Synthesis And Performance Study Of Nanoelectrocatalysts For Ethylene Glycol Oxidation And Water Splitting

Driven by the growing energy demand and increasing depletion of traditional fossil fuel such as petroleum and coal,researching and developing advanced energy conversion and storage device to meet the high requirement in the energy-demanding field have been urgently sought.Renewable and clean energy technologie is considered to be one of the most direct and effective means to reduce environmental and energy issues.The energy conversion system is considered to be the most promising technology due to its low energy consumption,low corrosion,and simple operation.And the central part of this technology is to develop new materials that can efficiently transfer energy.Catalysts play a decisive role in the performance of fuel cells and water splitting.Precious metal nanomaterials,especially Pt,Ru and Ir play much higher catalytic activity than those of other metal nanomaterials in many heterogeneous catalytic reactions.However,Precious metal nanomaterials resources are scarce and expensive,which greatly limits the practical application of commercialization.Therefore,exploring an inexpensive catalyst to substitute or partially substitute platinum,reducing the dependence on precious metal resources and reducing the cost of production is a key technology for achieving widespread use of energy conversion system.Based on the above considerations,we here focus on environmental and energy issues,and developing the catalytic electrolyzed water performance and reducing the precious metal content to prepare high-efficiency catalysts.In this paper,we successfully designed and synthesized nano-alloy Pt or Pd-based electrocatalysts for efficient fuel cells electrooxidation reactions,and thoroughly investigated the significant role of their morphology,structure and composition in determining their catalytic performance.We have also designed and synthesized transition metal carbide and transition metal phosphides,and studied the catalytic electroltzed water performance of these electrochemical catalests with specific morphology and structure.The main research contents and conclusions are summarized as follows:?1?Introduce the research background,review the development of fuel cells and the latest research progress of platinum-based and palladium-based nanomaterials,including their properties,synthesis and applications,summarize the research progress of electrocatalytic water splitting in transition metal carbide and transition metal phosphides,and finally introduce the research content and significance of this paper.?2?A kind of concave PtSn nanocube catalyst with adjustable composition was prepared by wet chemical method.Owing to the unique morphology and structure of concave nanocubes and the electronic effect between platinum and Sn,the as-obtained PtSn concave nanocubes show high activity and stability for electrocatalytic oxidation of ethylene glycol in alkaline medium.In particular,the mass activity of ethylene glycol oxidation?EGOR?of Pt₄Sn₁ concave nanocubes is 5.7 A mg^-1,and the specific activity is 11.5 mA cm^-2,which are 5.1 and 5.9 times higher than that of commercial Pt/C.The electrocatalytic performances of Pt₄Sn₁ concave nanocubes comparable to many excellent catalysts reported in literature,providing experimental and theoretical basis for the effective regulation of the catalytic performance of nanomaterials.?3?A unique three-dimensional dendritic Pd₃Pb nanocatalyst was synthesized by a simple wet chemical method.Owing to the unique three-dimensional dendritic nanostructure,alloy effect,and the electronic effect between Pd and Pb,the as-obtained Pd₃Pb nanocatalysts can greatly improve the electrocatalytic activity of ethylene glycol oxidation.In EGOR,the specific activity and mass activity of 3D Pd₃Pb NCs are 10.0 mA cm^-2 and 4.5 A mg^-1,respectively,which are 5.0 and 4.3 times higher than those of commercial Pd/C catalysts,and even higher than those of Pt-based electrocatalysts that previously reported.More importantly,the resulting 3D Pd₃Pb NCs show good stability in EGOR.These results show that Pd₃Pb with three-dimensional nanodendritic structure provides a theoretical and technical reference for the preparation of high-efficiency catalytic materials for ethylene glycol oxidation.?4?Three-dimensional PdAg nanoflower catalysts?3D PdAg NFs/NG?supported on nitrogen-doped graphene were prepared by one-pot method at room temperature by using nitrogen-doped graphene?NG?as carrier with high theoretical surface area,excellent chemical stability and high charge transfer efficiency.The 3D PdAg NFs anchored on the NG surface have smaller particle diameter,higher surface utilization efficiency,more uniform dispersion,and increased surface active sites.Because of its high conductivity,alloy effect and synergistic effect between 3D PdAg NFs and NG,the prepared 3D PdAg NFs/NG exhibits high catalytic activity and excellent stability in the electrooxidation of ethylene glycol.The results showed that the mass and specific activities of 3D PdAg NFs/NG were 5.8 A mg^-1 and 11.9 mA cm^-2,respectively,which were 5.4 and 5.95 times higher than those of commercial Pd/C.After long-term stability test,the 3D PdAg NFs/NG could also raetain much higher electrocatalytic activity than those of 3D PdAg NFs and commercial Pd/C catalysts.This study opens up a new way for the realization of electrocatalysts with both high catalytic activity and high stability.?5?A simple pyrolysis method to construct the bamboo-like N-doped carbon nanotubes?N-CNTs?that encapsulated with ternary FeCoNi alloy nanoparticles.By combining the advantages of FeCoNi alloy with N-CNTs,the as-fabricated FeCoNi N-CNTs have large active surface area,ultrahigh content of graphitic carbon,and aboudant active metal–C/N_x species to show high electrocatalytic performance for OER in alkaline media.The optimized Fe₁Co₁Ni₁@N-CNTs displays perfect electrocatalytic performance toward OER with an unexpectedly small onset potential of 1.43 V and an ultralow overpotential of 252 mV at 10 mA cm^-2,and remarkable long-time stability in alkaline media for OER.More importantly,by coupling Fe₁Co₁Ni₁@N-CNTs as the anode electrode,Pt/C as cathode electrode,a potential of only 1.52 V is needed to drive the water electrolysis to reach to the current density of10 mA cm^-2,comparable to the state-of-the-art IrO₂?Pt/C couple.This work provides new perspectives for constructing efficient and stable N-CNTs encapsulated non-precious metal electrocatalysts for OER.?6?The research on developing efficient and durable overall water splitting electrocatalysts that based on earth-abundant metals is of extreme importance,but still challenging.Herein,a facile one-pot method for constructing a class of ultrafine trimetallic oxyphosphide nanoparticles?FeCoMo P-O NPs?,with the merits of rich oxygen vacancies,large electrochemical active surface?ECSA?,fast electron transport and long-term stability,is reported.The optimal Fe₁Co₃Mo₃ P-O NPs show ultralow overpotentials of 111 mV and 231 mV for hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?at the current density of 10 mA cm^-2 in 1.0 M KOH,respectively.To get insight into the overall water splitting,the water electrolyte device fabricated by Fe₁Co₃Mo₃ P-O NPs as both the cathode and anode only requires a voltage of 1.604 V to achieve a current density of 10 mA cm^-2 associated with a long-time stability for at least 50 h.There are 67 figures,13 tables and 238 references in this thesis.