Alkaline water electrolysis
| Alkaline water electrolysis | |
|---|---|
| Typical Materials | |
| Type of Electrolysis: | Alkaline Water Electrolysis |
| Style of membrane/diaphragm | NiO/Asbestos/polysulfone matrix and ZrO2 (Zirfon)/polyphenil sulfide |
| Bipolar/separator plate material | Stainless steel |
| Catalyst material on the anode | Ni/Co/Fe |
| Catalyst material on the cathode | Ni/C-Pt |
| Anode PTL material | Ti/Ni/zirconium |
| Cathode PTL material | Stainless steel mesh |
| State-of-the-art Operating Ranges | |
| Cell temperature | 60-80 °C |
| Stack pressure | <30 bar |
| Current density | 0.2-0.4 A/cm2 |
| Cell voltage | 1.8-2.40 V |
| Power density | to 1.0 W/cm2 |
| Part-load range | 20-40% |
| Specific energy consumption stack | 4.2-5.9 kWh/Nm3 |
| Specific energy consumption system | 4.5-7.0 kWh/Nm3 |
| Cell voltage efficiency | 62–82% (HHV) |
| System hydrogen production rate | <760 Nm3/h |
| Lifetime stack | <90,000 h |
| Acceptable degradation rate | <3 μV/h |
| System lifetime | 20-30 years |
Alkaline water electrolysis is a type of electrolysis that is characterized by having two electrodes operating in a liquid alkaline electrolyte. Commonly, a solution of potassium hydroxide (KOH) or sodium hydroxide (NaOH) at 25-40 wt% is used. These electrodes are separated by a diaphragm, separating the product gases and transporting the hydroxide ions (OH−) from one electrode to the other. A recent comparison showed that state-of-the-art nickel based water electrolysers with alkaline electrolytes lead to competitive or even better efficiencies than acidic polymer electrolyte membrane water electrolysis with platinum group metal based electrocatalysts.
The technology has a long history in the chemical industry. The first large-scale demand for hydrogen emerged in late 19th century for lighter-than-air aircraft, and before the advent of steam reforming in the 1930s, the technique was competitive.
Hydrogen-based technologies have evolved significantly since the initial discovery of hydrogen and its early application as a buoyant gas approximately 250 years ago. In 1804, the Swiss inventor Francois Isaac de Rivaz secured a patent for the inaugural hydrogen-powered vehicle. This prototype, equipped with a four-wheel design, utilised an internal combustion engine (ICE) fuelled by a mixture of hydrogen and oxygen gases. The hydrogen fuel was stored in a balloon, and ignition was achieved through an electrical starter known as a Volta starter. The combustion process propelled the piston within the cylinder, which, upon descending, activated a wheel through a ratchet mechanism. This invention could be viewed as an early embodiment of a system comprising hydrogen storage, conduits, valves, and a conversion device.
Approximately four decades after the military scientist Ritter developed the first electrolyser, the chemists Schoenbein and Sir Grove independently identified and showcased the fuel cell concept. This technology operates in reverse to electrolysis around the year 1839. This discovery marked a significant milestone in the field of hydrogen technology, demonstrating the potential for hydrogen as a source of clean energy.