Transition Metal Pnictide Nanoparticles for Energy-Relevant Applications

非技术总结通过这个由NSF固态和材料化学计划支持的研究项目，建立了利用地球上丰富的过渡金属磷化物，砷化物或锑化物纳米颗粒的磁制冷（MR）新材料。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17%的电能。除了能源密集型之外，预计到2030年，不可避免的氟氯烃气体（HCFs）制冷剂泄漏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）内的磁极化来吸收和释放热量的过程。虽然理论上MR比标准的蒸汽压缩方法节能50%，但它尚未被广泛采用。这部分是由于缺乏同时具有以下特性的材料：（1）在感兴趣的温度区域中具有高性能，（2）可以以最小的能量损失有效地循环，（3）廉价，以及（4）基于具有高天然丰度的材料。一些地球上丰富的材料，已知是积极的MR，但不经常使用，因为从循环损失的效率低下。作为该项目的一部分，这些材料被制备为纳米颗粒。韦恩州立大学的布罗克教授和她的团队希望颗粒尺寸的减小能够减少磁极化的障碍，从而实现有效的循环。为了评估这一假设，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，作为该项目的一部分。除了为可行的MR技术的发展提供关键见解外，该项目还包括对学生进行跨学科合作研究的培训和指导，并介绍底特律地区的6 - 9年级学生，其中许多是少数民族，到材料化学在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磷属元素化物（磷属元素=第15族元素）纳米材料的基本特性，特别关注磁制冷（MR）。许多过渡金属磷属元素化物材料非常适合于MR应用，在室温附近显示出大的磁热效应（MCE，在极化和去极化期间磁熵的大变化）。最大的影响与TC下从铁磁到顺磁状态的一阶（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）。纳米结构化已被建议作为一种手段，以扩大MCE最大化的温度范围;混合不同TC的颗粒，以扩大可获得可观的磁熵的温度范围。在这个项目中，“材料的机会”，在纳米过渡金属pnictides功能磁热的搜索，通过三个目标追求。在目标1中，磁熵数据收集P掺杂的MnAs纳米颗粒样品和相关的单颗粒磁力显微镜数据，以辨别多分散性如何影响样品的整体行为，在大的温度范围内产生均匀的磁熵响应。在目标2中，创建了金属前体与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，在目标3中，解决了利用纳米材料进行磁制冷所面临的内在挑战，包括由于表面氧化而降低磁熵。利用减少策略的见解来瞄准MR的新锑阶段。除了为可行的MR技术的开发提供关键见解外，该项目还包括对跨学科合作研究的学生进行培训和指导，并介绍底特律地区6 - 9年级学生，其中许多是少数族裔，到材料化学，该奖项反映了NSF的法定使命，并通过使用基金会的知识产权进行评估，被认为值得支持。优点和更广泛的影响审查标准。

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.