Fabrication Based On Self-corrosion Principle Of Transition Metal(Fe,Ni) Compounds Micro/Nanotube Array Electrodes And Their Electrochemical Properties

With the rapid development of economy, the energy and environment problems become increasingly serious. Thus, the development of electrochemical power sources has attracted more and more attention. Transition metal compounds with the advantages of good electrochemical properties, abundant resources and environmental friendly nature have become one of the most promising electrochemical energy materials. However, the low conductivity and poor structural stability of the transition metal compounds have limited their further commercial application. Herein, in order to overcome these drawbacks, transition metal compounds micro/nanotube arrays are fabricated by a facile strategy based on self-corrosion principle, and their structures and electrochemical properties are characterized in detail.Based on the facile self-corrosion method, FeC2O4·2H2O nanotube arrays had been fabricated via the corrosion reaction between Fe film and oxalate acid. The effects of the oxalate acid concentration and water content in the oxalate acid ethanol solution on the morphology of corrosion products had been studied. Besides, the mechanism of tube formation had been investigated. The size of the FeC2O4·2H2O nanotubes increased with the increase of oxalate acid concentration, and the morphology changed from nanowires to microtubes with the increase of water content. The formation process of the FeC24·2H2O nanotubes was a dissolution-recrystallization induced ripening process. The interior part of the nanopillars dissolved from top to bottom, resulting in the formation of nanotubes.The anhydrous FeC2O4 nanotube array electrodes were obtained through heat treatment of the FeC2O4·2H2O nanotube array electrodes. During the heat treatment, the release of H2O and carbonization of oxalate resulted in the formation of porous dehydration product with small amount of carbon. The FeC2O4 nanotube array electrodes had shown superior lithium storage properties. At the current density of 0.76 A g-1, the electrode delivered a capacity of 1267 mAh g-1 after 200 cycles. Besides, after 200 cycles at the current density of 1.89,3.78,7.56 and 18.9 A g-1, the electrode showed capacities of 1009,988,859 and 629 mAh g-1, respectively.The FeOx nanotube array electrodes were obtained through heat treatment of the FeC2O4·2H2O nanotube array electrodes in H2 atmosphere. During the heat treatment, the release of H2O, CO or CO2 and carbonization of oxalate resulted in the formation of porous product with small amount of carbon. The FeOx nanotube array electrodes showed good lithium storage properties. At the current density of 4 A g-1, the electrode delivered a capacity of 880 mAh g-1 after 500 cycles. At current density of 0.6,1.2,3,6 and 8 A g-1, the electrode showed reversible capacities of 930,880,775,665 and 610 mAh g-1, respectively.Based on the facile self-corrosion method, NiC2O4·2H2O microtube arrays had been fabricated via the corrosion reaction between Ni film and oxalate acid. The tube formation mechanism had been investigated. The formation of NiC2O4·2H2O microtube was similar to the formation of FeC2O4·2H2O nanotubes. Core/shell MnO2@NiO microtube array electrodes were fabricated via the annealing of NoC2O4·2H2O microtube array electrodes and subsequent anodic electrodeposition of MnO2-Core/shell MnO2@NiO microtube array electrodes had shown good lithium storage properties. The capacity could reach 1573 mAh g-1 after 500 cycles at current density of 0.53 A g-1. The rise of the capacity and the high capacity much higher than the theoretical capacity resulted from the pseudo-capacitance-type behavior of polymer/gel film. MnO2 shell was very important to the enhancement of the electrochemical properties. The coated MnO2 could not only serve as active materials but also work as shell to protect the NiO core from deforming during cycling.Ni(OH)2/NiO/Ni microtube array electrodes were obtained via the reduction and subsequent electrochemical activation of the NiC2O4·2H2O microtube array electrodes. These electrodes showed good pseudocapacitive properties. At current density of 18.9 A g-1, the electrode delivered a capacitance of 1460 F g-1 after 15000 cycles. At current density of 5.3,10.5,15.8,26.3,52.6,105.3 and 157.9 A g-1, the electrode showed reversible capacities of 1541.1,1511.6,1494.7,1431.6,1228.1,1005.8 and 631.6 F g-1, respectively.Based on the facile self-corrosion method, mixed Ni-Fe oxalate nanotube arrays had been fabricated via the corrosion reaction between Ni-Fe alloy film and oxalate acid. The mixed Ni-Fe oxalate nanotube array electrodes showed good oxygen evolution performance because of their unique structural characteristics. In 0.1 and 1 M KOH electrolyte solutions, the electrodes showed oxygen evolution onset voltages of 1.50 and 1.48 V(vs. RHE), respectively. And the corresponding Tafel slopes were 43.3 and 35.3 mV dec-1, respectively. The electrodes also exbibited good oxygen evolution stability even at a larger current density of 20 mA cm-2.