Preparation And Study Of Nickel-based Electrocatalysts For High-performance Water Splitting

Since the beginning of the industrial revolution,humans have been consuming traditional fossil fuels?e.g.,coal,oil and natural gas?with unprecedented scale and speed to meet the rapidly growing energy demand of the world's economy.However,excessive energy consumption has led to a series of environmental problems,such as the increase of CO₂ emission,air pollution and global warming.These problems seriously limit the sustainable development of human society.Electrocatalytic water splitting?HER and OER?is considered to be a promising and marketable method,which converts the abundant water into clean energy sources only by using renewable electricity as the power source.As one of the hot research materials in the field of electrocatalysis,nickel?Ni?-based electrocatalysts?such as NiS₂ and NiFe-LDH?have attracted huge attention due to their high performance toward water splitting.However,their large-scale application is limited by relatively higher overpotential and poorer stability.To overcome these energy challenges and environmental problems,in this thesis,a series of experiments are rationally designed to reduce the overpotential and improve the stability of Ni-based electrocatalysts.Additionally,density functional theory?DFT?calculations were performed for in-depth and systematic studies of the reaction mechanism,so as to provide experimental data and theoretical support for synthesizing efficient Ni-based electrocatalysts.The main research contents are as follows:1.Bimetallic sulfide hybrid nanowire?NiS₂/MoS₂ HNW?was successfully prepared by in situ chemical vapor deposition?CVD?process and used as an efficient electrocatalyst for HER over a wide p H range.The results show that NiS₂/MoS₂ HNW with porous and one-dimensional?1D?structure obtains not only abundant active edge sites and pathways for efficient electron transfer,but also a large number of nanoscale heterointerfaces.Furthermore,DFT calculations prove that the formed heterointerface between?210?plane of NiS₂ and?002?plane of MoS₂ is able to facilitate the dissociation of H₂O and subsequently chemisorption of OH and H,thus making the NiS₂/MoS₂ HNW a high-efficient HER electrocatalyst over a wide p H range.The greatly decreased energy barrier of the Volmer step and promoted reaction kinetics of NiS₂/MoS₂ HNW that outperforms the single-component counterpart in HER behaviors are attributed to the enrichment of reactive sites and reconfiguration of electrons by the interfacial engineering of bimetallic sulfide.2.On the basis of the previous research,Mo/Ni bimetallic sulfide anchored three-dimensional?3D?N-doped graphene foam?3D MoS₂-NiS₂/NGF?composite material was fabricated through a designed template-assisted method and used as a bifunctional electrocatalyst for HER and OER.The results show that the 3D NGF with interconnected tubular structure not only significantly increases the contact area with MoS₂-NiS₂ but also provides a multiplex network for electron transfer and facilitates the desorption of gas products.Meanwhile,the heterointerface in MoS₂-NiS₂ facilitates the dissociation of H₂O and subsequently chemisorption of H and OH.The resulting MoS₂-NiS₂/NGF is capable of fully combining the merits of both 3D structure and bimetallic sulfide,obtaining more channels for ions transport,more abundant reactive sites and lower overpotential.The synergistic effect and chemical interaction between 3D NGF and MoS₂-NiS₂ are responsible for the outstanding HER,OER and overall water splitting performances as well as the excellent stability.3.V₂CT_x?V-MXene?was prepared by etching the precursor V₂Al C with HF solution and NiS₂ nanoparticles decorated V-MXene?NiS₂/V-MXene?sandwich-liked structure was further synthesized by using CVD treatment.Their intrinsic property and HER activities were studied by combining theoretical with experimental methods.DFT calculations predict that NiS₂/V-MXene interior has stronger interaction and electron transfer ability than that of the NiS₂ decorated Ti₃C₂T_x?NiS₂/Ti-MXene?.In agreement with the DFT calculations,the experimental results show that NiS₂/V-MXene exhibits better HER activities than that of the NiS₂/Ti-MXene.The sandwich-liked structure of NiS₂/V-MXene can not only prevent V-MXene flakes from restacking so as to expose more reactive sites,but also provide more contact interfaces and pathways for electron transfer and gas diffusion,thereby achieving excellent HER activity.4.The graphdiyne/nickel-ion layered double hydroxide?GDY/Ni Fe-LDH?composite electrocatalyst was synthesized through a facile hydrothermal method by using NiFe-LDH as the prototype of a low-cost OER catalyst.Benefiting from the large ? conjugate structure of GDY and the chemical interaction between-C?C-C?Cand Ni/Fe,the GDY/Ni Fe-LDH shows an outstanding OER activity with a low overpotential of 260 m V at 10 m A cm^-2 current density in 1.0 M KOH solution.In addition,the excellent activity of GDY/Ni Fe-LDH is also attributed to the honeycomb lattice structure and 3D porous structure of GDY that provides more dispersed pores and reactive sites,which ultimately promotes ion transport and electron transfer.Moreover,DFT calculations prove that GDY possesses the stronger capability for electron capture and transfer as compared with its sisters RGO and CNT,making it a promising carbon additive to boost the OER activity of electrocatalysts.