodes • Increased conductivity (increased salt amount, increased temperature) U electrolyte Page 13 =U Anolyte +U Oct. 13, 2014 Catholyte 0 2 4 6 8 10 12 14 pH 10 mm to 2.5mm ~10 mS/cm to ~380mS/cm ⋅ l ⋅ I = ρ +ρ Anolyte Catholyte A Corporate Technology Restricted © Siemens AG 2014. All rights reserved Optimization of System Efficiency (chemical approach) CO2ToValue Current density / mA cm-2 Current voltage characteristics Catholyt / Anolyte 0 -200 -400 0.1 M KHCO3 / 0.1 M KHCO3 10 mS/cm / 10 mS/cm @ -3.0 V: -7 mA/cm² -33 mA/cm² -71 mA/cm² -88 mA/cm² 0.5 M K2SO4 / 2.5 M KOH 72 mS/cm / 380 mS/cm 3.0 M KBr pH3 (H2SO4) / 2.5 M KOH 315 mS/cm / 380 mS/cm -600 -1.5 -3.0 -4.5 -6.0 Cell potential / V 4.0 M KBr pH3 (H2SO4) / 2.5 M KOH 379 mS/cm / 380 mS/cm Conclusions • Current densities can be raised, by increasing electrolyte conductivities (thus decreasing IR Drop) • For electrical conductivities > 350 mS/cm, the current densities can be increased up to 600 mA/cm² • For high current densities the I-V-curve gets rippled, due to the occurring high gas evolution at the electrode surfaces and the pulsed electrolyte flow, caused by the diaphragm pump Page 14 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved Toward Industrial Relevant Systems CO2ToValue Current density [mA/cm²] Current-Voltage characteristics 0 pH -100 conductivity -200 FY 13 FY 14 -300 -400 -6 -4 -2 0 Potential between Anode and Cathode [V] • By using Gas Diffusion Electrodes the current densities before hydrogen evolution becomes dominating can be increased • To increase system efficiency the system voltage was reduced by decreasing electrode distance (10 mm to 2.5 mm), increasing conductivity (10 mS/cm to ~300 mS/cm) and optimizing pH of electrolyte • The solubility of CO2 seems to play no role for the GDE approach • Further optimization potential is CO2 flow through GDE, increased pressure and choice of electrolyte Current Efficiency [%] 100 U: 4.0 V J: 4.5 mA/cm² A: 5.3 cm² FE: 88% SE: 29% 75 FE - H2 50 FE - CO 25 0 0 4V 5 10 15 20 Current Density [mA] Page 15 Oct. 13, 2014 10V 25 Corporate Technology GDE (2014 - no optimum) norm. Faradic Efficiency [%] Solid electrode (2013) 100 80 60 40 20 0 2V 0 U: 2.5 V J: 48.2 mA/cm² H2 A: 9 cm² CO FE: 93% 4.5V SE: 49% 50 100 150 200 Current density [mA/cm²] Restricted © Siemens AG 2014. All rights reserved CO2 reduction to CO at silver cathode CO2ToValue norm. Efficiency of CO [%] 100 80 60 40 20 0 ca. 10V 5 mA/cm² 9% SE September 2 2013 April 1 2013 • Simple U-tube • First proof of CO Page 16 Oct. 13, 2014 4V 5 mA/cm² 29% SE • Flow cell • Continuous production • 1cm distance Corporate Technology 2.5V 49 mA/cm² 49% SE 3.25V 110 mA/cm² 40% SE January 3 2014 February 4 2014 • 2.5mm distance • Gas diffusion electrode • Optimized electrolyte • Optimized gas and electrolyte flow Restricted © Siemens AG 2014. All rights reserved High pressure electrolysis setup CO2ToValue Electrolyte reservoir with gas separation Electrolysis cell WADose HPLC pump Anolyte circle Page 17 Oct. 13, 2014 Catholyte circle Corporate Technology mini Cori-Flow - mass flow meter Restricted © Siemens AG 2014. All rights reserved Alternative electrolytes (f.e. ionic liquids, solvents) CO2ToValue Characterization setup for small volume Cathode CO2 inlet Example: Anode CO2 Reduction Reference electrode Gas outlet H2 CO • Ionic liquids (IL) saturated with CO2 show an reduction to CO with high Faradic Eff. (~80%) and high Selectivity (nearly 100%) at reduced voltages, no hydrogen evolution was observed • Test of several ionic liquids showed promising candidates with broad electrochemically stable window • Optimization and long term evaluation in progress Page 18 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved CO2ToValue Electrochemical Reduction of CO2 to C2H4 Page 19 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved CO2 reduction on copper electrodes Products of CO2 reduction on copper Reduction products @ -1.1V vs. RHE: Major products Hydrogen Methane Formate CO Ethylene CO2ToValue K. P. Kuhl, E. R. Cave, D. N. Abram, and T. F. Jaramillo, Energy und Environmental Science 5, 7050 - 7059 (2012). 22% 24% 2% 2% 22% Indermediate products Ethanol 9% n-Propanol 2% Allyl alcohol 1% Minor products Methanol Glycoaldehyde Acetaldehyde Acetate Ethylene glycol Propionaldehyde Acetone Hydroxyacetone Page 20 Oct. 13, 2014 Corporate Technology 0.1% 0.5% 0.3% 0.1% 0.15% 0.01% 0.05% 0.01% Restricted © Siemens AG 2014. All rights reserved Ethylene Formation at Copper Based Electrodes CO2ToValue CO2 is selectively reduced to C2H4 Hero Data (solid electrode) In the beginning no CO2 reduction can be found 100 H2 CO CH4 C2H4 FE ges FE / % 80 60 40 Reproduction runs showed reproducible values Nearly no CO und CH4 products were found Stability over time Identification of the “real” catalyst ? 20 0 After 30 min. the maximum FE of C2H4 is up to 45 decreases over time, while hydrogen evolution increases (overall current increases) Stabilization of the “real” catalyst ? 0 30 60 90 120 t / min 150 180 Electrode formation ? Electrode morphology ? Transfer of catalyst to GDE possible Page 21 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved Summary CO2-Electrolysis CO2ToValue CO2 – Reduction to CO • Current densities and system efficiencies can be raised by increasing electrolyte conductivities • Increase of CO2 gas flow allows a reduction to CO at higher current densities • Increase of electrolyte flow increases achievable current densities • Product gas separation has to be improved • Gas-Diffusion-Electrodes with lower overpotential for CO and higher overpotential for H2 will improve selectivity CO2 – Reduction to C2H4 • Faraday efficiencies of ~ 40% were achieved for the C2H4 formation at solid, but nanofunctionalized copper electrodes • Copper alloys (Sn, Zn, Al and their mixture) show also C2H4 formation. • Stability of Electrodes under investigation • Transfer of catalyst to Gas-Diffusion-Electrode started / Switching to flow cells in progress Page 22 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved (Earth-) Alkali Metal Combustion Potential implementation matrix recycling CO2ToValue Charged energy carrier (seasonal) Option 1 Lithium Option 2 combustion combustion CO2 N2 (air) Electrical LiCl Electrolysis Li3N Energy CO H2O H2 Conversion of Li2CO3 to LiCl ammonia gasoline LiOH CO2 Absorber H2O Discharged energy carrier Li2CO3 Page 23 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved Project Results Spray Combustion and Flame Analysis CO2ToValue 4.0x104 CO concentration / ppm 3.5x104 3.0x104 2.5x104 2.0x104 1.5x104 1.0x104 5.0x103 0.0 0 50 100 time Spray Ignition / Flame Spectroscopy Ignition: − TGas>TIgnition, HV-spark Stable, self-sustaining flame demonstrated − In air and CO2 Flame Temperature: ca. 2000 K 30 kW Lithium Reactor Page 24 Oct. 13, 2014 Corporate Technology Combustion products in CO2: − Li2CO3, CO Restricted © Siemens AG 2014. All rights reserved 150 CO2ToValue Backup Page 25 Oct. 13, 2014 Corporate Technology Restricted © Siemens AG 2014. All rights reserved Power to Value Compound based Energy Storage Overcapacity of Renewable Electricity CO2ToValue CO2 from fossil-fired power plants N2 from air or IGCC or Oxyfuel plants + or Electrocatalysis Via Li/Na/Mg… mediator Synthetic fuels or chemical feedstock Li -Coal Methane (CH4) Ethylene (C2H4) Market Price 81 €/t Market Volume > 2400 Mt/y Page 26 Oct. 13, 2014 1000 €/t 141 Mt/y Corporate Technology Formic acid (HCOOH) Carbon monoxide (CO) Ammonia (NH3) 0.7 Mt/y 650 €/t (+ H2 Naphtha) > 210 000 Mt/y 500 €/t 131 Mt/y Restricted © Siemens AG 2014. All rights reserved
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