Preparation And Electrochemical Performance Of High Stability OER Electrodes

At present,the energy system based on fossil fuels has become increasingly unable to meet the growing energy demand due to the development of human society.In the meantime,global environmental issues such as environmental pollution and greenhouse effect brought about by the burning of fossil energy have also sounded the alarm for human beings.Therefore,the search for alternatives to fossil energy has become one of the topics sought by today’s scientific community.Hydrogen energy is clean energy which can be recycled without pollution and has high energy density.It can be used to cleanly and efficiently obtain hydrogen energy by electrolyzing water,and the use of seawater for electrolysis to produce hydrogen can alleviate the shortage of fresh water resources.The catalysts and electrode materials for electrolytic water reaction are hot research topics in the field of hydrogen storage.Oxygen evolution reaction is one of the important semi-reactions in the electrolysis of water.Among many high-performance catalytic materials for oxygen evolution reaction,hydrotalcite is one of the materials with higher performance in alkaline systems,but its long-term stability is not satisfactory due to the hydrotalcite dissolution or substrate corrosion.In view of the above problems,this topic studied how to improve the long-term stable catalytic performance of hydrotalcite,and conducted research and discussion from the following two aspects.(1)A phosphorus-doped sulfide metal protective layer loaded with a nano-flake NiFe-LDH array catalyst was deposited on the surface of pure nickel foam substrate by chemical vapor transformation and subsequent electrodeposition,and used as an oxygen evolution reaction electrode.The protective layer is an oblique hexagonal Ni3S2 with good electrical conductivity,in which partial phosphorus are doped and distributed uniformly.The surface of the protective layer under the electron microscope is particles of uniform size,and the catalyst uniformly covers the substrate surface uniformly after electrodeposition.The catalytic performance of SP-3:0.5 Ni foam+LDH electrode is equivalent to the overpotential of pure nickel foam under the same conditions,both of which are about 225 mV,indicating that the protective layer has similar conductivity with metal.In 1 M KOH solution containing 2 M NaCl,the electrode can stably electrolyze water for more than 300 h under the current density of 100 mA·cm-2 with a potential change of less than 10 m V.The electrode was tested for stability in high current density and high concentration salt solution,which was stable for 260 h and 130 h at a current density of 400 mA cm-2 in 1 M KOH solution containing 0.5 M NaCl and 2 M NaCl,respectively.The reason for the high stability of the electrode is mainly attributed to the special electrode protective layer,which is oxidized in situ to form sulfate and phosphate during the anodic oxidation to repel chloride ions from eroding the electrode substrate.This experiment also provides a new idea for exploring the anodic catalytic electrode for hydrogen production from salt water.(2)NiFe-LDH arrays were prepared on the surface of nickel foam by electrodeposition method,and used as OER electrodes to test the buffering effect of weak acid salts on the OER performance of NiFe-LDH/Ni foam electrodes under different current densities.The OER overpotential of the NiFe-LDH/Ni foam is about 220 mV.After the electrode was tested at 100 mA cm-2 for 100 h,the potential of solution containing carbonate was almost unchanged before and after the test.The potential change of the solution containing phosphate was within 10 mV,both of which had the effect of delaying the degradation of the electrode performance.When the current density is 400 mA cm-2,the buffering effect of carbonate is more excellent.After tested in the same conditions at a high current density of 1000 mA cm-2,the potential change of solution containing carbonate and tetraborate were 80 mV and 110 mV,respectively,which all had the effect of delaying the degradation of the electrode performance.The OER process causes the pH of the solution layer on the electrode surface to decrease,resulting in dissolution and destruction of the hydrotalcite structure.Since the weak acid salt has a buffering effect in a specific pH range,the pH of the solution layer on the electrode surface is maintained within a certain range,thereby slowing down the destruction of the hydrotalcite structure and facilitating the maintenance of performance.