| Abstract: | Thermal energy is all around us. How to control and utilize it is an important topic in advanced manufacturing. This dissertation is focused on the design and fabrication of photo-thermal and thermo-electric materials and systems and is divided into three topics: pH-responsive Au@silica semi-shell nanoparticles (NPs), thermo-osmotic ionogel (TOI), and HClO²́⁴-enhanced Fe(III/II) thermocells (TECs). pH-responsive photothermal therapy holds promise for non-invasive antitumor treatment, but the preparation of smart photothermal agents (PTAs) remains challenging. In the first topic (Chapter 3), a simple two-step approach was developed for the precise synthesis of anisotropic Au@silica semi-shell NPs, which were then used as pH-responsive PTAs for non-invasive antitumor therapy. In the synthesis of Au@silica semi-shell NPs, the isotropic solution-synthesized Au@silica core-shell NPs were firstly self-assembled on silicon wafers to form monolayer films by drop-casting technique. Then, Au@silica semi-shell NPs were obtained after selective and directional removal of part of the silica shell by reactive ion etching. After functionalization with pH-sensitive 4-mercaptobenzoic acid (4-MBA) molecules, the semi-shell NPs achieved pH-responsive rod-shaped assembly/disassembly in physiological saline solution, thereby exhibiting pH-responsive photothermal effects. In addition, the 4-MBA-semi-shell NPs have been successfully applied to in vitro photothermal therapy of tumor cells, showing great application potential in non-invasive antitumor therapy. Low efficiency in recovering low-grade heat remains unresolved despite decades⁰́₉ attempts. In the second topic (Chapter 4), a novel thermo-osmotic ionogel (TOI) composite was designed and fabricated to recover low-grade heat to generate electric power through thermo-induced ion gradient and selective ion diffusion. The TOI composite was assembled with crystalline ionogel (polymer-confined LiNO²́³-3H²́²O) film, cation exchange membrane, and hydrogel film. With a 90 ℗ʻC heat supply, the single TOI composite produced a high open-circuit voltage of 0.52 V, a differential thermal voltage of ~26 mV/K, a peak power density of 0.4 W/m℗ø, and a ground-breaking peak energy conversion efficiency of 11.17%. Eight pieces of such TOI composite were connected in series, demonstrating an open-circuit voltage of 3.25 volts. Such a TOI system was also demonstrated to harvest body temperature for powering a LED, opening numerous opportunities for powering wearable devices. This work opens a new door for efficient harvesting of low-grade heat by embedding thermo-osmotic conversion as an intermedia stage of thermo-electric conversion. In addition to thermo-ionic capacitors (Chapter 4), emerging thermocells (TECs) can convert a temperature gradient into electricity continuously and thus are promising for low-grade heat harvesting. However, it⁰́₉s challenging to simultaneously improve the thermopower (Se, a thermodynamics parameter) and ionic conductivity (ϳæ̀Ø, a kinetics parameter) of TECs due to the well-known inherent interdependence between thermodynamics and kinetics. In the third topic (Chapter 5), a simple perchloric acid (HClO²́⁴) incorporation method has been developed to enhance the charge density of the oxidant Fe(III) ions in the state-of-the-art n-type Fe(III/II)-ClO²́⁴ redox pair, thereby improving the Se and ϳæ̀Ø simultaneously. In Fe(III/II)-ClO²́⁴ electrolyte, the addition of HClO²́⁴ composed of protons and weakly coordinating anions suppresses the deprotonation of [Fe(H²́²O)²́⁶]℗đ¹́ð without inducing Fe(III)-anion coordination. The n-type TEC using HClO²́⁴-acidified Fe(III/II)-ClO²́⁴ as electrolyte and hydrophilic carbon fiber cloth as the electrode was charactered and demonstrated a Se of 1.5 mV/K (comparable to -1.4 mV/K of benchmark p-type Fe(CN)²́⁶℗đ¹́»/Fe(CN)²́⁶¹́þ¹́» TECs) and an excellent temperature normalized power density of 1.19 mW/m℗ø/K℗ø (2.64 times higher than that of the state-of-the-art n-type TECs using carbon electrodes), overcoming barriers for practical p-n integrated TEC applications. The electronic version of this dissertation is accessible from https://hdl.handle.net/1969.1/197832 |
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