Developing hierarchically porous MnOx/NC hybrid nanorods for oxygen reduction and evolution catalysis (original) (raw)
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Engineering manganese oxide/nanocarbon hybrid materials for oxygen reduction electrocatalysis
Nano Research, 2012
Manganese oxides are cost-effective and green materials with rich electrochemical properties. Continuous research efforts have been undertaken to obtain MnO x materials with improved activity and stability for catalyzing the oxygen reduction reaction (ORR). Here, we have developed a novel ORR catalyst by nucleation and growth of Mn 3 O 4 nanoparticles on graphene oxide (GO) sheets interconnected by electrically conducting multi-walled carbon nanotubes (MWCNTs). X-ray near edge absorption structure (XANES) spectroscopy revealed the partially reduced nature of GO and strong chemical coupling between the nanoparticles and the GO sheets. Incorporation of MWCNTs was found to improve the activity and stability of the hybrid by imparting higher conductivity to the hybrid material. Furthermore, surface oxidation of the manganese oxide nanoparticles through a calcination step was found to increase the density of ORR active sites. The strongly coupled and electrically interconnected Mn 3 O 4 /nanocarbon (Mn 3 O 4 /Nano-C) hybrid is one of the most active and stable manganese oxide-based ORR catalysts and shows promise for electrochemical energy conversion applications.
ChemCatChem, 2019
Herein, heteroatoms of N and P doped carbon layer over MnO2 nanorods surface was fabricated by an in situ anile polymerization reaction based on aniline and phytic acid (MnO2@PANI) following thermal annealing. A core-shell structure with manganese oxide as the core and N, P-doped carbon layer as the shell was revealed by structure and morphology analysis. Temperature dependence of phase structure and ORR activity was found by a series of physical and electrochemical studies for MnO2@PANI sample obtained at different annealing temperatures. The MnO2@PANI obtained at 800 o C exhibited the best catalytic performance, close to Pt/C for ORR; Specifically, the onset potential and half-wave potential were 0.92 and 0.76 V respectively, outperforming their counterparts of MnO2 and N, P-C alone. The improved catalytic performance can be attributed to the conductivity improvement and the synergistic effect of the intrinsic activity of manganese oxide and N, P-doped carbon layer. The current work demonstrated an efficient approach to boost the catalytic performance for ORR catalyzed by manganese oxide.
Technological hurdles that still prevent the commercialization of fuel cell technologies necessitate designing low-cost, efficient and non-precious metals. These could serve as alternatives to high-cost Pt-based materials. Herein, a facile and effective microwave-assisted route has been developed to synthesize structurally uniform and electrochemically active pure and transition metal-doped manganese oxide nano-balls (Mn 2 O 3 NBs) for fuel cell applications. The average diameter of pure and doped Mn 2 O 3 NBs was found to be ~610 nm and ~650 nm, respectively, as estimated using transmission electron microscopy (TEM). The nanoparticles possess a good degree of crystallinity as evident from the lattice fringes in high-resolution transmission electron microscopy (HRTEM). The cubic crystal phase was ascertained using X-ray diffraction (XRD). The energy dispersive spectroscopic (EDS) elemental mapping confirms the formation of copper-doped Mn 2 O 3 NBs. The experimental parameter using trioctylphosphine oxide (TOPO) as the che-lating agent to control the nanostructure growth has been adequately addressed using scanning electron microscopy (SEM). The solid NBs were formed by the self-assembly of very small Mn 2 O 3 nanoparticles as evident from the SEM image. Moreover, the concentration of TOPO was found to be the key factor whose subtle variation can effectively control the size of the as-prepared Mn 2 O 3 NBs. The cyclic voltammetry and galvanostatic charge/discharge studies demonstrated enhanced electrochemical performance for copper-doped Mn 2 O 3 NBs which is supported by a 5.2 times higher electrochemically active surface area (EASA) in comparison with pure Mn 2 O 3 NBs. Electrochemical investigations indicate that both pure and copper-doped Mn 2 O 3 NBs exhibit a bifunctional catalytic activity toward the four-electron electrochemical reduction as well the evolution of oxygen in alkaline media. Copper doping in Mn 2 O 3 NBs revealed its pronounced impact on the electrocatalytic activity with a high current density for the electrochemical oxygen reduction and evolution reaction. The synthetic approach provides a general platform for fabricating well-defined porous metal oxide nanostructures with prospective applications as low-cost catalysts for alkaline fuel cells.
MOF Derived Manganese Oxides Nanospheres Embedded in N-Doped Carbon for Oxygen Reduction Reaction
Inorganics
Manganese oxides (MnOx) have been regarded as promising catalyst candidates for oxygen reduction reaction (ORR) due to their natural abundance and extremely low toxicity. However, the intrinsic low conductivity of MnOx limits their application. In this work, Mn oxide embedded in N doped porous carbon (MnOx@C-N) electrocatalysts were prepared through a facile zeolitic imidazolate framework (ZIF-8) template method for ORR. The structure, morphology, and composition of the prepared materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Electrocatalytic performances of the prepared materials were investigated by linear sweep voltammetry. Benefiting from the well-defined morphology, high surface area, and porous structure, the MnOx@C-N electrocatalyst showed the highest ORR activity among all investigated materials with the limiting current density of 5.38 mA/cm2 at a rotation speed of 1600 rpm, the positiv...
In this article, a brief overview of manganese oxide nanomaterials (NMs) potential towards oxygen reduction reaction (ORR) for microbial fuel cell (MFC), bioremediations, and battery applications is discussed. It's known that using non-renewable fossil fuels as a direct energy source causes greenhouse gas emissions. Safe, sustainable and renewable energy sources for biofuel cell (BFC) and metal-air batteries hold considerable potential for clean electrical energy generators without the need for a thermal cycle. In an electrochemical reaction system, the four-electron reduction from molecular oxygen at the air-cathode surface to hydroxide ion or water at a reasonably low overpotential was the ultimate goal of many investigations and plays a vital role in metal-air batteries and fuel cell device systems. Different Mn x O y nanostructured materials, from Biofunctional structural catalysts up to their electrocatalytic contributions towards ORR are discussed. Brief descriptions of ORR, principle strategy and mechanism, as well as recent developments of cationic dopants and electrolytic media, effect on the air-cathode surface of manganese oxide nanocatalyst are also discussed. Finally, challenges associated with platinum and carbon support platinum in improving electron and charge transfer between biocatalyst and air-cathode electrode are summarized.
Journal of Materials Chemistry A, 2014
Developing low cost oxygen reduction catalysts that perform with high efficiency is highly desirable for the commercial success of environmentally friendly energy conversion devices such as fuel cells and metal-air batteries. In this work a three-dimensional, 3D, self-assembled Mn 3 O 4 hierarchical network has been grown on nitrogen doped reduced graphene oxide (NrGO), by a facile and controllable electrodeposition process and its electrocatalytic performance for oxygen reduction reaction (ORR) has been assessed. The directly electrodeposited MnO x on a glassy carbon electrode (GCE) exhibits little electrocatalytic activity, whereas the integrated Mn 3 O 4 /NrGO catalyst is more ORR active than the NrGO. The resulting electrode architecture exhibits an "apparent" four-electron oxygen reduction pathway involving a dual site reduction mechanism due to the synergetic effect between Mn 3 O 4 and NrGO. The 3D Mn 3 O 4 /NrGO hierarchical architecture exhibits improved durability and methanol tolerance, far exceeding the commercial Pt/C. The enhanced ORR performance of the room temperature electrodeposited Mn 3 O 4 nanoflake network integrated with NrGO reported here offers a new pathway for designing advanced catalysts for energy conversion and storage.
ACS Omega, 2018
The development of nonprecious catalysts for water splitting into hydrogen and oxygen is one of the major challenges to meet future sustainable fuel demand. Herein, thin layers of manganese oxide nanosheets supported on nitrogen-functionalized carbon nanotubes (NCNTs) were formed by the treatment of NCNTs dispersed in aqueous solutions of KMnO 4 or CsMnO 4 under reflux or under hydrothermal (HT) conditions and used as electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. The samples were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Our results show that the NCNTs treated under reflux were covered by partly amorphous and birnessite-type manganese oxides, while predominantly crystalline birnessite manganese oxide was observed for the hydrothermally treated samples. The latter showed, depending on the temperature during synthesis, an electrocatalytically favorable reduction from birnessitetype MnO 2 to γ-MnOOH. OER activity measurements revealed a decrease of the overpotential for the OER at a current density of 10 mA cm −2 from 1.70 V RHE for the bare NCNTs to 1.64 V RHE for the samples treated under reflux in the presence of KMnO 4. The hydrothermally treated samples afforded the same current density at a lower potential of 1.60 V RHE and a Tafel slope of 75 mV dec −1 , suggesting that the higher OER activity is due to γ-MnOOH formation. Oxidative deposition under reflux conditions using CsMnO 4 along with mild HT treatment using KMnO 4 , and low manganese loadings in both cases, were identified as the most suitable synthetic routes to obtain highly active MnO x /NCNT catalysts for electrochemical water oxidation.
Electrochimica Acta, 2008
The electrocatalytic evolution of oxygen gas is investigated at manganese oxide nanorods (nano-MnO x ) modified Au, Pt and GC electrodes in a wide range of pH values, ranging from highly acidic to highly basic. Morphological investigation has been carried out by a scanning electron microscopy (SEM), which revealed the deposition of nano-MnO x in a nanorod morphology. A significant enhancement of the electrocatalytic activity of the Au, Pt and GC electrodes towards the oxygen evolution reaction (OER) was observed upon the electrodeposition of nano-MnO x onto the aforementioned electrodes. The effect of the surface coverage of the manganese oxide and the pH of the electrolyte was investigated to seek an optimization. The highest cathodic shift in the onset potential of the OER was obtained in 0.5 M KOH irrespective of the substrate whereas the optimum loading (surface coverage) was about ca. 52%. The origin of the enhancement of the OER is addressed with the assistance of an X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. The preferential electrodeposition of crystallographically oriented nano-MnOx (in the manganite phase, ␥-MnOOH) is thought to play the primary role in the observed enhancement.
Journal of Applied Electrochemistry, 2018
Manganese oxide-based nitrogen-doped reduced graphene oxide (MnO/N-rGO) electrocatalyst was developed by a simple sol-gel process with aqueous KMnO 4 and sucrose by adding nitrogen-doped reduced graphene oxide. The physical characterizations were systematically evaluated by X-ray diffraction, field emission scanning electron microscope, transmission electron microscope, and X-ray photoelectron spectroscopy. The electrochemical and oxygen reduction properties of the electrocatalyst and support were studied by employing cyclic voltammetry and linear sweep voltammetry techniques on a rotating-disk electrode in alkaline (0.1 M KOH) solution and compared with commercial Pt/C catalysts. The synthesized catalyst possesses a high oxygen reduction activity and the rotating ring-disk electrode results illustrate a 3.8 e − transfer process. Stability tests performed for 10,000 potential cycles exhibited that the MnO/N-rGO catalyst is more durable than Pt/C catalyst. MnO/N-rGO as cathode catalyst in a single alkaline fuel cell studies gave a peak power density of 44 mW cm − 2 at 40 °C. Durability by accelerated stress test (AST) in fuel cell mode demonstrated MnO/N-rGO as alternative hybrid cathode catalyst which has excellent stability and durability of 67% more than commercial Pt/C.