GraphTED - graphene nanocomposite materials for thermoelectric devices

塞贝克效应是一种热电效应，通过这种效应，材料上的温度梯度被转换为可用于发电的电压。对化石燃料和碳排放的日益关注导致了对能源产生的所有方面和减少消耗的途径的详细审查。利用废热直接转化为电能的热电(TE)技术已经成为一个强有力的竞争者，特别是在汽车和发动机相关应用中。热电功率模块采用多对n型和p型TE材料。传统的金属TE材料(如Bi2Te3和PbTe)可使用50年，由于它们容易汽化、表面氧化和分解，不太适合高温应用。此外，许多都是有毒的。硅-锗合金也很成熟，在高达1200K的温度下具有良好的TE性能，但每瓦特的成本可以高达传统材料的10倍。在过去的十年里，氧化物热电材料因其灵活的结构、高温稳定性和令人鼓舞的ZT值而成为很有希望的TE候选材料，特别是钙钛矿(n型)和层状钴矿(例如p型Ca3Co4O9)，但它们还不具有商业可行性。因此，本研究致力于改善氧化物热电材料的热电性能，特别是钛酸锶(n型)和钴酸锶铋(p型)的热电性能。热电材料的转换效率用优值系数ZT(其中T是温度)来表征；ZT应该尽可能地高。要使Z值最大化，需要高的塞贝克系数(S)，再加上小的热导率和高的电导率。原则上，电导率可以通过改变阳离子/阴离子组成来调整。更大的挑战是同时降低导热系数。然而，在氧化物陶瓷中，由于声子是热的主要载体，晶格导电性主导着热的传输。这为一系列减少热传导的策略提供了基础；本质上是增加声子散射的微结构工程。通过在氧化物中引入小块石墨烯，就有可能产生降低导热系数和提高导电率的复合材料。这样，钛酸锶(n型)和钴酸锶铋(p型)的ZT特性都能得到提高。我们将制备这两种氧化物的复合材料，测定它们的结构、相含量和热电性能。验证后，我们将使用p型和n型复合材料构建热电模块，并将在与商业相关的测试环境中进行评估。

The Seebeck effect is a thermoelectric effect whereby a temperature gradient across a material is converted to a voltage,which can be exploited for power generation. The growing concern over fossil fuels and carbon emissions has led todetailed reviews of all aspects of energy generation and routes to reduce consumption. Thermoelectric (TE) technology,utilising the direct conversion of waste heat into electric power, has emerged as a serious contender, particular forautomotive and engine related applications. Thermoelectric power modules employ multiple pairs of n-type and p-type TEmaterials. Traditional metallic TE materials (such as Bi2Te3 and PbTe), available for 50 years, are not well suited to hightemperature applications since they are prone to vaporization, surface oxidation, and decomposition. In addition many aretoxic. Si-Ge alloys are also well established, with good TE performance at temperatures up to 1200K but the cost per wattcan be up to 10x that of conventional materials. In the last decade oxide thermoelectrics have emerged as promising TEcandidates, particularly perovskites (n-type) and layered cobaltites (e.g. p-type Ca3Co4O9) because of their flexiblestructure, high temperature stability and encouraging ZT values, but they are not yet commercially viable. Thus thisinvestigation is concerned with improving the thermoelectric properties of oxide thermoelectrics, specifically StrontiumTitanate (n-type) and Bismuth Strontium Cobaltite (p-type).The conversion efficiency of thermoelectric materials is characterised by the figure of merit ZT (where T is temperature); ZTshould be as high as possible. To maximise the Z value requires a high Seebeck coefficient (S), coupled with small thermalconductivity and high electrical conductivity. In principle electrical conductivity can be adjusted by changes in cation/anioncomposition. The greater challenge is to concurrently reduce thermal conductivity. However in oxide ceramics the latticeconductivity dominates thermal transport since phonons are the main carriers of heat. This affords the basis for a range ofstrategies for reducing heat conduction; essentially microstructural engineering to increase phonon scattering. Byintroducing small pieces of graphene into the oxide it is possible to produce composites which have reduced thermalconductivity and increased electrical conductivity. In this way the ZT characteristics of both Strontium Titanate (n-type) andBismuth Strontium Cobaltite (p-type) can be enhanced. We will prepare composites of the two oxides, determine theirstructures, their phase content and thermoelectric properties. After validation we will construct thermoelectric modulesusing the p-type and n-type composites which will be evaluated in commercially-relevant test environments.