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Anodic processes on Cu−10Al electrode in molten KF−AlF3−Al2O3(saturated) and suspensions were characterized using chronopotentiometric and cyclic voltammetric techniques. Effects of cryolite ratio (CR= x(KF)/x(AlF3)), temperature and particle volume fraction (ϕ) on the electrochemical behaviour of the anode were demonstrated. Initially, the anode was polarised in the galvanostatic mode in melt and suspensions (ϕ=0.12, 0.15) at 750 °C with 0.4 A/cm2current density. The anode potential in melt varied between 2.5 and 3.2 V and in suspensions (ϕ= 0.12) between 3.3 and 3.4 V. XRD analysis was conducted to study the oxide phases on the anode surface. Anode limiting current densities and mass transfer coefficients drastically decreased with the increase of ϕin the suspension. The results suggest that the Cu−10Al electrode works better in suspensions with CR of 1.4 and particle volume fraction of 0.09 at 800 °C.

The anodic behaviour of Ni42Fe38Cu20alloy at different sodium-potassium-cryolite-based electrolyte compositions was examined by chronopotentiometry, chronoamperometry, and linear sweep voltammetry at 1098 K for different electrolyte compositions. Steady-state anodic polarisation curves show that the anodic overpotential in electrolytes with molar ratio CR = (NaF+KF)/AlF3= 1.4 is significantly less than in electrolyte with CR = 1.3. Short-term galvanostatic polarisation curves indicate that the potential difference between the anode and reference electrode (Al) was stable in electrolytes with CR = 1.4 and potassium ratio KR = KF/(KF + NaF) = 0.3 and CR = 1.4 KR = 0.35. The linear sweep voltammetry method indicates the presence of a diffusion-controlled reaction at a potential below the onset of oxygen evolution, which can be attributed to oxide formation. Tafel curves indicate the presence of the reactions below the potential of oxygen evolution but show a similar overpotential level for the oxygen-evolving reaction as for carbon anodes. Furthermore, the effect of pre-oxidation and influence of consistent polarisation on the anode performance was explored. Pre-oxidised anodes have better stability and lower exchange current density in similar experimental conditions compared to untreated anodes. It was also observed that leaving anodes unpolarised could lead to their instability and fluoridation of both types of anodes, with less severe effect on the pre-oxidised anode.

The anodic behaviour of NixFeyCuzalloy at different sodium- and potassium-cryolite based electrolyte compositions was examined by chronopotentiometry, galvanostatic polarisation, and linear sweep voltammetry at 1098 K. Steady-state anodic polarisation curves show anodic overpotential in electrolyte with molar ratio CR=(NaF+KF)/AlF3=1.4 is significantly less than in electrolyte with CR=1.3. Short-term galvanostatic polarisation curves indicate the potential difference between the anode and reference electrode (Al) was stable in electrolytes with CR=1.4 and potassium ratio KR=KF/(KF+NaF)=0.3 and CR=1.4 KR=0.35. Linear sweep voltammetry method indicates the presence of a diffusion controlled reaction at a potential below onset of oxygen evolution, which can likely be attributed to oxide formation. The diffusion coefficient obtained from linear sweep voltammetry and chronopotentiometry are within a similar range. Tafel curves confirm the presence of a reaction below the potential of oxygen evolution, but indicate a similar overpotential level for the oxygen evolving reaction as for carbon anodes.

Due to environmental and economic concerns, carbon-free aluminium production has been an ultimate target for aluminium industries. For the last few decades, a considerable amount of research has been conducted to find a suitable inert anode that could replace the consumable carbon anodes for aluminium electrolysis. Material types such as metals, ceramics and cermets have been studied extensively. All the anode materials have their advantages and disadvantages. However, metallic alloys have been considered attractive anode material candidates due to their high electrical conductivity, thermal stability and easy fabrication and machining properties. For a successful adaptation of metallic anodes into the aluminium electrolysis cell, an electrolyte with a low-operating temperature and high alumina solubility is required. Another significant component of the carbon-free aluminium electrolysis cell is a wettable cathode. This overview discusses the research progress on inert anodes, wettable cathodes and electrolytes.

Electrochemical behaviour of aluminium ions from the Pt/?-Al2O3spent catalyst in the eutectic [LiF (63.6 wt.%)-AlF3(36.4 wt.%)]eutectic?5 wt.% CaF2melt was studied by the means of cyclic voltammetry, chronopotentiometry and chronoamperometry methods. Tungsten rod (diameter 2 mm) was used as a working electrode. The XRD method was used to study the composition of melt collected near the working electrode and the spent catalyst. The aluminium reduction kinetics was studied concerning varying parameters like spent catalyst content in the melt and the temperature. The reduction of Al3+ions on the tungsten electrode changed from diffusion-controlled to quasi-reversible process. The charge transfer coefficient and the diffusion coefficient were calculated from the data obtained from the above-mentioned methods. The estimated diffusion activation energy was 117.85 kJ.mole?1.