Recent progress on synthetic strategies and applications of transition metal phosphides in energy storage and conversion

Continuous advancements in the field of energy conversion and storage, including the development, evaluation of abundant and inexpensive materials with good electrochemical performance, aim to meet the future energy demands. Transition metal phosphides (TMPs) have recently emerged as excellent energy conversion and storage materials due to their highly active surface sites, electrical conductivity, thermal and structural stability. TMPs exhibit numerous other desirable properties, like hardness and chemical stability, which result from the presence of strong M - P bonds in the molecules. In this work, comprehensive review of recent advancements in research concerning TMPs and their applications in the area of energy conversion and storage was conducted. Additionally, the frequently employed synthetic strategies for the production of TMPs were investigated. Particularly, hydrogen and oxygen evolution reactions (HER and OER), dye-sensitized solar cells for energy conversion and storage, lithium-ion batteries, and supercapacitors were examined. TMPs display remarkable electrochemical behavior due to the synergistic effects of various compositions and surface structures. Moreover, the M-centers and P-sites possess high electrocatalytic activity. The P-sites of phosphides are negatively charged; thus, they attract protons, enhancing the HER/OER activities. Eventhough platinum-based electrocatalysts perform best in HER, their bifunctional properties have not been extensively studied due to poor OER activities. In energy storage, TMPs used as efficient and stable electrodes owing to their low charge-discharge potentials, high theoretical specific capacities, and a decreased ion-diffusion pathway. Finally, the challenges, future perspectives in the area of energy are discussed and several approaches for the improvement of multifunctional TMPs are proposed.