Microwave‐Assisted Synthesis of NiMn₂O₄ Grown on Nickel Foam as Electrode Material for High‐Performance Supercapacitors

Abstract

The spinel NiMn 2 O 4 has been directly grown on 3D nickel foam by combining a simple microwave-assisted hydrothermal with annealing process at different temperatures (350°C to 650°C), which can be used as a binder-free electrode for high-performance supercapacitors. The results indicate that the pure NiMn 2 O 4 can be obtained below 550°C. The as-prepared NiMn 2 O 4 at 450°C has the largest specific capacitance of 802 F g À 1 at 1 A g À 1 and excellent cycle stability (61 % capacity retention after 5000 cycles at 10 A g À 1 ) among all the obtained samples. This outstanding electrochemical performance may be attributed to its relatively large grain size, high specific surface area, and appropriate pore structure. This indicates that NiMn 2 O 4 grown on nickel foam shows great potential as an electrode material for supercapacitors.

Nanostructured Spinel Manganates and Their Composites for Electrochemical Energy Conversion and Storage

“…[66] Ultrasound and microwaves are both non-ionizing electromagnetic radiations that have greater penetration depth and a low thermal gradient, making them ideal for achieving enhanced nucleation rates (less reaction time) and forming high-purity AMO NCs. [48][49][50] Electro-deposition, on the other hand, involves the electrochemical growth of AMO NCs directly on substrates without using binders, which allows for control of the thickness and conformal growth. Although the ultrasound, microwaves, and electrodeposition methods are beneficially reported for the AMO NCs synthesis, there are still some limitations.…”

“…Figure 1 summarizes the methods of synthesizing AMO NCs. Various methods and strategies have been employed to synthesize AMO NCs and regulate their structural and morphological features, the most popular of which are solid-state, [23,[35][36][37] sol-gel, [38][39][40] co-precipitation, [41][42][43] hydro/solvothermal, [44][45][46][47] ultrasound/microwave, [48][49][50] and electro-deposition [51][52][53] techniques. In addition, solution combustion, [54] ion exchange, [55] reflux, [56] and microemulsion methods [57] have also been recently studied.…”

“…[ 92 ] The specific capacitance was found to be influenced by the particle size and morphology, where the nanosheets of NiMn 2 O 4 displayed a higher specific capacitance of 802 F g −1 at 1 A g −1 compared to the micro‐ and nanostructured particles. [ 49 ] Similarly, ultrathin CoMn 2 O 4 nanosheets provided a highly stable specific capacitance of 1529 F g −1 at 2 A g −1 , with almost 100% capacity retention even after 3000 cycles (Figure 4d,e), attributed to the larger surface area and high porosity of the nanosheet arrays. [ 45 ] Interestingly, Xu et al.…”

“…Nanostructured AMO Among metal oxide-based electrode materials, spinel manganates have blossomed in energy storage research due to their mixed-metal valence states, plentiful redox couples, and ultrahigh theoretical capacitance (>2000 F g −1 ). [49,89] Notably, the multiple oxidation states of Mn (B-site) combined with other 3d transition metals with higher oxidation potential (A-site) can provide high specific capacitance, energy density, and a long cycle life. [29] Besides, the active materials are required to have a suitable pore size and large specific surface area, which can be regulated by tuning the morphology.…”

Supercapacitor Electrodes: Is Nickel Foam the Right Substrate for Active Materials?

“…Ni foam is a popular porous substrate praised for its conductivity, high specific surface area, and low cost. It is often used when investigating active materials for supercapacitor applications, mainly as a substrate for metal oxides as anodes [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ]. In this work, Ni foam was used as a substrate for NiMn 2 O 4 and Ni-Mg ferrites to investigate their energy storage properties.…”