World demand for energy continues to increase. Based on figures in BP’s 2012 Statistical Review of World Energy,1 global primary energy consumption in 2011 was equivalent to a thermal power output of 16.35 TW, an increase of 2.5% on the previous year and around 30% compared with a decade earlier. 87% of this energy was generated from carbon-based fuels. BP’s World Energy Outlook 20302 predicts that global power output will rise to over 22 TW by 2030, and looking further, other growth models predict that energy consumption will at least double by 2050.3,4 In the short term, shale gas will fill the gap in terms of carbon-based energy resources, but renewable energy resources will have to play an increased role if there is to be any hope of pegging global CO2 emissions at a level that will reduce the impact of global climate change.
At present, renewables (including biofuels) account for only 2% of global primary energy consumption, but in reference 2 they are predicted to expand their share to around 6% by 2030. Since the potential for increases in the contribution from hydro and nuclear may be limited, this still leaves a huge increase in the consumption of oil, gas and coal. In the absence of viable carbon capture and storage technologies, this implies a massive increase in CO2 emissions, even if the replacement of coal and oil by gas leads to lower CO2 emissions per unit of energy generated.
Rapid expansion of terrestrial photovoltaics will go some way to addressing CO2 emissions from electricity generation. Scenarios considered by the Intergovernmental Panel on Climate Change estimate the potential for power generation by photovoltaics (PV) at around 600-800 GW in 2050, but still this represents only around 2% of the total primary power required.5 The main problem with photovoltaic power generation is intermittency. Large-scale deployment of PV will require the development of suitable electrical and chemical storage methods. Transport, which accounts for around 30% of primary energy consumption, is likely to remain based on liquid (or increasingly gas) fuels, although electric vehicles will of course have some impact.
The development of methods of storing solar energy in chemical fuels has therefore become an important research priority, and countries are beginning to react to the problem by establishing large programmes of research into solar fuels. In the United States, the Joint Center for Artificial Photosynthesis (JCAP) was established in 2010. It is the world’s largest research programme devoted to the development of an artificial solar fuel generation technology. Other centres in the United States include the Center for Bio-Inspired Solar Fuel Production at Arizona State University and the Research Triangle Solar Fuels Institute involving Duke, NC State and UNC Chapel Hill. Europe has been slower to address the issues, and the scale of funding is smaller than in the US. However, a new Solar Fuels programme has been started at the Helmholtz Centre in Berlin, and there are several initiatives elsewhere in Europe including the Nordic initiative for solar fuel development and The European Science Foundation’s EuroSolarFuels programme. At the same time, Japan, Korea and Singapore are starting advanced artificial photosynthesis centres. In the UK, the Royal Society of Chemistry has published a helpful booklet that introduces the topic of solar fuels to a non-specialist audience and identifies some of the key strategic issues.6
The Editors felt that the recent rapid expansion of light-driven generation of solar fuels provided the raison d’être for a new book to reflect current progress and to highlight some of the key issues that need to be addressed by the research community. Although work on light-driven water splitting has continued since the much-cited work of Fujishima and Honda,7 the recent upsurge of activity has brought new people and new ideas and methodologies. In this volume, we have tried to capture some of the energy and enthusiasm that is revitalizing this important research area. The chapters in the book cover a wide range of experimental and theoretical aspects that relate to the light-induced splitting of water and reduction of CO2, such as materials science, interfaces, heterogeneous catalysts and (photo)electrochemical processes. In addition, new developments related to photonics, light management, excitation energy transfer and third generation approaches have been included in order to emphasize the potential for innovation in the field. We are grateful to the contributing authors, who are all experts in their respective fields and scientific disciplines, and we hope that the book will not only provide an authoritative overview of some of the most important current research directions but also stimulate debate and critical assessment of research priorities.
Pasadena, California, USA