I knew one guy who was working for a company that did that. Bit it's not an ideal use of batteries. Semis avoid cities, they avoid stop and go. Long cruises negate the hybrid advantage.
Where hybrids shine are in heavy vehicles that do a lot of stop and go -> urban delivery trucks and contractor vehicles. This is where all out effort of electrification should start with, hybridizing these vehicles.
Also, if you're serious about CO2 emissions, the most effective way to decrease them is to enforce lowered speed limits.
