New insight about the working principles of bipolar membranes could guide future fuel cell design (2024)

New insight about the working principles of bipolar membranes could guide future fuel cell design (1)

Bipolar membranes are a class of ion-conductive polymers comprised of two oppositely charged layers, known as the cation-exchange and anion-exchange layer. These membranes are central to the functioning of various technologies, including electrolyzers and hydrogen fuel cells.

While many companies and start-ups are using bipolar membranes to develop new energy technologies, their underlying working principles and ion solvation kinetics have not yet been fully elucidated. Better understanding these principles could inform the future fabrication of these materials and facilitate their successful integration in various devices.

Researchers at Fritz-Haber Institute of the Max Planck Society recently carried out a study to examine the water dissociation and ion solvaton kinetics at the interface between the two layers in bipolar membranes. Their paper, published in Nature Energy, gathered valuable new insight that could guide the future design of these membranes and of promising electrocatalysts for fuel cells.

"We wanted to understand the fundamental working principles of bipolar membranes and how they connect to electrochemistry more broadly," Sebastian Oener, corresponding author of the study, told Tech Xplore. "Bipolar membranes exist for over 65 years, but previous explanations about their working principles were rather unsatisfactory. We wanted to change that, connecting two fields that were previously thought to be separate."

New insight about the working principles of bipolar membranes could guide future fuel cell design (2)

To conduct their study, Carlos Gomez Rodellar, first author and Ph.D. student in the Interface Science Department, had to tackle various research challenges in an experimental setting. Firstly, he had to setup and benchmark a system that would allow him to study the kinetics of bipolar membranes without undesirable interferences from the cross-over of electrolyte ions.

"This system had to apply continuously physical pressure on the membrane electrode assembly with the metal oxide catalysts inside the bipolar junction," Oener explained. "Finally, Carlos had to design the whole system in such a way that we could controllably change the temperature of the cell and the humidified gases to do Arrhenius analysis and extract the bias dependent activation entropy and enthalpy. All of this can be provided with a modified fuel cell test station."

The measurements collected by the researchers paint a comprehensive picture of the fundamental principles underpinning the functioning of bipolar membranes. Specifically, they unveiled bias-dependent relationships between the activation entropy and enthalpy inside the bipolar junction, which appears to be related to a bias dependent dispersion of interfacial capacitance.

The team also observed that solvation kinetics in bipolar membranes exhibit characteristics that are unrelated to the chemical composition of the catalysts employed, but are likely originating from entropic changes in the interfacial electrolyte. Collectively, these insights could help to develop better performing bipolar membranes for electrodialysis, CO2 electrolyzers and H2 fuel cells.

New insight about the working principles of bipolar membranes could guide future fuel cell design (3)

"There are many different applications of bipolar membranes that are being explored around the world, including at promising start-ups," Oener said. "There is really a lot of potential. Beyond bipolar membranes, we were also able to show that the same physics are at play when water is dissociated and hydroxide ions solvated at electrocatalyst interfaces."

The results gathered by the research group at the Interface Science Department of the Fritz Haber Institute demonstrate the importance of entropic changes on the solvent side at liquid-solid interfaces. Their work could thus also guide the design of new promising electrocatalysts to initiate specific chemical reactions, such as those required to generate green hydrogen from alkaline electrolytes.

"Regarding bipolar membranes, there are still open fundamental questions that we want to address," Oener added.

"For example, the water formation reaction is important when bipolar membranes are run in forward direction. We also explore several applications in collaboration with others. These include different types of fuel cells and electrodialysis type systems. When it comes to ion solvation in electrocatalysis, we have multiple projects that are either already in review or are getting close to be submitted. Stay tuned for more."

More information:Carlos G. Rodellar et al, Ion solvation kinetics in bipolar membranes and at electrolyte–metal interfaces, Nature Energy (2024). DOI: 10.1038/s41560-024-01484-z.

Journal information:Nature Energy

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New insight about the working principles of bipolar membranes could guide future fuel cell design (2024)

FAQs

What is the working principle of bipolar membrane? ›

Therefore, the working principle of bipolar membrane is the current flow without any water splitting in the depletion layer (Fig. 8). The properties of bipolar membrane result directly from its semiconductor nature, and the apparent production of H+ and OH ions is simply a consequence of the current flow.

What is the role of the bipolar plates in a fuel cell? ›

The bipolar plates in the fuel cell stack serve the purpose of supplying fuel to the anode and oxidant to the cathode and also provide the electrical conduction between the cells.

What is the working principle of a fuel cell? ›

How Fuel Cells Work. Fuel cells work like batteries, but they do not run down or need recharging. They produce electricity and heat as long as fuel is supplied. A fuel cell consists of two electrodes—a negative electrode (or anode) and a positive electrode (or cathode)—sandwiched around an electrolyte.

What are the materials used in bipolar plates in fuel cells? ›

Bipolar Plates

These plates, which may be made of metal, carbon, or composites, provide electrical conduction between cells, as well as providing physical strength to the stack.

How does bipolar membrane electrodialysis work? ›

Bipolar Electrodialysis uses the basics of electrodialysis but introduces a bipolar membrane which splits water into H+ and OH- within an electrodialysis stack. BPED takes advantage of this process to either split salt streams into acid and caustic products or can adjust the pH of a process stream.

What are the principles of bipolar junction transistor? ›

Bipolar transistors conduct current using both electrons and holes in the same device. Operation of a bipolar transistor as a current amplifier requires that the collector-base junction be reverse biased and the emitter-base junction be forward biased.

What is the bipolar fuel cell construction? ›

The bipolar plate structure looks as follows: As the name "bi" implies, the bipolar plate serves as a carrier plate for the two poles of the fuel cell. These poles are the negatively charged, H2-carrying anode plate and the positively charged, O2-carrying cathode plate.

How many bipolar plates are in a fuel cell? ›

A fuel cell stack installed in electrolysis plants and fuel cells is made up of 400 to 500 individual bipolar plates. There are many different technologies for the production of bipolar plates depending on the materials and the applications. They vary in terms of cycle time, filigree of the flow field and costs.

Why is it called a bipolar plate? ›

The bipolar plates are termed “bipolar” because they have flow fields on both sides. This design is very convenient when you have membrane electrode assemblies (MEAs) on both sides. In a fuel cell with a single cell, there are no bipolar plates because there is only one MEA.

What are the principle advantages of fuel cell? ›

Fuel cell technology creates water from oxygen and hydrogen while simultaneously generating energy. It functions similarly to a battery. However, it does not need additional recharging. It can generate power as long as fuel and oxygen are available.

What are the advantages and disadvantages of a fuel cell? ›

Fuel cell advantages and disadvantages

As energy converters, fuel cells are efficient and environmentally friendly. Compared to combustion engines, however, they are – as of today – also significantly more expensive. In combination with batteries, high power and high energy density can be optimally combined.

What is the first problem with fuel cells? ›

These fuel cells are at an early stage of development. Challenges exist in SOFC systems due to their high operating temperatures. One such challenge is the potential for carbon dust to build up on the anode, which slows down the internal reforming process.

What membrane is used in fuel cells? ›

Polymer electrolyte membrane (PEM) fuel cells, also called proton exchange membrane fuel cells, use a proton-conducting polymer membrane as the electrolyte.

What type of membrane is used in fuel cells? ›

In recent years, novel AFCs that use a polymer membrane as the electrolyte have been developed. These fuel cells are closely related to conventional PEM fuel cells, except that they use an alkaline membrane instead of an acid membrane.

What are bipolar plates for electrolyzers? ›

Bipolar plates are a key component of proton exchange membrane, alkaline and solid oxide fuel cells and electrolysers. They are machined with complex flow fields or channels that, when stacked, distribute gas and air, as well as conduct electrical current from one cell to the next.

What is the bipolar electrode method? ›

A bipolar electrode (BPE) is an electronic conductor in contact with an ionically conductive phase. When a sufficiently high electric field is applied across the ionic phase, faradaic reactions occur at the ends of the BPE even though there is no direct electrical connection between it and an external power supply.

What is the principle behind ion exchange chromatography? ›

Principle of Ion Exchange Chromatography

The molecules separated on the basis of their charge are eluted using a solution of varying ionic strength. By passing such a solution through the column, highly selective separation of molecules according to their different charges takes place.

How do anion exchange membranes work? ›

Anion exchange membrane in MFCs comprise positively charged cation groups such as NH4+, NR3+, NR2H+, NHR2+, SR2+ and PR3+ to the polymer matrix, thereby allowing the passage of negatively charged ions through the membrane [16,34].

How does a cation exchange membrane work? ›

The cation exchange membrane is a selective barrier separating the anode and cathode compartments. The role of the membrane is to be selectively permeable to cations, preferably protons moving from the anode to the cathode.

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