Alkaline Water Electrolysis for Hydrogen Production
Summary
Alkaline water electrolysis is a mature and cost-effective technology for producing hydrogen by splitting water molecules into hydrogen and oxygen using an aqueous alkaline electrolyte, typically potassium hydroxide. The process occurs in an electrolyser cell comprising an anode and a cathode separated by a diaphragm or membrane that permits ionic conduction while preventing gas mixing. At the cathode, water molecules gain electrons and evolve hydrogen gas, while at the anode, hydroxide ions are oxidised to form oxygen gas. The use of non-precious metal catalysts such as nickel, iron and cobalt alloys reduces capital expenditure compared with acidic systems, and the intrinsic stability of alkaline conditions enables long operational lifetimes. Key challenges include minimising the cell voltage by reducing kinetic overpotentials at both electrodes, lowering ohmic resistance through optimised diaphragm materials or zero-gap cell designs, and controlling gas crossover to achieve high product purity. Advances in electrode architecture, membrane technology and operating strategies have progressively improved current densities and energy efficiencies. As global markets pursue decarbonised energy carriers, alkaline electrolysis offers a flexible platform for coupling with intermittent renewable electricity and for scaling from kilowatt-scale installations to multi-megawatt stacks, thereby playing a central role in the transition to a low-carbon hydrogen economy.
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Alkaline Water Electrolysis for Hydrogen Production publication trend
The graph below shows the total number of articles in alkaline water electrolysis for hydrogen production across all publications each year (not limited to Nature Index journals).
Technical terms
Electrocatalyst: Material that enhances the rate of the hydrogen or oxygen evolution reactions at the electrode surface.
Electrolyte: Conductive liquid, typically potassium hydroxide solution, that provides ionic transport between electrodes.
Diaphragm (separator): Porous barrier that allows ion flow while preventing mixing of hydrogen and oxygen gases.
Current density: Electric current per unit electrode area, often expressed in A cm–2, indicating the reaction rate.
Overpotential: Additional voltage beyond the thermodynamic requirement needed to drive an electrochemical reaction at a given rate.
Gas crossover: Unwanted diffusion or convection of produced gases through the diaphragm, affecting product purity and safety.
References
- Non-Precious Electrodes for Practical Alkaline Water Electrolysis. Materials (2019).
- Evaluation of Diaphragms and Membranes as Separators for Alkaline Water Electrolysis. Journal of The Electrochemical Society (2021).
- Optimal operating parameters for advanced alkaline water electrolysis. International Journal of Hydrogen Energy (2022).
- Impact of power supply fluctuation and part load operation on the efficiency of alkaline water electrolysis. Journal of Power Sources (2023).
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