A pumping medium for an electro-osmotic pump made of porous silicon. The porous silicon may result in a lower required pumping voltage and a smaller form factor for an equivalent flow rate and pressure generation as compared to conventional glass frits. The porous silicon may also provide a better thermodynamic efficiency over conventional glass frits for use in electro-osmotic pumps. The increased efficiency of the porous silicon may provide an low-power, high flow rate, high pressure, small form factor, vibration-free pump for cooling microelectronic devices, such as integrated circuit chips.