New Catalytic Systems for Light-driven Hydrogen Evolution

Sammanfattning: Solar-driven reduction of water to produce hydrogen is one of the most promising ways to develop sustainable cleanenergy for the future. The challenge in photocatalytic hydrogen evolution research is to design inexpensive catalystsand construct efficient hydrogen production systems. In this thesis, different photocatalytic hydrogen productionsystems consisting of catalysts, photosensitizers and sacrificial agents (electron donors and proton source) has beendesigned and investigated based on non-precious molecular catalysts based on iron, cobalt, or molybdenum.[Ru(bpy)3]2+ and CdSe quantum dots were explored as photosensitizers. The photocatalytic hydrogen production ofthe studied systems was systematically investigated, and the attempts to establish essential steps of the mechanismof hydrogen evolution were made.Chapter 1 gives a short introduction about photocatalytic hydrogen evolution, including semiconductor-based and[Ru(bpy)3]2+-based photocatalytic hydrogen evolution systems. Chapter 2 relates to papers I and II in the thesis,and describes the study of light-driven hydrogen evolution by CdSe quantum dot/iron carbonyl cluster assembliesand a related graphitic carbon nitride based quantum dot/iron carbonyl cluster composite. It is shown that hole transferfrom CdSe quantum dots to biomimetic iron complexes dominates the fast charge transfer process and leads toenhanced hydrogen production. Chapter 3, corresponding to paper III, describes the study of photoinduced hydrogenevolution using cobalt compounds. The primary photochemical processes of three new Co(II) complexes in thephotocatalytic system have been probed by time-resolved spectroscopic analyses. Chapter 4, corresponding to paperIV, describes the study of molybdenum-organic sulfides as catalysts for photocatalytic hydrogen evolution. Timeresolvedphotoluminescence (TRPL) spectroscopy was used to investigate the charge carrier transfer dynamics forthe photochemical properties of derivatives of [Mo3S13]2-.The close connection between hydrogen generating activity and charge carrier transfer dynamics in photocatalyticsystems is a key theme of this thesis. Studies on the carrier dynamics can enhance the understanding of keyprocesses in the mechanism of photocatalytic hydrogen production, and thus facilitate the design of efficient androbust photocatalytic hydrogen evolution systems.