Platinum surfaces play a decisive role in catalysis in sensors, fuel cells, solar cells and other applications like neuronal stimulation and recording. Technical advances in nanotechnology contributed tremendously to the progress in these fields. A fundamental understanding of the chemical and physical interactions between the nanostructured surfaces and electrolytes is essential, but was barely investigated up to now. In this article, we present a wet-chemical process for the deposition of nanostructures on polycrystalline platinum surfaces. The electrochemically active surface area was increased by a factor of over 1000 times with respect to the geometrical surface. The influence of the nanostructures was examined in different acidic, alkaline, and neutral electrolytes. Comparing cyclic voltammograms of nanostructured and planar polycrystalline platinum revealed new insights into the microenvironment at the electrode-electrolyte interface. The characteristic features of the cyclic voltammograms were altered in their shape and strongly shifted with respect to the applied potential. In neutral buffered and unbuffered electrolytes the water window was expanded from 1.4 V to more than 2 V. The shifts were interpreted as local pH-changes and exhausted buffer capacity in direct proximity of the electrode surface due to the strong release and binding of protons, respectively. These polarized electrodes induce significant changes in the electrochemical potential of the electrolyte due to the high roughness of their surface. The electrochemical phenomena and the observed voltage shifts are crucial for the understanding of the basic mechanism at nanostructured electrodes and mandatory for designing fuel cells, sensors and many other devices.
Efficiency, selectivity and sensitivity are important issues in catalytic applications, such as fuel cells and electrochemical sensors. This paper discusses the catalytic activity of porous layers in heterogeneous reactions based on the impact of pore morphology on pore accessibility in liquids. We present three-dimensional simulations to discuss some critical geometrical characteristics that influence the overall catalytic activity of porous catalyst. Sensitivity is proportional to the overall catalytic activity of the surface area. However, selectivity depends on pore accessibility. Simulation results demonstrate that at constant k 0 , porous layers with small pores and large numbers of pores are selective to the species with high diffusion coefficient because of high pore accessibility. In contrast, porous electrodes with low number of large pores and a large top surface area are selective to the species with low diffusion coefficient because of low pore accessibility. Additionally, pore accessibility influences the diffusional resistance, which has an impact on the local pH-value. High diffusional resistance in the porous layer leads to an accumulation of reaction products and a modification in the concentration of buffer molecules, which change local pH-value and therefore the catalytic behavior.
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