Synthesis And Characterization Of Nickel-Based Chalcogenides And Their Applications In Electrocatalytic Energy Conversion And Storage

Environmental pollution and energy exhaustion have become one of the most serious problems at present.As the new clean and renewable energy technologies,electrocatalytic water splitting and the secondary metal-air batteries have attracted great attenion.The water oxidation is composed of two half reactions:the oxygen evolution reaction?OER?and the hydrogen evolution reaction?HER?,and electrocatalytic water splitting can directly convert electrical energy into chemical energy.Furthermore,the rechargeable metal-air batteries are composed of OER and oxygen reduction reaction?ORR?.As well known,electrocatalysts are the core part for the development of the above renewable energy technologies.Therefore,the exploration of highly efficient and stable electrocatalysts plays a crucial role in the electrocatalysis.As a new type of non-noble metal electrocatalysts,transition metal chalcogenides have attracted much attention owing to advantages of low-cost,environment friendly and outstanding chemical performance.The outermost electron configuration of nickel is 3d⁸4s² with the rich valence and the excellent chemical activity.Furthermore,according to the low cost,easy preparation and high performance,the nickel-based chalcogenides are also considered as the best alternative for precious metals.Therefore,optimizing and regulating the functional structure of nickel-based chalcogenides for structure optimization to further improve their catalytic performance is vital important.The specific work is as follows:?:We report a controllable N-doping strategy to synthesize a series of N-doped porous metallic NiMoO₄ nanowires with concomitant oxygen vacancy defects?N-V_o-NiMoO₄ NWs?for promoting the alkaline HER ability and durability.Both experimental and theoretical results demonstrate that the doped-N at NiO₆ octahedral sites and the abundant oxygen vacancy defects confined in N-V_o-NiMoO₄ NWs with modified electronic arrangement could enhance the metallic conductivity,affect the surface areas,and lower the adsorption energy of hydrogen,resulting in an increased HER property.However,the excess doped-N leads to an opposite effect due to the reduced valence state of Ni centers.Therefore,alkaline HER ability of N-V_o-NiMoO₄ NWs exhibits a volcano-like trend vs.the nitrogen content,with N₃-Vo-NiMoO₄ NWs being the best one.As a result,the N₃-V_o-NiMoO₄ NWs show an overpotential of 55 mV(10 mA cm^-2),and a Tafel slope of only 38 mV dec^-1 in 1.0 M KOH.?:A novel top-down strategy is reported to construct the oxide/sulfide heterostructures?N-NiMoO₄/NiS₂ nanowires/nanosheets?as a multisite HER/OER catalyst.Starting with the NiMoO₄ nanowires,nitridation in a controlled manner enables activation of Ni sites in NiMoO₄and then yields oxide/sulfide heterojunction by directly vulcanizing the highly composition-segregated N-NiMoO₄ nanowires.The abundant epitaxial heterogeneous interfaces at atomic-level facilitate the electron transfer from N-NiMoO₄ to NiS₂,which further cooperate synergistically toward both the hydrogen and oxygen generation in alkali solution.Furthermore,with N-NiMoO₄/NiS₂ grown carbon fiber cloth as the engineering electrode,the assembled N-NiMoO₄/NiS₂–N-NiMoO₄/NiS₂ system can deliver a current density of 10 mA cm^-2 with the cell voltage of 1.60 V in the water-splitting reaction.?:CuS/NiS₂ interface nanocrystals?INs?catalysts with atomic-level coupled nanointerface,subtle lattice distortion,and plentiful vacancy defects is reported.The lattice distortion of 14.7%in CuS,the strong atomic-level coupled interface of CuS and NiS₂ domains,and distinct vacancy defects can provide numerous effective active sites.A liquid Zn-air battery with the CuS/NiS₂ INs as air electrode displays a large peak power density(172.4 mW cm^-2),a high specific capacity(775 mAh gZn^-1),and long cycle life?up to 83 h?,making CuS/NiS₂ INs among the best bifunctional catalysts for Zn-air battery.More remarkably,the flexible CuS/NiS₂ INs based solid-state Zn-air batteries can power the LED even after twisting.?:We report the controlled synthesis of NiFe₂O₄/FeNi₂S₄ heterostructured nanosheets?HNSs?that are highly efficient in catalysing OER and ORR,therefore enabling neutral rechargeable zinc-air batteries.Associated with the formation of abundant oxide/sulfide interfaces over NiFe₂O₄/FeNi₂S₄ HNSs'surfaces,the catalyst's oxygen binding energy can be effectively tuned to enhance the OER and ORR activities,as revealed by the DFT calculations.When used as an air-electrode,the NiFe₂O₄/FeNi₂S₄ HNSs can deliver a power density of 44.4 mW cm^-2 and a superior cycling stability.