  Catalytic bimetallic Janus particles swim by a bipolar electrochemical
propulsion mechanism that results from electroosmotic fluid slip around the
particle surface. The flow is driven by electrical body forces which are
generated from a coupling of a reaction-induced electric field and net charge
in the diffuse layer surrounding the particle. This paper presents simulations,
scaling, and physical descriptions of the experimentally observed trend that
the swimming speed decays rapidly with increasing solution conductivity. The
simulations solve the full Poisson-Nernst-Planck-Stokes equations with multiple
ionic species, a cylindrical particle in an infinite fluid, and nonlinear
Butler-Volmer boundary conditions to represent the electrochemical surface
reactions. The speed of bimetallic particles is reduced in high-conductivity
solutions because of reductions in the induced electric field in the diffuse
layer near the rod, the total reaction rate, and the magnitude of the rod zeta
potential. The results in this work suggest that the auto-electrophoretic
mechanism is inherently susceptible to speed reductions in higher ionic
strength solutions.
