Nanostructured materials for electrochemical carbon dioxide reduction and biosensing

Abstract

The work included in this thesis aims to investigate a new metal nanostructure fabrication method and its unique applications. Strategies of nanostructure synthesis can be diverse, but a fast, scalable, and cost-effective method for 1D material fabrication in one step has not been reported yet. In this thesis, a room temperature ultrasonic nanoimprinting technique for 1D metal nanostructure fabrication has been developed. Working at room temperature, ultrasonic nanoimprinting rapidly fabricates multi-compositional nanostructures made of virtually all solid materials regardless of their ductility, hardness, reactivity, and melting points. As proof-of-concept, the applications of the fabricated nanostructures for electrochemical CO2 reduction and quorum sensing have been demonstrated.

First, the ultrasonic nanoimprinting method is introduced for complex 1D nanostructure fabrication, including pure metal nanowires, bimetallic nanorods, and metal nanorods with built-in nanogaps. The working principle of ultrasonic nanoimprinting is investigated by atomic resolution characterization and molecular dynamics simulation.

Second, Ag and Au based 1D nanostructure as catalysts for electrochemical CO2 reduction reaction are presented. The Ag@AgClx CSNWs offer high catalytic activity and selectivity towards CO, owing to the high conductivity of Ag core and abundant active sites on AgClx shell. Then electric field effect on ordered Au nanowires is investigated and (semi)quantified. At the same time, we show that high index facets play a crucial role in electrochemical CO2RR on Au nanowire catalyst, which works synergistically with concentrated electric field to optimize the CO2RR activity.

Third, Ag nanorods with build-in nanogaps are fabricated by using our ultrasonic nanoimprinting after depositing alumina sacrificial layer and Ag layer on the substrate by e-beam evaporation. As a biosensing platform, this substrate shows strong Raman signals for quorum sensing.

In summary, a fast, scalable, energy-efficient, and cost-effective 1D metal nanostructure fabrication method has been developed. The fabricated nanowires and complex 1D nanostructure show high potential for various engineering applications, including electrochemical CO2 reduction to fuel and quorum sensing.