Surface Structure on Hydrogen Adsorption at Platinum

Influence of Surface Structure on Hydrogen Adsorption at Platinum 

The heat of adsorption was determined [34] for the three faces after 260 cycles. It was independent of temperature between 0° and 80 °C for the (100) and (111) faces and between O and 40for the (110) face. 

The general shape of the W — Q curves is similar to that of the curves on polycrystalline platinum in Fig. 11. Large differences exist in the values at a given coverage. The heat decreases in the order (100) (111) (110) fore 0.8. 

The number of platinum atoms in the surface planes is 1.5 10 per cm for the (lll face, 1.3 10 for the (100) face, and 0.92-10 for the (110) face. This leads to theoretical values for Qh of 0-24 mcoul/cm, 0.21 mcoul/cm, and 0.15 mcoul/cm. The experimental sQh values are much larger on the three faces, especially after continued cycling. Will [34] estimated that the roughness factor increased from 1.87 after ten sweeps to 2.45 after 260 sweeps on the (100) face. The initial roughness of the virgin surfaces becomes greater with the number of sweeps. Each of the nominal faces exposes several crystal planes in different proportions. 

The fact that the current maxima have different heights for the faces but occur at nearly the same potentials led Will to a tentative assignment The left maximum was assigned to the removal of hydrogen atoms from the (110) plane, the right maximum to that from the (100) plane, and the third maximum to that from the (111) plane. It follows from this interpretation that hydrogen adsorption on cold-worked polycrystalline platinum occurs predominantly on crystallites that expose the (110) and (100) planes. 

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