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Investigation of stability and degradation phenomena in model M@C / PANI nanocomposite electrodes with 2D and 3D architecture

Subject Area Physical Chemistry of Solids and Surfaces, Material Characterisation
Term from 2020 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 429730598
 
Final Report Year 2023

Final Report Abstract

Electrocatalysis is the field of chemistry aiming at facilitating the exchange at electrons at interfaces between a solid electrode and a liquid electrolytic solution. Prominent applications of electrocatalysis include energy conversion (storage of electrical energy in electrical form by electrolysis and release of the stored energy back to electricity in fuel cells) and electrochemical sensing (for example for biomedical applications of chemical analysis such as in glucose sensing for patients living with diabetes). Increasing electrocatalytic turnover translates into a higher power density in energy conversion applications, and into a higher sensitivity in electroanalysis applications. This increase can be achieved either by the design and choice of intrinsically more active catalysts or by the control and optimization of the electrode’s geometry. Indeed, an increase in the electrode’s specific surface area by the introduction of a porous structure increases geometrically the number of sites at which electrons can be exchanged at the interface between solid and liquid. The fact that in technical applications, the porous electrode exhibits a highly complex and poorly controlled geometry and a distribution of catalyst particles embedded in a polymeric composite renders insight into the potential improvement of electrocatalytic turnover by geometrical means very difficult to obtain unambiguously. The CompElec project established methods for the preparation of electrode models in which the geometry of nanoscale pores is a simple design, most perfectly controlled, and systematically tunable. We established that atomic layer deposition (ALD), a chemical method for the coating of highly porous substrates with perfectly homogeneous thin layers of inorganic materials, is uniquely adequate for applications in electrocatalysis by delivering electrically conducting and catalytically active materials coatings with a precision on the order of a single nanometer. This was demonstrated in two distinct types of electrode geometries: ordered arrays of straight, parallel, cylindrical pores, on the one hand, and ordered three-dimensional stacks of spheres, on the other hand. We demonstrated the ability of electrodes generated in the latter type of geometry, which become so-called ‘inverse opals’ after removal of the template of spheres, to afford extraordinarily sensitive biosensing platforms. We also established in the former type of geometry that the fraction of individual pores which are electrically contacted and thereby electrocatalytically active depends on the degree of order of the pores, and we managed to reach 95% active fraction with an extreme perfection enabled by a mask consisting of a self-assembled monolayer of nanospheres. The results achieved with nanospheres monolayers have been generalized to solid-solid electrodes as those found in solar cells. By engineering the spheres arrangement, we have achieved a light scattering effect which enhances absorption of light in so-called ‘extremely thin absorber’ solar cells and has enabled us to make cells with a light absorbing layer thickness of 35 nm. This represents approximately 1% of the values encountered in stateof-the-art ‘thin-film’ solar cells, and 0.01% of those in classical silicon solar cells. The savings in terms of materials consumption scale accordingly.

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