Construction Of Nickel Based Electrocatalysts And Investigation Of Their Water Splitting Performance

Owing to the environmentally benign and high energy density nature,hydrogen has been regarded as a clean secondary energy.Water electrolysis to produce hydrogen is known as an efficient approach to realize large-scale application of hydrogen energy.Thus,designing and fabricating efficient electrocatalysts is the key to promote the development of electrolytic water hydrogen production industry.This dissertation selects nickel-based electrocatalysts as research object,and their local electronic states were regulated by the means of interface engineering,hetero-atom doping and single-atom modification to optimize the adsorption and desorption of surface water decomposition intermediates,thus improving the catalytic activity and stability of the materials.This work provides experimental reference and theoretical guidance for designing high-efficient catalysts for water electrolysis.The specific contents and results are outlined:（1）In order to realize the preparation of high efficiency bifunctional water electrolysis catalyst,and to reveal the microcosmic mechanism of interface construction regulating the catalytic activity of the materials.NiTe nanorods are used as a precursor,and then the composite nanostructures NiTe@RuO₂ and NiTe@NiFe-LDH containing NiTe/RuO₂ and NiTe/NiFe-LDH interfaces are constructed by different methods,and both of them are applied to basic hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）,respectively.NiTe@RuO₂ and NiTe@NiFe-LDH not only exert the characteristics of different nanomaterials,but also expose more catalytic active sites due to its unique heterogeneous interface coupling synergistic effect,thus significantly enhancing the HER and OER activities.In addition,using NiTe@RuO₂ and NiTe@NiFe-LDH as the cathode and anode to construct a full-cell for overall water splitting,which only needs a voltage of 1.58V to deliver 100 m A cm^-2.This provide a new perspective for the development and application of bifunctional water electrolysis catalyst.（2）A simple one-step hydrothermal method was used to doping trace rhodium（Rh）into NiFe-LDH nanosheets to simplify the preparation process and optimize the nanostructure design in this work.Rh doping can regulate the electronic structure of NiFe-LDH,so as to optimize the adsorption and desorption of OER reaction intermediates to improve catalytic activity and stability.When constructed an electrolyzer using NiFeRh-LDH as both anode and cathode for overall water splitting,which delivers current density of 100 m A cm^-2 with voltages of 1.56 V,and the stability up to 150 h,indicating that has a good application prospect.（3）In order to reduce the amount of precious metal and thus the cost of catalysts,this study adopts a simple one-step hydrothermal method to synthesize single-atom Ruthenium/Nickel-vanadium layered double hydroxide（Ru/Ni₃V-LDH）nanosheet composite and applies it to HER and OER.Both in situ X-ray absorption spectroscopy and operando Raman spectroscopic investigation clarify that the presence of atomic Ruon the surface of Ni₃V-LDH is playing an imperative role in stabilizing the dangling bond-rich surface and further leads to a reconstruction-free surface.The strong metal-support interaction between Ni₃V-LDH and monatomic Rufurther promotes the catalytic activity and stability of single atom catalysts.In situ X-ray fine absorption spectroscopy results show that the single-atomic Rusites provided the reactive sites and Ni₃V-LDH serves as a co-working catalyst for HER,whereas the reactive center transfers to Nisites for OER.When constructed an electrolyzer using Ru/Ni₃V-LDH as both the anode and cathode for overall water splitting,which only requires 1.63 V to yield a current density of 100 m A cm^-2,indicating an excellent catalytic performance.（4）To further reduce the driving voltage of electrolytic water,Urea Oxidation Reaction（UOR）with lower thermodynamic voltage was introduced in this study to replace OER process in electrolytic water,so as to realize ultra-low energy consumption and enable energy-saving hydrogen production.Herein,Rh single-atom was uniformly dispersed on ultra-thin NiV-LDH nanosheets by a simple ethylene glycol-assisted hydrothermal method,and it was used to catalyze HER and UOR simultaneously.Rh/NiV-LDH showed excellent HER activity in 1 M KOH solution,which only needs 12 m V overpotential to reach 10 m A cm^-2.Impressively,when the Rh/NiV-LDH was used as the cathode and anode to assemble an overall urea electrolyzer（UOR（+）||HER（-））,which only requires a small voltage of 1.47 V to deliver 100 m A cm^-2,and has a great competitive advantage and good application prospect.