The Psychic Blade ability says:
Whenever you take the Attack action, you can manifest a psychic blade from your free hand and make the Attack with that blade.
The blade vanishes immediately after it hits or misses its target...
Opportunity Attack says:
You can make an opportunity Attack when a Hostile creature that you can see moves out of your reach. To make the opportunity Attack, you use your Reaction to make one melee Attack against the provoking creature.
As far as I can determine, an Opportunity Attack allows you to make an attack, but you are not taking the Attack action. Psychic Blade specifies that the blades only manifest when you take the Attack action. It would seem that an opportunity attack with a psychic blade is impossible.
Can a Soulknife use a psychic blade for an opportunity attack?