Development of Plasmonic Copper Chalcogenide Nanocrystals for Efficient Solar Energy Conversion

概要

Solar energy conversion into hydrogen and oxygen by photoelectrocatalytic water splitting has been widely investigated, although current research focuses on the utilization of ultraviolet (UV) and visible (Vis) light and the infrared light (IR) accounting for 52% of the sunlight has been abandoned. The photoelectrochemical (PEC) system integrated with plasmonic materials as light absorbing material is one of the promising candidates to convert the IR light energy into chemical energy or electricity. Despite the great progress in development of plasmonic materials and improvement of photocatalysts, an entire use of infrared light using the plasmonic materials is still challenging. To improve the efficiency of the plasmon-induced photoelectrocatalysis by suppressing the ultrafast charge recombination, we need to deeply understand the plasmonic materials and rationally design the plasmonic photoelectrode.

Chapter 2. Band Engineering Tuned LSPR in Diverse-Phased Cu2-xSeyS1-y Nanocrystals
Tuning mechanism of localized surface plasmon resonance (LSPR) by band structure of ternary copper chalcogenide nanocrystals (NCs) was investigated. Copper-deficient copper chalcogenide NCs have attracted much attention as a typical degenerated semiconductor. However, how their band structures affect their plasmonic properties has not been thoroughly investigated. Moreover, the synthesis of colloidal Cu2-xSeyS1-y NCs with diverse crystal phases remains a challenge to date. A facile method to synthesize a variety of Cu2-xSeyS1-y NCs with different crystal phases was developed and the Cu2-xSeyS1-y NCs with four distinct phases were successfully synthesized. These Cu2-xSeyS1-y NCs exhibited different valence band maximum (VBM), conduction band minimum (CBM), and Fermi level (EF), resulting in the large LSPR peak shift. This result indicates that the modulation of VBM, CBM, and EF by Se/S alloying and the overlapping of VB and EF dominate the LSPR properties of alloyed Cu2-xSeyS1-y NCs. It is noted that not only the change of Cu vacancy but also the negative shift of VBM contribute to the blue shift of LSPR peak.

Chapter 3. Tunable Band Structure of Cu2-xSeyS1-y Promoted Near-Infrared Plasmon Driven Photoelectrocatalytic Oxygen Evolution
Photoelectrocatalytic water splitting has been vigorously investigated for efficient utilization of UV and Vis light, while the infrared light accounting for 52% of solar spectrum has been abandoned up to date. The plasmonic properties of Cu2-xSeyS1-y NCs in near-IR (NIR) region was applied to the photoelectrocatalytic water oxidation by the band engineering in the Cu2- xSeyS1-y/CdS system. Especially, p-type degenerated semiconductor Cu2-xSeyS1-y NCs with deep EF is an ideal material for IR-induced oxygen evolution reaction (OER) reaction. A plasmonic photoelectrode composed of Cu2-xSeyS1-y and CdS was designed and fabricated for NIR-light driven water oxidation under voltage. The Cu2-xSeyS1-y with deeper EF exhibited good photoelectrocatalytic OER activity under IR light irradiation. Change in carrier migration at Cu2- xSeyS1-y/CdS interface by tuning the band structure of Cu2-xSeyS1-y NCs, was found to be important for IR-induced photoelectrocatalytic OER.

Chapter 4. A Flexible CdS Nanorods-Carbon Nanotubes/Stainless Steel Mesh photoanode for Boosted Photoelectrocatalytic Hydrogen Evolution
A flexible reticular photoanode composed of CdS nanorods (NRs) and carbon nanotubes (CNTs) coated on stainless iron mesh was fabricated for efficient photoelectrocatalytic H2 evolution under visible light irradiation. These CdS-NRs/CNTs-based flexible photoanodes showed a record-breaking H2 evolution rate (728 mmol h–1 g–1) among the reported CdS-based photoanodes under visible light irradiation owing to the photoelectron transport channels and high separation efficiency of electrons and holes. This result suggested that a rational design of the photoelectrode architecture plays a key role in improving the carrier separation and transfer to drastically enhance the performance of solar energy conversion.