Bipolar Membrane Development to 

Enable Regenerative FCs

Co-PIs: KC Neyerlin, Todd Deutsch

Key contributors: Sadia Kabir, Svitlana Pylypenko, Samantha 

Medina

National Renewable Energy Laboratory

June 13th, 2018

DOE Hydrogen and Fuel Cells Program 

2018 Annual Merit Review and Peer Evaluation Meeting

This presentation does not contain any proprietary, confidential, or otherwise restricted information.

Project ID #: fc182 
NREL | 2

Overview

• Project start date: 01/01/18

• FY18 planned DOE funding: 

$150k

• Total DOE funds received to 

date: $200k

• A – Cost

• B – Durability

• C – Performance

Timeline and Budget Barriers

• Anion ionomer development 

program at NREL

• MEA fabrication group at NREL

• Fuel cell and electrolysis testing 

groups at NREL

• Colorado School of Mines –

materials characterization

Partners
NREL | 3

Relevance

• This project is directly addresses DOE FCTO’s interest in developing Reversible Fuel 

Cells

• The following section is from the FCTO’s Multi-Year Research Development & 

Demonstration (MYRD&D) plan, Section 3.4.4 Technical Challenges

– “Reversible Fuel Cells: Reversible fuel cells are of interest for energy storage 

applications and hold promise as an enabler for the implementation of 

intermittent renewable energy technologies. This technology allows for the 

storage of excess energy in the form of hydrogen during periods of low electricity 

demand that can then be used during times of peak demand. Reversible fuel cells 

are capable of operating in both power production (fuel cell) and energy storage 

(electrolysis) modes. Advantages of reversible fuel cell technology include high 

round-trip efficiency (60–90%), decoupled power and energy capacity, long 

cycle life, low self-discharge rate, and reliable and stable performance. A key 

challenge to reversible fuel cells is maintaining electrode function and 

performance during repeated cycles between fuel cell and electrolysis modes.” 

– “Cost and durability are barriers to the implementation of both reversible fuel 

cells and flow cells, but leveraging fuel cell R&D in the areas of membranes, 

electrocatalysts, electrode architectures, bipolar plates, and diffusion media for 

this technology would result in cost reduction and durability improvements.” 

• There are no codified technical targets in the MYRD&D specific to reversible fuel cells
NREL | 4

Relevance

• Objectives

– The ultimate goal of this project is the fabrication of a BPM with a dual fiber 

electrospun junction that can be employed in a stable, high performance RFC MEA. 

– Our initial focus will be on fabricating and optimizing the electrospun junction in a 

BPM with available materials (leveraging ongoing AEM development), and obtaining 

BPM device data in both fuel cell and electrolysis mode individually. 

– While electrode architecture/composition may have to be optimized or modified as 

the project progresses, the crux of this effort will be the optimization of the BPM 

junction interface.

– The key technical aspects of the project are focused on fabricating/optimizing the 

described electrospun junction morphology for subsequent implementation into 

MEAs for fuel cell, electrolyzer, and RFC devices. Membrane characteristics such as 

composition, fiber diameter, and the incorporation of catalysts/particulates at the 

interfacial/junction will be tested first in either individual fuel cell or electrolyzer

devices.

– A BPM with an electrospun junction has never been integrated into a fuel cell or 

water electrolysis MEA, much less a unitized RFC. These studies would represent a 

completely new field with significant promise to ameliorate some of the key 

challenges in RFC development, as well as provide significant gains to the BPM 

understanding.
NREL | 5

Approach

• Electrostatic voltage (4-50 kV) between a blunt tip needle and grounded substrate

• Charged polymer jet from a mixture of Nafion®/PFAEM ionomer and/or catalyst in carrier polymer (e.g. PEO)

• Solvent (IPA and water) evaporates from fiber as it travels from tip to substrate, filament also elongates during transit, 

narrowing diameter

– Relative humidity in chamber is a critical experimental variable

• 300-500 nm diameter nanofiber threads

• Randomly aligned nanofibers collected as mat of uniform thickness and fiber volume fraction on a membrane

• Unique aspect of our approach: Dual head electrospinning results in 3D interface of interpenetrating CEM/AEM 

fibers

Electrospinning
NREL | 6

Approach

Nafion®

sulfonated 

tetrafluoroethylene

Polyethylene oxide (PEO)

Chemistry

NREL’s proprietary

GEN 2 – PFAEM 

- Perfluoroalkyl 

polymer

Cation exchange: H+

Anion exchange: OH-

• Water-soluble, high MW, synthetic polymer

• Basic unit: (-CH2-CH2O-)n

• When dissolved in water: 

– Hydrophilic interactions through O; hydrophobic interactions through CH2CH2

Carrier polymer

• Sulfonic acid (SO3

-

) groups on Nafion®

conduct H+ cations and block anions

• Alkyl (N+) groups on PFAEM conduct 

OH- anions and block cations

• PEO added to enable electrospinning 

of Nafion® and PFAEM
NREL | 7

Approach

• Polymer dispersions electrospun concurrently on 

programmable, rotating, translating drum

• Substrate attached to drum

– Glass, membrane, conductive carbon tape, TEM 

grid, etc.

15 wt.% 

PFAEM+PEO

15 wt.% 

Nafion® +PEO
NREL | 8

Approach

Milestone Name/Description Criteria End Date Type

Electrospun Junction Synthesis/ Investigate spinning 

of PEM and AEMs through dual head spinning. 

Fabricate a BMP junction that 

has fibers of AEM penetrating 

into the PEM and PEM fibers 

penetrating into the AEM.

3/31/2018 Quarterly 

Progress 

Measure 

(Regular)

MEA testing / Experiments will examine static and 

dynamic operation, and include advanced cell 

diagnostics, including impedance, kinetics, cycling 

voltammetry (including CO stripping) and limitingcurrent measurements to help elucidate specific 

performance loss mechanisms. 

Using 3 different electrospun 

BPMs in MEAs, use 

polarization curves to begin 

elucidation of performance 

loss in both fuel cell and 

electrolyzer mode.

6/30/2018 Quarterly 

Progress 

Measure 

(Regular)

Reduced interfacial resistance for bipolar membranes/ 

Using both electrospun junctions and additives, we will 

reduce the high frequency resistance (at zero 

imaginary as measured by AC impedance) to less than 

or equal to 200 mWcm2.

Demonstrate ASR ≤0.2 Ω cm2

of BPM in fuel cell tests.

9/31/2018 Quarterly 

Progress 

Measure 

(Regular)

MEA testing and further optimization / Experiments 

will examine static and dynamic operation, and include 

advanced cell diagnostics, including impedance, 

kinetics, cycling voltammetry (including CO stripping) 

and limiting-current measurements to help elucidate 

specific performance loss mechanisms while targeting 

attainable routes to > 500 mA/cm2 in both fuel cell and 

electrolysis mode using BPM RFC approach.

Establish capability to achieve 

>500 mA/cm2 in both fuel cell 

and electrolysis mode using 

BPM RFC approach 

12/31/2018 Annual 

Milestone 

(Regular)

Milestones

Go/No-Go Go/No-Go 

Description Criteria Date

BPM RFC 

performance

Establish capability to achieve >500 mA/cm2 in both fuel cell and 

electrolysis mode using BPM RFC approach

12/31/2018

Completed

On-track

On-track

On-track
NREL | 9

Accomplishments and Progress

• Synthesized several bipolar membranes (BPM) composed of 

interpenetrating Nafion®/Perfluoroalkyl polymer fibers

• Preliminary depositions were on glass substrates

Bipolar Membrane 1 (Sk3a)

• Distance = 6 cm

• Duration = 20 min at 0.2 ml/hr

• Humidity = 25%

• Potential = 10 kV

Bipolar Membrane 2 (Sk3b)

• Distance = 6 cm

• Duration = 20 min at 0.2 ml/hr

• Humidity = 25%

• Potential = 5 kV

Bipolar Membrane 3 (Sk3b)

• Distance = 6 cm

• Duration = 20 min at 0.2 ml/hr

• Humidity = 30%

• Potential = 10 kV
NREL | 10

Accomplishments and Progress

• Characterized 

electrospun films

– Nafion® only, PFAEM 

only, three BPMs

– Optical microscopy

• Morphology

– Scanning electron 

microscopy (SEM)

• Morphology

– Energy dispersive x-ray 

spectroscopy (EDS)

• Elemental 

compositions

• Estimate Nafion® 

/PFAEM fractions

10 μm

PFAEM

Sk2 PFAEM (10kV-20RH)

Nafion®

Optical microscopy

10 μm
NREL | 11

Accomplishments and Progress

Sk1: Nafion® Sk2: PFAEM

Averages conditions F/S at.% F/N at.% F/C* at.% N/S at.%

Sk1: Nafion 6cm-10kV20RH 63.4 x 4.1 x

Sk2: PFAM 6cm-10kV20RH 35.6 20.0 3.4 1.8

Sk3a: Mixed 6cm-10kV25RH 30.0 24.6 3.2 1.3

SEM and EDS on electrospun membranes at Colorado School of Mines • Samples scraped on to conductive carbon tape

• 60-second EDS scans (5 keV) taken at 3 different regions for each mixed polymer with the corresponding elemental 

ratios of interest

• Some scans had regions with increased carbon tape contributions in the C ratios and are not ideal for showing 

meaningful comparisons

EDS to evaluate 

Nafion®/PFAEM 

fractions in BPMs 

Nafion®

• One S atom per 

repeating unit

• No N atoms

PFAEM

• One S atom per 

repeating unit

• Two N atoms per 

repeating unit

• N/S at. should be 2

BPMs

• N/S should be a proxy 

for relative polymer 

ratios

• N/S of 1.3 for Sk3a is 

close to 1 which 

would indicate a 

50%:50% mix 

C* affected by carbon tape
NREL | 12

Accomplishments and Progress

EDS results vary significantly from different areas sampled 

within the same membrane

Sk1

Nafion® fibers on carbon tape

Sk2

PFAEM fibers on carbon tape

Sk3a

PFAEM + Nafion® fibers on carbon tape

Sk1 Nafion® (10kV-20RH) EDS Ratios

Area C*/S at% F/S at% F/C* at%

1 21.1 71.7 3.4

2 10.5 53.3 5.1

3 17.7 65.2 3.7

Averages 16.4 63.4 4.1

Sample SD 5.4 9.4 0.9

C* affected by carbon tape

Sk2 PFAEM (10kV-20RH) EDS Ratios

Area C*/S at% F/S at% F/N at% F/C *at% N/S at%

1 7.3 32.9 22.5 4.5 1.5

2 9.9 39.3 19.8 4.0 2.0

3 14.2 42.2 19.4 3.0 2.2

4 12.0 28.0 18.4 2.3 1.5

Averages 10.8 35.6 20.0 3.4 1.8

Sample SD 3.0 6.4 1.8 1.0 0.4

Sk3a PFAEM+ Nafion® (10kV-25RH) EDS Ratios

Area C/S at% F/S at% F/N at% F/C at% N/S at%

1 8.2 25.2 27.0 3.1 0.9

2 6.8 26.8 26.2 3.9 1.0

3 14.1 37.9 20.6 2.7 1.8

Averages 9.7 30.0 24.6 3.2 1.3

Sample 

SD 3.9 6.9 3.5 0.6 0.5

SEM of fibers scraped on to conductive carbon tape
NREL | 13

Accomplishments and Progress

Sk3a PFAEM+ Nafion® (10kV-25RH)

Sk3b PFAEM + Nafion® (10kV-30RH)

Sk3c PFAEM + Nafion® (5kV-25RH)

Unstained Mixed Fibers: SEM image at x1k magnification and corresponding EDS Ratios

Area 1 Area 2 Area 3

Area C/S at% F/S at% F/N at% F/C at% N/S at%

1 8.2 25.2 27.0 3.1 0.9

2 6.8 26.8 26.2 3.9 1.0

3 14.1 37.9 20.6 2.7 1.8

Averages 9.7 30.0 24.6 3.2 1.3

Sample SD 3.9 6.9 3.5 0.6 0.5

Area C/S at% F/S at% F/N at% F/C at% N/S at%

1 71.8 60.1 10.3 0.8 5.8

2 45.9 68.7 15.7 1.5 4.4

3 38.5 67.5 18.6 1.8 3.6

Averages 52.1 65.5 14.9 1.4 4.6

Sample SD 17.5 4.6 4.2 0.5 1.1

Area C/S at% F/S at% F/N at% F/C at% N/S at%

1 46.0 36.7 9.5 0.8 3.9

2 38.5 42.2 15.0 1.1 2.8

3 38.3 36.8 10.4 1.0 3.5

Averages 40.9 38.6 11.6 1.0 3.4

Sample SD 4.4 3.1 2.9 0.1 0.5

Ideally N/S = 

• 2 for PFAEM

• 0 for Nafion®

• 1 for 1:1 mixture

N/S > 2 for Sk3b and Sk3c suggest EDS is not 

appropriate technique for evaluating polymer ratios
NREL | 14

Accomplishments and Progress

Lead acetate stained mixed fiber Sk3a PFAEM + Nafion® (10kV-25RH) SEM/EDS maps at x2500 magnification

Samples on conductive carbon tape

F S

C N Pb

EDS mapping to track N in PFAEM and Pb2+ to track H+ in Nafion®

Results are inconclusive
NREL | 15

Accomplishments and Progress

F-S map of mixed fiber F-N map of mixed fiber F-S-N map of mixed fiber

*elemental overlays were 

obtained using image j software

Lead stained mixed fiber Sk3a PFAEM + Nafion® (10kV-25RH) SEM/EDS maps at x2500 magnification

EDS mapping to track N in PFAEM and Pb2+ to track H+ in Nafion®

Results are inconclusive

Samples on conductive carbon tape
NREL | 16

Accomplishments and Progress: Responses to 

Previous Year Reviewers’ Comments

• This project was not reviewed last year
NREL | 17

Collaboration and Coordination

• NREL’s anion ionomer development program

– Federal lab 

– Within DOE FCTO

– Provide this project PFAEM polymer, we provide characterization results

• NREL’s MEA fabrication, fuel cell and electrolysis characterization groups

– Federal lab

– Within DOE FCTO

– Maintain equipment for MEA fabrication as well as fuel cell and electrolyzer

test stands that enable performance evaluation of BPM devices

• Colorado School of Mines

– University

– Outside DOE FCTO

– SEM and EDS characterization of electrospun membranes

• This project relies on a great working relationships that leverage 

materials and capabilities previously developed within NREL’s fuel 

cell and electrolysis group to achieve its objectives 
NREL | 18

Remaining Challenges and Barriers

• Identify appropriate technique for BPM 

optical/chemical characterization 

– Scanning transmission electron microscopy (STEM) 

coupled with EDS

– Stain one fiber precursor solution

• MEA fabrication and testing

– Turning spaghetti pile of nanofibers into functional 

MEA might pose challenges

• Introduction of water dissociation catalyst to reduce 

interfacial resistance
NREL | 19

Proposed Future Work

• For the remainder of FY18 

– Continue electrospun junction synthesis tuning deposition 

parameters based on feedback from characterizations

– Bipolar membrane characterization

– MEA testing and optimization

– Demonstrate stability and high fuel cell/electrolysis performance 

at high operating temperatures

• Key Year 1 Go/No-Go decision: 12/31/18

– Establish capability to achieve >500 mA/cm2 in both fuel cell and 

electrolysis mode using BPM RFC approach

• FY19

– focus on developing and demonstrating a reversible fuel cell MEA 

in a unitized test stand that will allow cycling in both fuel cell and 

electrolysis modes, and study durability including issues of 

operating in both individual modes

Any proposed future work is subject to change based on funding levels
NREL | 20

Technology Transfer Activities

• Technology-to-market plans: develop technology to a 

sufficiently advanced level to introduce to market

• Plans for future funding: engaging academic and 

corporate sector entities to partner on upcoming 

FOAs

• Potential for generating IP while developing new 

membrane architectures
NREL | 21

Summary

• This project is in its very early stages

• We are able to electrospin Nafion®, PFAEM, and membranes 

composed of a mixture of the two

• We characterized an initial set of membranes

• While the morphology looks as expected, the tools we have 

used for compositional characterizations have, so far, not been 

able to unambiguously give qualitative or quantitative results 

on electrospun BPMs

• Additional spectroscopic characterization techniques are 

required to evaluate the chemical compositions of the BPMs
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency 

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency

and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

www.nrel.gov

NREL/PR-5900-71400

Thank You
Technical Back-Up Slides
Reviewer-Only Slides
NREL | 25

Data Management Plan

• This project will maintain compliance with data management requirements 

of the Department of Energy and abide by the Office of Energy Efficiency 

and Renewable Energy data sharing and preservation requirements.

• To the greatest extent and with the fewest constraints possible, this project 

will make digital research data available to, and useful for, the broader 

scientific community, industry, and the public. 

• Technical reports, journal article accepted manuscripts, software, and 

scientific research datasets will be submitted to OSTI through the DOE 

Energy Link System. Data from this project deemed appropriate for public 

access will be made available through the NREL Data Catalog. 

• Data in this public release will be in a machine-readable digital format (e.g., 

comma-delimited).

• This project will not generate or use Personally Identifiable Information 

(PII). Any data containing national security implications, business 

confidentiality, or intellectual property will not be released in accordance 

with all laws and DOE regulations, orders, and policies.