Design And Synthesis Of Ruthenium-based Electrocatalysts And Study Of Their Acidic OER Electrocatalytic Performance

The large consumptions of fossil fuels have brought serious environmental pollution and imminent energy crisis.Developing sustainable clean energy is an effective way to deal with these issues.Hydrogen is considered as a promising clean energy carrier due to high energy density,pollution-free and high elemental abundance.Electrochemical water splitting in acidic electrolyte is considered to be a promising environmental-friendly hydrogen production technology for efficient production of high purity hydrogen.However,there is often a large overpotential for oxygen evolution reaction during electrochemical water splitting,which leads to a large amount of additional energy consumption.Therefore,it is urgent to develop some catalytic materials with excellent electrocatalytic performance as anodes to reduce the reaction energy barrier and the overpotential of oxygen evolution reaction.As the cheaper noble metal in platinum group,ruthenium dioxide has been shown to be the catalyst with great electrocatalytic potential for oxygen evolution reaction,but the electrocatalytic performance in acidic electrolytes need to be further optimized to improve the efficiency of noble metal.In this thesis,ruthenium dioxide was used as the research object.Two different ruthenium dioxide electrocatalysts were synthesized by referring to the relevant methods of defect engineering and support engineering,and the electrocatalytic performance of the electrocatalysts for oxygen evolution reaction in 0.5 M H₂SO₄ electrolyte was studied.For the first experiment in this paper,the ruthenium-rich and zinc-less precursor can be prepared by the reaction between the metal-organic framework containing zinc and ruthenium trichloride solution.Further,the nanorod-like electrocatalysts assembled by zinc-doped ruthenium oxide nanocrystals(3-5 nm)can be prepared by pyrolysis of the precursor in air.With the characterization analysis and electrocatalytic performance test,it is found that the introduction of zinc greatly improved the electrocatalytic activity and stability of ruthenium dioxide.By adjusting the doping ratio,it is found that the zinc-doped ruthenium dioxide nanocrystals with a zinc-ruthenium atom ratio of 6.4%exhibits the lowest overpotential(206 m V@10 m A cm^-2)and the best electrocatalytic stability for oxygen evolution reaction in 0.5 M H₂SO₄solution.It only shows an increase in overpotential of 11 m V after 10000 cycle scans.Moreover,it can work stably for more than 30 hours in the chronopotentiometric test.The excellent electrocatalytic performance can be attributed to the ultra-small nanocrystal size and the increase of low-valence ruthenium sites on the ruthenium dioxide surface caused by doping.The carbon materials possess large surface area and good tolerance to acid electrolyte.The electronic conductivity and specific surface area of electrocatalytic materials can be improve by using carbon as support materials.Based on this,in this thesis,the experimental scheme for synthesis of carbon-supported ruthenium oxide nanocrystals by low temperature annealing of ruthenium-based nanoparticles loaded on carbon by chemical precipitation method is designed.After characterization and performance test,it can be found the morphology and electrocatalytic effect of the synthesized electrocatalysts are greatly affected by the loading amount and the carbon type of the support.Among these carbon species,the ZIF-8 derived polyhedral porous carbon can effectively load and anchor ruthenium-based nanoparticles so that these nanoparticles still maintain good dispersion effect during annealing crystallization,which effectively prevent fusion and growth of the nanoparticles.The electrocatalyst synthesized by this method,composed of carbon carriers derived from ZIF-8 and ultra-small ruthenium oxide nanocrystals(1–3 nm),exhibit extremely high catalytic activity for oxygen evolution reaction in 0.5 M H₂SO₄ solution,which shows the overpotential of 173 m V at 10 m A cm^-2 current density.This method is equally applicable for other scenarios where the synthesis of ultra-small nanocrystals is required.