Transition‐Metal‐Doped α‐MnO₂ Nanorods as Bifunctional Catalysts for Efficient Oxygen Reduction and Evolution Reactions

Abstract

Nano-sized a-MnO 2 nanorods doped with Co or Ru were directly synthesized using a continuous hydrothermal synthesis process (production rate 10 g h À1 ) and investigated as relatively inexpensive (due to the small Ru content) bifunctional catalysts for both the Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER). The materials were extensively characterized using a range of analytical methods; these including Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopy measurements, which was accompanied by density functional theory studies, in order to elucidate the role of dopants in a-MnO 2 structure. Electrochemical ORR and OER investigations of the as-prepared doped a-MnO 2 nanomaterials were compared to more expensive Pt/C or RuO 2 catalysts. The doped manganese oxide nanomaterials were used as bifunctional catalysts in the positive electrode of zinc air batteries (with oversized zinc metal negative electrode and limited density of discharge window) and displayed excellent performance (the overpotential was 0.77 and 0.68 V for a-MnO 2 modified with 7.6 at% Co and 9.4 at% Ru, respectively). Overall, as a result of doping, this study achieved improved bifunctional catalytic activities of metal oxide catalysts, which was comparable to more expensive alternatives.[a] M.

Sulfur‐Rich Colloidal Nickel Sulfides as Bifunctional Catalyst for All‐Solid‐State, Flexible and Rechargeable Zn‐Air Batteries

“…The LSV scans of NiS x and NiS x /S‐rGO at a rotating rate of 1600 rpm were compared to that of Pt/C (20 wt% of Pt on C), the benchmark ORR catalyst (Figure d). Onset potential is determined as the potential at a current density of −0.1 mA cm −2 . The onset potential of NiS x /S‐rGO is about 0.91 V, about 0.1 V less positive than that of Pt/C.…”

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

“…Various non-noble materials have been developed for ORR or OER [4][5][6][7][8], including but not limited to carbon, polymer,…”

Effect of nickel ion doping in MnO2/reduced graphene oxide nanocomposites for lithium adsorption and recovery from aqueous media

“…XRD pattern of nickel loaded adsorbents remain similar, no peak of nickel contents observed because it presents in very small amount but slight increase in peak intensity of nickel loaded a-MnO 2 nanocomposites has been observed due to raise in size of nanorods and increase in crystallinity, gradually nickel doping assists the fabrication of a-MnO 2 nanorods. 32 Another reason of increment in intensity consider that the tunnel spaces of a-MnO 2 can allow to insert ions with radius lower than 1.5 A, as the radius of nickel ion (Ni 2+ ) is 0.72 A that promotes the insertion of Ni 2+ ions within the tunnel spaces in order to enhance the stability of a-MnO 2 . 27 FTIR analysis scanned in the range of 4000 to 450 cm À1 was used to conrm the presence of functional groups.…”