Construction And Electrocatalytic Properties Of NiCo-based Nanoarrays

Electrolytic splitting water into hydrogen is one of the promising solutions to the puzzle of renewable energy supply,storage and use over the long haul.However,the application of water electrolysis for large-scale and highly purified hydrogen is still difficult,due to its sluggish anodic oxygen evolution reaction and unstable cathodic hydrogen evolution reaction.The anodic oxygen evolution reaction?OER?and cathodic hydrogen evolution reaction?HER?of water electrolysis were studied in this paper.To reduce the overpotentials of OER and HER,a series of NiCo-based electrodes were prepared and their electrocatalytic performance were investigated.The main contents of the study are as follows:1.In situ growth of NiCo₂S₄ nanotube arrays on nickel foam?NF?have been synthesized by a two-step hydrothermal method.In addition,Ni₃S₂/NF,Co₃S₄/NF and NiCo₂S₄ particles electrodes were prepared for comparison.The HER properties of the synthesized electrodes were tested by three electrode system in a 1 mol/L KOH solution.The results showed that NiCo₂S₄/NF has the better HER performance than Ni₃S₂/NF,Co₃S₄/NF and NiCo₂S₄ particles.NiCo₂S₄/NF exhibited a overpotential of 183 mV at the current density of 10 mA/cm² and a Tafel slope of 121.5 mV/dec.In addition,NiCo₂S₄/NF showed no obvious attenuation of performance after stability test at the constant current density of 10 mA/cm² for 100,000 s and the morphology remained intact after the stability test.2.Ni_xCo_1-x?OH?_y naosheets were surpported on the nickel foam substrate via an easy-controlled electrodeposition method.The structure and morphology of Ni_xCo_1-x?OH?_y synthesized in different proportion of nickel to cobalt and electrodeposition time were analyzed.The OER activities of all the samples were tested with three electrode system in an alkaline environment.The results showed that when the ratio of nickel to cobalt was 1:1 with the electrodeposition time of 120 s,Ni_0.5Co_0.5?OH?₂ nanosheets showed the best OER performance.For the current density of 10 mA/cm²,Ni_0.5Co_0.5?OH?₂ required an overpotential of 306 mV and a Tafel slope of 64.9 mV/dec.3.A bifunctional NiCo/NiCo₂S₄@NiCo electrocatalyst supported on nickel foam was fabricated via hydrothermal and electrodeposition methods.Because of its unique hierarchical mushroom-like nanoarray structures and the beneficial effects of NiCo₂S₄with NiCo hydroxide,the activity and stability of NiCo/NiCo₂S₄@NiCo/NF were superior to most of the highly active noble-metal-free catalysts in a strong alkaline environment.Serving as an OER catalyst,NiCo/NiCo₂S₄@NiCo/NF only required an overpotential of 294 mV to acheive a high current density of 100 mA/cm².Serving as a HER catalyst,NiCo/NiCo₂S₄@NiCo/NF required an overpotential of 132 mV for 10mA/cm².In addition,NiCo/NiCo₂S₄@NiCo/NF as the bifunctional catalyst was applied for a water electrolyzer in extreme alkaline media,with a current density of 10 mA/cm²under a cell voltage of 1.55 V and excellent stability for over 27h.