An integrated system and method for driving a CO2 compressor to densify CO2 captured from the exhaust gas stream of an internal combustion engine on board a mobile source of CO2 includes operating a turbine that is operatively connected to the power input or drive shaft of the CO2 compressor, and operatively connecting a motor-generator to the turbine for (a) recovery of any excess power when the turbine-generated power exceeds the CO2 compressor power demand and (b) providing supplemental power when the turbine-generated power is insufficient to meet the CO2 compressor power demand.