Advanced Fuel Concepts

Recycling CO2 into Sustainable Hydrocarbon Fuels: Electrolysis of CO2 and H2

Sustainable Energy Conversion Technologies with Integrated Carbon Capture, Utilization, and Storage (CCUS)

 

Recycling CO2 into Sustainable Hydrocarbon Fuels: Electrolysis of CO2 and H2O

Great quantities of hydrocarbon fuels will be needed for the foreseeable future, even if electricity based energy carriers begin to partially replace liquid hydrocarbons in the transportation sector. Fossil fuels and biomass are the most common feedstocks for the production of hydrocarbon fuels. However, using renewable or nuclear energy, carbon dioxide and water can be recycled into sustainable hydrocarbon fuels in a non-biological process. Renewable/nuclear energy sources, as heat, electricity, or light, can drive the splitting of CO2 and H2O to reverse the process of combustion. Gasoline, diesel, or other hydrocarbons or alcohols can be produced and can directly substitute into the existing infrastructure and vehicles. Capture of CO2 from the atmosphere (a technology pioneered in our research group) would enable a closed-loop fuel cycle. These CO2-recycled fuels would therefore be carbon-neutral. When produced using solar energy, the fuel cycle would be similar to that of biofuels. However, since the fuels are produced in a non-biological process, they would not share the disadvantages of biofuels in terms of land use, resource use, interference with food supplies, and other impacts to the environment and biosphere.

The purpose of this work is to develop critical components of a system that recycles CO2 into liquid hydrocarbon fuels. We have examined the concept at several scales, beginning with a broad scope analysis of large-scale sustainable energy systems and ultimately studying electrolysis of CO2 and H2O in high temperature solid oxide cells as the heart of the energy conversion via a number of micro- and nano-scale experimental studies.

A process to produce such fuels has three stages: (1) CO2 capture, (2) storage of the renewable/ nuclear energy as chemical energy by dissociation of CO2 and/or H2O, and (3) fuel synthesis using the dissociation products. Dissociation by electrolytic methods – low-temperature or high-temperature electrolysis – is currently the most feasible. We identified a process based on high temperature co-electrolysis of CO2 and H2O to produce syngas (CO/H2 mixture) as a promising method. High temperature electrolysis makes very efficient use of electricity and heat (near-100% electricity-to-syngas efficiency), provides high reaction rates, and the syngas produced can be catalytically converted to hydrocarbons in well-known fuel synthesis reactors (e.g. Fischer-Tropsch).

 

Figure 1. Diagram of the envisioned closed-loop fuel cycle. CO2 is recycled into hydrocarbon fuels in a process based on: capturing CO2 from the atmosphere, co-electrolysis of CO2 and H2O in a solid oxide cell to yield syngas (CO/H2 mixture), and catalytic fuel synthesis from the syngas.

Our analysis of the energy balance and economics of an electrolysis-based synthetic fuel production process, including CO2 air capture and Fischer-Tropsch fuel synthesis, determined that the price of electricity needed to produce competitive synthetic gasoline (at $2/gal wholesale) is 2-3 U.S. cents per kWh. Fuel production may already be economical in some regions that have inexpensive renewable electricity, such as Iceland.The dominant costs of the process are the electricity cost and the capital cost of the electrolyzer, and this capital cost is significantly increased when operating intermittently (on renewable power sources such as solar and wind). Low cell internal resistance, low degradation, and low manufacturing cost each contribute to a low electrolyzer capital cost, and can be traded off. Our research addresses each of these avenues to affordability.

 

Figure 2. Diagram of electrolysis reactions occurring in a typical porous ceramic-metal composite at the three-phase boundary where the electron-conducting metal, ion-conducting ceramic, and gas phases meet (left). Scanning electron micrograph of the nano-structured surface of a new all-ceramic electrode material (right).

In collaboration with Risø National Laboratory for Sustainable Energy, DTU, in Denmark, we experimentally investigated the performance and durability of co-electrolysis of CO2 and H2O using state-of-the-art cells. High initial performance was observed but the long-term durability needs to be improved. Our recent research involves studying reaction mechanisms at the negative-electrode that limit performance and durability, using simplified-geometry electrodes. We have also recently developed new all-ceramic nano-structured electrode materials that exhibit exceptional electrocatalytic performance and could significantly improve the overall energy use and economics of the CO2-to-fuels system. Finally, we are beginning to investigate mass production and automated operation of electrolysis-based CO2-recycling systems to reduce the manufacturing cost and operating cost respectively.

For more information, check out the presentations from our most recent conference on Sustainable Fuels held on April 9 through 11, 2013.

Researchers

Christopher Graves, Research Scientist, Denmark Technical University cgra@dtu.dk

Klaus Lackner, Ewing-Worzel Professor of Geophysics, klaus.lackner@columbia.edu (PI)

Alan West, Professor of Chemical Engineering, acw17@columbia.edu (PI)


 

Sustainable Energy Conversion Technologies with Integrated Carbon Capture, Utilization, and Storage (CCUS)

Specific research projects on sustainable energy and materials conversion systems being performed by Professor Park’s research group include:

Accelerated Carbonation of Industrial Wastes

Sustainable Energy Conversion of Biomass & Municipal Solid Wastes

Electrostatic Phenomenon in Multiphase Flow Systems & Electrostatic Tomography

For a detailed description of Professor Park’s research on these topics, please visit her research group’s website.

 
Researchers
Tom Ferguson, PhD candidate, tef2108@columbia.edu

Kyle Fricker, PhD candidate, kjf2123@columbia.edu

Xiaozhou Zhou, PhD candidate, xz2220@columbia.edu

Ah-Hyung (Alissa) Park, Lenfest Junior Professor, ap2622@columbia.edu (PI)