Recycling CO 2 by Electrolysis of CO 2 and H 2 O Economics and Electrode Materials Christopher Graves crg2109@columbia.edu May 4, 2010 Sustainable Fuels Workshop Faculty House, Columbia Univ.
Comparisons Closed-loop fuel cycles
Non-biological Infrastructure compatible Energy dense fuels closed-loop CO 2 -neutral
1. Review options for CO 2 recycling to fuels (heard about many today) 2. Briefly discuss part of my (recently completed) PhD work
Energy conversions Energy conversion Thermolysis O 2 CO 2 Thermochemical cycle CO H 2 O High-temperature electrolysis Low-temperature electrolysis H 2 C x H y Photoelectrolysis/ photolysis Largely determines the land area footprint, energy use, and capital cost of the system
Electrolysis Current state-of-the-art: Efficiency is not allimportant; capital cost can easily dominate. Economics Capital cost: Low internal resistance Low degradation Low manufacturing cost
High temperature electrolysis Thermodynamic advantage more efficient Use less electricity, more heat Resistive losses turned into useful heat Run near thermoneutral voltage near-100% electricity to chemical energy efficiency Faster reaction rates No need for precious metal catalysts Lower capital cost (more fuel produced per cell area) Reduced system cost + improved system energy efficiency No need for separate reverse water-gas shift reactor to produce syngas Waste heat from exothermic fuel synthesis useful, to rise steam
Electrolysis economics Capital cost: Can be traded off Low internal resistance Low degradation Low manufacturing cost Alkaline: X Solid oxide:? Prior talk Steady-state Transients (e.g. oxidation)
System energy balance 70% electricity to hydrocarbon fuel efficiency Solar photovoltaic @ 10-20% = 7-14% solar to fuel effic.
System economics 0.5 A/cm2
Intermittent operation (e.g. solar) 0.5 A/cm2
Can be operated at much higher current density than the 0.5 A/cm 2 assumed for low degradation, still at near 100% efficiency
Intermittent operation (e.g. solar) 2 A/cm2
How to improve Study degradation mechanisms of existing electrodes Modify existing electrodes Develop new electrodes Ceramic materials offer a number of potential advantages Developing a high performance ceramic electrode could improve the economics of electrolysis
Ceramics can offer: Mixed ionic-electronic conductivity Reactive surface not only TPB enhanced reaction kinetics More tolerant to impurities that collect at TPBs Fine microstructures No metal mobility/agglomeration Stability through oxidation-reduction Composed mostly of oxygen and alkaline/rare earths Cost
Recent electrode structure developments
Very high performance Polarization resistance SM LM Donor-doped strontium titanates range SVM STM SMM SCM SFM SNM SNM-p 3% H2O/H2 50% H2O/H2 50% CO2/CO 850 C STNM 0.1 1 10 100 LSR P (kω cm)
Performance near open circuit not always indicative of true performance of these molybdates (and some other ceramics e.g. titanates). Some activate during reduction (electrolysis). Electrolysis Fuel cell mode
Summary (details in forthcoming papers) Sustainable Hydrocarbons by CO 2 Recycling Interesting energy carriers convenient gasoline like fuels produced from sustainable energy sources like solar and wind Feasible, and high temperature electrolysis is a very promising method Electricity price 2-3 cents per kwh for $2/gal synthetic gasoline New molybdate based ceramic electrodes Revealed interesting properties related to defect chemistry, decomposition to nanostructured surface Very high performance, promising materials for components of electrodes which could reduce the overall cost of the CO 2 -to-fuels system
Outlook Sustainable Hydrocarbons by CO 2 Recycling More thorough system analysis needed Heat management, complicated by intermittent operation R&D to mass-produce an integrated system and automate operation Co-electrolysis of CO 2 and H 2 O Optimize operating points and test with intermittent operation Modeling & simulations to further study where possible optimums are in the tradeoff between manufacturing cost, current density, and durability New molybdate based ceramic electrodes Study effects of modifying the composition and microstructure Optimize to incorporate into high performance electrodes
Thank you for your attention! Acknowledgements Columbia Klaus Lackner Alan West Paul Duby Risø Mogens Mogensen Sune Ebbesen Bhaskar Reddy Sudireddy All my colleagues Friends & family Funding: American Chemical Society Petroleum Research Fund SERC project, Programme Commission on Sustainable Energy and Environment, The Danish Council for Strategic Research
Current events could be avoided Fuels by CO 2 recycling land based, no need to pump from ocean floor