Electrocatalytic water splitting has been widely accepted as an environmentally friendly approach to generate clean H2. However, the sluggish oxidation half reaction, namely, the oxygen evolution reaction (OER), usually requires a high overpotential, which is the obstacle to high-efficiency overall water splitting to generate H2. Herein, we report the preparation of ultrathin nanosheet array Ni3S2 with a 9–14 nm nanosheet thickness grown directly on a commercial Ni foam substrate (Ni3S2/NF) by in situ vapor-phase hydrothermal (VPH) transformation of the nanosheet array structure Ni(OH)2/NF precursor. As a multifunctional electrocatalyst, the as-fabricated Ni3S2/NF-2 (VPH time of 2 h) displays excellent electrocatalytic activities toward the hydrazine oxidation reaction (HzOR) with a potential of 0.415 V (vs. RHE) to deliver a current density of 100 mA cm−2, an OER with an overpotential of 425 mV obtaining the same current density, and a hydrogen evolution reaction (HER) with an onset potential of −0.05 V (vs. RHE) in 1.0 M KOH media. A two-electrode system is therefore constructed using Ni3S2/NF-2 as both the anode and cathode, capable of achieving 100 mA cm−2 at 0.867 V in 1.0 M KOH with 0.2 M hydrazine. Density functional theory (DFT) calculations reveal that the adsorption of N2H4 molecules on the Ni3S2 (110) is more thermodynamically favourable than H2O, thus contributing to the high HzOR activity.
Replacing fossil fuels by electrocatalytic water splitting for producing hydrogen and oxygen is one of the most promising ways to solve the energy crisis and environmental pollution. In this work, a series of M doped N-Ni 3 S 2 (M = Cu, Fe, Co and Ce) material was firstly synthesized and in situ grown on nickel foam substrate by a typical two-step hydrothermal synthesis method. Two probe reactions, water oxidation and urea oxidation, were selected to investigate the catalytic performance of these materials. What is noteworthy is that the Fe doped N-Ni 3 S 2 material exhibits superior water oxidation properties with requiring only 270 mV of overpotentials to drive current densities of 100 mA cm −2 , which is one of the best activities reported so far. After a long time of durability measurement, the current density of the Fe doped N-Ni 3 S 2 material will be attenuated, suggesting that the surface of the material will be in situ oxidized to oxide or hydroxide, which is the true active species. For urea oxidation, the Co doped N-Ni 3 S 2 material shows superior catalytic performance with requiring only 1.36 V potentials to drive 100 mA cm −2 current densities. Density functional theory (DFT) calculation shows that different adsorption energy of water for N-Ni 3 S 2 , N-Cu-Ni 3 S 2 , N-Fe-Ni 3 S 2 and N-Co-Ni 3 S 2 leads to the different catalytic activity. Experimental results demonstrate that the improved catalytic performance is assigned to faster electron transfer rates, exposure of abundant active center and better conductivity due to N and cation doping. This work provides new lessons for doping engineering for water splitting reactions.
Junshan He,Jin Wang,Chao Wang,Li Guo,Yanzhong Wang
Metal-organic frameworks (MOFs) have garnered extensive attention in the area of oxygen evolution reaction (OER) electrocatalysis because of their remarkable specific surface area and tunable morphologies and composition. However, the low electrical conductivity and poor stability severely hinder their potential as high-performance OER catalysts. Herein, we employed 2-thiobarbituric acid as etching agent, sulfur source and ligand, and nickel-iron foam as the metal source and substrate, to synthesize Ni 3 S 2 /FeOOH@iron thiobarbituric acid-based framework (Fe-TBA) composite on the nickel-iron foam via a one-step hydrothermal method. Experimental findings reveal that Ni 3 S 2 can modulate the morphological structure of FeOOH@Fe-TBA as well as boost its stability, consequently delivering exceptional OER activity. It requires merely an overpotential of 232 mV to reach a current density of 10 mA cm −2 , and the Tafel slope is 43.1 mV dec −1 . Furthermore, when an overall water-splitting system is constructed where Ni 3 S 2 /FeOOH@Fe-TBA and Pt/C act as the anode and cathode, respectively, it operates at a mere 1.52 V under a current density of 10 mA cm −2 and maintains the stable performance for more than 100 h. This study offers a new strategy for fabricating sulfides/MOFs composites to realize highly efficient water oxidation.
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