General Approach for the Synthesis of Nitrogen-Doped Carbon Encapsulated Mo and W Phosphide Nanostructures for Electrocatalytic Hydrogen Evolution

Abstract

A general strategy for the synthesis of the core-shell nanostructure of nitrogen-doped carbon encapsulated MoP and WP (MoP@NC and WP@NC) and the electrochemical hydrogen evolution reaction (HER) are demonstrated. The synthetic procedure involves the self-assembling of polyoxometalate (M = Mo/W) and phytic acid on a polyetheleneimine backbone and the subsequent pyrolysis of the self-assembled supramolecular aggregates in an inert atmosphere without a traditional phosphidating agent. MoP@NC has a quasi-spherical shape with a MoP core (57 nm) and nitrogen doped porous carbon shell, whereas WP@ NC has a nitrogen-doped carbon coated rodlike nanostructure. MoP@NC has a large amount of pyridinic (∼59%) and Mo-bonded (∼33%) nitrogen. MoP@NC is highly active toward hydrogen evolution reaction (HER) and delivers the benchmark current density 10 mA/cm 2 at an overpotential of 52, 106, and 171 mV in acidic, alkaline and neutral pH, respectively. It shows a Tafel slope of 49 mV/dec, high turnover frequency (0.28 s −1 at η = 100 mV), and faradaic efficiency (96%) in acidic electrolyte. MoP@NC has remarkable durability in acidic and alkaline pH with a negligible increase in overpotential after 1000 extensive repeated potential cycles. The encapsulating nitrogen-doped carbon shell protects the active catalyst from corrosion and the catalyst retains its phase purity and structural integrity even after 10 h of long-time hydrogen evolution at constant potential. The outstanding HER activity of MoP@NC is accounted for by the small particle size, large surface area, and strong chemical coupling between MoP and nitrogendoped carbon.

An Electrocatalytically Active Nanoflake-Like Co9S8-CoSe2 Heterostructure for Overall Water Splitting

“…The intrinsic activity of the heterostructured catalyst was further confirmed by TOF analysis, calculated according to the established procedure. 59,60 Interestingly, the heterostructure has the highest TOF of 2.25 s −1 at η of 150 mV (Figure 4c). This is 3−5.5 times higher than that of CoSe 2 (0.75 s −1 ) and Co 9 S 8 (0.43 s −1 ).…”

A Solvent‐Free Strategy to Synthesize MoS2/Mo2C‐Embedded, N, S Co‐Doped Mesoporous Carbon as Electrocatalysts for Hydrogen Evolution

“…The performance of 2.0G4.0TMo1.0 is inferior to those of the carbide/ sulfide/Mo-based catalysts. [33][34][35] However, the synthesis strategy of 2.0G4.0TMo1.0 is a solvent-free process, which opens up a novel mothed to prepare porous electrocatalysts.…”

Advanced Oxygen Electrocatalyst for Air-Breathing Electrode in Zn-Air Batteries

“…The phosphidation of transition metals using phytic acid (PA) as an alternate phosphidating agent is known since 2015 . Various metal phosphide such as FeP, CoP, MoP, etc., have been synthesized in the past using PA for electrochemical water splitting, oxygen reduction, etc. − (Table ). Although the electrocatalytic activity of TMPs toward water splitting is extensively studied, limited works have been focused toward oxygen electrocatalysis.…”

“…Sing et al for the first time investigated the ORR activity of metal phosphide-based electrocatalysts, though the activity was inferior to that of the traditional catalyst . Subsequently, several other TMPs have been synthesized and their oxygen electrocatalytic activity has been investigated. − Recently, a new approach for the phosphidation of Co without using any traditional phosphidating agents is demonstrated . The carbothermal-reduction-assisted phosphidation of metal precursors (cobalt/iron polypyridyl complexes) was achieved at elevated temperature under inert atmosphere.…”