The fuel cell is a promising clean energy technology, which is not yet fully commercialized. There are different types of fuel cells based on the chemical reactions and charge transportation mechanisms employed, but the solid oxide fuel cell (SOFC) technology exhibits major potential for large-scale applications. This technology is, however, still subject to material and technology challenges accompanied with high costs. Though the literature on the SOFC technology is ample covering various aspects such as materials, devices, electrochemistry, and applications, the contributions on the latest discoveries such as the non-electrolyte fuel cell principles are rare.

This book is a unique collection of contributions on the development of solid oxide fuel cells from electrolyte based to non-electrolyte-based technology. Since the scientific discovery of the fuel cell principle some 180 years ago, a fuel cell has been constructed with three basic components, namely, the anode, electrolyte, and cathode, of which the electrolyte plays a key role for the operation of a fuel cell. The electrolyte serves several important roles such as ion transportation, and it supports the fuel cell redox reactions (hydrogen oxidation on the anode and oxygen reduction on the cathode). But it also provides a separator to block against electrons preventing them to pass through the device and forcing them to move through an external circuit, thus preventing the fuel cell from short-circuiting. Thus, the question: how could a fuel cell device at all work without the conventional electrolyte layer is highly justified?

This book aims at giving a more comprehensive understanding on the advances in fuel cells and to bridge the knowledge from traditional SOFC to the new concepts. We will track the development from the conventional SOFC to the non-electrolyte (layer) or single-component fuel cell, covering research on the anode, electrolyte, and cathode component materials, and development of devices and stacks for applications. A key area of underlying science of the book deals with semiconductor and semiconductor–ionic principles for non-electrolyte-based fuel cells.

This book is divided into three parts. Part I is on the conventional SOFC, providing an update on the latest development of anode, electrolyte, and cathode materials as well as the SOFC technologies. Part II discusses the non-electrolyte or semiconductor-based membrane fuel cells. This new concept fuel cell devices have been developed in recent years with extensive efforts and broad innovations from materials, technologies, devices, and scientific principles by crosslink research from semiconductor physics and band theory. This new type SOFCs had been developed from the single-layer fuel cells (SLFCs) or electrolyte (layer)-free fuel cells (EFFCs) in the first inventions toward semiconductor and semiconductor–ionic fuel cells. We start with the conceptual proof of this technology employing both existing SOFC state-of-the-art materials and then introducing new functional semiconductor–ionic materials to demonstrate various single-component and semiconductor–ionic fuel cell technologies without using the electrolyte separator. The emphasis of Part II is on various new semiconductors and semiconductor–ionic materials including the scientific principles, materials, device concepts, and fuel cell technology. Semiconducting materials with ionic properties and mobility and the physics of semiconductor energy band structures, which play a significant role in a single-component fuel cell. Part III of the book focuses on engineering efforts from materials, technology, device to stack developments, and various applications and new opportunities of SOFC using both the electrolyte and non-electrolyte technologies, including integrated fuel cell systems with electrolysis, solar energy, etc. Two important issues have been seriously addressed to accelerate SOFC commercialization: (i) technically the interfaces of the planar cell and stack and (ii) commercially designed SOFC stack products to meet demands of customers and applicable uses. The next commercial potential of these technologies will depend on their advantages and disadvantages, but the new semiconductor-based materials and technologies exhibit quite a few advantages over the conventional electrolyte-based fuel cells.

Though this book uses a specific fuel cell technology, the solid oxide fuel cells, as basis for describing advances in fuel cells, the intention is also to provide a stronger vision in fuel cell materials and technologies in general. Serious and concrete research efforts are necessary to strengthen this field and to provide new paths for innovations and breakthrough thinking on fuel cells.

The book will serve as important reference work to students, researchers, and technology developers in the fuel cell field. We hope this book would give readers fresh ideas, new knowledge, and inspiration.

10 August 2019