New Synthesis Strategies for Transition-Metal Phosphide Based Water Splitting Electrocatalysts

Abstract

Transition metal phosphides (TMPs) have emerged as an intriguing class of efficient electrocatalyst finding widespread application in hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Currently adopted wet chemistry and solid-gas synthesis techniques rely on the use of surfactants/ toxic organic solvents or toxic gas which restricts facile fabrication of TMPs. Moreover, hybridizing TMPs with suitable carbon support (graphene, carbon nanotubes etc.) favorably optimizes the electrochemical activity of TMPs. However, this is often achieved via post-synthesis modification further complicating the synthesis procedure. In an attempt to overcome these limitations, we have recently developed a solid state, phosphine free method to fabricate Co 2 P nanoparticles encapsulated N, P co-doped CNTs. These as prepared catalysts were applied as a bi-functional electrocatalyst for HER and OER. In order to increase the surface area and loading of Co 2 P nanoparticles, we next designed Co 2 P encapsulated CNTs grafted N, P co-doped hollow spheres via MOF-templated strategy with superior catalytic activity compared to Co 2 P@CNTs.[1] [2] We then introduced sub-2nm IrP 2 nanoparticles encapsulated bilayer N, P co-doped graphene as a novel electrocatalyst which exhibits better HER activity than benchmark Pt/C in acid, neutral as well as the alkaline medium. Interestingly, careful tuning of the reaction parameters also enables the synthesis of phase pure Ir 2 P. In conclusion, the versatile strategy developed here can be extended to fabricate a variety of TMPs with widely varied applications. [1] D. Das and K.K. Nanda, Nano Energy, 2017, 30, 303-311 [2] D. Das, A.Das, M.Reghunath and K.K Nanda, Green Chemistry, 2017,19, 1327-1335