Engineered spinel composite for enhanced water splitting catalysis: Fe 2 GeO 4 - Ni 3 Ge 2 O 5 (OH) 4 hetero-interface.

Abstract

Electrocatalysts that offer an improved intrinsic catalytic and kinetic activity with adequate stability in oxidative electrochemical environments are quintessential in the catalysis of oxygen evolution reactions (OER) for energy storage and conversion. Transition metal oxides serve as promising alternatives to the expensive precious metals as electrocatalysts. They exhibit innate electrochemical capabilities, possess structural diversity, as well as the ability to be doped and combined with other materials making them attractive research candidates in the search for eco- friendly, clean and cheap energy sources. In this thesis, a facile and controllable hydrothermal synthesis route was adopted for the fabrication of Fe 2 GeO 4 and Ni-Fe 2 GeO 4 (Ni 3 Ge 2 O 5 (OH) 4 ) heterostructures for water splitting experiments. The synthesized materials were characterized by XRD, SEM, EDS, and XPS methods and their electrocatalytic activity for OER evaluated with electrochemical techniques. The Fe 2 GeO 4 material demonstrated outstanding electrocatalytic properties for OER with overpotentials of 270 mV at a current density of 10mAcm -2 and a Tafel slope of 60mV/dec. The Ni-Fe 2 GeO 4 -3.17% exhibited even better OER electrocatalytic performance. It exhibited the highest overall performance at higher current densities of 30mAcm -2 and above with a Tafel slope of 42 mA/dec surpassing that of Fe 2 GeO 4 thereby making it the best performing as-synthesized material for OER. The formation of heterostructures by the addition of nickel to Fe 2 GeO 4 has markedly improve the electrocatalytic performances of Fe 2 GeO 4 through the formation materials consisting of two and three- dimensional phases. This thesis work demonstrates the possibility to modulate the morphology and improve the electrocatalyst activity of Fe 2 GeO 4 nanomaterials by addition of nickel ions into the fabric of spinels oxides (Fe 2 GeO 4 ) through facile hydrothermal methods.