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Gas diffusion electrodes (GDEs) for high-temperature polymer electrolyte fuel cells with different sizes of the used binder particles were evaluated by scanning electrochemical microscopy (SECM) with shear force (SF) supplement. The SF data provide means of checking the substrate morphology with respect to cracks formed during the drying process and with respect to aggregates from used binder of poly(fluoroethylene) (PTFE) simultaneously to the electrochemical data. Electron microscopy results show that a GDE prepared with smaller PTFE particles exhibits less PTFE aggregation and more regular cracks. The SECM images show a more homogeneous distribution and higher level of oxygen reduction reaction activity for the GDE prepared with smaller PTFE particles. The quantitative comparison is enabled by the SF setup that maintains a constant working distance toward the sample in the variant of the redox competition mode, in which a cyclic voltammogram was recorded for every grid position of the microelectrode probe. Mass transport limitations of oxygen during the experiment are avoided by dedicated shape of the microelectrode body. Images of microelectrode currents at specific potentials were extracted to map the local electrocatalytic activity of the GDE. The GDEs were processed to membrane electrode assemblies and applied in HT-PEFC single cell tests. The polarization curve agree with the SECM results that GDEs produced with smaller PTFE particles favor the MEA performance. The concept of zero-emission requires a rapid shift from traditional fuels to next generation of clean technologies 1 to mitigate local pollution in urban areas and to mitigate the emission of carbon dioxide. Polymer electrolyte water electrolyzers for the hydrogen production (from solar and wind power) and polymer electrolyte fuel cells (PEFC) for electricity production from hydrogen are considered one of the most promising clean power technologies. Both electrochemical components are equipped with membrane electrode assemblies (MEAs) consisting either of gas diffusion electrodes (GDEs) assembled with membranes or catalyst coated membranes (CCMs) combined with gas diffusion layers (GDLs). 2,3 In the high-temperature polymer electrolyte fuel cell (HT-PEFC), which is considered here, GDEs are commonly used. In order to apply the catalyst dispersion onto the GDL, various coating methods can be used such as blade coating, spraying and screen printing. [4][5][6] During the subsequent drying process of the dispersion, cracks in the catalyst layer may occur, 4,7 which segment the catalyst layer into parts of a few hundred micrometers extension. The cracks, which are clearly visible, are not electrochemically active. A review about the formation and analysis of the crack structure as well as an ex-situ analysis of the crack width distribution in GDEs of HT-PEFCs was given by Froning et al. 8,9 However, it is not yet clear how the crack structures within the catalyst layers affect the performance of the fuel cell. Furthermore, the influence of the morphol...

Background Equine odontoclastic tooth resorption and hypercementosis (EOTRH) is a destructive, painful and underdiagnosed dental disorder. Radiography is necessary to fully assess the disease as early stages occur on clinically normal teeth. Objectives To investigate the distribution pattern of appearance of EOTRH within the incisor arcade. In particular, we aimed to determine the influence of tooth position and horse age on the severity of EOTRH as well as on the frequency of the individual severity stages. Study design Retrospective cross‐sectional radiographic case study. Methods Digital radiographs of 142 horses (10 years and older) presented for routine dental examination at our Equine Hospital were obtained and evaluated for changes related to EOTRH. Radiological findings were classified in terms of EOTRH severity, and each tooth was evaluated individually (tooth stage). Results The tooth stages of EOTRH showed a bilateral symmetrical distribution pattern over the entire incisor arcade. There was a significant positive correlation between age and tooth stages (p < 0.001, rho = 0.48, 95% CI 0.43–0.51), and the frequency of higher tooth stages increased from central incisors to middle and corner incisors. Main limitations Individual head anatomy in some male horses lead to superimposition of the lower jaw corner incisors and canine teeth. The radiographic technique proved difficult in smaller and uncooperative horses. Differentiating between mild pathological signs of EOTRH and age‐related radiological changes was not possible in all cases. Conclusion These results reconfirm an age‐correlated progression of EOTRH. EOTRH affects the incisor arcade in a bilaterally symmetrical pattern with the corner incisors being the most severely affected.

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