Analysis of open-circuit potential transient and laser beam deflection transient simultaneously measured from Pd foil electrode pre-charged with hydrogen

In the present work open-circuit potential (OCP) transient and laser beam deflection transient were measured simultaneously from the impermeable Pd foil electrode pre-charged with hydrogen at -0.08-0.04 V (reversible hydrogen electrode (RHE)) in 0.1 M NaOH solution as a function of the pre-charging potential of hydrogen. The OCP is determined by a mixing of the potentials of two simultaneous reactions of anodic hydrogen oxidation MHads + OH- = M + H2O + e(alpha) and cathodic hydrogen underpotential deposition M + H2O + e(beta) = MHads + OH- below 0.15 V (RHE) and oxygen reduction 1/2O(2), + H2O + 2e(beta) = 2OH(-) above 0.15 V (RHE), coupled by a common corrosion rate. From the coincidence between the measured OCP transient and calculated corrosion potential transient, it is indicated that the plot of hydrogen oxidation rate versus reduced time calculated corresponds to the measured OCP transient and thus both transients are closely coupled each other. This means that the hydrogen self-discharge from the electrode proceeds with the rate of hydrogen oxidation at the electrode surface, calculated based upon the mixed potential theory from the measured Evans-Hoar diagram. By taking the value of self-discharge rate on one surface determined as a function of time and adopting the impermeable constraint on the other surface as the boundary condition for hydrogen diffusion through the electrode, hydrogen concentration profile across the electrode has been derived with time from the measured tensile deflection transient. (C) 2000 Elsevier Science Ltd. All rights reserved.