A numerical study of solutal convection in rotating shallow electrochemical cells is performed. Typical cases show complex interactions among the centrifugal, Coriolis forces and mass transfer process in the rotating cells, which depend on the Ek and Sc Ro(S) numbers. At low rotational speed (Ek is near 0.01) the inviscid core flow is unicellular and sandwiched between the top and bottom Ekman layers. When Ek is less than about 0.006, a series of secondary cells are induced by the Coriolis force in the core. It is found that the Coriolis force suppresses the centrifugal convection, reducing the mass transfer rate, especially at low Sc Ro(S). The present numerical results are shown to be in good agreement with our earlier scaling analysis as well as with our experimental mass transfer data.