Ionic Peltier Effect in Li Ion Battery Electrolytes

Thermoelectric transport, i.e., charge current driven by a temperature gradient (Seebeck effect) and heat current driven by an electric current (Peltier effect), provides fundamental insights on microscopic thermodynamics and kinetics of materials and enables devices that convert between heat and electrical work. The ionic Seebeck effect in ionic thermoelectric materials was reported more than one century ago while the reciprocal phenomenon, the ionic Peltier effect, remains unexplored due to experimental challenges. This work reports experimental observations and quantitative measurements of the ionic Peltier effect by an ultrasensitive temperature difference metrology (UTDM) with an extremely high temperature difference resolution up to 4 uK. UTDM enables the probing of sub-mK-level temperature responses of ionic Peltier effect even in the presence of parasitic Joule heat. We observe high ionic Peltier coefficients (up to 450 mV) in liquid electrolytes commonly used in Li-ion batteries. These high Peltier coefficients are approximately one order of magnitude greater than the Peltier coefficients of well-optimized electronic thermoelectric materials and comparable to Peltier coefficients of lightly doped silicon. Our work provides a platform to study the microscopic physics of ionic Peltier effect and understanding the thermodynamics and kinetics of ion transport in Li-ion batteries

Final Report: Thermal Conductance of Solid-Liquid Interfaces

Research supported by this grant has significantly advanced fundamental understanding of the thermal conductance of solid-liquid interfaces, and the thermal conductivity of nanofluids and nanoscale composite materials. • The thermal conductance of interfaces between carbon nanotubes and a surrounding matrix of organic molecules is exceptionally small and this small value of the interface conductance limits the enhancement in thermal conductivity that can be achieved by loading a fluid or a polymer with nanotubes. • The thermal conductance of interfaces between metal nanoparticles coated with hydrophilic surfactants and water is relatively high and surprisingly independent of the details of the chemical structure of the surfactant. • We extended our experimental methods to enable studies of planar interfaces between surfactant-coated metals and water where the chemical functionalization can be varied between strongly hydrophobic and strongly hydrophilic. The thermal conductance of hydrophobic interfaces establishes an upper-limit of 0.25 nm on the thickness of the vapor-layer that is often proposed to exist at hydrophobic interfaces. • Our high-precision measurements of fluid suspensions show that the thermal conductivity of fluids is not significantly enhanced by loading with a small volume fraction of spherical nanoparticles. These experimental results directly contradict some of the anomalous results in the recent literature and also rule-out proposed mechanisms for the enhanced thermal conductivity of nanofluids that are based on modification of the fluid thermal conductivity by the coupling of fluid motion and the Brownian motion of the nanoparticles

Polymer Brush‐Modified Microring Resonators for Partition‐Enhanced Small Molecule Chemical Detection

Silicon photonic microring resonators have emerged as a promising technology for the sensitive detection of biological macromolecules, including proteins and nucleic acids. However, not all species of interest are large biologics that can be targeted by highly specific capture agents. For smaller organic chemicals, including many toxic and regulated species, a general approach to improving sensitivity would be desirable. By functionalizing the surface of silicon photonic microring resonators with polymer brushes, small molecules can selectively partition into the surface‐confined sensing region of the optical resonators. This in turn leads to response enhancements in excess of 1000% percent, relative to non‐functionalized sensors, for representative targets including 4‐methylumbelliferyl phosphate, a simulant for highly toxic organophosphates, Bisphenol A, an industrial pollutant, as well as other small organic analytes of interest. There are many polymer brush chemistries compatible with silicon resonators, making this a general strategy towards tuning sensor selectivity and specificity by optimizing interactions between the agent(s) of interest and the polymer construct.Polymer brush‐modified microring resonators sensors can be utilized to enhance sensitivity and specificity for the detection of small molecule organic chemicals.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136268/1/slct201700082.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136268/2/slct201700082-sup-0001-misc_information.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136268/3/slct201700082_am.pd

Photoelectrochemical Behavior of Hierarchically Structured Si/WO_3 Core–Shell Tandem Photoanodes

WO_3 thin films have been deposited in a hierarchically structured core–shell morphology, with the cores consisting of an array of Si microwires and the shells consisting of a controlled morphology WO_3 layer. Porosity was introduced into the WO_3 outer shell by using a self-assembled microsphere colloidal crystal as a mask during the deposition of the WO_3 shell. Compared to conformal, unstructured WO_3 shells on Si microwires, the hierarchically structured core–shell photoanodes exhibited enhanced near-visible spectral response behavior, due to increased light absorption and reduced distances over which photogenerated carriers were collected. The use of structured substrates also improved the growth rate of microsphere-based colloidal crystals and suggests strategies for the use of colloidal materials in large-scale applications

An optical surface resonance may render photonic crystals ineffective

In this work we identify and study the presence of extremely intense surface resonances that frustrate the coupling of photons into a photonic crystal over crucial energy ranges. The practical utility of photonic crystals demands the capability to exchange photons with the external medium, therefore, it is essential to understand the cause of these surface resonances and a route to their elimination. We demonstrate that by modifying the surface geometry it is possible to tune the optical response or eliminate the resonances to enable full exploitation of the photonic crystal.Comment: 6 pages, 8 figures, submitted to PR

Tuning Coherent Radiative Thermal Conductance in Multilayer Photonic Crystals

We consider coherent radiative thermal conductance of a multilayer photonic crystal. The crystal consists of alternating layers of lossless dielectric slabs and vacuum, where heat is conducted only through photons. We show that such a structure can have thermal conductance below vacuum over the entire high temperature range, due to the presence of partial band gap in most of the frequency range, as well as the suppression of evanescent tunneling between slabs at higher frequencies. The thermal conductance of this structure is highly tunable by varying the thickness of the vacuum layers.Comment: add a paragraph at the end on the applicability of the mechanism to silicon; accepted by Applied Physics Letters (2008