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 0) of RbPb₂Nb₃O₁₀, HPb₂Nb₃O₁₀, and Pt/loaded HPb₂Nb₃O₁₀ (with Pt(NH₃)₄²⁺, denoted Pt_in/HPb₂Nb₃O₁₀) are estimated to be -0.14, -0.08, and 0.07 V us. 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 HPb₂Nb₃O₁₀ over RbPb₂Nb₃O₁₀. This proton reduction is significantly facilitated by the internal platinum loadings (with Pt(NH₃)₄²⁺); however, external platinization with PtCl₆^2- 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.