Mechanistic insight of in situ electrochemical reduction of solid PbO to lead in ChCl-EG deep eutectic solvent

• In situ reduction mechanism of solid PbO in ChCl-EG is preliminarily clarified.
• The gases produced at anode and cathode are monitored respectively.
• A mechanism model for the in situ reduction process has been proposed.
• Provide a basis for in-depth discussion on production of metals from oxides.

ABSTRACTThe in situ electroreduction mechanism of solid PbO in choline chloride-ethylene glycol deep eutectic solvent (ChCl-EG DES) is preliminarily clarified through systematical investigations at cell voltage 2.5 V and 353 K. Cyclic voltammetry of the cavity microelectrode loaded with PbO powders exhibits that solid PbO can be direct electrochemically reduced to metallic lead and increasing scan numbers is beneficial to the deoxidation process. Potentiostatic electrolysis with an assumed cathode of PbO pellet and a graphite anode shows that generated numerous gases are mainly composed of O2 with small amounts of Cl2 at anode whereas H2 is released and preferentially adsorbed on the surface of reduced metallic lead at cathode. Parts of Cl2 can remain in the electrolyte and react with it to form oxidizing Cl−3 ions. Besides, the dissolution-electrodeposition of PbO(s) → [PbO·Cl·EG]− → Pb(s) exists simultaneously with the direct deoxidation of PbO(s) → Pb(s) during the electrolysis process. ESI-MS analysis implies that complex anions [PbO·Cl·EG]− and [ChCl·O·EG]2− are formed in ChCl-EG-PbO solution before and after the deoxidation process, respectively. Furthermore, a reduction mechanism model of PbO bulk to metallic lead in ChCl-EG DES is proposed. The in situ electrolysis process takes place initially at the current collector/PbO/electrolyte 3PIs and then new formed Pb/PbO/electrolyte 3PIs expands until the whole bulk are metallized. These findings provide a basis for scientifically in-depth discussion on the implication and optimization of the electrochemical production of metals and alloys from metal oxides.

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