Preface

Research activities in photoelectrochemical (PEC) water splitting have risen dramatically in recent years. Although the lion's share of research efforts has centered on the synthesis and characterisation of PEC materials with an aim of improving the solar conversion efficiency, new directions within the field have emerged, ranging from theoretical studies for new materials discovery all the way to systems analysis on the gigawatt scale. Our objective, as editors, was to bring together the leading experts in the field to provide an authoritative and forward-looking survey of the different approaches to PEC water splitting, with particular emphasis on key issues and unsolved problems. This book summarises the present-day challenges that need to be solved before PEC water splitting can make the transition from the laboratory to large-scale application.

Theory plays a very important role in the further development of high performance PEC systems, through e.g. prediction of band alignments with the electrolyte, assessment of the stability of different materials at different pH and under bias, and the discovery of novel materials with attractive band gaps, stability, carrier transport and charge transfer. Although great strides have been made with empirical investigation of various semiconductors as well as combinatorial studies, theoretical approaches have the potential to greatly accelerate progress in this field. The first part of the book highlights some of these theoretical efforts.

Recent experimental developments comprise the second part of the book. Fundamental understanding of water splitting electrodes under operation are critical to the long-term goal of stable and efficient systems, and two chapters address this topic. The following chapters focus on the low cost and scalable synthesis of water splitting materials, as well as bipolar membranes, which allow increased flexibility of the electrolyte for each half reaction, greatly influencing the overall stability of the PEC cell.

The final part of the book focuses on systems analysis, which provides a roadmap of where we hope the fundamental research will lead us. These analyses provide important information for prioritising different avenues of present-day basic research, including PEC cell architecture and practical matters for scaling up these systems.

With a wide view of the field—ranging from theory all the way to systems analysis—we feel that the reader will gain a crucial insight into the remaining challenges for the PEC field, and find guidance for present-day research aims.

I would like to thank the authors of this book, as well as my co-editors Dr Stephan Lany and Prof. Roel van de Krol for their time and effort in this project. It is my hope that this book will become a key text that will inspire current researchers as well as newcomers to the field towards the advancement of practical systems to the market place.

S. David Tilley

Zurich