Controllable Synthesis Of Hierarchical Transition Metal Nanocomposite Electrocatalyst Materials And Their Study On Water Electrolysis Properties

Energy crisis and environmental pollution are two major problems which human beings are facing in the world,the use of fossil fuels not only bring serious environmental pollution,but also lead to the increasingly exhausted energy.Therefore,the search for new renewable energy has become the focus of current research.There are many types of renewable energy,among which hydrogen energy stands out among the numerous renewable energy with its unique advantages and becomes one of the hot spots in current scientific research.Firstly,hydrogen comes from a wide range of sources and is abundant in content.Secondly,the heat value and energy density of hydrogen are high.At the same time,hydrogen energy also has the advantages of renewable,clean and environmental protection.Electrolysis of water for hydrogen production is currently known as a relatively,environmentally,friendly and efficient method of hydrogen production,which can be widely used.The hydrogen production efficiency mainly depends on the catalytic activity of catalysts.Therefore,it is particularly important to find an efficient and environmentally,friendly catalysts with low cost.Based on this,this paper focused on the research of hierarchical transition metal-based nano-catalysts with good development prospects.In this paper,a series of highly efficient composite electrocatalysts were designed and synthesized for the electrolysis of hydrogen and oxygen production in aquatic products with nickel foam（NF）as the substrate and the transition metals Fe,Co and Ni as objects.This paper are includes the following research:（1）Ni₃S₂@Fe₂O₃@NF hierarchical composite catalyst materials with core-shell structure were synthesized on the nickel foam（NF）substrate by simple hydrothermal method with addition of sulfur source and iron source.Sublimated sulfur and ferrous oxalate were used as sulfur source and iron source.The morphology,composition and structure were characterized by XRD,SEM and XPS.In addition,the electrolytic water catalytic performance was tested,and the test results showed that the composite electrocatalyst have a good catalytic performance in both alkaline（1 M KOH）and neutral（1 M PBS）solutions.The test results of HER under alkaline conditions showed that the overpotential corresponding to the current density of 10 mA/cm² was 32.5 mV,and the slope of Tafel was 138.5 mV/dec.Meanwhile,OER test results under alkaline conditions（1 M KOH）show that the overpotential corresponding to 10 mA/cm² current density is 232.4 mV,and the Tafel slope is 54.3 mV/dec.At the same time,both HER and OER exhibited good stability in alkaline solution.More importantly,in the performance test of fully dissolved water,the voltage value corresponding to the current density of Ni₃S₂@Fe₂O₃@NF at 10 mA/cm² is only 1.55V and the performance of the 24-hour long cycle at this voltage is also very stable.（2）Here we take iron nitrate as the iron source and sublimated sulfur as the sulfur source.The hydrothermal method is adopted to firstly synthesize FeOOH@Fe₂O₃@NF precursor on the nickel foam（NF）substrate,and then soak it in 2 M Na₂S solution for 12 h for low-temperature sulfide,so that sulfur can replace part of oxygen in FeOOH to obtain Fe-O-S@Ni₃S₂@NF composite catalytic material of different hierarchies.After that,XRD,SEM,XPS and other means were used to characterize its morphology,composition and structure,and it was confirmed that Fe-O-S@Ni₃S₂@NF catalyst was successfully prepared.Then,we carried out tests on its catalytic performance in electrolysis of water.The test results showed that the catalytic performance of Fe-O-S@Ni₃S₂@NF catalyst after vulcanization was greatly improved under alkaline conditions（1 M KOH）.Fe-O-S@Ni₃S₂@NF catalyst HER test at 10 mA/cm² current density had a over potential of 188 mV and a Tafel slope of 173.1mV/dec.Fe-O-S@Ni₃S₂@NF catalyst OER test has a corresponding overpotential of 170.7mV and a Tafel slope of 45.3 mV/dec at 10 mA/cm² current density.Meanwhile,the Fe-O-S@Ni₃S₂@NF catalyst obtained after vulcanization showed excellent stability for 24hours.（3）Firstly,the MoS₂@Ni₃S₂@NF precursor was synthesized by a simple hydrothermal method,and then a layer of Co（OH）₂ was deposited on its surface by electrochemical deposition method,and finally the composite electrocatalytic material of Co（OH）₂@MoS₂@Ni₃S₂@NF was obtained.Then the morphology,composition and structure were characterized by means of XRD,SEM and XPS,and it was confirmed that the hierarchical Co（OH）₂@MoS₂@Ni₃S₂@NF materials were successfully synthesized.The test results of the catalytic performance of electrolytic water showed that the sample had the best catalytic performance when the deposition current was 5 mA and the deposition time was 1 min,and we labeled it asMoS₂@Ni₃S₂@NF-5.The test results of the composite catalytic material MoS₂@Ni₃S₂@NF-5 under the alkaline condition（1 M KOH）showed that the corresponding overpotential at 10 mA/cm² current density was 119 mV,and the Tafel slope was 153.5mV/dec.In addition,the OER test results of MoS₂@Ni₃S₂@NF-5 catalyst in 1 M KOH electrolyte showed that the corresponding overpotential at 10 mA/cm² current density was120 mV,and the Tafel slope was 153.3 mv/dec.In the stability test,the material showed good long-term stability.