Pulse-to-pause ratio

The formation of the smaller (and less different to each other) dendrites could be obtained by the increase of deposition overpotential. Unfortunately, the increased overpotential produces the hydrogen evolution in this system and the formation of degenerate dendrites and honeycomb-like deposits.76,77 Nevertheless, the dendritic growth in this system at larger overpotentials is possible by the application of appropriate square-wave pulsating overpotential (PO) regime. For example, the well-developed dendrites were formed with amplitude overpotential of 1,000 mV, deposition pulse of 10 ms, and pause of 100 ms (the pause to pulse ratio 10) (Fig. 26a). They can be well approximated by the cones shown in Fig. 23. Also, superficial holes due to attached hydrogen bubbles were formed between these dendrites, as can be seen from ref.78... 

The overpotential amplitude is larger than in the DC regime for one and the same average current density. Simultaneously, the diffusion overpotential remains constant, depending on the average current density only. Hence, the part of activation control in the overall amplitude overpotential increases with increasing pause to pulse ratio. 

Fig. 4.5 Pb deposits obtained from 0.10 M Pb(CH3COO)2+1.5 M NaCHjCOO + O.lS M CH3COOH on Cu substrate at a constant overpotential of (a) 75 mV for 50 s, (b) the same as in (a) but for 350 s at 0 mV, (c) the same as in (a) but for 100 s at —10 mV (anodic), and (d) by PO with /a = 75 mV, pause-to-pulse ratio 3 pulse duration, 0.5 s (Reprinted from Ref. [12] with kind permission from Springer and Ref. [26] with pmnission from Elsevier)...

Popov KI, Pavlovic MG, Removic GZ (1991) The effect of the pause-to-pulse ratio on the morphology of metal powder particles electrodeposited by square-wave pulsating... 

Fig. 5.8 (a, b) The pyramid-like and (c, d) dendritic structures of Cu obtained by the pulsating overpotential (PO) regimes with the same pause-to-pulse ratio 10, but with the different durations of deposition pulse (4) and pause (tp) (a, b) t = ms and tp = 10 ms, (c, d) = 10 ms and tp= 100 ms (Reprinted from Refs. [49, 50] with permission from Elsevier and Refs. [5, 23, 51] with kind permission from Springer)... 

Nikolic ND, Brankovic G, Pavlovic MG, Popov KI (2009) The effects of the pause to pulse ratio in the regime of pulsating overpotential on the formation of honeycomb-like structures. Electrochem Commun 11 421-424... 

Fig. 2.8 Silver powder particles obtained by square-wave pulsating overpotential. Overpotential amplitude 300 mV. Pulse duration 5 ms. (a) Pause to pulse ratio 1, xlOO (b) pause to pulse ratio 1, xlOOO (c) pause to pulse ratio 3, x 100 and (d) pause to pulse ratio 3, x 1000 (Reprinted from [23] with permission from the Serbian Chemical Society.)...

The first set of experiments was done applying square-waves PC with a constant pause duration, fp, of 10 ms, and deposition pulses, t, of 1, 2, and 50 ms (pause to pulse ratios, p, wherep = were 10,5,... 

In the second set of experiments, the constant deposition pulse of 10 ms and pause durations of 1(X), 50, and 2 ms were analyzed (pause to pulse ratios 10, 5, and 0.2, respectively). In this case, the average current efficiencies for hydrogen evolution reaction, were... 

Pulsating overpotential (PO) consists of a periodic repetition of overpotential pulses of different shapes [34, 35], Square-wave PO is defined by the overpotential amplitude, deposition pulse, tc, and pause, tp. The pause to pulse ratio is defined asp =... 

Fig. 4.11 The dependences of the average diameter of the surface holes, D, (square) and the number of holes per mm surface area of the copper electrode (circle) on the pause to pulse ratio (Reprinted from [36] with permission from Elsevier.)...

The decrease of the hole size and the increase of the number of formed holes with the increasing pause to pulse ratio can be primarily ascribed to the suppression of a coalescence of closely formed hydrogen bubbles [36]. The coalesced holes are observed in the honeycomb-Uke structures formed with pause to pulse ratios up to 2. Holes formed with the pause durations shorter than the deposition pulse were similar to those obtained at constant overpotential [36]. The bottom of these holes was very compact (Fig. 4.12a, b). The prolonging pause duration led to the change of the bottom of holes from compact to the one constructed of very disperse agglomerates of copper grains (Fig. 4.12c). The significantly smaller number of holes was formed with a pause duration of 1(X) ms and... 

Simultaneously, the morphology of electrodeposited copper formed around holes, as weU as inside holes, changed with the increasing pause to pulse ratio from cauliflower-Uke agglomerates of copper grains to dendrites. Very disperse agglomerates of copper grains were formed at the constant overpotential and by the PO... 

The values of the average current efficiencies of hydrogen evolution, i,av(H2), obtained for different pause to pulse ratios are given in Table 4.1 [41]. The following parameters of square-waves PO were... 

From Fig. 4.16, it can be seen that hmieycomb-like structures were formed with deposition pulses of 3,5,10, and 20 ms. The analysis of the honeycomb-like structures showed that the number of holes formed by the attached hydrogen bubbles did not change considerably with the length of deposition pulses of 3,5, and 10 ms (i.e., with pause to pulse ratios up to 1). The mUd decrease of the number of the formed holes was observed with a deposition pulse of 20 ms, what can be ascribed to the enhanced coalescence of neighboring hydrogen bubbles as well as to effects related to the current density distribution at the growing electrode by which some of the hydrogen bubbles remained captive in the interior of deposits [41],... 

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