Sævarsdóttir, Guðrún ArnbjörgGunnarsson, GudmundurHaarberg, Geir MartinSingh, Kamaljeet2025-11-172025-11-172025-04-29Singh, K 2025, 'Nickel–Iron–Copper-Based Oxygen Evolving Anode for Low Temperature Aluminum Electrolysis', Doctor, Reykjavik University, Norwegian University of Science and Technology, Reykjavík.978-9935-539-70-0978-82-326-9084-81503-8181978-9935-539-71-7978-82-326-9083-12703-8084240394768784ca89f-b629-4d1c-8ce8-d473c472e56fhttps://hdl.handle.net/20.500.11815/5958The Hall–Héroult process is, currently, the only industrial method for primary aluminum production. However, the process suffers from many inefficiencies, mainly because the carbon anodes are continuously consumed during electrolysis, producing greenhouse gas emissions—primarily CO2 and, intermittently, perfluorocarbons. Another inefficiency in the process is its high energy demand, essentially caused by a significant ohmic voltage drop resulting from the large anode-cathode distance created by the molten aluminum pool, and a high anodic overpotential due to the slow kinetics of the anodic process. Therefore, to eliminate greenhouse gas emissions and improve energy utilization in aluminum electrolysis a non-consumable, cost effective, and efficient oxygen evolving anode (OEA) is essential. Recent research has shown that the use of nickel–iron–copper-based alloys for the OEA offers promising performance in low temperature electrolytes. This performance advantage is attributed to their ability to form a protective nickel-ferrite (NiFe2O4) oxide scale during anodic reactions, coupled with their reduced wear rates under these operating conditions. Unfortunately, systematic studies on the effects of alloy composition and low temperature electrolyte composition on the formation and stability of the protective scale are lacking. The present work explored the use of various earth-abundant Ni–Fe–Cu-based alloys for the OEA in a range of low temperature KF-NaF-AlF3-Al2O3(sat.)-based electrolyte compositions for aluminum electrolysis at 800 ⁰C. Additionally, a TiB2 wettable aluminum cathode and a vertical electrode configuration were employed to develop a compact and energy efficient cell. To identify the optimal compositions and conditions for aluminum electrolysis in a 40 A laboratory cell, two electrolyte compositions, K-rich and Na-rich, were investigated using Ni–Fe–Cu alloys as anodes. It was found that the K-rich electrolyte composition in combination with Ni42-Fe38-Cu20 anode offered a low anode wear rate and stable electrolysis. This performance was attributed to the better alumina solubility of the electrolyte and the formation of a dense and protective NiFe2O4 oxide on the anode surface. The oxidation treatment of the Ni42-Fe38-Cu20 alloy, to pre-form an oxide scale, demonstrated its ability to form a multi-layered oxide scale of CuO, Fe2O3 and protective NiFe2O4. This indicated the effectiveness of the treatment in developing a protective oxide scale ex-situ, which was found satisfactory for meeting the requirements of the OEA. The use of the OEA leads to higher energy demands compared to the Hall–Héroult process with carbon anodes, primarily due to the increased reaction voltage. Therefore, to assess the energy efficiency in terms of overpotential on OEA, steady state anodic polarization curves were obtained on platinum and a series of Ni–Fe–Cu-based alloys. The polarization curve on the platinum anode exhibited two linear regions, showing good consistency with the proposed theoretical mechanism of oxygen evolution reaction. The polarization curve on alloys, both in oxidized and untreated conditions, however, exhibited a single Tafel region. At a normal current density of 0.8 Acm-2, the oxidized anodes Ni42-Fe38-Cu20 and Ni48-Fe47-Cu5 showed lower overpotentials after electrolysis compared to untreated anodes of same composition, respectively. This resulted from the fact that oxidized anodes exhibited better electrocatalytic activity with lower Tafel slopes, mainly due to the pre-formed conductive oxide scale through oxidation treatment.1144921677eninfo:eu-repo/semantics/embargoedAccessAluminum electrolysisInert anodesmolten salts/dk/atira/pure/researchoutput/researchoutputtypes/thesis/doc