Money (notes & coins in circulation) can be thought of as the longest duration, lowest coupon government debt which can ever be issued. The central bank does not pay interest on the notes it prints (although it is possible to pay interest on commercial bank reserves held at the central bank) and the central bank never has to redeem them. That legend on the ten pound note in your pocket that says “The Bank of England promises to pay the Bearer on demand the sum of Ten Pounds” will only result in the BoE giving you another, newer, crisper, ten pound note in payment for the one you attempt to redeem.