Dynamic alkaline water electrolysis: the pathto parity

Render of 20 MW Verdagy Dynamic AWE electrolyser (image: Verdagy)

Electrolysis of water to produce hydrogen using conventional equipment today is expensive, which limits its adoption and economic attractiveness.

Conventional hydrogen electrolysis technology revolves around proton exchange membrane (PEM) and traditional liquid alkaline water electrolysis (AWE), with neither being ideally suited to cost effectively and safely scaling up hydrogen production.

Dynamic AWE systems, such as Verdagy’s eDynamic®, are a breakthrough technology drawing upon decades of successful chlor-alkali electrolysis experience and innovated to be perfectly suited to capitalise on the increase in renewable energy. Dynamic AWE systems seamlessly integrate with renewable energy to provide a safe and low-cost pathway for scaling up hydrogen without the drawbacks of traditional AWE and PEM.

Traditional AWE was the first water electrolyser technology to see commercialisation, in the 1930s. A traditional AWE system is characterised by two electrodes submerged in a liquid alkaline solution and separated by a porous diaphragm. The electrolyte is commonly potassium hydroxide (KOH) or sodium hydroxide (NaOH) with concentrations ranging from 20 to 40 wt.%.

Traditional AWE electrolysers have been used for several decades and are generally considered mature, reliable and low cost. They also do not typically use precious metals such as platinum or iridium, which are required in PEM electrolysers. However, traditional AWE electrolysers still suffer from several disadvantages:

They exhibit low current densities (0.2 – 0.6 A/cm²), resulting in lower productivity, ie, lower quantities of hydrogen produced per unit area. Low current densities also necessitate very large systems, increasing materials usage, real estate, and construction costs.
Traditional AWE electrolysers suffer from high leakage or shunt currents from centralised manifolds with highly conductive electrolyte, which lowers their conversion efficiencies and increases operational costs. Depending on the stack size and load, shunt currents can reduce efficiencies by as much as 10 – 80% (see Figure 1).¹
Traditional filter-pressed AWE electrolysers also have limited dynamic operating range because of high gas crossovers, which limits their utilisation when paired with intermittent renewable energy sources.
In addition, they are also susceptible to rapid degradation requiring expensive stack replacements and significant productivity losses. The inability to digitally monitor degradation on a component level leads to sporadic maintenance.

Figure 1. Traditional AWE systems suffer from large shunt currents that significantly reduce cell efficiency, especially with decreasing load. The result is a limited dynamic range and increasing costs of hydrogen production. Source: Verdagy white paper, Dynamic Alkaline Water Electrolysis, the pathway to hydrogen achieving fossil fuel cost parity

PEM water electrolysis is an acidic system developed in the 1960s that offers dynamic and high current density operation in a compact footprint. Even after decades of innovation, operation has largely remained the same with the acidic environment necessitating the use of precious materials, such as platinum, iridium, and ruthenium, which are often applied as catalysts to internal flow field components, such as porous transport layers (PTLs) and gas diffusion layers (GDLs). These flow field components assist with control of liquid and protons (H+) and the improved transport within the system allows a PEM electrolyser to be operated with a dry cathode (electrolyte only flows to the anode chamber). The dry cathode enables easier pressurised operation along with higher current densities, greater dynamic range, and more compact footprints than traditional AWE electrolysers.

However, PEM electrolysers have their own set of disadvantages:

PEM electrolysers typically have relatively small membrane areas, which results in significantly more cells and components needed to match the same total equivalent area of a dynamic AWE cell system. This renders PEM substantially more expensive and uneconomic for most hydrogen electrolysis applications.
In addition to their higher initial costs, they also require precious metal catalysts that are expensive and scarce, increasing operational costs. Suppliers are attempting to reduce the use of platinum group metals (PGMs) by using thinner MEAs (membrane electrode assemblies); but this lowers system reliability and manufacturing yields.
PEM electrolysers suffer from lower durability of membranes, which significantly increases operational costs and decreases availability.
Like filter-pressed, traditional AWE systems, PEM electrolysers also do not have the ability to be digitally monitored at the component level. This means that degradation is not monitored or controlled at the component level and the only option to deal with significant degradation is to replace entire electrolyser stacks, leading to significant operational expenses and lost productivity.

Dynamic AWE systems are based on a single-cell, zero-gap architecture in which individual electrolytic cells are electrically connected but chemically isolated. Dynamic AWE systems incorporate cell designs that confer several advantages:

They achieve current densities up to 400% higher than those of traditional AWE electrolysers. These high current densities, coupled with large cell areas, allow dynamic AWE systems to achieve very high rates of hydrogen production in compact footprints.
Dynamic AWE systems achieve the widest dynamic operating ranges in the industry, irrespective of technology type, to enable seamless coupling with intermittent energy sources, which leads to high utilisation factors, lower hydrogen production costs, and the lowest carbon intensities. The pairing of single-cell architecture also ensures an efficiency loss of only 0.1% – 2% from shunt currents throughout the entire operating range (see Figure 2).¹
The single-cell architecture of Dynamic AWE systems (see Figure 3) eliminates the need for stack replacements, a significant expense inherent in PEM and traditional AWE electrolysers (see Figure 4). Equally importantly, digital monitoring of individual electrolytic cells facilitates performance upgrades to maximise plant revenues and profitability and proactive maintenance to maximise plant utilisation.
Dynamic AWE systems build on several decades of experience in the chlor-alkali industry to enable robust, low-cost, highly reliable systems optimised for hydrogen electrolysis. The capital expenditure/first cost required for Dynamic AWE systems is significantly lower than that of PEM electrolysers, and comparable to those of traditional AWE electrolysers, while offering higher productivity, higher electrolytic (or conversion) efficiency, field upgradable performance, and significantly smaller footprints and installation costs.

Figure 2. The low shunt currents of Dynamic AWE systems maximise hydrogen production efficiency and ensure high hydrogen production rates, resulting in lower energy capital costs relative to traditional AWE and PEM systems. Source: Verdagy white paper, Dynamic Alkaline Water Electrolysis, the pathway to hydrogen achieving fossil fuel cost parity

Figure 3. Verdagy’s advanced single cell architecture allows every cell in the plant to be individually monitored and serviced, enabling optimum operation and performance guarantees, while also eliminating stack replacements and achieving significantly lower operating costs. Source: Verdagy

Verdagy’s Dynamic AWE

Verdagy has designed and optimised its refinery-grade, Dynamic AWE eDynamic electrolysers for industrial scale applications. They have the highest current densities and hydrogen production rates of any alkaline electrolysers. They also provide real-time load matching to intermittent energy sources such as renewables and can accommodate varying electrical grid prices in order to maximise asset utilisation. They also completely eliminate stack replacements and offer dramatically reduced operating costs thanks to the use of electrolytic cells that have lifetimes of over 20 years. In addition, modular design enables them to offer the lowest installation costs and commissioning times.

In addition, each individual cell is digitally monitored and can be field upgraded to offer continuously improving performance and electrical conversion efficiency. While all other hydrogen electrolysers suffer from annual degradations in performance that lead to significant increases in annual energy expenses, Verdagy’s electrolysers are capable of providing annual performance improvements that significantly reduce annual energy costs, the single largest operating expense in a hydrogen electrolysis plant.

Verdagy’s electrolysers thus offer the lowest levelised cost of hydrogen (LCOH), high reliability, low installation and construction costs, maximum operating flexibility, and among the smallest footprints.

Verdagy’s Dynamic AWE electrolysers are able to provide maximum flexibility and direct coupling with renewable sources due to low gas crossover throughout the entire operating range (see Figure 5).

Figure 5. Gas crossover vs load for various water electrolysis technologies. Verdagy’s Dynamic AWE maintains low gas crossover throughout entire load range, enabling safe production of hydrogen gas with high purity. HTO = hydrogen to oxygen. Source: Verdagy white paper, Dynamic Alkaline Water Electrolysis, the pathway to hydrogen achieving fossil fuel cost parity

Traditional AWE and PEM systems suffer from unsafe amounts of gas crossover (above 2% hydrogen to oxygen (HTO)) as the load is reduced, which limits the total operating range and requires full shutdown when not enough power is available. Altering the operating conditions and components can limit the gas crossover for these systems, but with the sacrifice of efficiency. As systems move towards thinner membranes in the hope of improving cell efficiency, this only increases the amount of gas crossover. Gas recombination layers are being explored to combat unsafe amounts of gas crossover; however, this requires additional catalyst costs and reduces the amount of hydrogen produced.

In contrast, Verdady’s Dynamic AWE electrolysers can safely operate without sacrificing efficiency or requiring additional measures. The low gas crossover not only makes the system safe, but lower gas crossover also increases the purity and production rates of hydrogen.

Fastest path to parity

In summary, Dynamic AWE electrolysers can be characterised as combining the reliability, robustness and low-cost materials of construction of traditional AWE systems with the fast responsiveness and wider dynamic range of PEM systems, while designing out the disadvantages of both. Verdagy’s Dynamic AWE electrolysers use single-cell architecture to virtually eliminate loss of efficiency from degradation and shunt currents. In addition, Verdagy’s dynamic AWE electrolysers are also the only electrolysers in the world today that can achieve improved performance after being installed. Other electrolysers degrade each year. This combination provides plant owners with the lowest LCOH coupled with the assurance that they will always have state-of-the-art performance, and the fastest path to fossil parity costs.