Entwicklung neuartiger MnPc, NiCoOx, Mn$_{x}$Co$_{y}$CO$_{3}$ Systeme für den Einsatz als elektrochemische Elektrodenmaterialien in der alkalischen Wasserspaltung

• Development of novel MnPc, NiCoOx,Mn$_{x}$Co$_{y}$CO$_{3}$ systems for use as electrochemical electrode materials inalkaline water splitting

Broicher, Cornelia; Palkovits, Regina (Thesis advisor); Liauw, Marcel (Thesis advisor); Tüysüz, Harun (Thesis advisor)

Aachen : RWTH Aachen University (2020, 2021)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

Due to the ongoing depletion of fossile resources, the electrochemical splitting of water with non-noble metals is of increasing importance for the future energy supply. Watersplitting is composed of two half side reactions, i.e. hydrogen evolution reaction (HER)and oxygen evolution reaction (OER). The OER is characterized by a complex reaction mechanism and thus limits the overall reaction kinetics. This thesis provides new fundamental insights into the complex relation of material composition and morphology as well as their individual impact on OER activity and stability. Via a hard-templating route, materials based on Mn-Phthalocyanine (MnPc) and Spinel Nickel Cobalt oxide were obtained in order to achieve mesoporosity with tailored pore size of 4 nm. Furthermore,non porous Mn/Co-carbonates (MnCoCO3) with controlled particle size were synthesized. One part of the thesis discusses the synthesis and characterization of templated carbon based MnPc-catalysts. These show an ordered mesoporous CMK-3-replica structure as well as a significant OER activity with 10mA cm−2 at an overpotential (OP) of 470mV.Until now, MnPc-catalysts provide poor OER-stability. This is usually associated with carbon decomposition during OER in alkaline media. The performance can be mainly attributed to efficient graphitization and high Mn dispersion together with a tailoredMn2+ oxidation state. Transition metal oxides are well known to be stable under alkaline OER-conditions. In addition to insights into the reaction mechanism, a significant improvement of the catalytic activity could be obtained as a result of controlled templating compared to unstructured NiCoOx (350mV at 10mAcm−2). Furthermore, robust synthesis routes were developed to tailor the geometrical structure and particle sizes and to obtain different shapes of Mn/CoCO3 like spheres, cubes and rods. Electrocatalytic testsat 10mAcm−2 showed an OP of 360mV for 1,9 μm cubes. The effects of size and designof MnCoCO3-particles have thus a crucial influence of both OER activity and stability. The different OER-activites are explained by the content of MnCo2O4-Spinel structures in the MnCoCO3-particles which influence intrinsic catalyst activity.