Harvesting Energy from an Electromagnetic Generator
Your mosfet bridge will waste less voltage than diodes like you intended.You need enough Volts to drive the gates like george herold stated in comment. In fact at low input volts you will be worse off than diodes because the parasitic diode in all normal powermos is poor in terms of voltage drop and recovery.If you place shottkeys across the DS of each fet you will secure better performance at low voltages .Once you have done this there is still room for improvement.The voltage on C2 is more steady than the voltage on C1 .This voltage could be employed for running a gate drive circuit for the fets.I have done a circuit with 4   shottkeys and no pchannels ,just keeping the 2 nchannels .This could work better for you than what you have .