Syntheses And Oxygen Evolution Reaction Performance Of Ni Fe-based Oxide Electrocatalysts Under Alkaline Conditions

In the context of carbon peaking and carbon neutrality,how to deal with climate change and energy issues is the key of current development.Hydrogen production from water splitting plays a paramount role in reducing CO₂ emissions and promoting energy structure transformation.The sluggish kinetics of the oxygen evolution reaction（OER）at the anode of the water splitting reaction largely impedes the overall water splitting efficiency,and noble metal catalysts have problems such as high cost,low reserves and poor stability,which make it necessary to develop inexpensive and efficient non-precious metal catalysts.In this thesis,with Ni Fe-based oxide electrocatalysts as the main research objects,Ni Fe₂O₄/Ketjen carbon（KB）,Ni Fe（OH）_x@Ni Fe₂O₄/nickel foam（NF）and Fe-Ni O/NF electrocatalysts were rationally designed and prepared.By combining a variety of material characterization methods and electrochemical testing techniques,the structure,morphology and OER performance of the preparedcatalysts were comprehensively studied.The specific summary is as follows:（1）By introducing sodium tartrate,the metal ions are efficiently chelated with the participation of KB during the hydrothermal reaction to give the precursor,and the formation of high-purity Ni Fe₂O₄ is induced during the subsequent calcination process.The introduction of KB can greatly ameliorate the conductivity of Ni Fe₂O₄.Benefiting from the high-valent Ni³⁺and Fe³⁺with high oxidizing powers,large electrochemically active surface area,and three-dimensional structure favorable for mass transfer,the overpotential of Ni Fe₂O₄/KB records 258 m V registering a current density of 10 m A cm^-2 in 1.0 M KOH,the Tafel slope is only 43.01m V dec^-1,and the current density decreases by only 1%after 24 h long-term stability test,far outmaneuvring the commercialized Ru O₂.A novel method for preparing the KB supported high-purity nickel ferrite（Ni Fe₂O₄/KB）electrocatalyst was developed.Also,this synthetic strategy was successfully applied to the preparation of Co Fe₂O₄/KB catalyst,of which OER performance outmaneuvers commercial Ru O₂.（2）Ni Fe₂O₄ nanoarrays supported on the NF substrate were obtained by controllable oxidation using structure-controllable nickel-iron hydrotalcite（Ni Fe LDH）as the precursor,on which amorphous hydroxides（Ni Fe（OH）_x）were electrodeposited.Consequently,the Ni Fe（OH）_x@Ni Fe₂O₄/NF composite catalyst with a core-shell structure was harvested.Due to the reasonable topography of nanoarrays which facilitates the mass transfer and diffusion,the synergistic catalysis of the core-shell structure and its surface amorphous reconfiguration which is favorable for electron transfer and surface reactions,the Ni Fe（OH）_x@Ni Fe₂O₄/NF self-supporting electrode displays excellent OER catalytic performance in 1.0 M KOH solution.Specifically,only 226m V overpotential is required to reach a current density of 10 m A cm^-2,even at a large current density of 100 m A cm^-2,the overpotential is merely 285m V,and the corresponding Tafel slope is 51.74 m V dec^-1,In the chronoamperometry and the multi-current step test,Ni Fe（OH）_x@Ni Fe₂O₄/NF holds outstanding stability performance,and the comprehensive performance is far better than the comparative commercial Ru O₂/NF.（3）By using the p H-driven dissolution-precipitation process,with NF as the nickel source and substrate,the nickel hydroxide precursor（Ni（OH）₂/NF）was in-situ grown and through the subsequent controllable steps of calcination-doping-calcining,iron-doped nickel oxide nanoarraysgrown firmly on NF（Fe-Ni O/NF）were prepared.Thanks to the bottom-up synthesis strategy and efficient iron doping,Fe-Ni O/NF has good conductivity and structural stability,and the optimization of the electronic structure of the nickel oxide surface by iron doping brings significantly enhanced OER catalytic activity.In 1.0 M KOH solution,Fe-Ni O/NF exhibits an overpotentials of 228 and 275 m V at respective current densities of 10 and 100 m A cm^-2,a Tafel slope of 43.42 m V dec^-1,and excellent long-term durability.The overall OER performance of Fe-Ni O/NF surpasses that of commercial Ru O₂/NF,and the synthesis is simple and cost-friendly,which has the potential for large-scale application.