Study On Directed Design And Electro-oxidation Performance Of Nickel-based Hydroxide Nanoarrays

The rapid development of modern society requires a large amount of energy demand,mainly based on traditional fossil fuels,including coal,oil and natural gas.However,these types of non-renewable energy carriers will inevitably bring related environmental pollution.Therefore,there is an urgent need to explore and develop efficient energy conversion technologies.In the past few years,electrocatalytic energy conversion has received widespread attention due to its high energy economy and environmental friendliness.In various kinds of electrocatalytic processes,electro-oxidation of energetic small molecules such as urea oxidation reaction?UOR?and hydrazine oxidation reaction?HzOR?are promising energy conversion ways,which can be used to build direct fuel cells or electrolyzers,and can use the waste water containing urea or hydrazine to generate electricity or hydrogen.Among the energy-saving electrolysis technologies developed in recent years,UOR and HzOR have attracted widespread attention due to their durability and environmental protection.Although noble metal-based catalysts?such as platinum and rhodium?can effectively catalyze urea oxidation and hydrazine oxidation,they cannot be used on a large scale.Therefore,it is urgent to develop high-performance and inexpensive electrooxidation catalysts.In this paper,the author takes the high abundance nickel-based hydroxide as the research object,and optimizes the electrooxidation performance of the electrocatalysts for urea oxidation and hydrazine oxidation by means of element doping,structure control,phase transformation,etc.,which significantly improves the electrooxidation performance of the electrocatalysts.The main contents of this paper include:1.The authors designed and prepared the iron-doped?-Ni?OH?₂ nanosheet arrays supported on nickel foam by constructing hierarchical structural and electronic structure control methods.The synergistic optimization of catalytic active sites and intrinsic catalytic activities was achieved.Hierarchical nanosheets can provide a large surface area and two-dimensional electron transport channels,further exposing reactive sites,which is conducive to the generation of high valence species in the electrochemical process.Meanwhile,doping with an appropriate proportion of iron element can enhance the electrooxidation ability of the nickel component through the synergy between the elements.The nanosheet array catalyst has a low Initial potential of 1.321 V vs.RHE,and simultaneously has a high catalytic current density and excellent stability.This work provides a new idea for the design of new high-performance urea oxidation electrocatalysts for energy conversion in the future through element doping and electronic structure regulation to optimize the performance of electrocatalysts.2.By means of phase transformation and electronic structure control,the cerium doped hierarchical?-Ni?OH?₂ nanosheet array electrocatalyst loaded on nickel foam was designed and prepared,which can realize the triple functions of hydrogen evolution reaction,oxygen evolution reaction and urea oxidation reaction.The rare earth element cerium has 4f electronic configuration and 5d empty orbit can be used as the electron transfer station for catalysis.The electronic structure of the catalyst can be optimized and the catalytic activity can be improved by doping cerium in proper proportion.In addition,the unique hierarchical wire-on-sheet nanostructure involves hydrothermal crystallization and coordination etching.According to this idea,?-Ni?OH?₂ nanosheet array was prepared at the same time.It is found that?-Ni?OH?₂ has higher oxidation activity than?-Ni?OH?₂.The urea oxidation potential of the optimal cerium doped?phase nanoarray catalyst is 28 mV lower than that of the optimal cerium doped?phase.At the same time,the optimal cerium doped?phase catalyst has a large urea oxidation current density of 579.5 mA cm^-2 at 1.8 V vs.RHE,which is 2.4-12.9 times higher than that of other counterparts.In the two-electrode test,the optimal cerium doped?phase catalyst has the best activity,only 1.44 V can reach 10 mA cm^-2.The experimental results show that the catalyst has the highest electrocatalytic activity and superior structural stability,which provides a new idea for the optimization of pollution treatment and clean energy conversion electrocatalysts.3.Using the ternary CuNiCo layered hydroxide?CuNiCo LDH?as the precursor,the edge amorphous CuNiCo LDH was prepared by further Sulfurization,and hydrazine electrooxidation was significantly improved.The doping of copper can adjust the electronic structure and optimize the reaction kinetics of hydrazine oxidation.The sulfide induced edge amorphous structure enriched the coordination unsaturated ions with catalytic activity,which effectively improved the performance of catalyst.This work provides a catalyst for hydrazine assisted water splitting and direct hydrazine fuel cell,and provides guidance for the design of efficient hydrazine oxidation electrocatalysts in the future.