Atmos Power’s Alkaline Based Electrolysers : A Proven Solution for Large-Scale Green Hydrogen Production

Alkaline water electrolysis is a well-established technology with a long history dating back to the late 18th century. The phenomenon was first introduced by Troostwijk and Diemann in 1789 . Over the following decades, the technology saw steady advancements, with the first industrial alkaline electrolyser plant going into operation in 1902, producing hydrogen for ammonia synthesis in the fertilizer industry.

By the 1920s and 1930s, alkaline electrolysis experienced a boom due to high ammonia demand, with over 400 industrial units installed worldwide.

Atmos Power can offer both Alkaline as well as PEM based Water Electrolysers for Hydrogen Production

How does an Alkaline based Electrolyser work?

Alkaline water electrolysis is a mature and well-established technology for producing hydrogen and oxygen by splitting water molecules using electricity. The key aspects of how an alkaline electrolyser works are:

Electrodes and Electrolyte : The electrolyzer has two metal electrodes (typically nickel-based) immersed in an aqueous alkaline electrolyte solution, commonly 25-40% potassium hydroxide (KOH) or sodium hydroxide (NaOH).

Diaphragm / Separator : The two electrodes are separated by a porous diaphragm or separator, usually made of materials like zirconium oxide (Zirfon), or a polysulfone matrix. This diaphragm allows the transport of hydroxide ions (OH-) between the electrodes while separating the product gases.

Electrochemical Reactions : When an electric current is applied, water is split at the anode through the oxygen evolution reaction, producing oxygen gas. At the cathode, water is reduced through the hydrogen evolution reaction, producing hydrogen gas.

Anode (Oxygen Evolution): 4OH- → O2 + 2H2O + 4e-
Cathode (Hydrogen Evolution): 4H2O + 4e- → 2H2 + 4OH-

Operating Conditions : Alkaline electrolyzers typically operate at temperatures between 60-80°C and pressures below 30 bar. The current density ranges from 0.2-0.4 A/cm2 and the cell voltage is 1.8-2.4V.

Efficiency : Alkaline water electrolysis has a typical efficiency of around 70%.

Progress till today : alkaline water electrolysis remains the most mature and widely deployed technology for large-scale industrial hydrogen production. It offers several key advantages:

What are some of the strengths of Alkaline Based Hydrogen Electrolysers?

  • High efficiency : Alkaline electrolysis has a high efficiency of up to 80% for converting electrical energy into hydrogen gas.
  • Renewable energy source : Alkaline electrolysers can be powered by renewable energy like wind and solar, making it a clean and sustainable hydrogen production method.
  • Scalability : Alkaline electrolysis can be scaled up or down to produce hydrogen at any scale, from small fuel cells to large industrial plants.
  • Low operating costs : Alkaline electrolysis has relatively low operating costs as it doesn’t require expensive catalysts or high temperatures.
  • High-purity hydrogen : The process produces high-purity hydrogen gas suitable for fuel cells, chemical production, and other applications.
  • Safe and environmentally friendly : Alkaline electrolysis is a safe process that doesn’t produce greenhouse gases or other harmful emissions.
  • Flexibility in input water quality : Alkaline electrolyzers can use a variety of water sources including tap water, seawater, and wastewater.
  • Long history and proven reliability Alkaline electrolysis has been used industrially since the early 1900s, demonstrating its reliability.
  • Lower capital costs : Alkaline electrolyzers use non-precious metal catalysts like nickel and cobalt, reducing capital costs compared to PEM.
  • Ability to produce oxygen : As a byproduct, alkaline electrolysis produces high-purity oxygen gas which has various industrial and medical uses.
  • Flexibility in operating conditions Alkaline electrolyzers can operate over a wide range of current densities and temperatures.
  • Modular and compact design Alkaline electrolyzer stacks have a simple, modular design allowing for compact installations.
  • Potential for efficiency improvements : Ongoing research aims to develop advanced materials and designs to further increase alkaline electrolyzer efficiency.
  • Suitability for remote applications : Small-scale alkaline electrolyzers can produce hydrogen for energy supply in remote areas without grid access.
  • Potential for load balancing : Adjusting alkaline electrolyzer output can help balance electricity grid loads.
  • Ability to produce pure gases : Alkaline electrolyzers can produce pure hydrogen and oxygen for specialized applications like laboratories and hospitals.
  • Potential for cost reduction For large-scale systems, electricity costs and hydrogen value are the dominant factors, which can be optimized.
  • Potential for efficiency up to 94% : With advanced designs and materials, alkaline electrolyzer efficiency could reach 94%.
  • Potential for high production rates : Alkaline electrolyzers can achieve hydrogen production rates of up to 5 Nm3/h per m2 of electrode area.
  • Potential for long lifetimes : With proper water treatment and maintenance, alkaline electrolyzer stacks can operate for over 90,000 hours.

What are the disadvantages of Alkaline Based Hydrogen Generators?

  • Lower Current Densities : Alkaline electrolyzers typically operate at lower current densities (0.1-0.5 A/cm2) compared to PEM electrolyzers, limiting their efficiency and hydrogen production rates.
  • Sensitivity to Carbon Dioxide : The alkaline electrolyte used in these systems is sensitive to carbon dioxide, which can reduce performance and efficiency over time.
  • Lower Hydrogen Purity : The hydrogen produced by alkaline electrolyzers is not as pure as the hydrogen from PEM systems, typically around 99.5-99.9% purity.
  • Limited Part-Load Operation : Alkaline electrolysers have a limited minimum load range due to increased gas crossover at low power, making them less suitable for dynamic, renewable-powered operation.
  • Thermal Management Challenges : Maintaining optimal operating temperatures can be more challenging in alkaline systems compared to other electrolyzer technologies.
  • Slower Dynamic Response : Alkaline electrolysers generally have a slower dynamic response compared to PEM systems, making them less suitable for rapid load changes.
  • Larger Footprint : Alkaline electrolyser systems tend to have a larger physical footprint compared to PEM or solid oxide electrolyzers of similar capacity.
  • Potential for Electrode Degradation : The reverse current that can occur during shutdown/startup cycles can potentially lead to degradation of the electrodes over time.
  • Higher Water Consumption : Alkaline electrolyzers typically have a higher water consumption per unit of hydrogen produced compared to other electrolyzer technologies.

Ongoing research is focused on addressing these limitations by developing advanced electrode materials, separators, and system designs to increase efficiency and reduce costs. However overall, alkaline water electrolysis remains the most mature and widely deployed technology for large-scale industrial hydrogen production. Its long history, reliability, and ability to scale to multi-megawatt plants make it an attractive choice for green hydrogen generation from renewable electricity.

What is the Proton Exchange Membrane (PEM) based electrolyzer?

Proton Exchange Membrane (PEM) electrolyzersare an advanced technology for producing green hydrogen from renewable electricity through water electrolysis. PEM systems use a solid polymer electrolyte membrane to selectively transport protons from the anode to the cathode, where they combine with electrons to form hydrogen gas.

PEM electrolyzers (Proton Exchange Membrane) function similarly to alkaline electrolyzers but with some key differences. Here’s a breakdown of how they work:

Components

  • Water Feeding : Liquid water is fed to the anode and cathode sides of the cell.
  • Anode Reaction : At the anode, water splits into oxygen, protons (H+), and electrons (e-). The oxygen forms gas bubbles that flow out of the anode. However, the PEM only allows protons to pass through.
  • Proton Transport : The protons travel through the PEM towards the cathode.
  • Cathode Reaction : At the cathode, the protons combine with the electrons (which traveled through the external circuit) to form hydrogen gas. This hydrogen gas is then collected from the cathode side.

Process

  • Electrodes : PEM electrolyzers also use two electrodes, typically made of platinum due to its excellent catalytic properties for the reactions.
  • Proton Exchange Membrane (PEM) : This is the heart of the PEM electrolyzer. It’s a solid, permeable membrane that allows only protons (H+) to pass through while blocking electrons and oxygen.
  • Bipolar Plates : These distribute water and electricity throughout the cell and separate the product gases (hydrogen and oxygen).
  • Overall Reaction : The net reaction is the same as in alkaline electrolysis, splitting water into hydrogen and oxygen:

2H2O (l) -> 2H2 (g) + O2 (g)

PEM electrolysers offer several key advantages over other electrolyzer technologies:

  • High Efficiency : PEM systems can achieve electrical efficiencies of up to 80%, making them one of the most efficient ways to produce hydrogen from water and electricity.
  • Fast Response : PEM electrolyzers can rapidly adjust their hydrogen production in response to changes in electricity supply, allowing them to be paired with intermittent renewable sources like wind and solar.
  • High Purity Hydrogen : The hydrogen produced by PEM electrolyzers is very pure, typically 99.999% pure, making it suitable for use in fuel cells and other applications requiring high purity gas.
  • Compact Design : PEM electrolyzers have a relatively compact footprint compared to alkaline systems of similar capacity, simplifying installation and integration.

However, PEM electrolysers also face some challenges

  • Higher Costs : The use of expensive platinum group metal catalysts and the need for high-purity water make PEM systems more costly than alkaline electrolyzers.
  • Limited Durability : The membrane and catalysts in PEM electrolyzers can degrade over time, limiting their lifespan compared to alkaline systems.
  • Sensitivity to Impurities : PEM electrolyzers require very pure water, so extensive water treatment is necessary to remove impurities that can damage the membrane and electrodes.

Ongoing research is focused on developing more durable, cost-effective materials for PEM electrolyzers to improve their competitiveness. Integrating PEM systems with renewable energy sources is also a promising approach to produce low-cost green hydrogen.

Overall, PEM electrolysis represents a promising technology for efficiently producing high-purity hydrogen from renewable electricity. Its ability to rapidly adjust output makes it well-suited for grid balancing and integration with intermittent renewables. As the technology matures and costs decline, PEM electrolyzers are poised to play a key role in the emerging green hydrogen economy.

What are the Pros and Cons of Alkaline vs PEM Hydrogen Electrolysers

  • High Efficiency : PEM systems can achieve electrical efficiencies of up to 80%, making them one of the most efficient ways to produce hydrogen from water and electricity.
  • Fast Response : PEM electrolyzers can rapidly adjust their hydrogen production in response to changes in electricity supply, allowing them to be paired with intermittent renewable sources like wind and solar.
  • High Purity Hydrogen : The hydrogen produced by PEM electrolyzers is very pure, typically 99.999% pure, making it suitable for use in fuel cells and other applications requiring high purity gas.
  • Compact Design : PEM electrolyzers have a relatively compact footprint compared to alkaline systems of similar capacity, simplifying installation and integration.

However, PEM electrolysers also face some challenges

Alkaline Electrolysers

Pros

  • Proven, mature technology with over 100 years of industrial use
  • Lower capital costs due to use of non-precious metal catalysts
  • Ability to scale up to multi-megawatt plant sizes
  • Longer lifespans compared to other electrolyser types
  • Can operate over a wide range of current densities and temperatures
  • Modular, compact design for easier installation
  • Potential for high efficiency up to 94% with advanced designs
  • Potential for high production rates up to 5 Nm3/h per m2 of electrode area

 

Cons

  • Lower current densities (0.1-0.5 A/cm2) limiting efficiency
  • Sensitivity to carbon dioxide in the electrolyte, reducing performance
  • Lower hydrogen purity compared to PEM (99.5-99.9%)
  • Limited minimum load range and slower dynamic response
  • Corrosive alkaline electrolyte requiring specialized materials
  • Larger physical footprint compared to PEM or solid oxide
  • Potential for electrode degradation during shutdown/startup
  • Higher water consumption per unit of hydrogen produced

PEM ELECTROLYSERS

Pros

  • Higher efficiency, up to 90%
  • Longer lifespan due to more durable platinum-based electrodes
  • Ability to produce ultra-high purity hydrogen (99.999%)
  • More flexibility in operation, handling varying loads and pressures
  • Less corrosive electrolyte, reducing maintenance issues
  • Lower water consumption per unit of hydrogen
  • Higher current densities for more efficient hydrogen production
  • Less sensitivity to water impurities, reducing pretreatment needs
  • Compact, modular design for easier integration
  • Higher platinum utilization for cost and efficiency improvements

 

Cons

  • Higher capital costs due to use of precious metal catalysts
  • More energy-intensive operation compared to alkaline
  • Potential for faster degradation of components over time

In summary, alkaline electrolysers offer advantages in terms of lower costs, larger scale, and longer lifespans, making them well-suited for large-scale industrial hydrogen production. PEM electrolysers excel in efficiency, hydrogen purity, and flexibility, making them more suitable for applications requiring high-purity hydrogen. The choice between the two technologies will