Electrochemical oxide film formation at noble metals as a surface-chemical process

The simultaneous production of hydrogen and degradation of organic pollutants (4-chlorophenol, urea, and urine) was successfully achieved using titania photocatalysts which were modified with both anion adsorbates (fluoride or phosphate) and (noble) metals (Pt, Pd, Au, Ag, Cu, or Ni) The dual-function photocatalysis worked only when both components coexisted on the surface of TiO2, whereas TiO2 modified with a single surface component (F–TiO2, P–TiO2, or Pt/TiO2) was inactive under the same experimental condition Two main surface-modified photocatalysts, F–TiO2/Pt (surface fluorinated and platinized) and P–TiO2/Pt (surface phosphated and platinized), were similarly active for dual-function photocatalysis in the anoxic suspension under UV irradiation With these catalysts employed, the degradation of 4-chlorophenol (or urea) was accompanied by the concurrent production of H2 The synergistic effect greatly depended on the kind of metal and pH The activity of F–TiO2/Pt gradually decreased with increasing pH, which makes the application of F–TiO2/Pt limited to the acidic pH region On the other hand, P–TiO2/Pt exhibited a consistent activity over a wide range of pH, which makes P–TiO2/Pt a more practical dual-function photocatalyst The synergistic effect of anions and metal deposits on the surface of TiO2 enhanced the interfacial electron transfer and reduced the charge recombination which resulted in a maximum of 20-fold increase of H2 production compared to metal deposited TiO2 in the presence of 4-chlorophenol

Simultaneous production of hydrogen with the degradation of organic pollutants using TiO2 photocatalyst modified with dual surface components

The impact of electrolyte constituents on the interaction of hydrogen peroxide with polycrystalline platinum is decisive for the understanding of the selectivity of the oxygen reduction reaction (ORR). Hydrodynamic voltammetry measurements show that while the hydrogen peroxide reduction (PRR) is diffusion-limited in perchlorate- or fluoride-containing solutions, kinetic limitations are introduced by the addition of more strongly adsorbing anions. The strength of the inhibition of the PRR increases in the order ClO4− ≈ F− < HSO4− < Cl− < Br− < I− as well as with the increase of the concentration of the strongly adsorbing anions. Electronic structure calculations indicate that the dissociation of H2O2 on Pt(111) is always possible, regardless of the coverage of spectator species. However, the adsorption of H2O2 becomes strongly endothermic at high coverage with adsorbing anions. A comparison of our observations on the inhibition of the PRR by spectators with previous studies on the selectivity of the ORR shows that oxygen is reduced to H2O2 only under conditions at which the PRR kinetics is significantly limited, while the ORR proceeds with a complete four-electron reduction only when the PRR is sufficiently fast. Therefore, only a H2O2-mediated pathway that includes a competition between the dissociation and the spectator coverage-dependent desorption of the H2O2 intermediate is enough to explain and unify all the observations that have been made so far on the selectivity of the ORR.

https://pubs.rsc.org/en/content/articlepdf/2013/cp/c3cp50649e

M. A. Genshaw

Papers

Study of anion adsorption of platinum by ellipsometry

New method for studying ion adsorption