Rational design of non-precious metal based catalysts for highly efficient electrochemical oxygen evolution

Abstract

Electrolytic water splitting has the capability to store the electricity generated from renewable energy resources in the form of hydrogen (H2) fuel. Development of efficient, inexpensive electrolytic water splitting system, combining with hydrogen fuel cells, will provide continuous usage of intermittent renewable energies with minimum environmental impacts. The major hurdle impedes the large-scale applications of the electrolytic water splitting system is the sluggish oxygen evolution reaction (OER) at anode, which requires noble metal oxide based catalysts to lower the overpotential and generate hydrogen at an appreciable current density. However, these noble metals are costly and their supply is not sustainable. As a result, the development of efficient, non-precious metal-based OER catalyst materials is highly demanded. This thesis focuses on design, synthesis and characterisation of nanoscale transition metal based catalysts as a new class of cost effective electrocatalysts for highly efficient oxygen evolution. To this end, a range of novel nanostructured OER catalysts are synthesised including (1) mesoporous cobalt oxide catalysts embedded with gold nanoparticles (Au/mCo3O4), (2) a micro/nanostructured hierarchical 3D nickel-iron hydroxides electrode, (3) a multifunctional amorphous nickel-iron-colbalt hydroxides decorated 3D electrode, (4) nanocrystalline cobalt oxides anchored onto mildly oxidised multiwall carbon nanotubes, and (5) transparent Co3O4 nanoparticles/graphene electrode achieved by layer-by-layer assembly. New synthesis techniques are developed to synthesise these catalysts, and their catalytic properties are investigated with electrochemical techniques (cyclic voltammetry, rotating disc electrode voltammetry, chronoamperometry, chronopotentiometry). The atomic, electronic and surface structures of these catalysts are investigated with a variety of physical characterisations (X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy), and correlated with their catalytic properties. The intrinsic catalytic activity and structure-property relationships of these catalysts are also established. Importantly, the results suggest that, via rational design, transition metal based catalysts that exhibit comparable, or even superior OER catalytic activity to benchmark RuO2 and IrO2 catalysts can be achieved with significantly reduced fabrication cost.