The near elimination of hysteresis in Pd/Cr2O3 composites

Abstract

Although its value varies with the microstructure, hysteresis always accompanies hydride formation and decomposition in Pd(pure)-H, e.g., it is present even in nano-crystalline and thin films. Internal oxidation of Pd 0.93 Cr 0.07 alloys leads to a pure Pd matrix containing nano-crystalline chromia precipitates. The characteristic hysteresis of Pd-H almost disappears in this form of Pd. The reasons for this are discussed.

H2 Solubility in Pd/Cr2O3 Composites Prepared by Internal Oxidation of Pd−Cr Alloys: Equilibrium Pressure-Composition-Temperature Data

“…Plateau pressures after the second cycle do not change with further cycling (323 K) for the IOed (1098 K) Pd 0.97 Cr 0.03 alloy, but there is a greater degree of sloping (Figure 7). (Larger changes can be seen for isotherms measured at higher temperatures, e.g., g373 K. 29 ) Initially there is a sharp dilute f hydride transition for the IOed (1098 K) Pd 0.97 Cr 0.03 alloy which becomes more gradual after one cycle (323 K). Although no further changes are found after the second cycle (Figure 7), changes continue for a Pd 0.97 Cr 0.03 alloy IOed at 998 K.…”

“…Hysteresis, 1 / 2 R T ln( p f / p d ), for the IOed Pd 0.93 Cr 0.07 alloy decreases as a result of this cycling from 1070 J/mol H (Pd) to 945 J/mol H (first) to 470 (third) J/mol H each evaluated at r = 0.30 (Figure ). The almost complete elimination of hysteresis for an IOed Pd−Cr alloy has been described elsewhere . The effect of cycling on the plateau p H 2 seems to level-off after about 4 cycles and plateau pressures have been evaluated after four and more cycles at r = 0.3.…”

“…Plateau pressures after the second cycle do not change with further cycling (323 K) for the IOed (1098 K) Pd 0.97 Cr 0.03 alloy, but there is a greater degree of sloping (Figure ). (Larger changes can be seen for isotherms measured at higher temperatures, e.g., ≥373 K …”

“…The almost complete elimination of hysteresis for an IOed Pd-Cr alloy has been described elsewhere. 29 The effect of cycling on the plateau p H 2 seems to level-off after about 4 cycles and plateau pressures have been evaluated after four and more cycles at r ) 0.3. Van't Hoff plots for cycled IOed Pd 0.93 Cr 0.07 (Figure 11) show that both plateau p H 2 are smaller than those for Pd(b) and that they are very close, merging at higher temperatures.…”

Thermodynamics of hydrogen absorption (desorption) in unoxidized and internally oxidized Pd–Ti alloys

“…16, 18), the isotherms become more sloping and have smaller capacities and hysteresis than Pd. Earlier it was shown by Wang et al [22] that similar changes from the behavior of Pd occurred in IOed Pd-Cr alloys but to an even greater extent than for the Pd-Ti alloys. For example, some isotherms, which have not been shown elsewhere, for an IOed Pd 0.95 Cr 0.05 alloy are shown in Fig.…”