Alkaline Water Electrolysis: electrodes
Water electrolysis to produce hydrogen is a process that occurs at the anode and cathode (the electrodes) of an electrochemical cell. When an electric current passes through the electrodes, it drives the electrolysis process, splitting water into hydrogen at the cathode and oxygen at the anode. When energy comes from renewables, hydrogen is labeled green.
To learn more about developing high-efficiency electrodes for alkaline water electrolysis to produce green hydrogen, we spoke with Dr. Chiara di Bari, PhD, Product Manager for Alkaline Water Electrolysis Electrodes in De Nora.
In her role, Chiara supervises the electrode development process and serves as the point of contact between R&D and clients.
Developing high-performance electrodes for water electrolysis means minimizing the reaction overpotential and initiating the reaction at an electrochemical potential as close as possible to ΔE° = -1.23 V.
As outlined in the figure below, this number is rarely matched in experimental conditions because we need to account for the overpotential of the process (ohmic losses, mass transport, electrical resistance for oxygen and hydrogen production), which adds to the theoretical minimum cell voltage required to trigger water electrolysis.
This is achieved through the use electrocatalytic coatings. A standard electrode for lab-scale demonstrations (100 cm²) is composed of a metal substrate coated with an electrocatalytic layer. The metal substrate, typically nickel, serves as an electron conductor, while the electrocatalytic coating promotes hydrogen evolution at the cathode and oxygen evolution at the anode in the electrochemical cell.
These coatings consist of carefully formulated blends of transition and rare-earth metals, developed in our R&D facilities. These are applied to bare nickel substrates to enhance the efficiency of electrochemical hydrogen and oxygen production.
Electrodes undergo a series of evaluation tests that predict coating behavior under different wear conditions, which replicate industrial plant operations. The first analysis to assess electrode performance is the SEP (single-electrode potential), which measures the electrochemical potential of the newly developed electrode.
In addition, accelerated lifetime tests evaluate the robustness and durability of the electrodes.
Every year, De Nora’s R&D centers perform approx. 2 million testing hours on electrodes through 300 cell tests, which operate 24/7. These accelerated life tests (ALTs) can simulate 5 to 10 years of field performance in a few months of operation, allowing the prediction of electrode durability and efficiency with exceptional accuracy. Our testing centers are equipped with pilot cells that are able to replicate water electrolysis in real-life conditions. Single-Electrode Potential (SEP) and accelerated lifetime tests enable the simulation of different operational setups, such as plant coupling with renewables or grid connection.
In addition, our R&D labs are globally connected. Tests are automatically recorded and evaluated in the Global Database, a powerful living archive. This asset, integrated with AI and [LB2.1]machine learning models, forms the foundation of our advanced analytics.
The newly developed anodes and/or cathodes are also tested in a pilot electrochemical zero-gap configuration to assess BOL (beginning of life) performance and stability over time under continuous or intermittent operation. Operative conditions mimic industrial standards: KOH solution (30% w/w), temperature ~90 °C, current density based on different applications. By checking these parameters, we can assess how the components (anode, cathode, and diaphragm) affect overall cell performance and identify the best electrode configurations for different applications. Other tests last thousands of hours and evaluate the cell's robustness over extended periods. These are usually accelerated tests that can project the robustness and lifetime for 8 years.
Because renewable energy is inherently variable, the electrolyzer runs only intermittently. Consequently, both the anode and cathode must withstand this intermittent operation, which imposes particularly demanding conditions on the electrodes. Therefore, it is essential to formulate coatings able to follow load variations and frequent starts & stops across a wide range of configurations, cell potential and operating conditions.
Alternatively, to prevent coating degradation, one can apply a small external electrical current to the electrolyzer. This method ensures the electrodes remain within safe potential ranges and is only applicable to atmospheric alkaline stacks.