Preparation Of Transition Metal-based Electrocatalysts Doped With Nitrogen And Sulfur And Study On Its Oxygen Evolution Performance

With the continuous increase in energy demand,the rapid depletion of fossil fuels and the intensification of environmental pollution,the development of clean and renewable new energy is of great significance.Hydrogen energy has become one of the most ideal candidates due to its advantages such as high energy density and zero pollution.Among them,hydrogen production by electrolysis of water is an important means to solve current energy and environmental problems.However,the oxygen evolution reaction（OER）in electrolyzed water involves a four-electron transfer process and requires a high reaction energy barrier,which greatly limits the efficiency of hydrogen production by electrolysis of water.Although noble metal catalysts（Ir/Ru and Pt-based materials）can produce hydrogen at lower voltages,their high cost and scarcity greatly limit their wide application.With the continuous deepening of research,transition metal-based catalysts have gradually come into people’s sight due to their abundant reserves,low price,and good OER activity and stability.Through reasonable structural design,doping modification and other methods It can reach or exceed the catalytic performance of noble metal-based catalysts.In this paper,doping is the research direction.The transition metal-based catalyst is doped with N,S,and Ce by the one-pot hydrothermal method to prepare excellent catalysts.The performance improvement is revealed through XRD,XPS and other characterizations and electrochemical tests.The main content of the mechanism is as follows:（1）N-doped Co Fe hydroxide nanosheets（N-Co Fe-O_xH_y-T）with microporous,mesoporous and macroporous hierarchical porous structures were successfully synthesized by one-step hydrothermal method with triethanolamine（TEOA）as precipitant.The overpotential of the synthesized N-Co Fe-O_xH_y-T was as low as 253m V at a current density of 10 m A/cm²,the Tafel slope was 41 m V/dec,the double-layer capacitance(C_dl)was 6.72 m F/cm²,and the charge transfer resistance(R_ct)was 2.29Ω,which were far better than those of Co Fe-O_xH_y-U and commercial Ru O₂ catalysts prepared by using urea as a precipitant.In addition,the two-electrode overall water splitting system N-Co Fe-O_xH_y-T（+）||Pt/C（-）needs only 1.53 V in 1.0 M KOH solution to reach a current density of 10 m A/cm².（2）S-doped Ni Fe layered double hydroxides（LDHs）nanosheets were prepared on iron foam（IF）by hydrothermal method,and a phenomenon that the S in Ni Fe LDHs can leach out during the OER process and then induce chemical evolution and in situ structure self-reconstruction was reported for the first time.Under the optimal conditions,the OER electrocatalyst O-NFO-S5,which was reconstructed by S-doping and leaching-induced structure,exhibited low overpotentials of 196 and 224 m V and38.2 m V/cm² at current densities of 10 and 100 m A/cm²,respectively.The HER electrocatalyst H-NFO-S60 only needed an overpotential of 167 m V to reach a current density of 100 m A/cm²,and its Tafel slope was 127 m V/dec.Constructing the best-performing OER and HER electrocatalysts into a two-electrode integral water splitting device can achieve a current density of 10 m A/cm² at an ultra-low battery voltage of1.43 V,which provides a new idea for electrochemical overall water splitting.（3）By using nickel foam（NF）as the precursor,a hydrothermal method was used to design and synthesize S-Ni（OH）₂/Ce O₂ nanocomposites co-doped with S and Ce.After the electrochemical performance test,the overpotential of S-Ni（OH）₂/Ce O₂was only 200 m V at a current density of 10 m A/cm²,and the Tafel slope was 51.56 m V/dec.After calculation,the S-Ni（OH）₂/Ce O₂ double-layer capacitor(C_dl)was 9.35 m F/cm²,and the charge transfer resistance was 2.57Ω,which is far better than commercial Ru O₂.After being tested by chronopotentiometry for 150 h,there was basically no change in the potential.The best OER electrocatalyst S-Ni（OH）₂/Ce O₂ and HER electrocatalyst S-Ni（OH）₂ were assembled into a two-electrode integrated water decomposition device,and the current density of 10 m A/cm² was achieved only at 1.51 V battery voltage.