Energetic characterizations of particulate RbPb2Nb3O10 electrodes

Electrochemical studies on layered perovskite lead niobates, RbPb2Nb3O10 and HPb2Nb3O10, were carried out. Mott-Schottky plot analysis suggests these materials are n-type semiconductors; the flatband potentials (pH O) of RbPb2Nb3O10, HPb2Nb3O10, and Pt-loaded HPb2Nb3O10 (with Pt(NH3)(4)(2+), denoted Pt-in/HPb2Nb3O10) are estimated to be -0.14, -0.08, and 0.07 V ys. SCE, respectively, and shifted negatively by ca. 60 mV per pH unit. Electrochemical probing with Fe(CN)(6)(3-/4-), Ru(NH3)(6)(3+2+), and MV(2+/+/0) not only confirms these results but suggests proton reduction is much favored at RPb(2)Nb(3)O(10) over RbPb2Nb3O10. This proton reduction is significantly facilitated by the internal platinum loadings (with Pt(NH3)(4)(2+)); however, external platinization with PtCl62- does not give a similar catalytic effect. Admittance analysis suggests midgap states are populated in the interior of HPb2Nb3O10. With these inner surface states, electron transfer is greatly eased and a favorable proton reduction results at the HPb2Nb3O10 particles.