A triboelectric nanogenerator (TENG) is of great interest as an emerging power harvester owing to its simple device architecture with unprecedented high efficiency. Despite the substantial development of new constituent materials and device architectures, a TENG with a switchable surface on a single device, which allows for facile control of the triboelectric output performance, remains a challenge. Here, we demonstrate a supramolecular assembly route for fabricating a novel TENG based on an alkali metal-bound nanoporous film, where the alkali metal ions are readily switched among one another. Our soft nanoporous TENG contains numerous SO3- functional groups on the surface of nanopores prepared from the supramolecular assembly of sulfonic acid-terminated polystyrene (SPS) and poly(2-vinylpyridine) (P2VP), followed by soft etching of P2VP. Selective binding of alkali metal ions, including Cs+, K+, Na+ and Li+, with SO3- groups enables the development of mechanically robust alkali metal ion-decorated TENGs. The triboelectric output performance of the devices strongly depends on the alkali metal ion species, and the output power ranges from 11.5 to 256.5 μW. This wide-range triboelectric tuning can be achieved simply by a conventional ion exchange process in a reversible manner, thereby allowing reversible control of the output performance in a single device platform.