Correct schottky diode selection
From your search results I just picked this one to go off in my explanation. https://www.diodes.com/assets/Datasheets/ds30018.pdf (B170/B)
Its all about how the system is designed. If your system is designed to work at 50V and there are limiters in place to keep max voltage under 60V then a 60V diode would be fine. Therefore, you should pick a diode with a reverse voltage that is higher than a voltage you expect to see. 25% higher than the max voltage is a good metric to go by, but higher is for the most part normally better.
As for output current it pretty simple. 700mA is your average rectified current. Pick a diode with a higher average rectified current, like 1A.
For more information. The diode only conducts current when the mosfet is off. Therefore, your average current is actually less than 700mA because of the Ton time. These two images here show what happens during the off state of your mosfet. As you can see current through the diode starts at Imax and falls over time to Imin. These values can be found by using the &quot;9.2.2.2 Output Inductor Selection&quot; section of your technical documentation. Assuming a 40% ripple current will show that your peak current will be .98 A. Which is under even the average rectified current of the diode I picked.


Sources: https://en.wikipedia.org/wiki/Buck_converter