The application of a Pb2+ conducting solid electrolyte (Pb-beta" alumina) to electrochemical control of catalyst performance is reported. XPS data show that pumping of Pb to/from a thin film platinum catalyst from/to the solid electrolyte provides a controlled, reversible, and reproducible way of altering the surface composition of the resulting Pt/Pb surface alloy under conditions of acetylene hydrogenation. With increasing Pb concentration a large increase in partial hydrogenation selectivity occurs from 20% (pure Pt surface) to 85% (similar to26% Pb surface alloy). The results demonstrate that the surface composition and catalytic performance of bimetallic alloy catalysts can be dramatically and reversibly altered under working conditions by electrochemical means.