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Alkaline water electrolysis is regarded as a promising technology for sustainable energy conversion. Spinel oxides have attracted considerable attention as potential catalysts because of their diverse metal valence states. However, achieving the required current densities at low voltages is a challenge due to its limited active sites and suboptimal electron transport. In this study, we present a novel bifunctional catalyst composed of MnCo 2 O 4.5 nanoneedles grown on NiS nanosheets for water electrolysis. Remarkably, MnCo 2 O 4.5 @NiS demonstrates exceptional catalytic activity, requiring 187 and 288 mV to achieve a current density of 100 mA cm −2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. The impressive performance of MnCo 2 O 4.5 @NiS is demonstrated by the lower value of voltage 1.44 V needed to deliver the current density of 10 mA cm −2 , which outperformed the 1.66 V required for a commercial Pt/C||RuO 2 system. Detailed structure analysis and density functional theory (DFT) calculations reveal that the MnCo 2 O 4.5 @NiS heterostructure enhances electron transfer at the interface, promotes the formation of oxygen vacancies and tunes the electronic structures of Mn and Co. These findings underscore the potential of MnCo 2 O 4.5 @NiS as an efficient and cost-effective electrocatalyst for hydrogen production.
The oxygen evolution reaction kinetics in industrial zinc electrowinning is sluggish, resulting in low electrocatalytic activity and substantial energy expenditure (about one-third of energy was wasted due to the strong polarization effect). Herein, the paper described a core-shell structured MnCo 2 O 4.5 @C modified PbO 2 electrode through the pyrolysis and co-electrodeposition as a promising candidate for zinc electrowinning. As a result, the obtained Pb-0.2%Ag/ α -PbO 2 / β -PbO 2 -MnCo 2 O 4.5 @C composite electrode showed a sandwich-like structure, where Pb-0.2%Ag as a core, α -PbO 2 as a mid-layer, and β -PbO 2 -MnCo 2 O 4.5 @C served as an electrocatalytic layer. It also possessed improved OER catalytic activity , only required 680 mV to achieve a current density of 50 mA cm −2 and a Tafel slope of 216.04 mV dec −1 in an acidic solution containing 50 g L −1 Zn 2+ and 150 g L −1 H 2 SO 4 . The current efficiency increased by 0.7% and the cell voltage reduced by 360 mV as compared to a conventional Pb-0.76%Ag alloy electrode, leading to a remarkable energy-consumption reduction of 283.5 kW h for producing per ton metallic zinc. Furthermore, Pb-0.2%Ag/ α -PbO 2 / β -PbO 2 -MnCo 2 O 4.5 @C exhibited a prolonged service life, which worked about 44 h under an ultra-high current density of 2 A cm −2 . Hence, this paper provides the strategy to design and construct non-precious, high-performance catalyst for electrolysis and other applications.
In this article, a novel supercapacitor electrode of pistil-like MnCo2O4.5@PANI nanorods supported by nickel foam with enhanced specific capacitance and cycle performance is fabricated through a facile method. Benefiting from the excellent electrical conductivity of the shell material PANI and the short ion transport path and high specific surface area of the MnCo2O4.5 nanorods, the electrode made of MnCo2O4.5@PANI exhibits a large specific capacitance of 1098 F g−1 at a current density of 1 A g−1. In addition, the MnCo2O4.5@PANI electrode also displays a superior cycling stability with 83.2% capacitance retention after 5000 cycles at a high charge/discharge current density of 10 A g−1 and an excellent rate performance of 61.45% at 10 A g−1. These results demonstrate that the prepared MnCo2O4.5@PANI composite electrode material has a great potential for advanced energy conversion and storage equipment.
Methane is the second most prevalent greenhouse gas after carbon dioxide in global climate change, and catalytic oxidation technology is a very effective way to eliminate methane. However, the high reaction temperature of methane catalytic oxidation is an urgent problem that needs to be solved. In this work, a series of MnCo2O4.5catalysts were prepared using carbon spheres as templates, combined with metal ion adsorption and calcination processes. Excitingly, the catalytic oxidation activity of MnCo2O4.5spherical catalyst with irregular nanoparticles on the surface for lean methane (T90= 395 °C) is higher than that of pure phase Co3O4(T90= 538 °C) and Mo3O4(T90= 581 °C) spherical catalysts and even surpasses most precious metal catalysts. The main reasons are as follows: (1) The spherical core with irregular nanoparticle morphology significantly increases the specific surface area, creating abundant active sites; (2) through the optimized distribution of oxygen vacancies, rapid oxygen migration through this structure can quickly enter the catalytic zone; (3) the hierarchical wall structure expands the interface and provides spatial accommodation for the catalytic process. Meanwhile, the structure of the ball wall further expands the reaction interface, providing sufficient space for the occurrence of reactions. Rich and highly active oxygen vacancies are evenly distributed on the surface and inside of the ball. The extraordinary performance of low-temperature methane combustion catalysts has opened a promising new path, which is expected to inject strong impetus into the global energy transition and environmental protection.
Current applications of carbon-based supercapacitors are limited by their low energy density. One promising strategy to enhance the energy density is to couple metal oxides with carbon materials. In this study, a porous MnCo2O4.5 nanoneedle/carbon aerogel hybrid nanostructure was synthesized by assembling MnCo2O4.5 nanoneedle arrays on the surface of channel walls of hierarchical porous carbon aerogels derived from chitosan for the supercapacitor application. The synthetic process of the hybrid nanostructure involves two steps, i.e. the growth of Mn–Co precursors on carbon aerogel by a hydrothermal process and the conversion of the precursor into MnCo2O4.5 nanoneedles by calcination. The carbon aerogel exhibits a high electrical conductivity, high specific surface area and porous structure, ensuring high electrochemical performance of the hybrid nanostructure when coupled with the porous MnCo2O4.5 nanoneedles. The symmetric supercapacitor using the MnCo2O4.5 nanoneedle/carbon aerogel hybrid nanostructure as the active electrode material exhibits a high energy density of about 84.3 Wh kg−1 at a power density of 600 W kg−1. The voltage window is as high as 1.5 V in neutral aqueous electrolytes. Due to the unique nanostructure of the electrodes, the capacitance retention reaches 86% over 5000 cycles.
Herein, the MnCo 2 O 4.5 microflowers (MFs) assembled by two-dimensional (2D) porous nanosheets were prepared through an initial solvothermal reaction with a subsequent annealing process. In this architecture, many interconnected 2D thin nanosheets were self-assembled together to form a 3D hierarchical MF with plenty of open channels. Such structure endows these MnCo 2 O 4.5 MFs with large specific surface area of 156.85 m 2 /g for energy storage and provides rich ion diffusion pathways for ion transportation, thus the as-prepared MFs can exhibit good overall electrochemical performance in both hybrid supercapacitor (HSC) and lithium-ion battery (LIB). For the utilization in supercapacitor, the MFs deliver a specific capacity of 287.02 C/g at 1 A/g as well as a rate capability with 73.3 % capacity retention at 8 A/g. The energy density of the HSC assembled by MFs and activated carbon can reach up to 30.33 W h kg −1 at 959.35 W kg −1 . When applied as the anode for Li-ion battery, a specific capacity of 1340.8 mA h g −1 at 0.1 A/g and cycling performance with low capacity loss of 0.73 mAh/g per cycle after 200 cycles at 0.5 A/g can be achieved. This work uncovers a repeatable and facile synthetic strategy to prepare transition metal oxides with large specific surface area and good overall electrochemical property.
The MnCo 2 O 4.5 @MnO 2 composite nanomaterial was successfully designed and synthesized via successive hydrothermal and subsequent calcination methods, in which MnO 2 nanosheets coated on MnCo 2 O 4.5 nanoneedle arrays were directly grown on Ni foam. Compared with pristine MnCo 2 O 4.5 nanoneedle electrode, MnCo 2 O 4.5 @MnO 2 composite electrode exhibits a high specific discharge capacitance of 1155 F g -1 at a current density of 1.43 A g -1 , the capacitance retention of 93.4% after 5000 cycles, and low initial internal resistance of 1.9 Ω. The results reveal that the rational design of MnCo 2 O 4.5 @MnO 2 electrode with such structure and composition is an effective strategy to improve electrochemical performances of MnCo 2 O 4.5 . Due to unique nanostructure and brilliant electrochemical properties of MnCo 2 O 4.5 @MnO 2 electrode, the fabricated hybrid supercapacitor based on MnCo 2 O 4.5 @MnO 2 positive electrode and activated carbon negative electrode delivers the wide operating voltage window of 1.6 V, a capacitance retention of 87.8% after 8000 continuous charge-discharge cycles at a current density of 1.33 A g -1 , the maximum energy density of 40.8 Wh kg -1 at a power density of 263.9 W kg -1 , and highest power density of 1336.6 W kg -1 to achieve an energy density of 24.4 Wh kg -1 . Herein, the designed MnCo 2 O 4.5 @MnO 2 composite is a distinguished candidate material for hybrid supercapacitor.
Graphical Clean up, clean up : A new heterostructured photocatalyst, MnCo 2 O 4.5 deposited TiO 2 nanotube arrays, was synthesized via a two-step anodization and chemical bath deposition method. The catalyst exhibited enhanced photocatalytic activity in the degradation of tetracycline under visible light irradiation compared with pure TiO 2 nanotube arrays. A novel type of heterostructured photocatalyst, MnCo 2 O 4.5 deposited TiO 2 nanotube arrays (TNAs), was successfully synthesized via a two-step anodization and chemical bath deposition method. The decoration of MnCo 2 O 4.5 nanoparticles on anatase TNAs significantly enhances its photocatalytic degradation activity of tetracycline (TC). The optimized 140MnCo 2 O 4.5 /TiO 2 nanotube arrays (140 M/TNA) catalyst exhibited the highest photocatalytic degradation of TC with an efficiency of 93.1 % after 2 h illumination. Meanwhile, the material showed good stability after a 5 cycle test. The mechanism of increased activity is attributed to the MnCo 2 O 4.5 /TiO 2 heterostructure, which extends the response range to visible light and promotes electron–hole separation. Further radical capture experiment reveals that . O 2 − is vital as an active species for degrading TC in this system. The photocatalyst obtained via this rational synthesis strategy can effectively remove organic pollutants from waste water under visible light irradiation.
Rational construction of core@shell heterostructured photocatalysts is the key to realize efficient hydrogen production from water splitting attributing to the accelerated photoinduced charges separation/transfer and enhanced light absorption ability. In this work, two-dimensional (2D) ZnIn 2 S 4 (ZIS) nanosheets were in-situ grown on phosphorus doped MnCo 2 O 4.5 (P-MnCo 2 O 4.5 ) nanospheres to construct P-MnCo 2 O 4.5 @ZIS heterostructured photocatalysts for efficient photocatalytic hydrogen production. The optimized 6 wt% P-MnCo 2 O 4.5 @ZIS composite presents remarkable photocatalytic hydrogen evolution rate of 4197 µmol g −1 h −1 (8 times of single ZIS) along with excellent cycling stability, which is comparable to most previous reported ZnIn 2 S 4 -based or even noble-metal involved catalysts. The improved photocatalytic performance is resulted from the distinguished heterostructure and components of P-MnCo 2 O 4.5 @ZIS, in which the close contact interface facilitates the separation/transfer and inhibits the recombination of charges, and the uniform distribution of ZIS nanosheets on P-MnCo 2 O 4.5 increases the active sites and fortifies the light absorption. The present work comes up with a prospective method for establishing core@shell ZIS-based heterostructured photocatalysts for efficient hydrogen generation.
The Na–O2 battery system is attracting increasing attention due to its superiority in specific capacity and cost. However, its practical implementation is hindered by many issues, such as high charge–discharge overpotential, limited cycling life, and poor reversibility, all of which result from the mediocre O2 electrode. Herein, to surmount these critical challenges, hierarchical Co3O4@MnCo2O4.5 nanocubes (h-Co3O4@MnCo2O4.5 Ns) with a yolk–shell structure are designed for the first time as the novel O2 electrode. h-Co3O4@MnCo2O4.5 Ns are synthesized from a metal–organic framework via a template-assisted method, which is demonstrated to be helpful in creating a high specific surface area of 130.4 m2 g−1, a hierarchical macro- and mesoporous structure, and synergistic yolk-shelled Co3O4@MnCo2O4.5 active sites. These unique structural properties endow h-Co3O4@MnCo2O4.5 Ns with remarkably enhanced electrocatalytic activity towards both the ORR and OER. The Na–O2 battery based on h-Co3O4@MnCo2O4.5 Ns displays an ultrahigh initial discharge capacity of 8400 mA h g−1, ultralow charge–discharge overpotential of 0.45 V, long cycling life of 135 cycles, and excellent rate capability.
Surface chemistry and bulk structure jointly play crucial roles in achieving high-performance supercapacitors. Here, the synergistic effect of surface chemistry properties (vacancy and phosphorization) and structure-derived properties (hollow hydrangea-like structure) on energy storage is explored by the surface treatment and architecture design of the nanostructures. The theoretical calculations and experiments prove that surface chemistry modulation is capable of improving electronic conductivity and electrolyte wettability. The structural engineering of both hollow and nanosheets produces a high specific surface area and an abundant pore structure, which is favorable in exposing more active sites and shortens the ion diffusion distance. Benefiting from its admirable physicochemical properties, the surface phosphorylated MnCo2O4.5hollow hydrangea-like structure (P-MnCoO) delivers a high capacitance of 425 F g−1at 1 A g−1, a superior capability rate of 63.9%, capacitance retention at 10 A g−1, and extremely long cyclic stability (91.1% after 10,000 cycles). The fabricated P-MnCoO/AC asymmetric supercapacitor achieved superior energy and power density. This work opens a new avenue to further improve the electrochemical performance of metal oxides for supercapacitors.
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