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- 2017 (2) (entfernen)
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- Catalysis (1)
- Electrochemistry (1)
- Multi-sample analysis (1)
- Porosimetry (1)
- Porous materials (1)
- SAXS (1)
- SEM (1)
- Spectroscopic ellipsometry (1)
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- Thin film metrology (1)
Efficient water electrolysis requires electrode coatings with high catalytic activity. Platinum efficiently catalyzes the hydrogen evolution reaction in acidic environments, but is a rare and expensive metal. The activity achieved per metal atom can be increased if small Pt particles are dispersed onto electrically conductive, highly accessible and stable support materials.
However, the addition of Nafion, a typical binder material used in the manufacture of electrode coatings, can decrease catalytic activity by the blocking of pores and active surface sites. A new approach is reported for the direct synthesis of highly active Nafion-free Pt/C catalyst films consisting of small Pt nanoparticles supported in size-controlled mesopores of a conductive carbon film. The synthesis relies on the co-deposition of suitable Pt and C precursors in the presence of polymer micelles, which act as pore templates. Subsequent carbonization in an inert atmosphere produces porous catalyst films with controlled film thickness, pore size and particle size. The catalysts clearly outperform all Nafion-based Pt/C catalysts reported in the literature, particularly at high current densities.
The practical performance of surface coatings in applications like catalysis, water splitting or batteries depends critically on the coating materials’ porosity. Determining the porosity in a fast and nondestructive way is still an unsolved problem for industrial thin-films technology. As a contribution to calibrated, non-destructive, optical layer characterisation, we present a multi-method comparison study on porous TiO2 films deposited by sol-gel synthesis on Si wafers. The ellipsometric data were collected on a range of samples with different TiO2 layer thickness and different porosity values. These samples were produced by templated sol-gel synthesis resulting in layers with a well-defined pore size and pore density. The ellipsometry measurement data were analysed by means of a Bruggeman effective medium approximation (BEMA), with the aim to determine the mixture ratio of void and matrix material by a multi-sample analysis strategy. This analysis yielded porosities and layer thicknesses for all samples as well as the dielectric function for the matrix material. Following the idea of multi-method techniques in metrology, the data was referenced to imaging by electron microscopy (SEM) and to a new EPMA (electron probe microanalysis) porosity approach for thin film analysis. This work might lead to a better metrological understanding of optical porosimetry and also to better-qualified characterisation methods for nano-porous layer systems.
1. IntroductionPorous materials, especially porous thin films play an importantrole in chemical and physical technology in every case where thecontact area between two media has to be maximised. From cataly-sis to photochemistry and photovoltaics, the applications of porouslayer materials are diverse and numerous [1–6].The accurate and non-destructive characterisation of porousfilms for layered systems poses a challenge. This applies especiallyfor the key parameter of porous films, their porosity, i.e. the mix-ing ratio between the Matrix of the film (host material) and thepore volume which is empty or filled with a fluid medium (inclu-sions). This parameter influences most of the physical and chemicalproperties of a porous thin film and is therefore essential for theunderstanding as well as the optimisation of this class of materials.