Tuning hydrogen sorption properties of Pd by its alloying with Ru, Rh, and Pt: the study of binary alloys in concentrated alkaline media

Abstract

The hydrogen electrosorption process was examined in 6 M KOH on Pd binary alloys, containing Rh, Ru, and Pt. Pd-alloys were electrochemically deposited on Au substrate. The electrodes were subjected to activation procedure—hydrogen pretreatment procedure (HPP) at first in 0.5 M H2SO4 and then in 6 M KOH. It was noticed that it was possible to achieve comparable reversibility of hydrogen electrosorption process in acid and in concentrated base. The obtained values of the α→β phase transition potential, hysteresis extent, and maximum hydrogen absorption capacity show good agreement with the data from acidic medium. The observed kinetics of hydrogen electrosorption were strongly hindered in concentrated alkaline media, whereas the influence of the electrolyte on the thermodynamic functions of hydrogen absorption is less pronounced.

Hydrogen electrosorption properties of electrodeposited Pd-Ir alloys

“…3b. In the case of Pd-Ir alloys the shapes of electrosorption isotherms are similar (S-shape) than that obtained for Pd and Pd-based alloys in different electrolytes [3][4][5]9]. In the HEI three main parts can be distinguished: (1) first plateau assigned to the hydrogen absorbed in the α-phase (solid solution of hydrogen in the alloy) and hydrogen adsorbed, (2) the abrupt increase in the values of H/(Pd+Ir) corresponding to α→β phase transition, and (3) second plateau assigned to hydrogen absorbed in the β-phase (hydride) [33].…”

“…Before the main measurement, each of the Pd-Ir alloy electrode was polarized in the socalled "hydrogen region" (potential range: −0.1÷0.3 V), to obtain repetitive results. This approach, called hydrogen pretreatment procedure (HPP), was previously used for Pd and Pd-based electrodes in aqueous and non-aqueous electrolytes [4,5,9]. Figure 3a shows cyclic voltammetry behavior of Pd-Ir alloys of various compositions after HPP.…”

“…In the HEI three main parts can be distinguished: (1) first plateau assigned to the hydrogen absorbed in the α-phase (solid solution of hydrogen in the alloy) and hydrogen adsorbed, (2) the abrupt increase in the values of H/(Pd+Ir) corresponding to α→β phase transition, and (3) second plateau assigned to hydrogen absorbed in the β-phase (hydride) [33]. In the contracted alloys the potential of the α→β phase transition decreases with increasing amount of the alloying metals [9,11,12]. It is due to the fact that in contracted alloys greater work than in pure Pd is needed for lattice expansion during hydrogen absorption.…”

“…The process of hydrogen electrosorption has been examined in details in Pd [1][2][3][4][5][6], whereas hydrogen absorbing properties of some of Pd-based binary alloys are still unknown. The literature contains studies on a variety of Pd-M-H systems with different M elements such as Rh, Ru, Pt, Au, Ni, Cu, and Ag [7][8][9][10][11][12][13][14][15][16][17][18] but there is no information about Pd-Ir alloys in the aspect of hydrogen electrosorption.…”

“…Since the gaps in the Pd dband are partially filled by the alloying metal electrons, less gaps remain for the electrons from absorbed hydrogen. However, in Pd alloys with metals characterized by an increased number of free electronic states in d-band below Pd Fermi level, such as Rh and Ru, in a certain composition range greater hydrogen capacity is observed [9,11,12,28]. Since Ir has the electronic structure similar to Rh, it can be expected that Pd-Ir alloys will possess hydrogen absorption properties close to those of Pd-Rh.…”