In a recent paper Payne 1 gives a very interesting and informative review of Time-Domain Reflectometry (TDR) but he fails in his attempt to apply this technique to transient electrochemical kinetic and double-layer analysis. He states that the conventional electronic techniques of Bockris and coworkers 2-4 and of Schuldiner and coworkers 5'6 were extended up to, and possibly beyond, their limits. He then proceeds to do just what he criticized by attempting to extend the galvanostatic pulse technique beyond its useful limit with an abortive application of TDR technique including an equally unfortunate use of a sampling oscilloscope.
At the conclusion of his discussion of his application of TDR, Payne in effect admits that because of high frequency transmission line losses, the technique is inapplicable to electrochemical measurements at the very time region of interest in his study! In order to avoid these line losses, he placed his cell at the point of measurement where the incident and reflected waves were superimposed. In other words, by eliminating the transmission line between cell and probing point, Payne eliminated the characteristic advantage of TDR obtained by comparison of the refected and incident pulses. He observed instead the voltage changes on the working electrode, due in part to the response of the mismatched termination (electrochemical cell) to the pulse applied from the pulse generator. In short, he used the conventional step technique he criticized. This does not mean that reflections of the applied pulse were not experienced in Payne's measurements. In addition to those to be expected from the mismatched cell termination there were reflections from load parameters and discontinuities back toward the pulse generator caused by many factors which were either unknown or very difficult to analyze, including bias voltage connections and pickoff probes causing "small distortions" for which compensating adjustments were made externally.
The TDR equations 8,9 which Payne used in analyzing his potential-time response are suitable for a clearly defined reflection of an accurately generated constant voltage pulse down a transmission line. Because his display included these superposed, ill-defined reflections, the use of the simple TDR equations is highly optimistic and of questionable accuracy. Making the current pulse absorbed in the cell constant (rather than the applied incident voltage pulse) by adjusting the pulse-shaping controls of the pulse generator further confuses the analysis since this adjustment has an