Hydrogen.gov | A. Proton Exchange Membrane Fuel Cells

A. Proton Exchange Membrane Fuel Cells

Description: Proton exchange membrane fuel cells (PEMFCs) work with a polymer electrolyte in the form of a thin, permeable sheet, and operate at relatively low temperatures (typically about 80 deg.C). To speed the reaction, a platinum catalyst is used on both sides of the membrane. Hydrogen atoms are ionized at the anode, and the positively charged protons diffuse through the porous membrane and migrate toward the cathode. The electrons pass from the anode to the cathode through an exterior circuit. At the cathode, the electrons, hydrogen protons and oxygen from the air combine to form water. The PEM electrolyte passes hydrogen protons and inhibits the migration of electrons and heavier gases. PEMFC efficiency is 40-50%. PEMFCs have been demonstrated in the 50-200 kW range. High-temperature (100-140 deg.C) PEMFC membranes, currently in development, would increase efficiency (by greater proton conductivity) and resistance to impurities.

1. Chemical Sensors

a) Carbon Monoxide
Description: Measure the CO concentration at the entrance to fuel cell stack, preferential oxider outlet, and reformer outlet.
Goals: Size, Cost

i. Gallium nitride, integrated CO and temperature sensor

ii. Low-temperature, amperometric devices

iii. High-temperature devices based on proton-conducting oxides

b) Hydrogen, fuel processor outlet
Description: Measure over a wide range of concentrations and temperatures, in the presence of other constituents in the reformate stream.

c) Hydrogen, ambient
Description: Measure ambient concentrations, for safety purposes, in the presence of other species found in ambient air.

i. Electrochemical sensors

ii. Micro-machined thin-film sensors

a. Interfacial stability

iii. Gallium nitride, integrated CO and temperature sensor

iv. Sensors based on oxygen-conducting ceramics

d) Ammonia, sulfur compounds, and contaminants
Description: Measure concentration of H2S, SO2, organic sulfur compounds, ammonia, and contaminants in the presence of other constituent gases.

i. Solid-state sensor arrays

e) Oxygen
Description: Measure oxygen concentration at the cathode exit.

g) Fuel processor sensors
Description: For reactor control

h) Reference methods and standards
Description: Accurate and uniform measurement of the concentrations of sulfur, ammonia, oxygen, carbon monoxide, and other process gases or contaminants in hydrogen.

i. Analytical methods

ii. Physical-property-based methods
Description: Use reference equations of state and selected properties such as speed of sound and the dielectric constant.

2. Physical System Sensors

a) Flow rate
Description: Measure flow rate of reformate or hydrogen into the fuel cell at 1-3 atm total pressure.

i. Combine acoustic methods for gas composition and flow rate measurement.

b) Temperature
Description: Fast-response for in-situ applications, operation in high-humidity reformate streams, insensitivity to flow velocity.

c) Relative humidity
Description: For the anode and cathode gas streams, high-temperature, high-humidity operation.
Goal: <1% accuracy

i. Solid state, in-situ probes

3. Air and Thermal Management

a) Air Components
Goals: Low cost, High efficiency, Lubrication-free

i. Compressors and blowers

a. Turbo

b. Torroidal intersecting vane

c. Hybrid scroll

ii. Expanders

iii. Motors

iv. Motor controllers

b) Thermal Design
Goals: Low cost, High efficiency, Reduced size

i. Heat exchangers

ii. Condensers

iii. Heaters

iv. Radiators

v. Heat recovery systems

vi. Heat rejection materials

vii. Humidifiers

viii. Other system humidification techniques

4. Intermediate-Temperature Membranes and Stacks
Description: Operating temperature 120-200°C. New membranes are needed that provide sufficient proton and water conductivity, and lower gas permeability, at these temperatures. Access to this temperature regime would significantly improve CO tolerance, reduce the need for precious metal catalysts, and improve heat rejection in the stack – thus providing lower cost, higher efficiency and greater durability – compared to conventional, lower-temperature PEMFCs.

a) Catalysts

i. Adhesion to new polymer membranes
Description: Investigate new electrode structures and other approaches

ii. Catalyst structure and formulation
Goal: Reduce platinum loading while maintaining CO tolerance and oxygen reduction properties

a. Improve the fundamental understanding of local structure in a catalyst layer.

b. Nano- and micro-structured electrocatalyst materials

iii. Analyze effect of sulfur impurities on catalyst performance.

b) Bipolar plates
Goals: Low cost, Light weight, Corrosion-resistant, Impermeable

i. Materials

ii. Coatings

c) Membrane materials
Description: Standard, perfluorsulfonic acid-based membranes such as Nafion lose conductivity as they begin to dehydrate above 100 deg.C. New membranes are needed that provide the required proton conduction and selectivity at higher temperatures.

i. Polymeric materials

ii. Inorganic

iii. Hybrid

d) Other components

i. Gas diffusion layer

ii. Seals

iii. Interconnects

e) Manufacturing processes

i. Membranes

ii. Catalyst deposition

f) Testing and Analysis

i. Single cell

ii. Sub-scale (5-10 kW) stack

iii. Investigate long-term stability and durability, efficiency, power density

iv. Standard methods and membranes to characterize performance of PEMFC membranes.

5. System Analysis

a) Drive cycle modeling
Description: Simulated automotive drive and durability cycles

b) Water management

i. Flow channel design

ii. Flow modeling

c) System model
Description: Develop a validated system model, with periodic benchmarking, of the integrated fuel cell power system, subsystems, and components.

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