462065 Economic Production of Syngas from CO2 and H2O: New Routes to Synthetic Fuels

Wednesday, November 16, 2016: 9:12 AM
Van Ness (Hilton San Francisco Union Square)
Zengcai Liu, Robert Kutz, Hongzhou Yang, Richard I. Masel and Syed Dawar Sajjad, Dioxide Materials, Boca Raton, FL

Economic production of syngas from CO2 and H2O could produce new routes to synthetic fuels. In this paper we will describe recent work on the electrolysis of CO2 in a 5 cm² alkaline electrolyzer using standard Fuel Cell Technologies fuel cell hardware. Previous work had demonstrated CO2 conversion with steady state currents of 50 mA/cm² or less at 3 V. In this paper we find that by optimizing the composition of the membrane and ionomer we can raise the current to 280 mA/cm² at 3V and 600 mA/cm² at 3.25-3.35 V.

Table 1 shows how the performance of the electrolyzer varies with membrane composition for several different membranes using bare silver cathode catalysts, ruthenium anode catalysts and a variety of membranes. In all cases the measurements were done by sandwiching the membrane between two pieces of carbon cloth that were coated with membrane, mounting the resultant MEA in 5 cm² fuel cell hardware, supplying humidified CO2 to the cathode, applying 3 V, waiting 20 minutes to 1 hr for the current to stabilize and recording the current.

Membrane

Faradaic Efficiency

Current at 3V

(mA/cm2)

Current for carbon containing products

(mA/cm2)

Nafion 117

0%

72

0

Neosepta

34%

24

8

Acid doped CMI-7000

0.02%

35

0.007

Alkali doped AMI-7001

25%

10

2.5

SPEEK

2.5%

5

0.13

Alkali doped PVA

52%

15

7.5

Alkali doped PEI/PVA

16%

10

1.6

H3PO4 doped PBI

14.7%

8

1.2

Sustainion™ X1

95%

80

75

Sustainion™ X2

93%

80

72

Sustainion™ X3

83%

25

20.8

Notice that the faradaic efficiency for the conversion of CO2 to CO varies from 0 to 95%. While the current varies from 5 to 80 mA/cm². Sustainion™ membranes give higher currents and faradaic efficiency than the others. These results demonstrate that the membrane composition makes a significant difference to the electrolyzer performance.

We have also determined shows how the polarization curve of the cell varies as we add different amounts of Sustainion™-X5 to the cathode layer in a cell with a Sustainion™-X4 membrane. Notice that one can obtain currents of 1.4 amps (280 mA/cm²) at 3 volts with a Sustainion™-X4 membrane and and Sustainion™-X5 ionomer.

Steady state runs were done at 200 and 600 mA/cm². The cell is able to sustain 200 mA/cm² a 2.9 V and 600 mA/cm2 at between 3.25 and 3.35 V. By comparison, the closest competitor needed almost 7 V to obtain the same current.

These results demonstrate that one can use electrolyzers with Sustanion™ membranes to convert CO to CO2 at industrially important rates

Acknowledgement

Parts of this work were supported by ARPA-E under contract DE-AR0000345 and by 3M. The opinion are those of the authors and may not reflect the opinions of ARPA-E.


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See more of this Session: Novel Approaches to CO2 Utilization I
See more of this Group/Topical: Topical Conference: Advances in Fossil Energy R&D