Date of Award

2023-08-01

Degree Name

Doctor of Philosophy

Department

Environmental Science and Engineering

Advisor(s)

Chintalapalle V Ramana

Abstract

Hydrogen fuel is a clean energy source primarily because it emits no carbon dioxide (CO2). Sustainable energy alternatives have attracted the scientific community and policymakers as concerns over global warming and depletion of fossil fuels have increased significantly. Substituting H2 gas as a primary source for our daily energy consumption under the guideline of the hydrogen economy concept has not progressed as anticipated because of inadequate efficiency associated with the generation (electrolyzer) and utilization (fuel cell) devices. However, there are challenges associated with hydrogen that must be overcome for it to become a truly sustainable and widespread energy source. The full potential of electrocatalysts fabricated from earth-abundant metals has yet to be exploited to replace Pt-group metals due to inadequate efficiency and insufficient design strategies to meet the ever-increasing demands for renewable energies. To improve the electrocatalytic performance, the primary challenge is to optimize the structure and electronic properties by enhancing the intrinsic catalytic activity and expanding the active catalytic surface area. A significant overpotential limits the HER, while efficient electrocatalysts based on platinum group metals (PGMs) have demonstrated relatively low overpotentials across a wide pH range of electrolytes. However, the large-scale utilization of PGM-based electrocatalysts is hindered by two main factors: scarcity and high cost. This dissertation focused on developing alternative catalysts that could replace or reduce the reliance on PGMs. The presented work employed abundant and low-cost transition metals such as Ni and Mo to discover and optimize new materials with maintaining high catalytic activity and stability for the HER. First, we report synthesizing a 3D nanoarchitecture of aligned Ni5P4-Ni2P/NiS (plate/nanosheets) using a phospho-sulfidation process. The durability and unique design of prickly pear cactus in desert environments by adsorbing moisture through its extensive surface and ability to bear fruits at the edges of leaves inspire this study to adopt a similar 3D architecture and utilize it to design an efficient heterostructure catalyst for HER activity. The catalyst comprises two compartments of the vertically aligned Ni5P4-Ni2P plates and the NiS nanosheets, resembling the role of leaves and fruits in the prickly pear cactus. The Ni5P4-Ni2P plates deliver charges to the interface areas, and the NiS nanosheets significantly influence Had and transfer electrons for the HER activity. Indeed, the synergistic presence of heterointerfaces and the epitaxial NiS nanosheets can substantially improve the catalytic activity compared to nickel phosphide catalysts. Secondly, we report synthesizing a 3D structure of Mo2N-MoP@Mo heterostructured catalysts. To attain the current densities of 10 and 100 mA cm-2, the Ni-catalyst showed overpotentials of 75 and 115 mV, and Mo-catalyst exhibited 65 and 110 mV, respectively. The Tafel slopes were found to be 50 and 65 mV dec-1 for the champions. The longevity of both catalysts was investigated, and the electrochemical impedance spectroscopy (EIS) revealed inducing S and N non-metals was the underlying reason for the modification and durability of structures.

Language

en

Provenance

Recieved from ProQuest

File Size

123 p.

File Format

application/pdf

Rights Holder

Navid Attarzadeh

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