Supercapacitors as redox mediators for decoupled water splitting

With the help of the redox mediator, decoupled water-splitting allows O 2 and H 2 to be produced at different times, at different rates, and even in different cells, which promotes both the operation safety and the utilization of renewable power sources. However, the current densities and stabilities of these redox mediators are commonly low, which require further improvements for practical applications. Here, we propose to use supercapacitors as solid state redox mediators for decoupled water splitting. For demonstration, Na 0.5 MnO 2 (pseudocapacitor) and active carbon (double layer capacitor), are both used as the redox mediator. These supercapacitors show superior current density (1 A/cm 2 ) and ultralong cycle-life (8000 cycles) compared with commonly investigated battery-based mediators (NiOOH/Ni(OH) 2 ). Our research proves supercapacitors can be used as redox relay with high current density and stability, which may bring new insights in the design of decoupled water splitting systems. We propose to use supercapacitors as solid state redox mediators for decoupled water splitting to allow O 2 and H 2 to be produced at different times, at different rates. Na 0.5 MnO 2 (pseudocapacitor) and active carbon (double layer capacitor), used as the supercapacitor based mediator show superior current density (1 A/cm 2 ) and ultralong cycle-life (8000 cycles) compared with commonly investigated battery-based mediators (NiOOH/Ni(OH) 2 ).