Relationship between Electronic Structure and Hydrogen-Uptake Kinetics

Striking changes have been observed in the photoemission energy-distribution curves from two phases of Pd overlayers on (110) Nb surfaces. In the commensurate (110) phase the Pd $4d$ band is found to have an edge about 1.5 eV below $E_{\mathrm{F}}$, similar to that of a noble metal. When the transition to the incommensurate Pd(111) phase occurs, the Pd $4d$ bands broaden and cross the Fermi level. As the density of Pd $4d$ states increases near $E_{\mathrm{F}}$, a dramatic increase in the hydrogen-uptake rate through the Pd is observed.