Year

2020

Degree Name

Doctor of Philosophy

Department

Institute for Superconducting and Electronic Materials

Abstract

The energy crisis is becoming one of the biggest global concerns with increasing energy demand, and the heavy consumption of fossil fuels in the past century has raised irreversible environmental pollution. Therefore, it is of great urgency to establish a global-scale clean and sustainable energy system. Among various strategies, converting sustainable energies (e.g., solar and wind power) into chemical fuels that can be flexibly stored and transported is a preferable choice. Hydrogen gas (H2) is an ideal energy carrier owning to the highest gravimetric energy density (142 MJ kg-1) among all the chemical fuels and zero-emission of pollutants during chemical conversion. Water electrolysis can realize sustainable clean energy-to-hydrogen conversion, which will be the game-changer once the cost and efficiency of this hydrogen production process can compete with conventional steam reforming. As compared with proton exchange membrane water electrolyzers (PEMWEs), anion exchange membrane water electrolyzers (AEMWEs) not only offer a milder alkaline working environment that increases the stability of precious metal-based electrocatalysts, but also allow for the use of earth-abundant electrocatalysts for oxygen evolution reaction (OER). However, the biggest challenge associated with alkaline water electrolysis is the sluggish hydrogen evolution reaction (HER) kinetics, which is two to three orders of magnitude lower than that in acidic solutions. Therefore, the current top-priority is to develop high-performance electrocatalysts for alkaline HER. Heterostructures generally maintain physicochemical properties that differ from their individual counterparts, thus are potential for a wide range of applications. In particular, rational manipulation of heterointerface would trigger favourable electronic and synergistic effects, which are of critical significance for the electrochemical performance. This thesis aims to design and synthesize heterostructures with well-defined and regulatable heterointerface towards fast alkaline HER kinetics.

Platinum (Pt) is the state-of-the-art electrocatalyst for the most efficient HER in acidic media due to the optimum hydrogen binding energy (HBE). Nevertheless, its alkaline HER kinetics is particularly sluggish due to the high activation energy required for promoting water dissociation step. Therefore, it is crucial to lower the water dissociation energy barrier to ensure rapid proton supply, thereby expediting the overall alkaline HER rate. In the first work, new platinum/nickel bicarbonate (Pt/Ni(HCO3)2) heterostructures were designed for alkaline HER. Notably, the specific and mass activity of Pt nanoparticles (NPs) in the Pt/Ni(HCO3)2 heterostructures are substantially improved as compared to the bare Pt NPs. The Ni(HCO3)2 substrate not only provides abundant water adsorption/dissociation sites, but also modulate the electronic structures of Pt NPs, which determine the elementary reaction kinetics of alkaline HER. Moreover, the Ni(HCO3)2 nanoplate offers a platform for the uniform dispersion of Pt NPs, ensuring the maximum exposure of active sites. The results demonstrate that Ni(HCO3)2 is an effective catalyst promoter for alkaline HER.

Download

Share

COinS
 

Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.