REPOSITORY > RESULTS

Abstract

We are speeding full throttle towards a climate catastrophe and we have only until 2030 to take action to avoid the most devastating and unimaginable consequences. The lack of political and corporate will to change the status quo of “business as usual” is causing mass protests and civil disobedience globally. The rich elite is relying on science to find a “technological miracle” which will enable continued ever-growing profits while making the global economy carbon neutral. The hydrogen economy could be part of the solution. Water electrolysers convert water to hydrogen with electricity and fuel cells convert hydrogen back to water producing electricity. Hydrogen can therefore be used as an energy vector instead of fossil fuels. The research field of the sluggish oxygen evolution reaction (OER) requires innovation in order for electrocatalytic water electrolysis to become economically viable. The cost, stability, and activity of the electrocatalyst need to be improved. One way to achieve this is to use stable and electrically conductive ceramic support for the nano-sized Ir electrocatalyst, such as titanium oxinitride (TiON).
One key parameter that governs the properties of TiON is the N/O ratio. By having ways of determining the N/O ratio, newly synthesized TiON material samples can be evaluated and compared to other similar samples. Different analytical methods, such as scanning transmission electron microscope (STEM) energy dispersive x-ray spectroscopy (EDXS), scanning electron microscope (SEM) EDXS, electron energy loss spectroscopy (EELS), x-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) with CHNS elemental analysis were evaluated for N/O ratio determination.
An experimental platform, called NanoLab, was developed to gain insight into the effects of catalyst composition and structure on its stability and activity. Novel concepts such as identical location (IL) transmission electron microscopy (TEM), anodic oxidation of TEM grids, and modified floating-electrode-based electrochemical analysis were combined to enable accelerated development of electrocatalysts. NanoLab facilitates the observation of the electrocatalyst’s local surface, morphology, composition, and structure which can all be followed with atomic resolution and understood in depth after each step of the synthesis procedure and electrochemical treatment. NanoLab was used to investigate the stability of the TiON-Ir support – electrocatalyst system. Together with density functional theory calculations, it was shown that Ir nanoparticles and Ir single atoms stabilize the TiON support which reduces oxidation during OER. NanoLab was also used together with in-house developed algorithms to understand structural transformations in TiON-supported Ir nanoparticles. The processed atomic resolution images revealed many degradation processes where surface roughening was found to be the predominant one. The reduced oxidation tendency of TiON-supported Ir nanoparticles was also confirmed.
Additionally, carbon TiON nanocomposite nanofibres (CTiON-NCNFs), synthesized with electrospinning and subsequent nitridation, were measured for electrical conductivity as single nanofibres and as bulk fabric. The electrical conductivity was better than similar amorphous carbon nanofibres, which makes them good candidates to be a support material for electrocatalysts and wiring material for electrochemical applications in general. Additional analytical methods were used to determine the morphology, crystal structure, chemical composition and N/O ratio from which electrical conductivity could be estimated and compared with experimental results.