| dc.description.abstract | As the world’s energy demand grows and environmental challenges mount, there is a growing
push to find sustainable energy sources and efficient solutions for energy conversion, such as water
splitting, fuel cells, metal-air batteries, etc. Energy-efficient occurrence of the crucial electrochemical
reactions, such as hydrogen evolution (HER), oxygen evolution (OER), and oxygen reduction (ORR), is
at the core of these systems. The development of carbon-based electrocatalysts is the mainstay of
this thesis, which are cost-effective, highly efficient, and endure for these key reactions. The synthesis
and structural tuning of carbon nanostructures to maximize their efficiency by creating the active
sites through N-doping and exposing them to the reactants through enhancing the surface area and
pores. Furthermore, transition metal (TM) nanoparticles embedded in nitrogen-doped carbon
frameworks offer a cost-effective and promising combination of catalytic parameters through
reduction of activation barrier due to synergy effect, and stability in alkaline environments.
To demonstrate the synergy effect, several TM elements such as Fe, Co, Ni, and the combination of
these elements are used. As a part of this work, a CVD-based pyrolysis method was used to
synthesize nitrogen-doped carbon frameworks with Fe, Co, or Ni nanoparticles. Despite using a fixed
nitrogen precursor, the resulting samples exhibited varying nitrogen concentrations, which is effective
for ORR. Benefiting from the O2 adsorption property, these nanostructures are utilised as effective
gas sensors. Moreover, Ni nanoparticles encapsulated porous carbon nanostructures with various
concentrations of N-doping in carbon shells are explored for hydrogen generation in alkaline media
(aq. 1 M KOH). The variation of nitrogen concentrations in carbon layers creates defects, which
enhance the surface area and porosity, exposing extensive active sites for catalytic reactions.
Furthermore, these nanostructures are efficiently utilized as a cathode for energy storage devices,
especially Zn-air batteries (ZAB). We have shown that the monometallic (Co) nanoparticles
encapsulated CNTs or carbon nanostructures synergistically enhance the performance of ZAB. We demonstrated that, the effectiveness of the synergy effect increases as two metals are alloyed (CoRu).
The variation in metal content (Co:Ru :: 3:1, 1:1, and 1:3) further affects the electronic structure and
reduces the adsorption/desorption of oxygen intermediates, and improves ORR/OER kinetics, which
enhances the ZAB performance. Further alloying as trimetallic alloy (i.e., Fe-Co-Cr) helps
strengthening the synergy effect. Additionally, variation in the metallic content in the alloy adds
value-added electronic modulation, which is beneficial for improving the performance of ZAB.
Hence, in this thesis, we have designed and demonstrated the highly efficient metal particles
embedded graphitic frameworks as electrocatalysts for HER, OER, and ORR in alkaline medium. | en_US |
