# Introduction to PEM Electrolyzers and Hydrogen Energy

## The Role of Hydrogen in Future Energy Systems
Hydrogen is emerging as a cornerstone of low-carbon energy systems due to its flexibility and compatibility with renewable power {cite}`IEA2019`.

## Overview of Water Electrolysis Technologies
There are three main types of electrolyzers: alkaline (AEL), proton exchange membrane (PEM), and solid oxide (SOEC). Their key differences are summarized below.

| Technology | Strengths | Limitations | Best use case |
|---|---|---|---|
| AEL | Mature, lower cost, robust long-term operation | Lower current density, slower dynamic response, bulkier systems | Large-scale steady hydrogen production |
| PEM | High current density, compact design, fast response, high-purity hydrogen | Higher cost, reliance on noble catalysts, membrane durability concerns | Coupling with variable renewable electricity |
| SOEC | High efficiency potential at high temperature, possible heat integration and co-electrolysis | Lower technology maturity, thermal cycling constraints, higher system complexity | Industrial sites with available high-temperature heat |

## Advantages and Challenges of PEM Electrolyzers
Key advantages include high current density and rapid response. Challenges include material cost and membrane durability.

## Structure and Goal of This Book
This book addresses modeling and control of PEM electrolyzers, intended for engineers and researchers working in hydrogen energy.