In Situ Potentiometric, Resistance, and Dilatometric Measurements of Palladium Electrodes During Repeated Electrochemical Hydrogen Absorption

Journal Article · Fri Sep 15 04:00:00 EDT 2000 · Fusion Science and Technology

OSTI ID:20845767

Numata, Hiroo; Ohno, Izumi ^[1]

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1. Tokyo Institute of Technology (Japan)

The physicochemical properties of the Pd-H system were studied by in situ potentiometric, resistance, and dilatometric measurements in each of three applied pulse modes, A, B, and C, and repeated H absorption and desorption. Potential, resistance ratio, and an increase in dilation ({delta}l/l{sub 0}) were measured simultaneously after H equilibrium was attained with the Pd electrode. During continuous absorption, structural phase transition ({alpha} [right arrow] {beta}) and void formation occurred, and the values of the H/Pd ratio in the limiting {alpha} phase, in the {alpha} + {beta} phase coexistence, and in the transition and the {beta}+voids coexistence regions are consistent with those obtained from the Pd-H isotherm at 40 deg. C. Hydrogen absorption caused the dilation, from whose slope the molar volume was obtained as 0.64 ({alpha} phase) and 0.40 ({alpha} + {beta} phase) cm{sup 3}/mol. The resistance increased in proportion to the H/Pd ratio and was kept constant at 1.7 to 1.8 over R{sub tr}.For the first absorption through the {beta} phase (>{beta}{sub min}), the electrode potential shifted with an increase in dilation, which suggests nonequilibrium PdH{sub 2-x} precipitation followed by conversion to the {beta} phase and void formation. Although there was a remarkable lack of any dependence on the number of repetitions of the values of the limiting resistance and potential corresponding to the {alpha} + {beta} and {beta} + void coexistence, the onset of the {beta} phase, {beta}{sub min}, increased as the number of repetitions increased. The volumetric ratio for an increase in the H/Pd ratio corresponds to the absorption in high-density defect areas surrounding voids. During repeated absorption and desorption in the C applied pulse mode, the apparent molar volumes of the {alpha} + {beta} phase coexistence show that absorption proceeds inhomogenously, in contrast to the first absorption in the A applied pulse mode.

• OSTI ID: 20845767
• Journal Information: Fusion Science and Technology, Journal Name: Fusion Science and Technology Journal Issue: 2 Vol. 38; ISSN 1536-1055
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ABSORPTION
APPARENT MOLAL VOLUME
CONVERSION
DENSITY
DESORPTION
ELECTRODES
EQUILIBRIUM
HYDROGEN
ISOTHERMS
PALLADIUM
PHASE TRANSFORMATIONS
POTENTIALS
PRECIPITATION
PULSES