Role of Cu-Ion Doping in Cu-α-MnO₂ Nanowire Electrocatalysts for the Oxygen Reduction Reaction

Abstract

The role of Cu-ion doping in α-MnO2 electrocatalysts for the oxygen reduction reaction in alkaline electrolyte was investigated. Cu-doped α-MnO2 nanowires (Cu-α-MnO2) were prepared with varying amounts (up to ∼3%) of Cu2+ using a hydrothermal method. The electrocatalytic data indicate that Cu-α-MnO2 nanowires have up to 74% higher terminal current densities, 2.5 times enhanced kinetic rate constants, and 66% lower charge transfer resistances that trend with Cu content, exceeding values attained by α-MnO2 alone. The observed improvement in catalytic behavior correlates with an increase in Mn3+ content at the surface of the Cu-α-MnO2 nanowires. The Mn3+/Mn4+ couple is the mediator for the rate-limiting redox-driven O2/OH– exchange. O2 adsorbs via an axial site (the eg orbital on the Mn3+ d4 ion) at the surface or at edge defects of the nanowire, and the increase in covalent nature of the nanowire with Cu-ion doping leads to stabilization of O2 adsorbates and faster rates of reduction. A smaller crystallite size (roughly half) for Cu-α-MnO2 leading to a higher density of (catalytic) edge defect sites was also observed. This work is applicable to other manganese oxide electrocatalysts and shows for the first time there is a correlation for manganese oxides between electrocatalytic activity for the oxygen reduction reaction (ORR) in alkaline electrolyte and an increase in Mn3+ character at the surface of the oxide.

Nanostructured MnO2 as Electrode Materials for Energy Storage

“…High EA was also reported for MnO 2 particles dispersed on high surface area carbon [138]. Davis et al [139] studied the catalytic activity of Cu-doped α -MnO 2 nanowires. Due to the similarity of the Al 3+ and Mn 4+ atomic radius, aluminum can substitute Mn or be located in tunnel of α -MnO 2 .…”

Efficiently Enhancing Electrocatalytic Activity of α-MnO2 Nanorods/N-Doped Ketjenblack Carbon for Oxygen Reduction Reaction and Oxygen Evolution Reaction Using Facile Regulated Hydrothermal Treatment

“…Then, the Mn 3+ had its one σ* electron transferred to O-O π* orbital and converted back into Mn 4+ [32]. Therefore, higher Mn 3+ content results in more available adsorption sites for O 2 , which eventually improves the electrocatalytic activity for ORR [26,29,32,38].…”

Graphene-based transition metal oxide nanocomposites for the oxygen reduction reaction

“…72 The integration of CuO x on carbonaceous materials to obtain enhanced properties for applications, such as stable catalytic activity of the ORR, are considered as efficient cathodes for practical applications. Thus, a copper oxide/nitrogendoped reduced graphene oxide (CuO/N-rGO) nanocomposite was synthesized through the aqueous coprecipitation method.…”