利用電化學石英晶體微天平探討錳鐵氧化物超高電容器之反應機制

Abstract

利用氧化定電位沉積法可以將硫酸錳與硫酸鐵所組成特定比例的先驅溶液，成功於基材上電鍍製備錳鐵氧化物。並且經由X光繞射分析與化學元素分析可發現，錳鐵氧膜在經過鍛燒後會呈現結晶的97.4% MnFe2O4與2.6% Fe3O4之共沉積材料。此外，在低溫下鍛燒的錳鐵氧膜電極所呈現的電流曲線較接近偽電容的性質。 另外，噴鍍製備的錳鐵氧化物在包含LiCl、NaCl、KCl、CaCl2以及Na2SO4等多種鹽類水溶液中的偽電容儲電反應也被更深入的研究。藉由電化學石英晶體微天平(EQCM)與X光光電子光譜(XPS)分析結果發現，在尖晶石結構四面體位置上的錳離子之還原/氧化反應，主要是由各種鹽類溶液中的陽離子於錳鐵氧材料內部嵌入/遷出程序，而達成反應平衡。當在NaCl、LiCl與CaCl2電解液中，相對是由H3O+、Li+ 與Ca+2在錳鐵氧內部嵌入/遷出所造成偽電容現象；此外，在KCl溶液中，主要是由K+化學吸附於錳鐵氧表面並伴隨著H3O+在內部的嵌入/遷出程序以達成偽電容機制。

Electrodeposition of MnFe2O4 film was succesfully prepared by using anodic electroplating method from optimized precusors composed of MnSO4 and FeSO4 solutions. After calcination of as-deposited film, from EDX and XRD analysis, film composition was attributed to 97.4% amount of MnFe2O4 and 2.6% amount of Fe3O4, as a co-deposited MnFe2O4 film electrode. In addition, film electrodes annealed at low temperature showed more likely current profiles for supercapacitors in NaCl(aq). Furthermore, pseudocapacitive charge-storage reaction of MnFe2O4 in several aqueous alkali salts, alkaline salts and sulfate solutions, including LiCl, NaCl, KCl, CaCl2 and Na2SO4, has been studied on sprayed MnFe2O4 thin-films. Electrochemical quartz-crystal microbalance and X-ray photoelectron spectroscopy data further indicated that, the predominant reduction/oxidation of the Mn ions at the tetrahedral sites of the spinel was mainly balanced by insertion/extraction of the solution cations, H3O+, Li+ and Ca+2 into/from the ferrite structure while in NaCl, LiCl and CaCl2 electrolytes respectively, or balanced by some extent of chemisorption of K+ on ferrite surface along with insertion/extraction of H3O+ into the bulk materials in KCl solution.