The short answer is yes, probably, the Commander is sterile. When Offred goes for her routine appointment at the gynecologist, he says as much to her and offers to get her pregnant himself. She is horrified by the doctor's suggestion and is sure that he could be an Eye (a spy for the government) or that he might report her as disloyal and disobedient if she declines his offer—but the fact is that Offred has had a child before, and so we know it is most likely possible for her to become pregnant again. However, the Commander has never fathered a child, and, because of his age, it is extremely likely that he cannot do so. The doctor implies that this is the case himself.