Bipolar energy harvesting circuit
I found an article about a "Zero Voltage Diode", which is actually using a 2N7000 mosfet to act much like a very-low-drop diode. Several of the links are dead, but archive.org has copies.



Searching on a few parts retailers, I found the TI SM74611 Smart Bypass Diode with a forward voltage drop of 26mv at 8A, which is not insignificant compared to the 250mv startup voltage, but is still extremely tiny for a diode.

I know that I've seen somewhere information about a type of diode that conducts with 0v bias in one direction (reverse, iirc) and blocks up to a small voltage (maybe 500mv to 1v) in the other, but I can't remember what that type was called or where I read about it.