Transition Metal Pnictide Nanoparticles for Energy-Relevant Applications

非技术总结通过这项由NSF固态和材料化学计划支持的研究项目，建立了用于磁制冷(MR)的新材料，利用地球上丰富的过渡金属磷化物、砷化物或锑纳米粒子。传统的制冷和空调是基于惰性气体的压缩和膨胀，这一过程消耗了全球高达17%的电能。除了能源密集型外，到2030年，氢氯氟烃气体(HCF)不可避免的制冷剂泄漏预计将占全球温室气体排放量的13%。磁制冷是一种依靠固体材料(而不是气体)中的磁极化来吸收和释放热量的过程。虽然理论上MR的节能制冷能力比标准的蒸汽压缩方法高50%，但它还没有被广泛采用。这部分是由于缺少同时具有(1)感兴趣的温度区域的高性能、(2)能以最小的能量损失有效地循环、(3)廉价的、以及(4)基于高自然丰度的材料的材料。一些地球资源丰富的材料已知对MR具有活性，但由于循环损失的低效而不被常规使用。作为该项目的一部分，这些材料被制备成纳米颗粒。韦恩州立大学的布罗克教授和她的团队预计，颗粒尺寸的减小将减少磁极化的障碍，从而实现高效的循环。为了评估这一假设，作为该项目的一部分，研究人员对一系列具有不同成分的结构相关材料进行了测试。除了为可行的磁共振技术的发展提供关键的见解外，该项目还包括培训和指导学生进行跨学科协作研究，并通过外展活动的动手活动向底特律地区的6-9年级学生(其中许多是少数族裔)介绍材料化学。技术总结在NSF固态和材料化学计划的支持下，该项目建立了与替代能源应用相关的过渡金属镍酸(pniogen=第15族元素)纳米材料的基本特征，特别是专注于磁制冷(MR)。许多过渡金属磁石材料非常适合于磁流变应用，在室温附近表现出很大的磁热效应(MCE，极化和去极化过程中磁熵的大变化)。最大的影响与TC时从铁磁状态到顺磁状态的一级(突然)相变有关，但这些相变也相当尖锐(不跨越感兴趣的温度范围)。纳米结构被认为是一种拓宽MCE最大化温度范围的方法；将粒子与不同的TC混合，以扩大可以获得明显磁熵的温度范围。在这个项目中，通过三个目标来寻求在纳米级过渡金属颗粒中寻找功能磁热材料的“材料机会”。在目标1中，收集了P掺杂的MNAs纳米颗粒样品的磁熵数据，并将其与单颗粒磁力显微镜数据进行关联，以辨别多分散性如何影响样品的整体行为，即在大的温度范围内产生均匀的磁熵响应。在目标2中，建立了金属前体与P(三辛基膦)的相对反应性标度，作为设计新的、更复杂的MCE材料(三元和四元磷化物相)的一种方式。最后，讨论了纳米材料在磁制冷开发中所面临的内在挑战，包括表面氧化导致的磁熵降低。除了为可行的磁共振技术的开发提供关键见解外，该项目还包括培训和指导学生进行跨学科协作研究，并通过基于液晶传感器的动手活动为一年一度的韦恩州立大学STEM日活动介绍底特律地区6-9年级的学生(其中许多是少数族裔)学习材料化学。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYThrough this research project, which is supported by the Solid State and Materials Chemistry program at NSF, new materials for magnetic refrigeration (MR) that exploit earth-abundant transition metal phosphide, arsenide or antimonide nanoparticles are established. Traditional refrigeration and air-conditioning are based on the compression and expansion of an inert gas in a process that consumes a whopping 17% of the electrical energy consumed globally. In addition to being energy intensive, inevitable refrigerant leaks of the hydrochlorofluorocarbon gases (HCFs) are projected to contribute 13% of the global greenhouse gas emissions by 2030. Magnetic refrigeration is a process that relies on magnetic polarization within a solid material (not a gas) to absorb and release heat. While MR is theoretically capable of 50% more energy-efficient refrigeration than standard vapor-compression approaches, it is not widely adopted yet. This is due in part to an absence of materials that are simultaneously (1) high-performing in the temperature region of interest, (2) can be efficiently cycled with minimal energy losses, (3) are inexpensive, and (4) are based upon materials with high natural abundance. Some earth-abundant materials known to be active for MR but are not routinely used because of inefficiencies from cycling losses. As part of this project these materials are prepared as nanoparticles. Prof. Brock and her group at Wayne State University expect the decrease in the size of the particles to reduce barriers for magnetic polarization, thereby enabling efficient cycling. To evaluate this hypothesis, the researchers carry out tests on a series of structurally-related materials with different compositions as part of this project. In addition to providing key insights to the development of viable MR technologies, the project also includes training and mentoring of students in interdisciplinary collaborative research and introduction of Detroit-area 6th-9th grade students, many of which are minorities, to materials chemistry through hands-on activities for outreach events.TECHNICAL SUMMARYWith support from the Solid State and Materials Chemistry program at NSF this project establishes the fundamental characteristics of transition metal pnictide (pnicogen = Group 15 element) nanomaterials relevant to alternative energy applications, specifically focusing on magnetic refrigeration (MR). Many transition metal pnictide materials are well-suited to MR applications, displaying a large magnetocaloric effect (MCE, a large change in magnetic entropy during polarization and depolarization) near room temperature. The largest effects are associated with first-order (abrupt) phase transitions from the ferromagnetic to the paramagnetic state at TC, but these are also quite sharp (do not span the temperature range of interest). Nanostructuring has been suggested as a means to broaden the temperature range over which MCE is maximized; blending particles with differing TC's to extend the temperature range over which appreciable magnetic entropy can be attained. In this project, "materials opportunities" in the search for functional magnetocalorics among nanoscale transition metal pnictides, are pursued via three aims. In Aim 1, magnetic entropy data is collected on P-doped MnAs nanoparticle samples and correlated to single particle magnetic force microscopy data to discern how polydispersity affects the ensemble behavior of the samples, in terms of producing uniform magnetic entropy responses over large temperature ranges. In Aim 2, a relative reactivity scale for metal precursors with P (trioctylphosphine), is created as a way to design new, more complex MCE materials (ternary and quaternary phosphide phases). Finally, in Aim 3 intrinsic challenges that face the exploitation of nanomaterials for magnetic refrigeration are addressed, including reduction of the magnetic entropy due to surface oxidation. Insights from the reduction strategy are leveraged to target new antimonide phase for MR. In addition to providing key insights to the development of viable MR technologies, the project also includes training and mentoring of students in interdisciplinary collaborative research and introduction of Detroit-area 6th-9th grade students, many of which are minorities, to materials chemistry through a hands-on activity based on liquid crystal sensors for the annual Wayne State University STEM day event.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.