Preface

The increasing energy demand over the past century has been mostly fulfilled via fossil fuel burning with tremendous economic, social, and environmental impacts. The first energy crisis in the mid-seventies led to a wave of intensive research to find alternatives to fossil fuels and ways to promote CO₂ reduction to produce fuels. After this initial productive period however, research on CO₂ reduction reverted to a steady, low level, until, over the last decade, we have witnessed a vibrant revival. This was certainly triggered by the progressive awareness to reach sustainability in all areas of our life, notably regarding energy consumption and chemical feedstock origin. In this context, a key and challenging task is to develop technologies that use CO₂ as a carbon source, heading towards a circular economy. In this endeavour, CO₂ electroreduction is a cornerstone, and tremendous progress has been made in recent years in this field. It thus seemed timely and appropriate to gather in this book the current state-of-the-art on CO₂ electrochemistry, covering various aspects from fundamentals to applications, from molecular catalysis to nanostructured materials, from bio-hybrid devices to integrated photoelectrochemical approaches. The goal in producing this book is to provide an overview of the current trends in CO₂ electrochemistry. To that aim we have gathered ten chapters, written by leading experts in the field, covering all domains to show how fundamental knowledge can provide stimulating tools for technological developments, and vice versa.

The first chapter by Kubiak and co-workers gives a complete overview of homogeneous molecular catalysts for CO₂ electroreduction with details on the progress in mechanism deciphering that may lead to rational design of new catalysts, with emphasis on the role of proton donor, electronic effects, and multi-metallic center cooperativity. They also report on advances in methodology for catalyst benchmarking. This chapter is complemented by a contribution in Chapter 2 on heterogenization of molecular catalysts by Costentin, Daasbjerg, and Robert, exposing immobilization strategies, the activity and durability of such supported molecular catalysts and specific mechanistic aspects.

Chapters 3 and 4 present heterogeneous metallic catalysts for CO₂ electroreduction. Interrelated phenomena including catalyst composition and environment are first described by Clark and Bell, discussing effects on activity and selectivity. Then, Roosmeisl, Strasser, and co-workers focus on the design of heterogeneous catalysts at the nanoscale with a rational approach fed by theoretical insights.

The quantum calculation approach is further developed for homogeneous catalysis of CO₂ reduction in Chapter 5 by Neese, Ye, and co-workers. They emphasize how mechanistic insights obtained by computational investigations could provide important guidelines to design tailored CO₂ reduction catalysts with higher efficiency and enhanced product selectivity.

New concepts have recently emerged in the field of electrocatalysis and, in particular, those regarding single-atom catalysts. This approach bridges homogeneous and heterogeneous systems and provides an exciting new area of research. It is introduced by Nam and co-workers in Chapter 6. Integrating a molecular catalyst moiety in a conductive electrode provides future directions to achieve efficient and selective catalytic systems and further integration of combined functionalities that can be used to develop photoelectrochemical devices, as described by Wang in Chapter 7.

An additional step of complexity can be reached by designing biological–inorganic hybrid systems, such as those detailed by Nocera and co-workers in Chapter 8, to achieve CO₂ conversion to fuels via exploitation of the biological machinery for CO₂ dark fixation associated with the efficiency of artificial light harvesting and water splitting.

All this new progress is only achievable thanks to new analytical tools such as the in situ spectroscopic techniques reviewed by Urakawa and co-workers in Chapter 9.

In the last chapter, Smith, Berlinguette, and co-workers open the door to large scale applications of CO₂ electroreduction via a description of electrolyzers capable of converting CO₂ into carbon-based fuels and chemicals at high current densities.

Finally, we would like to thank all the chapter authors for their efforts and contributions, which we believe form a remarkable account of the state-of-the-art of CO₂ electrochemistry, and a perfect entry for scientists willing to join this vibrant and exciting field. We would also like to express our gratitude to Connor Sheppard, Editorial Assistant at the Royal Society of Chemistry, for his continuous enthusiasm and patience during the preparation of this book.

Marc Robert, Cyrille Costentin and Kim Daasbjerg