reaction (HER) are coupled in the single compartment between two electrodes, in which the inherent co-generation of oxygen and hydrogen inevitably hinders the operational flexibility and increases the practical cost. [3] Therefore, it is urgent to develop a feasible electrolyzer system to separately produce and collect hydrogen.Decoupled water electrolysis, firstly proposed by Symes and Cronin, [4] is an effective strategy to achieve gas separation by inducing redox mediators. The mediators with appropriate redox potentials can couple with OER and offer electrons and protons for subsequent hydrogen evolution reaction (HER), which can completely decouple HER and OER in spatial and temporal separation with three-electrode system. [5] To date, many types of redox mediators have been developed to decouple HER and OER, with the neglection of energy requirement. The high energy consumption in above water electrolysis, derived from the sluggish kinetics of anodic OER is unavoidable, [6] where higher than 1.6 V input energy is required because of the high theoretical water electrolysis voltage of 1.23 V. [7] Recently, small molecule organics including alcohols, urea, glucose, hydrazine, etc, have been developed as favorable fuel candidates to replace OER due to the lower overpotentials. [8] Among them, hydrazine, a carbonfree and environmentally friendly liquid fuel, can be oxidized by transition metal catalysts at the low voltage of −0.33 V, effectively decreasing the input electrical energy. [9] Besides the much lower voltage, hydrazine oxidation reaction (HzOR) only releases inert and environmentally benign nitrogen. [9c,d,10] Although the energy for electrolytic hydrogen generation can be significantly decreased via replacing OER by HzOR, the extra energy input is still required to drive the electrolysis, adverse to practical and economical applications. Therefore, it is highly desired to develop a decoupled electrolyzer system for efficient hydrogen generation.Encouraged by the Zn-CO 2 batteries combined resource utilization/production with energy storage system, [11] a rechargeable alkaline Zn-Hz battery, based on decoupled hydrazine splitting by two temporally separate cathodic reactions of HzOR at charging and HER at discharging, can achieve efficient and separate hydrogen generation. Totally different from the typical decoupled electrolysis, the decoupled hydrazine splitting in the Zn-Hz battery is realized by bifunctional electrocatalysts with two-electrode system based on two separate electrochemical ). This Zn-Hz battery, driven by temporally decoupled electrochemical hydrazine splitting on the cathode during discharge and charge processes, can generate separated hydrogen without purification. When the highly active bifunctional cathode of 3D Mo 2 C/ Ni@C/CS is paired with Zn foil, the Zn-Hz battery can achieve efficient hydrogen generation with a low energy input of less than 0.4 V (77.2 kJ mol −1 ) and high energy efficiency of 96%. Remarkably, this battery exhibits outstanding long-term stability f...

Designing artificial nitrogen fixing devices with functions of light energy adsorption and driven nitrogen species upgrade and oxygen evolution is highly attractive. However, advanced catalytic materials for key NO 3 --to-NH 4 + and OH --to-O 2 reactions are rather rare. Herein, first principle calculations are performed to pre-screen target catalysts and then the effective catalyst in the experiment is successfully prepared, with which, a high power density Zn-nitrate electrochemical cell is demonstrated. The cathode catalyst can promote both reductive NO 3 --to-NH 4 + and oxidative OH --to-O 2 reactions in low-overpotential pathways, contributing to the total battery reaction: NO 3 -+ 3H 2 O → NH 4 + + 2OH -+ 2O 2 . The resulting electrochemical cell shows over 90% NO 3 --to-NH 4 + selectivity, a high power density over 25 mW cm -2 , and stable 35 h cycling at 12.5 mA cm -2 . Moreover, this Znnitrate electrochemical cell can work driven by the photovoltaic cell with the solar-to-NH 3 efficiency up to 19.5%. This study demonstrates a theoretically screened catalyst realizing a photovoltaic driven high-rate Zn-nitrate electrochemical cell system, which mimics soybean system upgrading N species and producing oxygen.