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The second type of cell we have used for our studies of species adsorbed onto platinum black is the mini-cell (Fig. 2) [9].

Fig. 2. A. Diagram of the mini-cell. A, Sample chamber; B, electrolyte reservoir; C, ports for counter and reference electrodes; D, platinum wire for contact with the platinum black sample. (B) Mini-cell probehead set for 15N NMR data acquisition.

The mini-cell has higher sensitivity over the electrochemical NMR cell due to an enhanced filling of the RF coil. The tradeoff is that the mini-cell cannot be used directly in sample preparation, since it is difficult to obtain a voltammogram with this configuration. This limits its use to adsorbates that can withstand transfer from a more conventional „powder" electrochemical cell. The mini-cell has been used with and without electrochemical-lead filtering during signal averaging. We found that it was unnecessary to use RF filters for 13C NMR signal acquisition from enriched sodium cyanide (13CN") adsorbed onto PC platinum black, but for less-sensitive nuclei such as nitrogen-containing adsorbates (C15N"), RF filtering is essential. Clearly, more complex features such as skin depth, RF penetration and sample granularity also affect sensitivity, the main point being that, even in a „harsh" environment, external RF pickup can be greatly reduced even with electrodes being in direct contact with the NMR sample during data acquisition.

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