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Hydrogen is gaining popularity in modern society as a source of clean energy with a wide range of applications in transportation, power generation and storage, space exploration, and many other industrial sectors. Cost-efficient polymers developed by Ecolectro Inc., a US-based company specialized in the manufacturing of advanced materials for electrochemical applications, pave the way towards the production of high-performance hydrogen fuel cells and electrolyzers for low-cost hydrogen generation.
The concept of the hydrogen economy, or the use of hydrogen as a non-polluting alternative of the traditional fossil fuels, first emerged in the 1970s. Hydrogen became attractive because when it is burned to produce heat or reacted with oxygen from the air in a fuel cell to produce electricity, the only waste product is water.
One of the most promising approaches to use hydrogen as an energy source is in conjunction with fuel cell technology. A fuel cell is an electrochemical device that directly converts chemical energy into electricity, and the only byproducts are water and heat. In such a device, the hydrogen is oxidized electrochemically in a much more efficient way than combustion. A fuel cell can run and produce electricity indefinitely, as long as it is supplied with fuel (hydrogen) and oxygen (usually air).
How Does a Hydrogen Fuel Cell Work?
The operation of a hydrogen fuel cell is similar to an electrical battery - the device has two electrodes (anode and cathode), which are separated by an electrolyte (that can be liquid, solid, or a polymer membrane). Oxygen comes into contact with the cathode, while hydrogen is fed to the anode.
A catalytic reaction on the anode strips the negatively charged electrons (e-) from the hydrogen atoms converting them to positively charged ions (H+, or protons). The flow of free electrons can be used as an electrical current to power external loads before reaching the cathode. The electrolyte between the electrodes selectively allows only the charged ions to pass through, closing the electrical circuit by re-combining electrons, protons, and oxygen on the cathode to yield water.
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Fuel Cell Production Is Limited by Precious Metal Catalyst Availability
Despite the numerous advantages of modern polymer electrolyte hydrogen fuel cells, their widespread commercialization remains a challenge mainly due to the very high manufacturing cost.
The current state of the art in fuel cell production relies on the use of a proton exchange membrane (PEM) as a polymer electrolyte that is made of perfluoro-sulfonic acid polymers (such as the Nafion membrane).
However, PEM fuel cells require very active catalyst material on the electrodes, usually manufactured from the platinum group metals that are highly expensive and with minimal supply, which significantly hinders the large-scale manufacturing of hydrogen fuel cells.
Cheaper Catalyst Materials Can Make Fuel Cell Technology Sustainable
Identifying the precious metal catalyst requirement as the main bottleneck for the hydrogen fuel cell technology, the US-based company Ecolectro Inc. developed novel polymer materials for use in next-generation, cost-efficient hydrogen fuel cells.
The company's co-founders, Dr. Gabriel Rodriguez-Calero and Dr. Kristina Hugar spent many years at Cornell University developing advanced materials for energy storage and generation until they decided to team up their efforts in an attempt to ensure a green and sustainable future for all.
Building on the extensive research and engineering experience of the company's team, Dr. Rodriguez-Calero and Hugar took a very innovative approach by combining the advantages of PEM-based fuel cells with those of the alkaline fuel cells.
In the alkaline fuel cell, an alkaline liquid electrolyte (usually an aqueous solution of potassium hydroxide) permits the transport of negatively charged hydroxide anions (OH-) towards the anode of the cell (rather than protons towards the cathode as in PEM fuel cells).
The main advantage of the alkaline fuel cell is that the oxygen reduction reaction takes place in an alkaline environment (high pH), which allows the use of less expensive catalysts, such as nickel and cobalt, that exhibit high catalytic activity and stability in an alkaline environment.
Innovative Polymer Materials for Cost-Efficient Hydrogen Fuel Cells
Ecolectro's scientists have developed hydrocarbon-based cost-efficient polymers with an exceptionally stable tetrakis(dialkylamino) phosphonium cations appended to the polymer backbone chain. Using these materials, Ecolectro offers a range of products that can be used in the next generation of alkaline fuel cells.
A polymeric anion exchange membrane (AEMs), branded Tetrakis, which is designed to be used as a hydroxide transport medium in alkaline fuel cells, offers several advantages over the existing alkaline fuel cell technology.
The cationic moieties are fixed to the polymer chains (and not mobile as in a liquid electrolyte), which significantly reduces the electrolyte degradation. The hydrocarbon-based polymer material provides outstanding mechanical properties, allowing the fabrication of thin and robust membranes needed for high-performance operation.
Recyclable Cost-Efficient Polymers as Building Blocks for Anion Exchange Membranes
Ecolectro’s cost-efficient polymers do not require expensive platinum or palladium catalyst, a feature that can significantly reduce the cost of hydrogen fuel cells. The hydrocarbon-based polymer matrix permits the recycling of the catalyst material at the end of the component’s life (unlike the perfluorinated polymers used in PEM that hamper the recycling of the platinum catalyst).
Tetrakis AEMs offer unmatched chemical stability, high conductivity, and are mechanically robust. In-house tests have shown no chemical degradation for more than 120 days of accelerated alkaline testing conditions, and a hydroxide ionic conductivity of 22 mS cm-1 (at room temperature).
According to Ecolectro's team, these parameters demonstrate the suitability of their AEMs for use in commercial fuel cell technology.
The company also offers specially formulated ionomer solutions that can be used to enhance the electrochemical interface between the electrode, catalyst, and the polymer membrane for better performance.
The whole range of polymer alkaline exchange materials developed by the company allows it to fabricate complete membrane electrode assemblies with inexpensive non-platinum electrode catalysts, ready to use in cost-efficient hydrogen fuel cells.
Next-Generation Electrolyzers for Sustainable Hydrogen Generation
More importantly, Ecolectro's range of anion exchange materials and membrane electrode assemblies can be utilized in electrolyzer devices that use electrical current to split water molecules into hydrogen and oxygen (not unlike the operation of a fuel cell in reverse).
Cost-efficient electrolyzers can become an attractive and commercially-viable method of ultrapure hydrogen generation, which is an essential chemical feedstock and a non-polluting fuel (currently sourced mainly from natural gas processing).
Plans for Clean and Sustainable Future
These perspectives motivate Ecolectro's drive to provide an efficient and robust approach to clean renewable electricity and hydrogen generation.
The value of the Ecolectro's breakthrough developments is also recognized and supported by the US Department of Energy, the Advanced Research Projects Agency-Energy, and the New York State Energy Research and Development Authority, which would help the company to expand its portfolio of alkaline exchange ionomers and membranes, and manufacturing capabilities to meet the growing demands for cost-efficient renewable electricity and sustainable hydrogen generation.
References and Further Reading
FuelCellsWorks (2019) Ecolectro Announces SBIR Funding to Tailor Fuel Cell Membranes to Electrolyzers for Solar Hydrogen Production [Online] www.fuelcellsworks.com Available at: https://fuelcellsworks.com/news/ecolectro-announces-sbir-funding-to-tailor-fuel-cell-membranes-to-electrolyzers-for-solar-hydrogen-production/ (Accessed on 16 August 2020).
Wiredinsider (2019) Ecolectro: Building a Path to Cleaner Fuel Cells and a More Livable World. [Online] www.wired.com Available at: https://www.wired.com/wiredinsider/2019/01/ecolectro-building-a-path-to-cleaner-fuel-cells-and-a-more-livable-world/ (Accessed on 16 August 2020).
Green Car Congress (2018) Ecolectro secures $1.7M ARPA-E award for development of alkaline exchange membranes and ionomers for fuel cells and electrolyzers. [Online] https://www.greencarcongress.com Available at: https://www.greencarcongress.com/2018/12/20181202-ecolectro.html (Accessed on 16 August 2020).
K. M. Hugar et al., (2019) Protocol for the Quantitative Assessment of Organic Cation Stability for Polymer Electrolytes. ACS Energy Lett., 4, 1681−1686. Available at: https://doi.org/10.1021/acsenergylett.9b00908
W. You, K. M. Hugar, and G. W. Coates (2018) Synthesis of Alkaline Anion Exchange Membranes with Chemically Stable Imidazolium Cations: Unexpected Cross-Linked Macrocycles from Ring-Fused ROMP Monomers. Macromolecules 51 (8), 3212-3218. Available at: https://doi.org/10.1021/acs.macromol.8b00209
H. A. Miller et al., (2020) Green hydrogen from anion exchange membrane water electrolysis: a review of recent developments in critical materials and operating conditions. Sustainable Energy Fuels, 4, 2114. Available at: https://doi.org/10.1039/c9se01240k
N. Ramaswamy and S. Mukerjee, (2019) Alkaline Anion-Exchange Membrane Fuel Cells: Challenges in Electrocatalysis and Interfacial Charge Transfer. Chem. Rev., 119, 11945–11979. Available at: https://doi.org/10.1021/acs.chemrev.9b00157