"Spock's Brain" is probably the most MST3K worthy episode in TOS. So nit-picking it is gratuitous. However, I ran across a passage in THE STARFLIGHT HANDBOOK (Eugene Mallove & Gregory Matloff, John Wiley & Sons, Inc. 1989) that seemed relevant.
During the opening tease, Scotty is gushing over an ion-propelled ship. "They could teach us a thing or two!" Meanwhile the Enterprise
flashes between the stars at multiples of the speed of light. I guess "ion" sounded technical to the writer.
Pioneers in optimizing fusion-rocket trajectories include G. M. Anderson and Conley Powell. Although their work specifically addressed fusion rocketry, their analyses could, in fact, be applied to fission and antimatter rockets and even high performance nuclear-electric propulsion. Anderson, then a professor at the USAF Institute of Technology, published his optimization analyses in several papers between 1968 and 1974. Although he focused on fusion rockets, he also extended his calculations to antimatter, fission, and electric propulsion.
Using the calculus of variations, Anderson derived relativistically correct results for a flight time limited to 40 years and a mass ratio limited to 10,000. He discovered that of all the rockets considered—antimatter photon rockets (Ve = c), ideal nuclear-fusion rockets (Ve = 0.0893 c), ideal nuclear-fission rockets (Ve = 0.0388 c), and conservative ion rockets (Ve = 0.000316 c)—only the ion rocket is inherently not capable of carrying out the mission.
—chapter 10, pg. 157
Later in the episode, Scotty again remarks on "ion power"—
Ooh! Do it again!
SCOTT: Captain, that power we picked up above, we're getting closer.
KIRK: A lot of it?
SCOTT: Enough to push this planet out of orbit.
KIRK: What source?
SCOTT: Either a nuclear pile a hundred miles across or
KIRK: Or what?
SCOTT: Ion power.
In a similar vein, in the BUCK ROGERS episode "Buck's Duel to the Death," our hero must confront a gangster called the Traybor who uses electricity as a secret weapon—casting bolts like Zeus. Apparently, no one in the 25th century uses olde fashioned electricity anymore, so it's up to Buck to deal with this problem...
Again, we have a writer who is unfamiliar with any physics. Electrical charge is one of the most fundamental aspects of all
matter. So even if New Chicago is powered by an antimatter plant, electricity (and ions!) still comes into the picture somewhere.