Nickel and nickel phosphide nanoparticles embedded in electrospun carbon fibers as favourable electrocatalysts for hydrogen evolution

The needle-less electrospinning method is used for a preparation of carbon, carbon/nickel, carbon/nickel/nickel phosphides and carbon/nickel phosphides fibers of a continual length and a high specific surface area. The prepared fibers were produced in a large scale as a potential electrode material for electrocatalytic hydrogen evolution reaction (HER). The polyacrylonitrile (PAN) was used for a preparation of spun solution and subsequent precursor fibers formation. The phosphoric acid of 0.5 or 5 wt% was added to the spun solution in order to increase conductivity of the spun solution as well as to provide a source of phosphorus in the final fibers. The exactly defined temperature schedules of calcinations and atmosphere were suggested according to the results obtained from TG/DSC analysis. The phosphoric acid in the electrospun PAN precursor fibers is responsible for the cyclization and aromatization during stabilization of the electrospun precursor fibers. The XRD analysis confirmed the formation of phosphides at different molar ratio of NiCl2:H3PO4. The final morphology, porosity and position of the incorporated nickel or nickel phosphides nanoparticles can be designed by the calcinations temperature and used atmosphere. A possible mechanism for a formation of nickel, nickel/nickel phosphide and nickel phosphide nanoparticles was suggested. The linear sweep voltammetry, impedance spectroscopy and Tafel slopes measured in 0.5 M H2SO4 solution confirmed that the highest HER activity exhibit carbon fibers containing the nickel and nickel phosphide nanoparticles after the heat treatment in the hydrogen reduction atmosphere. (C) 2016 Elsevier B.V. All rights reserved.