Anodic Behaviour of Ni-Fe-Cu electrode In Molten Fluoride Salts

Abstract

The anodic behaviour of NixFeyCuz alloy 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.