What Is a Hydrogen Electrolzyer?

A hydrogen electrolyzer is an electrochemical device that consumes electrical power to split water into hydrogen and oxygen. Hydrogen electrolyzers are used for hydrogen production and are considered as part of a green energy production–storage distribution system when combined with a renewable power source, a hydrogen tank, and fuel cell systems such as fuel cell electric vehicles.

The three main types of hydrogen electrolyzers—alkaline, polymer electrolyte membrane (PEM), and solid oxide—focus on differences in electrolyte materials. A PEM hydrogen electrolyzer decomposes water using a semipermeable membrane that allows proton transport and blocks the electron flow. Because of this characteristic, this kind of hydrogen electrolyzer is also known as a proton exchange membrane electrolyzer.

As shown below, water enters the electrolyzer at the anode. When direct current (DC) electricity is applied between two electrodes, negatively charged oxygen in the water molecule gives up its electrons and results in protons, electrons, and oxygen at the anode. The protons pass through the membrane toward the cathode, where the protons combine with electrons and produce hydrogen.

PEM electrolyzers are valued because of their greater energy efficiency, wider operating temperature, and easier maintenance relative to other kinds of hydrogen electrolyzers.

Creating software models of hydrogen electrolyzers enables you to simulate different levels of fidelity of the hydrogen production. Simscape Electrical™ and Simscape Fluids™ help you create hydrogen electrolyzer models so that you can:

• Assess the electrothermal performance of the electrolyzer stack using a hydrogen electrolyzer model that describes the detailed electrochemical reaction
• Design, simulate, and optimize the performance of a hydrogen production system using a hydrogen electrolyzer model with functional details for component and balance-of-plant sizing
• Develop and fine-tune an electrolyzer control system using a hydrogen electrolyzer model suitable for hardware-in-the-loop testing
• Perform technoeconomic studies of hydrogen production systems using renewable energy sources and hydrogen electrolyzer models

Simscape™ and Simscape Electrical provide model libraries for simulating hydrogen electrolyzers. You can use these models to analyze the hydrogen electrolyzer as an electric load within a larger electrical system. With Simulink^®, you can use electrolyzer models to support the development of electrolyzer system controls, such as closed-loop controls and supervisory logic design. Using Embedded Coder^® and HDL Coder™, it is easy to automatically generate readable, efficient C/C++ or HDL code for the controller, validate the control design using hardware-in-the-loop testing, and deploy the code to embedded processors or FPGA/SoC targets.

To build a model of a hydrogen electrolyzer, you can start with the Simscape Electrical electrolyzer model. This model provides the amount of hydrogen produced and water consumed based on the electrical energy provided and the water temperature. The hydrogen electrolyzer model represents a stack of series-connected individual electrolyzer cells with customizable configurations such as the number of cells, water purging logic, transport area, distance between electrodes, and the number of electrode pairs. Additional options for parametrization include electrolysis efficiency, efficiency temperature, electrical resistivity, and pH value assumptions.

With Simscape Electrical and Simscape Fluids, you can customize a complete PEM electrolyzer model. This includes the electrolyzer stack and balance-of-plant components such as heat exchangers, dehumidifiers, pressure regulators, water and oxygen recirculation paths, and water management. This first principles–based hydrogen electrolyzer model with detailed electrochemistry, thermal-liquid networks, and moist air networks enables you to develop a PEM electrolyzer at both the component and system levels. This level of model detail lets you:

• Simulate hydrogen electrolyzer behaviors with different component specifications and under different operating conditions
• Design controls for thermal, pressure, and water management
• Monitor and manage key operational metrics, such as electrolyzer stack temperature, voltage, electric power consumption, water consumption, and hydrogen production level

A hydrogen electrolyzer model, as part of an electrical system, provides a framework for performing trade studies to economize electrolyzer stack efficiency, hydrogen production, and water consumption. A hydrogen electrolyzer model with electrochemical reactions, water and hydrogen handling, and thermal management systems, can be combined with a renewable energy source (such as a solar array or a wind farm) and an energy storage system to model a green hydrogen production system such as a microgrid.

Running simulations with a system model enables you to evaluate the operational characteristics of producing green hydrogen over an extended period by consuming power from the renewable energy source alone, or from a combination of the renewable energy source and the energy storage system.