electrolysis without membranes - wordpress.com · 9/29/16 d. esposito, closing the carbon cycle 2...

1 9/29/16 D. Esposito, Closing the Carbon Cycle

Electrolysis without Membranes

Glen O’Neil, Oyin Talabi, David Brown, Cory

Christian, Ji Qi, Jack Davis, Anna Dorfi

Dan Esposito

Department of Chemical Engineering

Lenfest Center for Sustainable Energy

Columbia University

Closing the Carbon Cycle Conference

Tempe, AZ, September 29th, 2016


Mission

The mission of the Lenfest Center for Sustainable Energy (LCSE) is to advance science and develop innovative technologies that provide sustainable energy for all humanity while maintaining the stability of the Earth’s natural systems.

Research Themes Six interconnected, topical research areas that fall under the overall theme of sustainable energy conversion and utilization pathways:

I. Novel Materials/Nanotechnology for energy conversion, utilization and storage with a reduced environmental footprint.

II. Novel Reaction Pathways for sustainable energy materials conversion

throughout the engineered and natural elemental cycles, including innovative device development (e.g. 3-D printed reactor systems).

III. Catalysis for novel reaction pathways.

IV. Separations using smart, multi-functional materials for sustainable energy and materials.

V. Energy Storage and Systems Integration for optimized deployment of renewable energy.

VI. Earth Systems for sustainable energy extraction, conversion and waste storage (e.g. waterless or CO2-rich

fracking of shale, enhanced oil recovery, geothermal heat recovery with integrated CO2 conversion, and CO2 storage).


Electrochemical Production of Fuels

H2O

O2

H+

V

membrane

H2

Side-view of PEM electrolysis cell.

e-

e-

(+) (-)

Cathode Anode

H2O Electrolysis

Red.:

Ox.:

Overall:

H2O →2e- 2H++0.5O2

2H++2e- → H2

H2O → H2 +0.5O2


Electrochemical Production of Fuels

H2O

O2

H+

V

membrane

CO2

CxHyOz


e-

e-

(+) (-)

Cathode Anode

Red.:

Ox.:

CO2 Electrolysis

Overall:

n(H2O →2e- + 2H+ + 0.5O2)

xCO2 + 2nH++ 2ne- →CxHyOz

xCO2 + nH2O → CxHyOz

CxHyOz= CO, CH4, HCOOH, CH3OH, C2H4, and more

H2O Electrolysis

Red.:

Ox.:

Overall:

H2O →2e- 2H++0.5O2

2H++2e- → H2

H2O → H2 +0.5O2


http://blog.capterra.com/wp-content/

“Hydrogen Economy”

Renewable “Hydrocarbon

Economy”

H2 CxHyOz

Sometimes it may seem as if we have two choices..


http://blog.capterra.com/wp-content/

Renewable “Hydrocarbon

Economy”

“Hydrogen-carbon Economy”

“Hydrogen Economy”

H2 CxHyOz

But it is important to remember that H2

and CHO’s are complementary


Examples of the “Hydrogen Carbon” Economy

CO2 + 4 H2 → CH4 + 2 H2O

Example 2: Sabatier Process

Example 1: Fischer Tropsch Process

Example 3: Methanol Synthesis

Fischer-Tropsch

H2

CO + O2

(-CH)n

3b. CO2 + 3H2 → CH3OH + H2O

Ethylene, Propylene, acetic acid, and others

3a. CO + 2H2 → CH3OH

liquid

H2O

CO2 Electrolyzer


Economics of H2 from Low Temperature Water Electrolysis

$4-5 /kg H2[1]

Where are we today?

(Production Cost Only)

Note: Production of H2 from CH4- reforming is ≈$2/kg H2. (2012)[2]

$2-4 /kg H2 DOE Hydrogen & Fuel Cells Program target cost for production & delivery in order to compete with gasoline at the pump.[1]

What’s it going to take?!

[1.] 2012 DOE‐FCTP MYRD&D cost status and targets for Hydrogen Production. [2] S. Dillich, et al., “Hydrogen Production Cost Using Low-Cost Natural Gas”, DOE report, (2012), available online.

1. Polymer Electrolyte membrane (PEM) electrolyzer http://www.hydrogenics.com

2. Alkaline electrolyzer (unipolar) Harrison, Levine, “Electrolysis of Water” (2007)

(+) (- )

O2 H2

Gas collection

30% KOH or NaOH

Separation Diaphragm


Economics of H2 from Low Temperature Water Electrolysis

[1.] W. Colella, et al., “Techno-economic Analysis of PEM Electrolysis for Hydrogen Production”, (2014) available online.

Breakdown of H2 production costs by water electrolysis. Data from [1]

[1] Study by Strategic Analysis based on $0.07/kWh electricity & PEM electrolyzer system(≈$100/kW) with 97% availability factor. ^Includes indirect, O&M, and replacement

Electricity

Soft Costs^

Capital Costs

The cost of H2 produced by electrolysis is

usually dominated by the cost of electricity.

1. Polymer Electrolyte membrane (PEM) electrolyzer http://www.hydrogenics.com

2. Alkaline electrolyzer (unipolar) Harrison, Levine, “Electrolysis of Water” (2007)

(+) (- )

O2 H2

Gas collection

30% KOH or NaOH

Separation Diaphragm


Considerations for H2 Production from PV/Wind-Electrolysis:

1. The price of electricity from renewables is decreasing……….

2.4 cents/kWh

http://www.pv-magazine.com/news/details/beitrag/breaking--world-record-low-price-entered-for-solar-plant-in-abu-dhabi_100026145/#axzz4LYZnCkaP



Beyond Sunshot: http://energy.gov/eere/sunshot/photovoltaics-research-and-development

Influence of cost of electricity on cost of H2. Analysis based on electrolyzer efficiency of 75% (HHV). Note: DOE target is upper limit for production and delivery.

DOE target (Upper limit)

1. The price of electricity from renewables is decreasing……….

Beyond



[1.] U.S. EIA, Electric Power Monthly, (2015) https://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_6_07_b [2.] “Time of Use Pricing in Ontario” https://www.keyframe5.com/smart-meters-time-of-use-tou-in-ontario/

Low PV/Wind capacity factor and time of use pricing mean that electrolyzers would likely sit idle most of the time.

Average capacity factor for utility-scale PV power generators in the U.S.

(2015): CF= 28.6%. [1]

2. BUT often only for 25-40% of the time……….

Time of use(TOU) pricing scheme in Ontario Canada (Summer, Weekdays)[2]

Time of use pricing


Capacity factor for PV/Wind Electrolysis or time-of-use pricing

Cost Considerations for H2 Production from PV/Wind-Electrolysis:

Relationships between capital cost and capacity factor at fixed cost of electricity.

Key Assumptions

• 4 ₵/kWh electricity

• Electrolyzer efficiency

of 75% (HHV)

• System lifetime=10 yrs

• non-discounted analysis

• Installation=12% CapEx

Capital costs become much more important at low capacity factors.

Electrolyzer capacity factor

Electrolyzer


PEM Electrolyzer System Capital Cost Breakdown [1]

•Balance of system (BOS) components are important •Electrolyzer stack is the most expensive single component

^ ≈ 60% of stack cost is from MEA (membrane + electrodes)

Stacks^

[1.] W. Colella, B. James, et al., “Techno-economic Analysis of PEM Electrolysis for Hydrogen Production”, (2014) available at: http://energy.gov/sites/prod/files/2014/08/f18/fcto_2014_electrolytic_h2_wkshp_colella1.pdf

Capital Costs for a PEM Electrolyzer System

balance of

system H2O

O2

H+

V

membrane

H2


e-

e-

(+) (-)

Cathode Anode


PEM Electrolyzer Stack

PEM electrolyzer http://www.hydrogenics.com

Single cell

PEM Stack (6 cells). [1]

[1.] V. Mehta, J. Power Sources, 114 (2003). [2] W. Colella, et al., “Techno-economic Analysis of PEM Electrolysis for Hydrogen Production”, (2014) available online.

•60% of stack cost is from MEA[2] •An MEA design requires many parts and assembly steps[1]

16 9/29/16 D. Esposito, Closing the Carbon Cycle [1.] W. Colella, B. James, et al., “Techno-economic Analysis of PEM Electrolysis for Hydrogen Production”, (2014) available at: http://energy.gov/sites/prod/files/2014/08/f18/fcto_2014_electrolytic_h2_wkshp_colella1.pdf

Key components in PEM Stack

• End plates • Flow field plates • Gaskets/seals • Fasteners

• Membrane • Gas diffusion layer • Anode catalyst • Cathode catalyst

Membrane electrode assembly (MEA) PEM electrolyzer http://www.hydrogenics.com



17 9/29/16 D. Esposito, Closing the Carbon Cycle [1.] W. Colella, B. James, et al., “Techno-economic Analysis of PEM Electrolysis for Hydrogen Production”, (2014) available at: http://energy.gov/sites/prod/files/2014/08/f18/fcto_2014_electrolytic_h2_wkshp_colella1.pdf

Key components in PEM Stack

• End plates • Flow field plates • Gaskets/seals • Fasteners

• Membrane • Gas diffusion layer • Anode catalyst • Cathode catalyst • Device body

Question: At the most basic level, how many parts are really needed?




Membraneless Laminar Flow Cells based on “Flow-by” Electrodes

[6.] E. Choban, P. Kenis, et al., J. Power Sources 128 (2004) [7.] Braff, Bazant, et al., Nat. Comm. (2013).

Advantages of a Membraneless Cells: • Decreased capital costs • Electrolyte-agnostic • No membrane degradation and fouling • Simple: new manufacturing possibilities

Co-laminar membraneless fuel cells,[6,8] and flow batteries[7,8]

Membraneless Laminar flow Cells: • Utilize “flow-by” electrodes with

inherent limitations in scalability[8]

Membraneless electrolyzer with separation based on the Segre-Silberberg effect.[9]

[8.] E. Kjeang, et al., J. Power Sources, 260 (2014) [9.] S. Hashemi, D. Psaltis, et al., Energy Env. Sci., (2015).

membraneless microfluidic device

H2O


Membraneless Electrolyzer w/ Flow-Through Electrodes[1],[2]

[1.] M.I. Gillispie, et al, J. Power Sources, 293 (2015). [2.] J. Hartvigsen, et al., ECS Transactions, 68 (2015)

O2 H2

Mesh Anode

Mesh Cathode

H2O H2O

H2O H2O

Membraneless electrolyzer based on circular mesh electrodes in a face-to-face configuration.[1]

Illustration of “void fracture” caused by gas accumulation in the absence of insufficient fluid flow.[1]

Low fluid flow rate

H2 O2

H2 O2

Zoomed-in View

High fluid flow rate


Membraneless Electrolyzer with Angled Flow-Through Electrodes

[1.] D. Esposito & G.D. O’Neil, U.S. Patent application, (2015). [2.] O’Neil, Christian, Brown, Esposito, J. Electrochem. Soc. 163 (11) F3012-F3019 (2016)

Aqueous electrolyte

Electrolyte + electrolysis

products (H2 or O2)

Mesh flow-through electrode

Schematic top-view of membraneless electrolyzer based on flow-through mesh electrodes[1,2]

H2O → 0.5O2+2H++2e-

2H+ +2e- → H2

• Same advantages over conventional PEM devices as other membraneless devices • Inherently more scalable • Expected to be more tolerant to flow-characteristics than co-laminar flow cells • Extremely simple design should decrease assembly/ manufacturing costs

Advantages of Proposed Design:


Flow-Through Electrodes: Electrodeposited Pt on Ti Mesh

Pt-Ti mesh anodes and cathodes fabricated by electrodeposition

Titanium (Ti) mesh flow-through electrode with electrodeposited Pt catalyst

SEM image of Pt deposits

1 mm


Electrolyzer Fabrication with 3D Printing

Cathode (- )

Anode (+)

Electrolyte Inlet

H2

O2 20 min.

60 min.

150 min.

Baffle Divider

Flow channel

Channel dimensions Width: 1.3 cm Height: 0.7 cm Length: 7.0 cm


High speed video of gas generation and removal from 45 degree cell. Video was recorded at 500 frames per sec. and converted to “edge detection” view.

Conditions

• Flow rate: 6.5 mL/s (Re≈35)

• 45⁰ cell

• Electrolyte: 0.5 M H2SO4

• Current density=100 mA/cm2

Does it Work?: Basic Operation of Angled Flow Through Electrodes

5 mm (+) (-)

H2O


Does it Work?: Basic Operation of Angled Flow Through Electrodes

Fluid flow sweeps bubbles away from electrodes into downstream collection channels and significantly reduces mass-transport and iR losses associated with bubbles on the electrode surface

(+)

(+)

(-)

(-)

Flow

Stagnant

Flowing electrolyte 30 degree cell in 0.5 M H2SO4

Electrolysis current at 2.5 V in 0.5 M H2SO4 with various fluid velocities.

Cu

rre

nt

de

nsi

ty /

mA

cm

-2


Efficiency:

2-electrode current-voltage curve taken in flowing electrolyte.

30⁰ cell

0.5 M H2SO4

Electrolysis efficiency based on ΔG=-237 kJ/mole H2.

• Electrolysis efficiency in 0.5 H2SO4 is OK but relatively low compared to commercial electrolyzers.

30⁰ cell

0.5 M H2SO4

η=51% η=56%

=η= ΔG/nF = ΔEcell

ΔV ΔV

Electrolysis efficiency

ΔEcell

ΔV


Evaluating Electrolyzer Performance

=ΔV = ΔEcell + ηHER + ηOER + ηmt+ iRs

• Losses in electrolyzer can be broken down into separate components as commonly performed in fuel cell loss-analyses

Kinetic overpotential

losses

Mass transfer losses

Ohmic losses

Cell Potential (Nernst Eqn.)

η= ΔG/nF = ΔEcell Electrolysis efficiency:

ΔV

ΔG=237 kJ/mole ΔEcell

o=1.23 V ΔV

Applied Voltage


Loss Analysis for Operation in 0.5 M H2SO4

• Oxygen evolution kinetic overpotential losses greatly limit performance • Future efforts to move away from Pt

ΔV=2.4 V @100 mA cm-2

ΔEcell=1.23 V

ηHER =0.18 V

ηOER =0.91 V

iRS=0.19 V

ηMT < 0.05 V

Voltage losses for 30⁰ cell at 100 mA cm-2 in 0.5 M H2SO4 under flowing electrolyte. 3-electrode CV measurement for Pt-Ti mesh

electrode in 0.5 M H2SO4.

H2O → 0.5O2+2H++2e-

2H+ +2e- → H2

ηOER

ηHER


Electrolyzer Operation in Different Electrolytes

• Device operation in three different solutions highlights versatility of membraneless electrolyzers.

• Highest efficiency observed for KOH electrolyte (best kinetics)

Cu

rren

t d

ensi

ty /

mA

cm

-2

Electrolyte

Efficiency @ 50 mA cm-2

1 M Na2SO4

0.5 M H2SO4

1 M KOH

^ evaluated at an operating current density of 50 mA/cm2 under flowing electrolyte

41 % 50 %

56 % 67 %

67 % 81 %

based on ΔG

based on HHV

50 mA cm-2

100 mA cm-2

[1.] O’Neil, Christian, Brown, Esposito, J. Electrochem. Soc. 163 (11) F3012-F3019 (2016)


• Collection efficiencies of ≈ 90 % demonstrated • GC analysis of collected gas gives ≈ 2.8% cross-over rate

Conditions: -30⁰ electrolyzer -215 mA cm-2 -Electrolyte: 0.5 M H2SO4 -Flow velocity: 6.6 cm s-1

Volume of H2 collected in cathode effluent channel compared to 100% collection efficiency as expected from Faraday’s Law.

Collection Efficiency and H2 Purity

H2 collected

Collection efficiency:

H2 generated ηc =


Side view of passive membraneless electrolyzer assembly consisting of “asymmetric” electrodes.

Electrolysis cell for evaluating the performance of asymmetric electrodes.[1]

[1.] J. Davis, J. Qi, D. Esposito, (In Preparation) .

Can the electrolyzer be simplified even further?


Can the electrolyzer be simplified even further?

[1.] J. Davis, J. Qi, D. Esposito, (In Preparation) .

High speed video of asymmetric Pt/Ti electrodes operating at 40 mA cm-2 in 0.5 M H2SO4.[1]

Sensor

(+) (-)

Dissolved H2 detected in between two mesh electrodes as a function of current density using an electrochemical sensor.


Conclusions 1. Bringing down the capital cost of electrolyzers

will become increasingly important for making fuels produced from renewable energy competitive with fossil fuel energy.

2. A simple, “3-component” membraneless electrolyzer was made and demonstrated in this study.

3. Much room for improvement from initial results, but potential exists for simple, low-cost electrolyzers beyond the MEA cell architecture.


• Esposito Research Group at Columbia University

-Glen O’Neil -Ji Qi

-Cory Christian -Jack Davis

-David Brown -Oyin Talabi

-Anna Dorfi

• Columbia Start-up funds

• Chris Hawxhurst (GC)

Acknowledgements


[email protected] https://danesposito.wordpress.com/

Questions?

electrolysis without membranes - wordpress.com · 9/29/16 d. esposito, closing the carbon cycle 2...

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