Design,Synthesis And Catalytic Performance Of Nano Electrocatalysts With Highly Active And Stable Ultra-small Or Ultra-thin Structures

Ultra-small or ultra-thin nano structured electrocatalysts can deliver more superior catalytic performance than their corresponding bulks.That is because they possess higher density of active sites.However,the stability is limited by their large specific surface energy.They are spontaneously aggregated and easily dissolved in acid and basic solution.In result,their active components and sites will be sacrificed.Therefore,the design and development of highly active and stable ultra-small or ultra-thin nano structured electrocatalysts are urgent in the area of electrocatalysis.Based on this purpose,we have designed and synthesized three kinds of nano structured electrocatalysts,respectively.And we also have studied their corresponding catalytic activity and stability in this thesis.1.To zreo dimensional?0 D?Rh nanoparticles,ultra-thin carbon nanosheets are designed as supporters.A facile and scalable salt-templated approach has been adopted to produce ultra-small Rh nanoparticles?NPs?on ultra-thin carbon nanosheets with the assistance of calcination under inert gas.The rhodium oleates are used as the sources of rhodium and carbon.In result,the average size of Rh NPs is 1.6 nm.The thickness of carbon nanosheets is 1² nm.More importantly,the acquired Rh/C hybrid nanosheets display a comparable oxygen reduction reaction?ORR?activity to commercial Pt/C catalyst,which may be ascribed to the extra-small size of Rh NPs and the 2D defect-rich amorphous carbon nanosheets.The carbon nanosheets can facilitate the charge transfer and stabilize Rh NPs.Moreover,Rh/C nanosheets present the optimal current density and best durability with the minimum decline during the entire test,so that?93%activity after20,000 s is achieved,indicating a good lifetime for ORR.In contrast,commercial Pt/C and commercial Rh/C exhibit worse durability,so that?74%and?85%activities after 20,000s are maintained,respectively.This work opens a novel and facile way for the rest of the precious metal NPs to be supported on ultra-thin carbon nanosheets for heterogeneous catalysis.2.To two dimensional?2 D?Ni?OH?₂ nanosheets?NS?,kniteed conductive carbon cloth?CC?was designed as a supporter.We employ a methanol-guided strategy for one-step in situ growth of single-layered?-Ni?OH?₂ NS on CC?SL Ni?OH?₂ NS/CC?.To be specific,unlike water,methanol can swiftly wet the CC,and the water-deficit environment can better control the hydrolysis of Ni²⁺.Without the use of any other pretreatment and modification method,SL Ni?OH?₂ NS with a thickness as small as⁰.8nm are grown on CC,and they densely cover every CC fiber in the form of nanowalls.These nanowalls pack closely and form abundant 3D open-network structures,which enable the active surfaces of SL Ni?OH?₂ NS to be exposed maximally.While in the case of aqueous solution,we could observe that the carbon fibers are covered with non-uniform,brick-like hexagonal?-Ni?OH?₂ NS with a thickness of 10 nm.Combined with the superior conductivity of CC for electron transport,the resulting SL?-Ni?OH?₂ NS/CC integrated electrode displays excellent urea oxidation reaction?UOR?performance.A current density as high as 436.4 mA/cm² at 0.5 V vs.Ag/AgCl is achieved,which represents the best UOR performance among the reported nickel-based electrocatalysts.The resulting SL Ni?OH?₂NS/CC integrated electrode also displays excellent stability for long-term use.In comparison with the UOR performance of ML Ni?OH?₂ NS/CC,the UOR performance of SL Ni?OH?₂ NS/CC is enhanced nearly 35 times before the chronoamperometry?CA?test.After the CA test for 36,000 s,a 131 times enhancement is obtained.It is worth to be noted that our approach is an universal method to grow SL Ni?OH?₂ NS on other conductive substrates besides CC.The facile and well-controlled preparation process opens a new way to synthesize a wide range of transition metal-based heterogeneous catalysts.3.To three dimensional?3 D?FeP microspheres,porous FeP superstructured?FeP SS?microspheres constructed from ultra-small FeP NPs are prepared through a self-templating gas-solid phosphorization reaction of urchin-like FeOOH microspheres.The size of FeP NPs is 2-3 nm.Since the ultra-small FeP NPs are arranged in a loose manner with the connection of carbonized SDS instead of being densely packed in the resulting FeP microspheres,the FeP SS microspheres with high porosity exhibit highly active and exceptionally stable hydrogen evolution reaction?HER?performance even at a low loading mass of the electrocatalyst.At a loading mass of 0.566 mg/cm²,an overpotential of 66 mV is achieved.At a loading mass as low as 0.142 mg/cm²,the highest mass activity of up to70.4 mA/mg with a?₁₀ of 102 mV is achieved,which is superior to that of all other non-precious metal electrocatalysts.The chronopotentiometry test at a current density of10 mA/cm² for 24 h shows that the overpotential increases slightly from 66 mV to 80 mV,indicating a fairly stable HER process.This work provides an effective strategy to design non-precious metal-based nanomaterials with a rationally assembled macroscopic structure as advanced electrocatalysts.