Solar Fuel Production for a Sustainable Energy Future: Highlights of a Symposium on Renewable Fuels from Sunlight and Electricity

69 Synthesis of fuels from sunlight, water and carbon dioxide, without competing with food production, is an important route for sustainable development beyond fossil fuels. The magnitude of the challenge is very significant that requires scientific breakthroughs in materials and processing for creating economic opportunities.1 There are two straightforward conversion pathways for conversion of solar energy to fuels.2 The most important one is the photoelectrochemical (PEC) hydrogen production via water splitting, which combines the electrical generation and electrolysis into a single system. The other pathway is replicating plant photosynthesis process with water and CO2. These direct solar fuel pathways, especially the PEC water splitting approach, have attracted attention world-wide due to their renewable fuel generation and benefit to the environment. In electrochemical and photoelectrochemical techniques, the electrodes combine with catalysts, inhibitors, and an electrochemical flow reactor to convert CO2 to organic fuels. In PEC water splitting, the grand challenge of 10% solar-to-hydrogen (STH) efficiency and 10 year lifetime was defined as the “holy grail of chemistry.”3 The requirements for a successful PEC water splitting device is displayed in Fig. 1, as shown with a p-type semiconductor case. To achieve efficient PEC water splitting at an illuminated semiconductor (SC),