Introduction

This chapter provides an overview for this book from a historical perspective. It starts from the early ages in 1800s-1900s from the invention of fuel cells and their development into five different fuel cell families, i.e. polymer electrolyte membrane fuel cell (PEMFC), alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), and solid oxide fuel cell (SOFC), where the electrolyte is the key. Therefore, relevant materials and technologies are important. However, in the latest developments since 2011, the electrolyte (layer)-free fuel cell (EFFC) has suddenly changed this fuel cell scenario, becoming a very interesting and promising new fuel cell R&D. Thus new fundamentals and issues beyond fuel cell itself are introduced.