The evolution of traditional Alkaline Water Electrolysis

Water electrolysis has been known for over 200 years, with the first experiment using a voltaic pile to split water dating back to 1800.
By 1902, more than 400 industrial water electrolysis units were in operation. Additionally, different commercial alkaline water electrolyzers were developed in the 20th century to generate the hydrogen needed to produce ammonia using hydroelectricity.
Nowadays, alkaline water electrolysis (AWE) is a mature technology and the most prominent solution for green hydrogen production, as it is a well-established, relatively simple technology, efficient, competitive, and can be coupled with renewable energy sources such as solar or wind power.

Alakaline Water Electrolysis (AWE) is a type of electrolysis that occurs in an alkaline environment, meaning at basic pH, typically using a highly concentrated solution of potassium hydroxide (KOH) or sodium hydroxide (NaOH) as the electrolyte.
The process occurs in an electrolysis cell, which consists of two electrodes (an anode and a cathode) separated by a diaphragm and immersed in the electrolyte solution.

When an electric current is passed across the electrodes, water molecules at the cathode (negative electrode) are reduced, meaning they gain electrons and form hydrogen gas (H2):

At the same time, the hydroxyl ions at the anode (positive electrode) are oxidized, losing electrons and forming oxygen gas (O2):

Overall, the reaction can be represented as:

Since its origin, alkaline water electrolysis has experienced huge advancements and traditional AWE has been replaced by new and advanced alkaline water electrolysis. Building on the centenarian knowledge of traditional AWE, the latest technology boasts better current densities, energy efficiency, and a smaller footprint. In fact, AWE jumped from 0.1 – 0.25 A/cm2 to above 1.0 A/cm2 of current densities while having lower or similar specific energy consumptions.

The graph below shows the performance of the new De Nora’s AWE compared to the traditional AWE. Considering a specific current density expressed as hydrogen production (Faraday’s law), we observe that the improved AWE powered by De Nora offers considerably lower electric energy consumption than traditional AWE. Similarly, if we consider a specific electric energy consumption, one can work at significantly higher current densities (expressed as hydrogen production).

This is because De Nora uses state-of-the-art electrocatalytic coatings applied on the electrodes, an improved diaphragm, and a zero-gap cell configuration to lower overpotential and ohmic resistances.

To minimize the cell overpotential, the advanced De Nora’s AWE moved away from the traditional use of nickel and nickel Raney plates to employ as electrodes. In fact, research at De Nora has been focusing on finding the most performing materials to utilize as electrocatalytic coatings to apply to the surface of nickel electrodes. Efforts were directed towards investigating the most robust coatings able to withstand reverse currents, higher current densities, and pressurized conditions. For example, to create new cathodes, the selection of electrocatalytic coating revolved around using mixtures of transition metals as well as rare-earth metals to guarantee the high robustness of the electrodes.

Similarly, novel diaphragms are thinner than those used in the traditional AWE and made of innovative materials such as plastic polymers and some inorganics (zirconia) that substitute old-fashioned asbestos. These polymers have enough porosity to allow ions to move across the diaphragm, give higher flexibility to the system, and prevent the crossover of the produced gasses – oxygen and hydrogen.

Finally, traditional AWE uses a finite gap configuration, meaning there’s a space between the electrodes and the diaphragm. This penalizes the cell's performance as the gap represents an ohmic resistance, causing a cell potential drop. In a zero-gap configuration, which is the standard set-up for the advanced De Nora’s AWE, the electrodes are in direct contact with the diaphragm, and this minimizes the ohmic drop due to moving ions across the electrolyte.

Alkaline water electrolysis has been evolving through the years, and the new and improved De Nora’s AWE differentiates it from the traditional AWE for its higher current densities, better energy consumption, and smaller footprint. Research at De Nora worked towards finding the most robust materials to employ as electrocatalytic coatings as well as reducing ohmic resistance by adopting a zero-gap configuration. Taken together, these new features make the new AWE stand out among other water electrolysis techniques for the low cost of the equipment, maturity of the technology, and energy efficiency, and it’s the most suitable technology for the commercialization of green hydrogen.