Between 0 and 1A drawn...
the datasheet you linked to - shows the forward voltage curve from 0.6V @ 0.01A, up to 0.9V drop @ 1A
(page 2 - top RH corner)
I wouldn't dream of pulling any more than 500mA max through the Arduino board.
(PCB tracks, chip & I/O pin limitations etc)
So a single 1N4004 diode should serve you well.
The cpu will be happy - worst case 5.5V minus 0.6 == 4.9V
Although you'd always be better off with with...
a 5V regulated supply into the 5V pins,
or a 9V supply into the VIN pin