S1 SUPPORTING INFORMATION Comparison of non-precious metal cathode materials for methane production by electromethanogenesis Michael Siegert 1 , Matthew D. Yates 1 , Douglas F. Call 1,2 , Xiuping Zhu 1 , Alfred Spormann 3 , Bruce E. Logan 1* 1 Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA, USA 2 Syracuse University, Department of Civil and Environmental Engineering, Syracuse, NY, USA 3 Department of Civil and Environmental Engineering and Department of Chemical Engineering, Stanford University, Stanford, CA, USA *Corresponding author: Bruce E. Logan, 231Q Sackett Bldg, Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA 16802, Email: [email protected]; Phone: +1 814-863-7908, Fax: +1 814-863-7304
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MMC- cathode materials SI 1-23-14 - Penn State Engineering · Comparison of non-precious metal cathode materials for methane production by electromethanogenesis Michael Siegert1,
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SUPPORTING INFORMATION
Comparison of non-precious metal cathode materials for methane
production by electromethanogenesis
Michael Siegert1, Matthew D. Yates1, Douglas F. Call1,2, Xiuping Zhu1, Alfred Spormann3, Bruce E. Logan1*
1Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA, USA
2Syracuse University, Department of Civil and Environmental Engineering, Syracuse, NY, USA 3Department of Civil and Environmental Engineering and Department of Chemical Engineering,
Stanford University, Stanford, CA, USA *Corresponding author: Bruce E. Logan, 231Q Sackett Bldg, Department of Civil and
Environmental Engineering, The Pennsylvania State University, University Park, PA 16802, Email: [email protected]; Phone: +1 814-863-7908, Fax: +1 814-863-7304
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Medium. The vitamins solution contained (100× stock concentration in mg L–1): pyridoxine
OR, USA) equipped with an electron dispersive X-ray spectroscopy (EDX).
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References
(1) Wolin, E. A.; Wolfe, R. S.; Wolin, M. J., Viologen dye inhibition of methane formation by Methanobacillus omelianskii. J. Bacteriol. 1964, 87, (5), 993-998. (2) Pisciotta, J. M.; Zaybak, Z.; Call, D. F.; Nam, J.-Y.; Logan, B. E., Enrichment of microbial electrolysis cell biocathodes from sediment microbial fuel cell bioanodes. Appl. Environ. Microbiol. 2012, 78, (15), 5212-5219. (3) Thauer, R. K.; Kaster, A.-K.; Seedorf, H.; Buckel, W.; Hedderich, R., Methanogenic archaea: ecologically relevant differences in energy conservation. Nat. Rev. Microbiol. 2008, 6, (8), 579-591. (4) Lide, D. R., CRC handbook of chemistry and physics. 89 ed.; CRC Press, Inc.: Boca Raton, 2008.
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Table S 1: Batch cycle times in days. Batch cycle 6 was the potential split cycle. Asterisks (*) denote actual batch cycles 7 because of oxygen intrusion into 1 reactor with an iron sulfide cathode and 2 reactors with graphite electrodes. Plus (+) indicates graphite reactors that ran over 116 days during cycle 2. All results displayed in the article were shifted accordingly, i.e. failed cycles (cycle 2 of iron sulfide and graphite and cycle 6 of steel) are never shown because no methane was produced. The reference electrodes failed during cycle 6 of one steel reactor and the entire cycle was repeated.
Hydrogen (or e- + H+) is needed to make methanogenesis from elemental carbon (C0, graphite) thermodynamically feasible (reaction 3). However, the near infinite abundance of water (1/[H+]under MMC reactor conditions makes all reactions involving water and protons thermodynamically feasible.
aReaction condition ΔGMMC°: [methane] = 98 Pa (GC detection limit), [hydrogen] = 10 Pa (limit for cytochrome methanogenesis),3 [formate] = 1 mM, [acetate] = 1 mM, [bicarbonate] = 30 mM, [H+] = 0.1 μM at pH 7, [H2O] = 1/[H+] all other concentrations 1 M
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Table S 3: Correlation factors R2 of methane production rates over poised potentials. The poised
potentials were -550 mV and -650 mV during cycle 6 and -600 mV during cycle 5.
Material R2
Pt -0.93
Steel -0.96
Ni -0.75
ferrihydrite -0.83
magnetite -0.94
FeS -0.19
MoS2 -0.86
C-brush -0.95
C-black -0.59
graphite -0.83
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Table S 4: List of materials used in the experiment and their respective energies of formation
ΔGf° taken from reference 4. Coulombic recoveries of cycle 2 were selected to show that ΔGf° of
0 tend to be closer to 100% than negative or unspecified ΔGf°.
Cycle time in daysCycle time in daysCycle time in days
100
50
0
FeS
MoS2
C-brush
C-black
graphite
0 25
CH
4 p
rod
uce
d in
µm
ol
CH
4 p
rod
uce
d in
µm
ol
Figure S 1: Methanogenesis in open circuit controls. Note that cycle 2 lasted longer than depicted but no methanogenesis was observed in any of the reactors until the cycle ended.
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Carbon brush
Platinum
0
I in
mA
-0.5
-1.0
-1.5
-2.0
-2.5
nabiotic
= 3nabiotic
= 3
Abiotic (+/- errorn)
Inoculation cycleLast cycle
Carbon black Graphite
0
I in
mA
-0.5
-1.0
-1.5
-2.0
-2.5
nabiotic
= 3nabiotic
= 5
MagnetiteFerrihydrite
0
I in
mA
-0.5
-1.0
-1.5
-2.0
-2.5
nabiotic
= 4 nabiotic
= 3
Iron sulfide MoS2
nabiotic
= 3 nabiotic
= 4
-0.6-0.7
0
I in
mA
-0.5
-1.0
-1.5
-2.0
-2.5-0.5 -0.4 -0.3 -0.2 -0.1
E vs. SHE in V
-0.6-0.7 -0.5 -0.4 -0.3 -0.2 -0.1
E vs. SHE in V
NickelSteel0
I in
mA
-0.5
-1.0
-1.5
-2.0
-2.5n
abiotic= 3 n
abiotic= 3
Figure S 2: Linear sweep voltammograms of the cathodes at different stages of the experiment: before the abiotic cycle 0 (bold continuous lines with error margins as fine lines), right after inoculation (dashed lines) and right before the final cycle (fine dashed lines). Abiotic volatmmograms show the average value of n reactors whereas the bold is the average and the fine lines are the error margins (standard deviation of n reactors).
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1 2 3 4 5 6 7 8 9 keV
CA
A-EDX B-EDX
B
C-EDX
0.5 keV1.0 1.5 2.0 2.5 1 2 3 4 5 6 7 8 9 keV
C
FeNaZn S
OCr
SiP Cr
Cr
Fe
FeNi
Ni
NiZn Zn
C
F MoMo
Mo&S
Mo
S
CCa
O
F
Ni
Zn
Al
P
S
Ca NiZnCu CuZnMo
10 μm 5 μm 10 μm
Figure S 3: ESEM micrographs taken of particles found on different carbon black electrodes and their respective EDX scans: A, steel particle, B, MoS2 particle; note that the molybdenum and the sulfur EDX bands overlap, C, carbon black-only with a presumably precipitated particle. All particles were overgrown by microbes indicating that they were present before colonization.
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C
ou
lom
bic
rec
ove
ry in
%
1000
100
1
10
10000
Pt
stee
l
Ni
ferr
ihyd
rite
mag
net
ite
FeS
Mo
S2
C-b
rush
C-b
lack
gra
ph
ite
Cycles 2-5Cycles 3-5
Figure S 4: Coulombic recoveries for duplicate reactors over several cycles illustrating the decrease of the errors. Mean values are shown for cycles 2-5 in dark blue and for cycles 3-5 in light green. Errors are standard deviations of the mean.
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¼H2
CH4
1000
100
1
10
Gas
pro
du
ced
nm
ol
cm–
3 d
–1
Pt
stee
l
Ni
ferr
ihyd
rite
mag
net
ite
FeS
Mo
S2
C-b
rush
C-b
lack
gra
ph
ite
Figure S 5: Gas production rates for hydrogen (mean) and methane (confidence intervals). The difference to the figure in the main text is that here, 95% confidence intervals over all cycles and duplicate reactors were calculated for methanogenesis. Shown are the mean values with their corresponding standard deviations within these confidence intervals.