Reducing the Ag consumption of industrial Pb-Ag anode for metal electrowinning via embedding Ag@γ-MnO2 into Pb matrix

Abstract

PbAg (0.5–1.0 wt.%) alloys are widely employed as commercial anodes in non-ferrous metal electrowinning. To reduce silver consumption, we developed a novel Pb-Ag@γ-MnO₂ composite anode through a two-step strategy: (1) in-situ synthesis of Ag nanoparticle-decorated γ-MnO₂ (Ag@γ-MnO₂) via sequential MnO₄⁻/Mn²⁺ redox reaction and Ag⁺ chemical reduction, followed by (2) uniform dispersion of 2.0 wt.% Ag@γ-MnO₂ particles in a Pb matrix using powder metallurgy. Systematic comparisons with industrial PbAg(0.5 wt.%) alloy and Pb composites containing individual Ag or γ-MnO₂ dispersoids (2.0 wt.%) revealed superior performance of the Pb-Ag@γ-MnO₂ composite anode. During galvanostatic polarization at 50 mA·cm⁻² in 160 g·L⁻¹ H₂SO₄, the Pb-Ag@γ-MnO₂ anode exhibited a 40 mV lower stable potential (1.33 V) than the PbAg(0.5 wt.%) benchmark. Electrochemical impedance spectroscopy and DFT calcultion confirmed its faster oxygen evolution reaction (OER) kinetics, evidenced by a lowest charge transfer resistance of 1.73 Ω·cm², linked to optimized adsorption/desorption of oxygen intermediates due to Ag nanoparticles decoration. Microstructural analysis revealed that Pb-Ag@γ-MnO₂ has a remarkably thinner (∼2.5 μm) and denser oxide layer compared to the porous 15–25 μm layer on PbAg alloys. Notably, with <0.08 wt.% total Ag content, an 84% reduction from conventional PbAg alloy anodes, the Pb-Ag@γ-MnO₂ achieved comparable performance to industrial counterparts. These findings establish Ag@γ-MnO₂ as dual-functional active sites that synergistically enhance OER activity while dramatically decreasing precious metal consumption.