Adsorption Characteristic Study Of H₂PO₂～- On Transition Metal (Nickel And Copper Etc.) Surfaces By Density Functional Theory

Hypophosphite, H₂PO₂^-, is one of the most widely used reductant in the electroless depositions. In the present work, the adsorption characteristics of H₂PO₂^- on Ni(111), Pd(111), Pt(111) and Cu(111), Ag(111), Au(111) surfaces have been investigated by means of the density functional theory(DFT) and the cluster models with Gaussian 03W software. The calculated results indicated that the most stable orientation of H₂PO₂^- was found to have its two oxygen atoms interact the surface with two P-O bonds pointing downward, where we found that the oxygen atom, instead of hydrogen, should play the anchoring role. The adsorption energies of H₂PO₂^- on Ni(111), Pd(111), Pt(111) surfaces are larger than on Cu(111), Ag(111), Au(111) surfaces, and H₂PO₂^- adsorbs on Ni(111), Pd(111), Pt(111) surfaces more closely than on Cu(111), Ag(111), Au(111) surfaces. The results of the Mulliken population analysis showed that the donation from lone pair of O atom in H₂PO₂^- to the s orbitals of substrate atoms and the d orbitals back donation from substrate to P atom in H₂PO₂^- play very important roles in the adsorption on the transition metals. The d orbitals of Cu, Ag, Au are essentially fulfilled, but the d orbitals of Ni, Pd, Pt are not fulfilled. Thus the electron transfer amount is larger on Ni, Pd, Pt surfaces than on Cu, Ag, Au surfaces. These conclusions could serve as partial justification to understand why H₂PO₂^- is a good reductant in the Ni, Pd, Pt-electroless deposition but cannot be used in the Cu, Ag, Au-electroless deposition.In succession we studied the adsorption of hypophosphite on single crystal nickel surfaces, the result showed that Ni(210) surface is more catalytically active for the oxidation of H₂PO₂^- than Ni(111) and Ni(100) surface.Further the oxidation mechanism of H₂PO₂^- in electroless deposition process was studied by means of the density functional theory (DFT). Two reaction pathways via three-coordinate compound obtained by primary dehydrogenation from H₂PO₂^- and via five-coordinate compound by primary addition of OH^-, were examined. The calculated results showed that the oxidation mechanism of H₂PO₂^- is different on different metal surfaces. The oxidation process may occur via three-coordinate pathway and via five-coordinate pathway on Ni surface and on Pd surface, respectively.