4.25 Electrolyzers

Electrolyzer technologies have been gaining more attention, as they serve as a potential hydrogen production method that is capable of producing high-purity hydrogen from water and able to meet hydrogen demands at various capacities. In this contribution, water electrolysis technologies for hydrogen production are discussed in the context of different electrolysis processes, including the historical development, theoretical thermodynamic, and electrochemical principles. Electrode and electrolyte materials are reviewed for the various types of electrolyzers, and the current state-of-the-art applications and technologies are presented. Numerous illustrative examples are provided to cover critical concepts and provide deeper understanding. Alkaline, proton exchange membrane (PEM), and solid oxide electrolyzers are commercially available or at an advanced level of demonstration and in the foreseeable future are expected to be available in the market. The theoretical and technical background of each of these electrolyzers is presented and discussed. Additionally, the limitations of these electrolyzers are highlighted in the context of the research and development efforts of the scientific community to overcome these challenges. A case study is also presented to demonstrate how the thermodynamic and electrochemical models can be used to predict and evaluate the performance of a high temperature solid oxide electrolyzer where the cell potential, the different cell polarizations, and cell efficiencies are evaluated. The contribution includes a section on the environmental impact of electrolyzers under which the impact of electrolyzers on the environment is discussed and compared with other hydrogen production methods utilizing life cycle assessment as a comparative measure. Lastly, the economics of electrolyzers is discussed to compare the cost of hydrogen production using state-of-the-art electrolyzers with the cost of conventional technologies. The contribution concluds with remarks reflecting on the main concepts covered in this contribution along with future directions.