Identifying reliable and sustainable sources of electricity is a significant challenge of the present time. However, most energy-generation mechanisms produce unavoidable low-grade waste heat as a byproduct while harvesting (or converting) electrical energy from conventional or renewable energy sources. Each year, over 60% of the primary energy is wasted as heat. Accordingly, considerable efforts are being made to convert this waste heat into usable electrical energy using diverse energy conversion materials. In this review, three actively investigated energy conversion mechanisms beyond thermoelectrics, i.e., (1) pyroelectric, (2) thermomagnetic, and (3) thermogalvanic generators, are reviewed and compared from the viewpoint of fundamental theories, critical parameters for high energy conversion efficiency, and current status of materials and devices. The challenges and opportunities in low-grade waste-heat recovery are discussed in terms of material science and structural design. This review provides an overview of the current progress in thermal-energy-harvesting research, future challenges, and opportunities.

确定可靠且可持续的电力来源是当前的一项重大挑战。然而，大多数能源生产机制在从传统或可再生能源收集（或转换）电能时，都会不可避免地产生低品位废热作为副产品。每年，超过 60% 的一次能源以热能的形式被浪费。因此，人们正在做出相当大的努力来使用不同的能量转换材料将这种废热转换成可用的电能。在这篇综述中，三个积极研究的热电之外的能量转换机制，即。，从基础理论、高能量转换效率的关键参数以及材料和器件的现状的角度对（1）热电、（2）热磁和（3）热电发电机进行了回顾和比较。从材料科学和结构设计的角度讨论了低品位余热回收的挑战和机遇。这篇综述概述了热能收集研究的当前进展、未来的挑战和机遇。