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Design, Construction and Investigation of the Behavior of Electrocatalysts Based on Some Transition Multi Metals Nanostructures toward Electrochemical Water Splitting

Hafezi Kahnamouei, Mohammad | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54813 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Shahrokhian, Saeed
  7. Abstract:
  8. Energy and the environment issues are among the most important concerns of the present age. Global demand for energy is growing rapidly and energy demand is projected to double within the next 15 years. However, today most of the energy consumption comes from fossil fuels, which have limited and unstable reserves and are among the sources of environmental pollution. Hence, the production and conversion of clean energy from renewable sources is considered as an intelligent solution to significantly reduce dependence on fossil fuels and protect the environment. Fuel cells, metal-air batteries, and water electrolysis are among the simplest, most efficient, and most reliable technologies among several energy conversion systems controlled by electrochemical reactions. Water electrolysis has attracted a lot of attention due to the production of hydrogen and oxygen. On the other hand, water oxidation reaction or oxygen evolution reaction (OER) is the main reaction of all these systems to perform their reversible process together with hydrogen evolution reaction (HER) in water electrolysis and/or oxygen reduction reaction (ORR) in metal-air batteries. Therefore, the development of effective and inexpensive electrocatalysts for electrolysis of water, especially the process of water oxidation due to the more complex reaction, is an essential need to improve the efficiency of the process to obtain clean and consistent fuels.In the first part, a practical strategy for preparing an efficient tri-metal electrocatalyst (NiCoFe) with a new frame/cage -like three-dimensional structure for oxygen evolution reaction (OER) was presented. To do this, firstly frame/cage-like CoFe PBA nanostructure was synthesized through a simple precipitation reaction in aqueous medium. The precursor was then thermal treated under two different atmospheres of argon (CoFeA-TT) and air (CoFeO-TT) to investigate their effect on increasing catalytic sites at 300 ° C. In the last step, electrodeposition of NiCo-S nanosheets was electrodeposited as a shell layer on them and electrochemical evaluation was performed toward OER. The electrochemical measurements demonstrated that the deposition of NiCo-S on CoFeA-TT (NiCo-S@CoFeATT) has the best catalytic performance and can drive the benchmark current density of 10 mA cm−2 at a low overpotential of 268 mV with a Tafel slope of 62 mV dec−1 and an excellent long-term catalytic stability in an alkaline medium. Its outstanding electrocatalytic performances are endowed from frame/ cage-like structures, highly exposed active sites, accelerated mass and electron transport, and the synergistic effect of multiple hybrid components.In the second part, as in the first part, the single-step synthesis of the CoFe Prussian blue analog (CoFePBA) frame/cage-like structure was done without any etching step. Following in a comparative study, CoFePBA precursors converted and doped by P, Se, and S vapors (CoFeS, CoFeSe, and CoFeP) through annealing the precursors by sodium hypophosphite, selenium, and sulfur powder. Finally, NiCoS nanosheets arrays electrodeposited as a shell layer on them. The electrochemical measurements demonstrated that the deposition of NiCoS on CoFeS (NiCoS@CoFeS) has better catalytic activity than NiCoS@CoFeSe and NiCoS@CoFeP. It can drive the current density of 100 mA cm−2 at a low overpotential of 293 mV with a Tafel slope of 40.6 mV dec−1 and has a preeminent long-term catalytic durability in alkaline medium. Its excellent electrocatalytic performances are benefited from frame/cage-like and nanosheets structures, good synergistic effects between multiple hybrid components (Ni, Co, Fe, and S), which lead to producing the high exposed active sites and accelerating mass and electron transports.In the third part, an ultrafast and feasible strategy used for constructing an S-doped bimetallic Iron/Nickel oxy(hydroxide) (S-(Fe/Ni)OOH) as a superior electrocatalyst for oxygen evolution reaction (OER). It is prepared by consequence electroplating of nickel nano-cones arrays (NiNCAs) on carbon cloth (CC) and stainless steel mesh (SSM) and then formation of S-(Fe/Ni)OOH layer on them by ultrafast one-step oxidation solution-phase method in the solution of Fe3+ and sodium thiosulfate at room temperature. The derived composite material (S-(Fe/Ni)OOH@NiNCAs on SSM and CC) exhibited high electrocatalytic activity toward OER as well as good durability. The electrochemical measurements demonstrate that the S-(Fe/Ni)OOH@NiNCAs-CC and S-(Fe/Ni)OOH@NiNCAs-SSM can drive the benchmark current density of 10 mA cm−2 at low overpotentials of 248 and 245 mV, and current density of 100 mA cm-2 at overpotentials of 327 and 312 mV with a Tafel slope of 77 and 65 mV dec−1, respectively. Their outstanding electrocatalytic performances are benefited from porous, highly exposed active sites, accelerated mass and electron transport, and synergistic effects. The prepared composite electrodes act better than the most advanced priceless catalysts and noble commercial RuO2 catalyst. This work provides an effective and efficient approach to design porous architecture catalysts on a three-dimensional substrate (SSM and CC) with high performance for energy-relevant and electro-catalysis reactions
  9. Keywords:
  10. Electrocatalysts ; Linear Sweep Voltammetry ; Oxygen Evoloution Reaction (OER) ; Metal Oxyhydroxide ; Nickel-Cobalt Sulfide ; Water Electrolysis ; Core-Shell Composite ; Cobalt Iron Prussian Blue Analogues

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