  Charged colloidal particles propel themselves through asymmetric fluxes of
chemically generated ions on their surface. We show that asymmetry in the
surface charge distribution introduces a new mode of self-phoretic motion for
chemically active particles that produce ionic species. Particles of sizes
smaller than or comparable to the Debye length achieve directed self-propulsion
through surface charge asymmetry even when ionic flux is uniform over the
particle surface. Janus nanoparticles endowed with both surface charge and
ionic flux asymmetries results in enhanced propulsion speeds of the order of
$\mu$m/s or higher. Our work provides a theoretical framework to quantitatively
determine the velocity of asymmetrically charged nanoparticles undergoing ionic
self-diffusiophoresis, and suggests an avenue for specifying surface properties
that optimize and regulate self-propulsion in ionic media.
