Synthesis Of Spinel-based Nanocatalysts And Their Application In Oxygen Evolution Reaction

With the rapid development of industry,the conventional fossil fuels such as coal,oil and natural gas have been exploited on a large scale,not only brought serious environmental problems,but also threatened the national energy security.In recent years,all countries in the world have been devoting themselves to the development of new energy sources.Among those energy sources,solar and wind energy storage is large,but their wide industrial applications are limited due to concentrated distribution.Therefore,it is a good strategy to develop energy conversion and storage system technologies such as metal?Li or Zn?-air batteries,polymer electrolyte fuel cells?PEFCs?and waterelectrolyzers to solve the problem.Waterelectrolyzer is a highly efficient and reliable technology;hydrogen energy has many advantages such as high energy density and zero pollution combustion in the burning process.However,the reaction rate of hydrogen production is limited by anodic oxygenation?OER?due to the inherently sluggish kinetics during the electrolysis of water.Therefore,it is important to develop OER electrocatalysts.At present,precious metals Ru?Ir and their oxides are known as mainly commercial catalysts,in order to reduce costs and achieve sustainable development,precious metal catalysts must be replaced by excellent performance,rich reserve and environment-friendly non-precious metal catalyst.Based on spinel nanocatalysts used in OER reaction,two kinds of spinel composites based on different carbon carriers are prepared,and the influence of the catalysts on the electrochemical performancesare thoroughly studied.The main research is as follows:1.Hierarchical nitrogen-enriched porous carbon materials derived from Schiff-base networks supported FeCo₂O₄ nanoparticles for efficient water oxidationElectrocatalysts with excellent properties can be prepared by loading spinel on N-containing carbon materials with large specific surface area.In this part of the work,we choose the Schiff-Base SNW with simple preparation process as carbon precursor,and SNW with high nitrogen content and a rigid molecular skeleton is synthesized from melamine and terephthalaldehyde monomers,the nitrogen-enriched porous carbon material NPC-450°C is obtained by high-temperature carbonization,and the FeCo₂O₄@NPC-450°C catalyst is synthesized in one step by hydrothermal method.For the OER catalytic reaction,the catalyst FeCo₂O₄@NPC-450°C has a potential of only 330 mV at a current density of 10 mA cm^-22 and a Tafel slope of 50 mV dec^-1,compared with the NPC-450°C and the active site FeCo₂O₄,FeCo₂O₄@NPC-450°C shows better OER catalytic performance.Through the stability test,FeCo₂O₄@NPC-450°C in alkaline solution can maintain stable catalytic activity for more than 25hours.The results show that use of N-carbon material as a carrier can not only improve the conductivity of the catalyst but also prevent the aggregation of active nanoparticles in the catalytic process.In addition,the synergy between FeCo₂O₄ and NPC-450°C can further increase the catalytic activity of the catalyst.FeCo₂O₄@NPC-450°C shows good catalytic performance for OER provides the possibility for non-precious metal catalyst replaces precious metal catalyst.2.ZnCo₂O₄ nanoparticles derived from dual-metal-organic-frameworks embedded in Multiwalled Carbon Nanotubes:a favorable electrocatalyst for the water splittingThe metal-organic framework?MOF?with a 3D designable topological structure is synthesized by organic ligands and metal ions or clusters,own the advantages of uniform morphology,controllable size,and high specific surface area.Based on the above factors,in this part of the work,zeolite imidazolate frameworks?ZIF-67 and ZIF-8?are used as MOF materials and embedded in MWCNTs to obtain high performance OER electrocatalyst,ZnCo₂O₄ nanoparticles embedded in Nitrogen-doped Carbon Nanotube is successfully synthesized from ZIF-67/ZIF-8-MWCNT precursor via two-step calcination in a nitrogen and air atmosphere.The dical><full-title>Rsc Advances</full-title>ZnCo₂O₄@C-MWCNTs are studied and the results are as follows:?1?During the carbonization process,uniformly distributed ZnCo₂O₄ nanoparticles are generated from Zn²⁺and Co²⁺ions,N-doped mesoporous carbon are formed from2-methylimidazole,and ZnCo₂O₄ nanoparticles are in-situ encapsulated by N-doped mesoporous carbon;?2?The morphology and pore structure of the MOF material are maintained by MOF derivative materials;?3?The content of MWCNT has a great influence on the catalyst performance,the N-doped mesoporous carbon provides a pathway for electron transfer to improve the catalytic performance;?4?Electrochemical tests show that the initial potential of ZnCo₂O₄@C-MWCNTs is 1.45 V.When the current density reaches 10 mA cm^-2,the overpotential is only 327 mV and Zn Co₂O₄@C-MWCNTs shows excellent OER catalytic performance.?5?It is worth noting that the potentials of ZnCo₂O₄@C-MWCNTs in alkaline solution are almost constant at different current density for at least 25 hours,indicating that the stability of the catalyst is very well.This work shows that the MOF-derived catalyst has a better catalytic effect than the directly calcined spinel ZnCo₂O₄-MWCNTs catalyst.The dual MOF-doped MWCNT catalyst design concept can be applied in the preparation of other novel catalysts.