engleski

Investigation of Hydrogen Evolution on GdNi4Al and Polypyrrole-coated GdNi4Al Electrodes

GdNi4Al is an intermetallic compound with a well-defined crystallographic structure (CaCu5 type) exhibiting gas-phase-hydrogen sorption/desorption properties (1). In this work, electrocatalytic properties for the hydrogen evolution reaction (h.e.r.) were investigated on a GdNi4Al catalyst obtained by arc melting of its pure components, in order to characterize its electrocatalytic activity and stability. Electrocatalytic properties were evaluated on the basis of electrochemical data obtained from cyclic voltammetry and impedance spectroscopy measurements, performed in oxygen free 1 M NaOH, at room temperature. Selective oxidation of the less noble metals in the alloy (Gd, Al) coupled with formation of Raney Ni domains due to dealloying of Al (electrolyte pH = 14), leaves the rough surface layer of the catalyst with an increased concentration of metallic Ni, and results in high stability and electrocatalytic activity ( jo = 1.45 ´ 10-5 A cm-2) of this material for the h.e.r. In order to prevent decomposition of the GdNi4Al electrode at high current densities (h.e.r. overpotentials > -0.2 V) the electrode surface was modified in two ways: with an in situ formed electronically conducting polypyrrole (PPy) film (0.86 mm) and a graphite-paraffin coating (~0.3 &#8211 ; 0.5 mm). The PPy layer on the surface of the GdNi4Al electrocatalyst prevents the formation and growth of a potential-consuming surface oxide to a certain extent, which, as a consequence, results in a smaller Tafel slope (bc  75 mV) and a greater catalytic activity for the h.e.r. ( jo = 1.80 ´ 10-5 A cm-2). In contrast to the polypyrrole coated electrode, the GdNi4Al electrocatalyst modified by a graphite-paraffin layer showed significantly worse catalytic properties (bc > 1 V).

h.e.r.

nije evidentirano