The maximum hydrogen (deuterium) loading ratio in the Pd|H2O (D2O) electrochemical system

Abstract

Based on the Volmer-Heyrovsky-Tafel mechanism, Frumkin adsorption and thermodynamic data of hydrogen (deuterium) absorption in Pd, effects of surface parameters on the hydrogen (deuterium) loading ratio into Pd in the hydrogen (deuterium) evolution reaction are discussed. There is a change of mechanism from the Volmer-Tafel route to the Volmer-Heyrovsky route when the current density rises, and there exists the maximum loading ratio at a certain current density when the symmetry factor of the Heyrovsky step is less than that of the Volmer reaction. The theoretical results fit the experimental data presented before very well; other factors that affect the loading ratio are discussed as well.

Engineering Palladium Surfaces to Enhance the Electrochemical Storage of Hydrogen

“…Finding a similar predictor for j oH for various materials appears to be more complex, requiring additional DFT modelling of the Heyrovsky reaction on different surfaces or taking measurements and fitting the data with kinetic models to elucidate the rates of the reactions. 2 The DFT modelling shown in Figure 3, suggest experimenting with different surfaces consisting of Pt (to enhance j oV ), Bi, and Pb (to decrease j oT ) on the Pd could further enhance the electrochemical insertion of H.…”

“…For comparison, a H 2 fugacity exceeding 2400 atm is required to obtain the equivalent PdH 0.87 by H 2 gas loading. 2,26 The addition of a small amount of Pt to the Bi UPD layer reduced the cathodic overpotentials compared to the Bi layer alone, but still required larger cathodic overpotentials than the Pd control. The η 2 vs η curve shifted toward lower cathodic overpotentials, again indicating an increase in j oV /j oT .…”

“…This work sets out to provide further engineering insight to assist in the optimization of surface alloys for enhancing the amount of electrochemically stored H under given electrolysis working conditions. Previously published mathematical relationships show a connection between the exchange current densities for the reactions and the chemical potential of H. [2][3][4][5][6] Since exchange current densities are material properties, one can study a multitude of different combinations of surface additions to fine tune these properties and maximize the stored H under given electrolysis working conditions. Instead of spending the exorbitant amount of time and resources necessary to experimentally observe the effects of materials, density functional theory (DFT) calculations were used to screen materials for further study.…”

Effects of self-stress on the hydrogen absorption into palladium hydride electrodes of plate form under galvanostatic conditions

“…Volmer, Tafel and penetration reactions taking place in the hydrogen evolution reaction at the same time [30,40]. The rate of the Volmer step is the applied current density, the rates of the Tafel and penetration steps are…”

“…In this paper, we will discuss self-stresses generated in b-phase PdH x electrodes based on the stress induced diffusion theory developed by Larché and Cahn [22][23][24] and presented more extensively in a review paper by Baranowski [27], and Pd H electrode kinetics discussed in Zhang et al [30][31][32]. Although there has been much work concerning the self-stress in solid solutions of hydrogen in metal, no theory has been applied to the metal hydride situation up to now.…”