Metal phosphides: topical advances in the design of supercapacitors

Abstract

World-wide increased energy consumption and demand has made the need for high-energy storage systems with longer life critical. Hence, extensive research and development on supercapacitors based on efficient and robust electrode materials are being carried out. Many materials based on metal oxides, polymers, carbon-based materials, metal chalcogenides, and their composites have been explored to reach saturation to obtain the milestone capacitance value and hence, energy density. Recently, metal phosphides (MPs) have arisen as a unique class of potential candidates for high performance supercapacitors owing to their inherent semi-metallic nature and high electrical conductivity. Aid of fascinating properties, MPs has driven to reach demarcation outlined by champion metal oxides based electrodes for supercapacitor applications. We systematically reviewed the phosphides family including the phosphides of nickel, cobalt, iron, and copper to give a clear understanding in terms of their versatile applications in supercapacitors. Aside from mono-metal phosphides, an extensive analysis of the literature about multi-metal phosphides with combined benefits from two or more metal species has been explored. To further exploit their interesting properties, MPs have been integrated with other functionally active materials to form binary composites or even ternary composites. The present review article concentrates on modern research findings in the synthetic routes of nanostructured MPs in correlation with the structures, morphologies, and their electrochemical energy storage performances. Subsequently, the importance of strong synergistic effects existing in MP-based nanocomposites is highlighted along with some representative works on the fabrication of symmetric/asymmetric supercapacitor devices. Finally, the current challenges and future opportunities in real energy technology device applications of MPs are proposed.