Proton Exchange Membrane Electrolyzer Technologies From the EESC Lab
Hydrogen power is one of several forms of energy expected to play a major role in a sufficiently advanced de-carbonized energy system, with electrolysis being a promising route for the green production of hydrogen from renewable energy sources.
Among various other electrolyzer technologies, Proton Exchange Membrane Electrolyzer Cells (PEMECs) have emerged as an ecologically friendly method for producing hydrogen from renewable resources for energy use. However, these (along with nearly all other electrolyzer setups) suffer from (1) complicated and costly electrode production, (2) performance degradation of ionomer catalyst coatings, (3) reactant/product transport issues through the micropores of porous transport layers (PTLs) and liquid-gas diffusion layers (LGDLs), and (4) degradation of catalytic activity across the anode and cathode as a result of long-voltage-cycling. Electrolyzer stacks which (1) utilize substantially less platinum-group metals, (2) which are ionomer-free, (3) are produced by facile synthesis methods, (4) encourage high mass transport, and (5) reduce overall cost are necessary to encourage more widespread adoption of hydrogen power as a green alternative.
Researchers Mench, Aaron, and Zhang in the Electrochemical Energy Storage and Conversation Laboratory (EESCL) and NanoHELP Lab in the University of Tennessee Department of Mechanical, Aerospace, and Biomedical Engineering (MABE Department) have developed a portfolio of patent-pending technologies which have the potential to revolutionize the field of hydrogen fuel production.
Catalyst Coating Compositions and Methods of Application
One of they key cost factors in PEMEC construction are expensive catalyst materials like iridium and other platinum-group metals. Dr. Zhang and team developed technologies to create cost-effective catalyst layers which utilize up to 90% less of these expensive catalyst materials without sacrificing performance, stability, or manufacturing capability. The following methodologies have been developed and utilized by Dr. Zhang and the EESCL to create single and dual-electrodes designs with thin ionomer- free catalyst layers.
I. In-Situ Growth via Electroplating
This methodology allows for electroplating of an ionomer-free iridium-based, platinum nanosheet, or a bimetallic nanostructured catalyst layer uniformly onto a substrate at room temperature and ambient pressure with minimal surface preparation. This technology can be applied to a variety of substrate materials and designs (Ti, Ni, Cu, carbon paper, carbon cloth, TTLGDL, etc.). Lab scale models have demonstrated the following:
II. In-Situ Growth via Chemical Synthesis
This methodology allows for chemical application of various types of ionomer-free catalyst layers (IrMOx) [M can be Ru, Rh, Au, Pt, Os, Pd, etc.] at low temperature and ambient pressure. Lab scale models have demonstrated at 1.60 V at 2000 mA/cm2 with an IrO nanosheet electrode as thin as 25 um with catalyst loading 0.28 mg/cm2 with an ultralow degradation rate.
III. Nitriding
This methodology allowing for the creation of a TiN-coated substrate which is easy to prepare and implement for industrial applications, with a low catalyst-loading while demonstrating enhanced cell performance by reducing the interfacial contact resistance and improved catalyst activity. Lab scale models have demonstrated 1.86 V at 2000 mA/cm2 with an Ir-TiN electrode as thin as 25 um with catalyst loading 0.3 mgIr/cm2 .
Ionomer-Free Catalyst Layer
Electrode Function
Fabrication Method
Substrate Material Tested
Catalyst Loading (mg/cm2)
Catalyst Layer Thickness*
Membrane Thickness
Working
Temp.
Performance at 2000 mA/cm2
MoS2
Cathode
Chemical
FYZ, Ti, Ni, Cu, C
0.14
<100 nm
Nafion 115
(~125 um)
80 oC
2.3 V
Pt nanosheet
Electroplate
0.025
~ 43 nm
Nafion 117
(~175 um)
1.9 V
IrOx Nanosheet
Anode
0.28
<500 nm
Nafion 212
(~50 um)
1.8 V
1.6 V
Modified IrOx
0.30
Bimetallic IrRuOx
0.34
1.6V
Ir-TiNx
Nitriding
FYZ, Ti
0.3
<150 nm
Bimetallic Ir(M)Ox :
M = Ru,Rh,Au,Pt,Os,Pd)
FYZ, Ti, C, Cu, Ni
0.22
N/A
Ir w/ Microchanneling
Electroplate/Chemical
FYZ
0.26
Microchanneled Thin Tunable LGDL
(TTLGDL)
Proton Exchange Membrane Electrolyzer Cells (PEMECs) and Proton Exchange Membrane Fuel Cells (PEMFCs) are typically arranged in sandwich configurations, including bipolar plates, porous transport layers (PTLs), and catalyst layers for the anode and cathode sides. However, for conventional PTLs, pileup of microfibers and particles can lead to large contact resistance, which greatly impedes mass transport through the system, as well as overall efficiency of the electrolysis/fuel cell operation. Subsequent thin/tunable liquid/gas diffusion layer (TTLGDL) developments decrease thickness as a solution to the PTL contact resistance problem, but still rely on the existence of micropores for mass transport. Due to the sandwich structure of PEMECs, as well as the properties of flow fields, reactant and product transport under the solid land area is often greatly impeded. Researchers at the University of Tennessee have developed a novel flow-enhanced liquid/gas diffusion layer (FELGDL) containing in-plane microchannels (depicted below) ensuring that all of the active areas in the pores are open to reactions and not blocked by the land area. In this way, mass transport, efficiency, and performance of electrolyzers and fuel cells are greatly enhanced, especially when combined with the catalyst coating technology described previously in this document, as shown by the chart in Figure 3 (below), illustrating a dramatic increase in mass transport in FELGDLs and LGDLs when catalyst coated and utilizing the novel microchanneled proton exchange membranes.
Fluid Flow Field Plate
Researchers at the University of Tennessee have developed an optimized flow field for use with a variety of diffusion layers which results in significantly less obstruction to mass transport of reactants and products. This Fluid Flow Field Plate can result in greatly increased efficiency and performance of the electrolyzer stack
Figure 1: Schematic of Fluid Flow Assembly (100) with Bipolar Flow Plate Field (110) for use in conjunction with the LGDL and PEMEC stack.
Inventors
DR. DOUG AARONDR. FENG-YUAN ZHANGDR. MATTHEW MENCH