Preparation Of Nickel-iron Based Self-supported Electrode And Its Oxygen Evolution And Selectivity Research In Seawater

Hydrogen production by water decomposition is a sustainable technology,which can reduce the demand for fossil fuels and solve the problem of environmental pollution in the future.Due to the increasing population and serious water pollution,fresh water is becoming a limited resource.Seawater is one of the most abundant resources on the earth,and it is becoming more and more attractive to use seawater instead of fresh water for electrolytic hydrogen production.The key challenge of hydrogen production by electrolysis of seawater is to solve the competition between oxygen evolution reaction（OER）and chlorine evolution reaction（Cl ER）on the anode.Therefore,it is of great theoretical and practical significance to develop electrocatalysts with high selectivity for oxygen evolution reaction to realize seawater electrolysis.Precious metal catalyst has excellent OER catalytic performance in alkaline electrolytic water,but its performance is unstable in seawater electrolysis process and has the problem of high cost,so it is not suitable for large-scale commercial application.Non-noble metal electrocatalysts have become a research hotspot in recent years.In this paper,a self-supporting electrode material of transition metal hydroxide was constructed on carbon fiber cloth substrate,and its oxygen evolution selectivity in natural seawater and electrocatalytic performance in alkaline seawater were studied.The specific work is as follows:（1）NiFe-LDH/CC nanosheet array composite electrodes with different metal ratios were prepared on the surface of carbon fiber cloth（CC）by hydrothermal method.The morphology and structure of the prepared materials were characterized by SEM and XRD,and their oxygen evolution performance and selectivity were investigated.The results show that Ni₂Fe₁-LDH/CC has the best OER catalytic performance in natural seawater,and its oxygen evolution selectivity is 52.7%.In addition,the OER catalytic performance of electrode materials in alkaline seawater was tested by standard three-electrode system.The overpotential of Ni₂Fe₁-LDH/CC at a current density of 100m A·cm^-2 is only 296 m V,and the slope of Tafel is 43.1 m V·dec^-1.（2）Theδ-MnO₂ nanosheet modified NiFe-LDH/CC composite electrode was prepared by hydrothermal method and its oxygen evolution performance and selectivity were investigated.The results show that the oxygen evolution selectivity of MnO₂-NiFe-LDH/CC electrode material is 61.1%,indicating that MnO₂ can improve the competitiveness of the catalyst against OH^-in real seawater.In alkaline seawater,the overpotential of MnO₂-NiFe-LDH/CC at 10 m A·cm^-2 and 100 m A·cm^-2 is 284 m V and363 m V,respectively.The cycles stability test showed that the electrode material had good stability,and the potential shifted to the right only by 8 m V after 6000 cycles test.（3）The precursor NiFe-LDH/CC was synthesized on the surface of CC by hydrothermal method,and then intercalated with different anions.NiFe-(CO3^2-)-LDH/CC,NiFe-(SO₄^2-)-LDH/CC,NiFe-（NO₃^-）-LDH/CC,NiFe-（H₂PO₂^-）-LDH/CC composite electrode materials were prepared respectively.The morphology and electronic structure of the prepared materials were analyzed by SEM,XRD and XPS,and the electrochemical properties and oxygen evolution selectivity of the prepared materials in alkaline seawater and natural seawater were investigated.The experimental results show that ion intercalation can improve the oxygen evolution selectivity of electrode materials,and the optimum electrode material NiFe-（H2PO2^-）-LDH/CC has a selectivity of 65.2%.At the same time,the composite electrode showed excellent OER performance in alkaline seawater,and only 288 m V overpotential was required to achieve a current density of 100 m A·cm^-2.In addition,NiFe-（H2PO2^-）-LDH/CC electrode material has excellent stability,after 6000 cycles stability test,the potential shift to the right only 4 m V.