Nucleation and Growth of Porous MnO2 Coatings Prepared on Nickel Foam and Evaluation of Their Electrochemical Performance

Abstract

Porous MnO2 was uniformly electrodeposited on nickel foam in MnSO4 solution, which was applied as the electrode of supercapacitors. The nucleation/growth mechanisms of porous MnO2 were investigated firstly. Then two kinds of electrochemical measuring technologies, corresponding to the cycle voltammetry (CV) and galvanostatic charge-discharge, were adopted to assess the electrochemical performance of MnO2 electrodes. The results demonstrated that the deposition of MnO2 on nickel foam included four stages. Prior to the deposition, an extremely short incubation period of about 2 s was observed (the first stage). Then the exposed nickel foam was instantly covered by a large number of MnO2 crystal nuclei and crystal nuclei connected with each other in a very short time of about 3 s (the second stage). Nucleation predominated in the second stage. The sharply rise of current was caused by the increase in substrate surface area which due to nucleation of MnO2. Grain boundaries grew preferentially due to their high energy, accompanied with a honeycomb-like structure with the higher surface area was formed. However, accompanied with the electrochemical reactions gradually diffusion-controlled, the current presented the decline trend with increasing the time (the third stage). When the electrochemical reactions were completely diffusion-controlled, the porous MnO2 coating with an approximately constant surface area was formed (the fourth stage). MnO2 coatings deposited for different time (30, 60, 120, 300 s) exhibited a similar specific capacitance (CV: about 224 F/g; galvanostatic charge-discharge: about 264 F/g). Comparatively speaking, the value of MnO2 deposited for 600 s was highest (CV: 270 F/g; galvanostatic charge-discharge: 400 F/g).

Manganese Carbonate (Mn2(CO3)3) as an Efficient, Stable Heterogeneous Electrocatalyst for the Oxygen Evolution Reaction

“…These peaks can be attributed to Ni foam oxidation and reduction. The second redox peak appeared at 0.87 and 0.68 V vs Ag/AgCl, which relate to the oxidation of Mn 2+ to Mn 3+ and reduction of Mn 3+ to Mn 2+ . From the data obtained from CV, the constant potential at 1.1 V for electrodeposition of MnCO 3 was selected.…”

“…The second redox peak appeared at 0.87 and 0.68 V vs Ag/AgCl, which relate to the oxidation of Mn 2+ to Mn 3+ and reduction of Mn 3+ to Mn 2+ . 43 From the data obtained from CV, the constant potential at 1.1 V for electrodeposition of MnCO 3 was selected. The potential of 1.1 V was selected because at a higher anodic potential, the Ni foam starts precipitating out and mixing with the electrolyte.…”

Preparation of Manganese Oxide Nanoparticles with Enhanced Capacitive Properties Utilizing Gel Formation Method

“…The development of potential power sources to compete with ever-increasing energy demands is a significant worldwide issue . With the growth of the market for portable electronic devices and hybrid electric vehicles, the need for energy storage devices is increasing. , Batteries, fuel cells, and supercapacitors are the most efficient and effective electrochemical energy conversion and storage technologies. − Due to various advantages, including environment-friendly, high power density, low cost, and so on, supercapacitors have attracted massive attention in recent research activities in the energy sector. − However, supercapacitors have a lower energy density than batteries, and hence increasing their energy density to that of batteries is desirable. , While the performances of supercapacitors are mainly determined by the electrode material rather than the construction mechanism, it is important to develop the most effective electrode materials from available sources using facile routes. , …”

“…Reports have been found on the capacitive properties of MnO 2 prepared by different methods. For instance, Huang et al found a capacitive value of 400 F g –1 for MnO 2 synthesized by an electrochemical deposition technique, Xi et al found a value of 200 F g –1 , Wan et al synthesized MnO 2 by chemical precipitation method and obtained a capacitive value of 200 F g –1 , Ali et al developed a powdered nanoflower morphology of MnO 2 by electrowinning and obtained the capacitive value of 294 F g –1 , and Goikolea et al used polyol method to prepare MnO 2 and found capacitance equal to 130 F g –1 . All of the reported values are in the moderate range and still, there is an excellent opportunity to work with enhancing the capacitive performance of MnO 2 (1370 F g –1 ) .…”

“…Because of their high theoretical specific capacitance, nanostructured metal oxides of transition metals have been identified as viable electrode materials for supercapacitors recently. ,− , Various metal oxides of transition metals, including oxides of manganese, ,,, nickel, iron, and titanium, have been reported for their potentiality as supercapacitor electrode materials. Even though ruthenium oxide has very high specific capacitance (720 F g –1 ) and still performs electrochemically better as an electrode material, the high cost and toxicity of hydrous ruthenium oxide have limited its usage. , As a result, considerable efforts have been put into exploring possible low-cost and available electrode materials with good capacitive properties.…”