A universal high-efficient and reusable 'on–off' switch for the on-demand hydrogen evolution

Although a few “on–off” approaches such as the pH-adjusting, temperature-adjusting, and controlling by light upon photo-catalysts have been reported, the “on–off” control of the on-broad and on-demand hydrogen production still faces many challenges. Herein, we first report the usage of Zn2+/EDTA-2Na system as an unprecedented, universal, high-efficient, and reusable “on–off” switch for the on-demand H2 evolution upon the hydrolysis of ammonia borane, sodium borohydride and dimethyl aminoborane. This “on–off” switch has been demonstrated to be efficient and reusable in various heterogeneous and homogeneous metal catalysts for on-demand H2 evolution. The detailed characterizations have confirmed that Zn2+ ions attached and located at the surface of catalyst, covered its active sites on the surface, and turned off the H2 production. The H2 generation was switched on by the addition of EDTA-2Na, due to its strong coordination ability with Zn2+ ions. In addition, the Zn2+/EDTA-2Na switch has been successfully reused several times without any activity loss in the “on–off” control of H2 evolution. This switch is of great importance in the practical application for highly efficient, on-site and on-demand H2 evolution under ambient conditions.