Alkaline water electrolysis
[4][7] 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 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.
[citation needed] 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 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.
[9] 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.
The ionic conductivity is supplied by the aqueous alkaline solution, which penetrates in the pores of the diaphragm.
Asbestos diaphragms have been used for a long time due to their effective gas separation, low cost, and high chemical stability; however, their use is restricted by the Rotterdam Convention.
[12] The diaphragm further avoids the mixing of the produced hydrogen and oxygen at the cathode and anode,[13][14] respectively.
[11] Typically, Nickel based metals are used as the electrodes for alkaline water electrolysis.
Ni is considered as more stable during the oxygen evolution,[18] but stainless steel has shown good stability and better catalytic activity than Ni at high temperatures during the Oxygen Evolution Reaction (OER).
[5] High surface area Ni catalysts can be achieved by dealloying of Nickel-Zinc[5] or Nickel-Aluminium alloys in alkaline solution, commonly referred to as Raney nickel.
[21] The latter approach might be interesting for large scale industrial manufacturing as it is cheap and easily scalable, but unfortunately, all the strategies show some degradation.
In comparison to Proton exchange membrane electrolysis, the advantages of alkaline water electrolysis are mainly:[25] One disadvantage of alkaline water electrolysers is the low-performance profiles caused by the commonly-used thick diaphragms that increase ohmic resistance, the lower intrinsic conductivity of OH− compared to H+, and the higher gas crossover observed for highly porous diaphragms.
