Fabrication And Performance Of Nickel-based Electrocatalysts From Graphite Powder As Anode Electrode Of Scrap Power Battery

The rapid rising of new energy electric vehicle industry creates great opportunity for development of ternary power lithium-ion batteries（LIBs）.However,as more ternary power batteries are produced,the wave of obsolescence LIBs may reach a new peak in the next few years.Particularly,the waste anode graphite material are discarded again during the process of recycling noble metals,resulting in a waste of resources.Expanded graphite,as a new type of carbon material,has been used in the field of electrocatalytic water decomposition to produce hydrogen by improving its own structural characteristics through surface oxidation,surface coating,and amorphous carbon coating.However,it is still a huge challenge to develop it into an efficient,stable and economical bifunctional electrocatalyst.Furthermore,noble metal-based commercial catalysts（Pt/C,RuO₂,and Ir O₂）are rare and expensive which limits their wide application in the field of electrolyzed water splitting.Besides conventional noble metal-based catalysts,nickel-based compounds are also the most potential catalysts for the oxygen evolution reaction（OER）on the planet which have attracted widespread attention from experts at home and abroad due to their high activity and stability.Therefore,nickel-based transition metal oxides highlighted by electrocatalytic water splitting research.In this paper,graphite powder as anode electrode of scrap power battery is used as research objects.Hydrothermal-calcination method and B,as a non-metallic element,doped by chemical reduction method are used to prepare electrode materials with excellent electrochemical（HER and OER）performance.And the morphology,structure,and the performance of electrocatalytic water splitting are systematically studied.The research of this thesis is divided into the following parts.（1）Synthesis nickel oxide/expanded graphite oxide composite catalysts for HER and OER under different reaction conditions:Different proportions of NiO nano particles loaded on expanded graphite oxide（EOG）materials were prepared by hydrothermal-calcination method,namely NiO/EOG（3:1）-200,NiO/EOG（3:2）-200,NiO/EOG（3:3）-200 and NiO/EOG（3:4）-200.SEM indicates that increasing the initial amount of nickel salt resulted in the increase of NiO nano particles supported on expanded graphite oxide（EOG）.When the molar ratio of nickel salt to graphite is 3:2,the as-prepared NiO/EOG（3:2）-200 shows the better electrocatalytic activity for both HER and OER.NiO/EOG（3:2）-200 electrode affords 10 m A cm^-2 at overpotentials of only 75m V for HER and 266 m V for OER,the corresponding Tafel slope are calculated to be 70 and92 m V dec^-1,respectively.This may be attributed to the synergistic effect of the inherent characteristics of transition metal oxides and the appropriate material addition ratio.NiO/EOG（3:2）-100,NiO/EOG（3:2）-150 and NiO/EOG（3:2）-200 electrocatalysts were prepared to determine the effect on morphology and catalytic activities at different hydrothermal reaction temperatures.It was found that increasing the hydrothermal temperature can enlarge the interlayer spacing and further form a sandwich hollow structure,which can provide a specific surface area for penetration and increase the number of active sites,resulting in improved electrocatalytic water properties.（2）Nonmetal B doped nickel oxide-expanded graphite oxide composite for Overall Water Splitting:To further improve the electrocatalytic water splitting performance of nickel oxide-expanded graphite oxide composite,we synthesized amorphous Na-B-O@Ni₃B/EOG by chemical reduction of Ni Cl₂ using Na BH₄.When annealed at 600℃（Ni-B-O@Ni₃B/EOG-600）,the catalyst releases oxygen more efficiently than the commercial electrode Ir O₂.At the same time,the excessively high annealing temperature affects the surface morphology of catalyst,resulting in particles aggregation and reduction of specific surface area.The effect of boron content and surface oxidization layer on catalytic activity was explained by studying the electrocatalysis properties for overall water splitting on as-prepared Ni-B-O@Ni_xB/EOG-600 catalysts.Particularly,Ni-B-O@Ni₃B/EOG-600,as one bifunctional electrocatalyst prepared,the two-electrode electrolyzers can afford 10 m A cm^-2 at around 1.58V for overall water splitting.It is found that the surface oxidation layer is composed of boron oxygen and nickel oxide.And this oxidation layer will contribute to form the active OOH*intermediate towards efficient OER,while its activity towards HER is weak,and thus leading to a decrease in HER activity.Besides that,high boron content can increase the content of surface nickel species and will results in lower OER overpotential.