影響電化學製備二氧化錳生成結構的要素

Factors Influencing the Structure of Electrochemically Prepared MnO2

黃裕超(Yu Chao Huang)

指導教授 ： 唐宏怡

國立暨南國際大學/科技學院/應用化學系/碩士(2007年)

https://doi.org/10.6837/NCNU.2007.00131

摘要

近年來具有一維通道結構的二氧化錳被廣泛的研究，因為其應用價值相當高，可以作為分子篩、燃料電池中的催化劑、也可作為鋰離子電池的陰極材料；不同的結構相有不同的應用領域。而中心孔洞的大小可以藉由不同的合成方式來控制生成。本研究為利用電化學方法來取代傳統水熱法，在室溫中合成具有2×2結構相的二氧化錳，並且探討在製程中影響中心孔洞大小的因素。研究中發現兩項常壓下會影響一維結構的主要因素，分別為電解液中陽離子半徑的大小以及[MnO4-] / [Mn+2]的比值。為了要在中性水溶液中生成α-MnO2中心陽離子大小必須大於1.41 Å，而在酸性條件下一維結構的大小除了離子尺寸影響外也與[MnO4-] / [Mn+2]的濃度比值大小有關。而在酸性溶液中，以H+、Li+、Na+做為中心陽離子且電解電壓定為2.2V時所合成的二氧化錳為γ-MnO2，當電解電壓提高為2.8V時所生成的二氧化錳為α與γ的混合相，當電壓提高到大於5V的時候所生成的二氧化錳為α相。化學滴定說明，錳離子的平均價態隨著電壓高低而增減，表示隨著電壓的改變電解液中[MnO4-] / [Mn+2]的值也跟著改變，最後得到含氧缺陷的非計量二氧化錳。

關鍵字

α-MnO2、一維、電化學合成、鹼性電池

並列摘要

The α- and γ-phases of MnO2 prepared by an electrochemical method under ambient conditions have been systematically studied. The structures of MnO2, formed under different pH and electrochemical potential (pH-Ev) conditions, are found to depend on the radius of counter cation and the [MnO4-] / [Mn+2] concentration ratio. In order to achieve the α phase for MnO2 formation under neutral pH condition, the radius of counter cation must be equal to or greater than 1.41 Å, the size of the K+ cation. The [MnO4-] / [Mn+2] concentration ratio, which is related to the pH-Ev conditions, also affects the structure of MnO2 produced. For samples prepared under acidic condition with the counter ions of H+, Li+, or Na+ at 2.2 V, the structure of electrolysis products display the γ-MnO2 phase while those prepared at 2.8 V electrolysis produce a mixture of γ-MnO2 and α-MnO2 phases. Furthermore, the valence state of manganese was found to decrease as the applied potential was reduced from 5.0 volts to 2.2 volts. This implies that the lower [MnO4-] / [Mn+2] ratio or the less oxidative condition is responsible for the non-stoichiometric MnO2 structure with oxygen deficiency.

並列關鍵字

α-MnO2、one-dimension、electrosynthesis、alkaline battery

參考文獻

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