Anode cycling

The copper contained in the electrolyte, anodes and cathodes, and the normal circulating scrap load is equal to about 10% of the annual copper production of a typical electrorefinery. Some refineries (27) have changed from the traditional 25—30 day anode cycle to a 9—14 day cycle using smaller anodes to reduce the copper inventory in spite of the higher resulting scrap load. 

Figure 40. XPS C Is and FIs spectra of graphitic anodes cycled in 1.0 M LiAsFe/EC/DMC electrolyte. 5% VC was used as additive in the left spectra. Note the different scales for the two FIs spectra. (Reproduced with permission from ref 404 (Figure 10). Copyright 2002 Elsevier.)...

The INCO, Thompson plant in Manitoba, Canada, electrolyzes 240 kg sulfide anodes in a sulfate-chloride electrolyte. The approximate composition of the electrolyte is 60 g L x Ni2+, 95 g L 1 SC>42, 35 g L 1 Na+, 60 g L 1 Cl-, and 16 g L 1 H3BO4, and the temperature is 60 °C. Nickel, cobalt, and copper dissolve from the anode, while sulfur, selenium, and the noble metals form an insoluble sludge or slime, from which they can be recovered. The anode sludge contains 95% elemental sulfur, sulfide sulfur, nickel, copper, iron, selenium, and precious metals. Nickel is deposited on to pure nickel starting sheets. The anode cycle is 15 days and the cathode cycle is 5 to 10 days. Electrolysis is carried out at a current density of 240 A m-2 giving a cell voltage of 3 to 6 V [44, 46]. 

The distance between falKng current in the cathodic cycle and rising current of the subsequent anodic cycle increases more and more. This potential difference corresponds directly to a delay of oxide formation indicating a kinetic hindrance, in spite of the constant potential sweep rate. 

In the subsequent anodic cycle, the capacity remains constant until the former oxide formation is exceeded. Simultaneously with the increasing current C decreases further. This behavior is discussed in more detail in Sect. 3.2.3.2.5. 

Pig. 5.11 NMR of surface species collected from graphitic anodes cycled in LiPF /EC/EMC 30 70 upper), 20 80 middle), and 10 90 below) (reproduced with the permission by American Chemical Society from [43])... 

Other oxygen-containing compounds may also be present in the SEI. The O Is spectrum of the anode cycled containing STD with 2 % DMDO electrolyte is slightly different from that of the anode containing STD electrolyte. In addition to the C-O and C=0 peaks observed with the STD electrolyte, a new peak at -534.3 eV is... 

As expected from equation [8.13], the lithiated nickel oxide electrode becomes transparent during the cathodic cycle (Li" insertion) and coloured in the following anodic cycle (Li" extraction). It is interesting to note that the electrochromic efficiency of lithiated nickel oxide is 0.04mCcm" at 633 nm (25), i.e. of the same order as that of tungsten oxide. 

Figure 8.13 illustrates the response of this EW in terms of cyclic voltammetry. In the cathodic cycle the window is transparent (combination of WO3 in the pristine state and of fully lithiated LiyNi03) and in the anodic cycle the window becomes reflective (dark blue, lithiated LixW03). However, as in the previously discussed case of ECDs, the temperature-dependent conductivity of the electrolyte is of crucial importance for this EW, whose response becomes manifest only above 60°C, namely at temperatures higher than the crystalline to amorphous transition point. In fact, at this temperature the solid-state EW operates with a good transmittance variation (i.e. from 20% to 55%) and with an excellent cyclability (Figure 8.14). However, the response time is slow, thus confirming that more versatile windows require the relacement of PEO-based polymer electrolytes with electrically improved materials having fast ion transport at ambient and subambient temperatures [40].

MC (free-standing polished nm, -lO o O.lVs-i Polished Anodic (cycle X 5, Cathodic (cycle X 5,... 

The supporting electrolyte type and concentration of formic acid impact the observed overpotentials. The two most commonly used supporting electrolytes are either H2SO4 or HCIO4. Specific bisulfate anion adsorption onto Pt surface sites from H2SO4 adversely increases the onset potential of formic acid electrooxidation. The top of Fig. 3.8 shows an unfavorable increase in the onset potential for OHads in the anodic cycle by 0.1 V on a Pt ( 2.3 nm)/C catalyst in the presence of 0.1 M H2SO4 versus 0.1 M HCIO4 [65]. In the presence of 0.5 M formic acid, the initial response in the forward anodic sweep at potentials below 0.4 V versus SCE is... 

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