Description
Currently, there are two distinct commercial water electrolysis technologies that operate at low temperatures— alkaline and PEM (proton-exchange membranes) electrolyzers. Alkaline electrolyzers, a commercially more mature technology among the two, contain two electrodes immersed in a liquid alkaline electrolyte consisting of a concentrated KOH solution. In contrast, PEM electrolyzers use a solid proton conducting polymer as the electrolyte and deionized water. As a result, PEM electrolyzers have many advantages over alkaline electrolyzers, such as a relatively simple system design and being able to operate safely at higher current densities. A third technology, currently at the precommercial stage, alkaline exchange membrane (AEM) systems, has the potential to place water electrolysis on a new cost reduction trajectory.
PEM water electrolysis has been known for many years; however, due to expensive components, such as membranes and bipolar plate materials and limited lifetime, PEM electrolyzers became established only in relatively small-scale niche applications, such as laboratory hydrogen and oxygen generators, life support systems, fuel supply for small fuel cell systems, etc. In general, PEM water electrolysis systems can provide a relatively simple, scalable, and easily deployable source of high-purity hydrogen for smaller retail and commercial applications near the point of consumption. In recent years, hydrogen PEM fuel cells made significant progress toward commercialization, resulting in growing interest in technologies for hydrogen on-site production, such as PEM water electrolysis. Thus, the use of PEM water electrolysis for hydrogen fuel production became a vector of interest for fuel cell deployment opportunities in such sectors as sustainable mobility, material handling, and back-up power.
The rapid development of relatively small-scale PEM fuel cell technology also contributed to a “leapfrog” effect in the fundamental understanding of the requirements and functionalities of certain components and attributes of the PEM electrolysis technology that are both common for PEM fuel cells and electrolyzers, such as manufacturing aspects, components (membranes, plates, catalyst), flow-field design, etc. However, new trends in PEM water electrolysis systems development opened up new technology gaps and requirements that have not been discussed before with respect to PEM water electrolysis. For example, hydrogen is considered as one of the best solutions for large-scale energy storage that comes from renewable and intermittent power sources such as wind and solar electricity. If zero-carbon power sources, such as renewable or nuclear power, are used in combination with large-scale PEM water electrolysis, the resulting system will become suitable for large-scale clean and economically attractive hydrogen production and energy storage applications. Water electrolysis provides a sustainable solution for hydrogen production and is very well suited to be coupled with renewable energy sources. Thus, yet another vector of hydrogen applications for energy storage, called powerto- gas, is emerging and large utility companies are becoming involved.
To address technology gaps for large-scale PEM water electrolysis systems, the following areas require additional development: improved stack performance, scale up to megawatt size, grid integration, high pressure operation, high current density operation, degradation of components associated with transient operation, and a variety of market issues. All of these gaps relate directly to increased participation of PEM water electrolysis systems in hydrogen markets for various applications, not limited to fuel cells only. Megawatt scale-up, needed for such applications as power-to-gas and on-site refueling stations, includes requirements to reduce capital costs by 50% on a per kilowatt basis and availability of low-cost testing facilities; for example, electricity costs for PEM electrolysis megawatt testing can alone be a great challenge. Another challenge that the PEM water electrolysis industry has hardly discussed before is the large-scale manufacturing of cathode catalyst- coated membranes and stack components, availability of iridium, etc.
It is expected that demand for hydrogen as a fuel for fuel cells in both transport and stationary applications will continue to grow, alongside hydrogen for energy storage (the power-to-gas vector), thus generating more and more demands for PEM water electrolysis systems of large capacities.
It is well recognized that PEM water electrolysis systems are robust and dynamic. These systems can offer a fast response to volatile renewable energy sources. Due to the use of a dense proton-exchange membrane, PEM water electrolysis systems are capable of producing hydrogen at relatively high and practical discharge pressure, suitable, for example, for the injection of hydrogen into the grid of natural gas pipes. PEM water electrolyzers can also be scaled up to address various demands for energy storage.
Addressing climate change and the associated need for increasing renewable energy supply makes energy storage a critical technological component of the future energy landscape. PEM water electrolysis when coupled with renewable energy sources and when electrolytic hydrogen is used to capture CO2 to produce synthetic methane via the Sabatier reaction can also be attractive as an additional power-to-gas application reducing CO2 emissions.
Due to the ever-increasing desire for green energy, the last decade has seen regained research interest in PEM electrolysis. However, significant challenges still remain for PEM electrolysis to be a commercially feasible largescale hydrogen production solution. These challenges include the insufficient durability of the catalysts and membrane, high cost associated with the use of platinum group metal-based catalysts, corrosion of the current collectors and separator plates, and the development of a stack concept for the megawatt power range.
The intention of this book is to provide a comprehensive research source for PEM electrolysis, discuss fundamental aspects as well as examples of applications, provide a review of the state-of-the-art technologies and challenges related to each of the components of the PEM electrolysis, identify various failure modes and failure mechanisms, and discuss component degradation testing methods and protocols.
This book provides researchers and technology engineers with the most comprehensive and updated knowledge on PEM electrolysis technology, thus helping them identify technology gaps and develop new materials and novel designs that lead to commercially viable PEM electrolysis systems. We believe that students and professionals in disciplines such as electrochemical engineering, electrochemistry, material science in electrocatalyst development, material science in polymer development, and chemical and mechanical engineers working on energy storage and clean technologies will find this book useful.