Preparation Of Ruthenium Based Catalysts And Their Electrocatalytic Performance For Oxygen Evolution

As a representative green energy source,hydrogen has been highly sought due to its high energy density and sustainability.The decomposition of water into hydrogen and oxygen by electrocatalysis is considered one of the most promising method to alleviate or even solve the environmental pollution and energy crises,and has received widespread attention.Water splitting is composed of two basic reactions（i）the hydrogen evolution reaction（two-electron process）and（ii）the oxygen evolution reaction（four-electron process）.The overall electrolytic rate has been limited by the complicated multi-step proton-coupled electron transfer in the OER,which is a kinetically slow process that requires a large overpotential to carry out the reaction.It is worth noting that water decomposition can be carried out in acidic and alkaline media.Nevertheless,the reactivity of the former is several times slower than that of the latter.Moreover,the development of acidic electrolytic cells is vital due to their high ionic conductivity and few side reactions.However,the existing developed non-noble metal OER electrocatalysts have difficulty in maintaining catalytic activity and stability in acidic media due to leaching,degradation,and surface reconstruction of active species.Therefore,the preparation of a catalyst with excellent OER performance under acidic conditions has been the focus of water decomposition research.To date,ruthenium-based catalysts are still the most advanced acidic OER electrocatalysts due to their nice activity and long-term stability,which may overcome the prospective issues in alkaline media and be meaningful for improving the work efficiency of polymer electrolyte membrane（PEM）electrolysers.Based on numerous studies on the activity and stability of Ru,Ru O₂,Ir,and Ir O₂ in acidic and alkaline media,OER activity follows this trend:Ir O₂<Ru O₂≈Ir<Ru.In view of this,many efforts have been made to explore effective Ru catalysts for OER.However,Ru catalysts have a problem of poor stability because the inevitable oxidation at high potential（Ru+2H₂O→Ru O₂+4H⁺+4e^-;Ru O₂+2H₂O→Ru O₄（aqueous solution）+4H⁺+4e^-）.This oxidation leads to a decrease in catalytic activity,limiting its wide application.Based on this problem,we propose two methods to improve the stability of ruthenium-based catalysts,encapsulation strategy and ion doping strategy.1.Ru@FLC has been synthesized by encapsulation strategy.The interfacial engineering of Ru via few-layer carbon（Ru@FLC）was carried out,in which FLC can significantly suppress the corrosion of Ru in acid media,ensuring the efficient interfacial charge transport between Ru and FLC.As a result,a low overpotentials@10 m A·cm^-2 of 258 m V and small Tafel slopes of 53.1 m V/dec for oxygen evolution OER were achieved in acid media.DFT calculations disclose that outer FLC could induce charge redistribution and effectively optimize intermediates free energy adsorption,resulting in greatly reduce the energy barrier for OER.Our work may offer a new avenue to produce progressive OER electrocatalysts for energy-related applications in acid solution.The work in Chapter 3 may pave a promising way for improving the OER activity and durability of Ru-based materials in acidic media.2.For the sake of promoting the catalytic activity,the introduction of exogenous metal to induce atomic distortions by ions doping method has been proven effective in improving the catalytic activity.In addition,the metal doping engineering also can modulate the electronic structures of electrocatalysts,which will further upgrade the catalytic performance.On the other hand,2D materials had been considered to be ideal candidates for use in water splitting due to its atomically thin structure,quantum confinement effects and high electron mobility.In this aspect,it is expected that constructing two-dimensional ions doped Ru O₂ nanosheets with lattice distortion is highly desirable for OER in acidic media.Herein,multiple alkali metal doped ruthenium dioxide nanosheets（Li-Ru O₂,Na-Ru O₂,K-Ru O₂）with rich lattice distortion were successfully fabricated via simple molten salt method.The lattice distortions increase the active sites exposure.In detail,the Li-Ru O₂exhibits optimal OER activity in acidic media and reaches a low overpotential of 169 m V at 10 m A·cm^-2in 0.5 M H₂SO₄solution.Meanwhile,Li-Ru O₂ exhibited good durability in the potential measurement test during 24 h operation with negligible overpotential increase.This work is expected to pave a creative strategy to fabricate active and stable acidic OER catalysts.