Entropy-directed metal–organic frameworks drive solar-electrolytic water splitting

We report a water splitting system based on flow-type electrolytic cells, which are catalyzed by the catalysts composed of anodic high-entropy metal–organic framework (MOF) and cathodic low-entropy nickel, iron-MOF. These MOF catalysts have shown excellent activities for overall water splitting characteristic of small applied voltage (1.64 V at 10 mA cm−2) and strong durability for 100 hrs. Based on these catalysts, a tandem system has been assembled by connecting several flow-type water-splitting cells in series, which require 3.3 V for two cells and 5.32 V for three cells to reach 10 mA cm−2. Further, a solar-to-hydrogen production system has been demonstrated by coupling the tandem water splitting cells with photovoltaic panels, which show high Faradaic efficiencies (98.93 %, 98.95 %, and 98.40 %) and energy efficiencies (18.80 %, 18.80 % and 18.70 %) for single-, two-, and three-cells, respectively. The present work would provide new insights into the design of efficient energy-conversion systems for many applications.