Recent advances in the “on–off” approaches for on-demand liquid-phase hydrogen evolution

Hydrogen (H2) has been extensively considered as a clean and renewable energy carrier and the most promising alternative to conventional fossil fuels for future energy supplies due to its ultrahigh energy density and zero pollution. Selective “on–off” switches for on-demand liquid-phase H2 evolution are crucial and challenging for efficient utilization and production of H2. At present, the on-demand liquid-phase H2 evolutions are mainly controlled by five types of switches, namely catalyst-transfer switch, phase-transfer switch, pH-adjusting switch, temperature-adjusting switch, and light-adjusting switch. In this minireview, an overview of these “on–off” approaches with a particular emphasis on the recent advances in mechanism exploration and applications has been presented. Finally, we provide the future research directions and perspectives for overcoming the challenges in the commercialization of a promising approach.