  We investigate the possibility that electrically neutral porous spheres
electrophorese in electrolyte solutions with asymmetric affinity of ions to
spheres on the basis of electrohydrodynamics and the Poisson-Boltzmann and
Debye-Bueche-Brinkman theories. Assuming a weak electric field and ignoring the
double-layer polarization, we obtain analytical expressions for electrostatic
potential, electrophoretic mobility, and flow field. In the equilibrium state,
the Galvani potential forms across the interface of the spheres. Under a weak
electric field, the spheres show finite mobility with the same sign as the
Galvani potential. When the radius of the spheres is significantly larger than
the Debye and hydrodynamic screening length, the mobility monotonically
increases with increasing salinity.
