以定電位法在鋅箔上自鹼性含鋅離子溶液中製備氧化鋅奈米結構

Fabrication of Nano-structured Zinc Oxides on Zinc Foils in Alkaline Zinc Containing Solutions by a Potentiostatic Process

本研究之目的在含有鋅離子的鹼性溶液中，使用電化學氧化法於鋅箔上製備氧化鋅奈米結構。首先使用拋光後的鋅箔（10 mm×10 mm，t = 0.62 mm），在未添加以及添加0.25 M的Zn(NO3)2和0.25 M的NaNO3之NaOH （2 M）鹼性溶液中，以三極式恆電位儀進行動態極化曲線掃瞄，掃描速率為1 mV/s。由開路電位（即OCP = -0.25 V）下250 mV為起點，開始向高電位掃描至2.0 V （vs. SHE）。由動態極化實驗結果，選擇四個不同操作電位（-0.5 V、-0.7 V、-0.9 V、-1.1 V）進行定電位陽極氧化反應。此實驗以鋅箔為工作電極，304不銹鋼為相對電極，Ag/AgClsat為參考電極，在含0.25 M Zn（NO3）2的2 M NaOH鹼性溶液中進行一小時，分別量測其對應的電流，並以FE-SEM觀察其表面結構之形貌。由FE-SEM照片顯示，在-0.5 V和-0.7 V的反應電位下，鋅箔上會生成氧化鋅奈米線之結構；然而，在-0.9 V和-1.1 V電位下則獲得片狀的氧化鋅奈米結構。由EDX分析可知上述兩種結構，其氧和鋅的比例都接近1：1。以XPS分析奈米結構之化學組成，結果得知皆為為氧化鋅（Zn-O）鍵結（1021.9 eV）。並由反應方程式推導氧化鋅奈米結構形成的機制示意圖。

This work attempts to fabricate nano-structured zinc oxides on zinc foils in alkaline solutions containing zinc ions by electrochemical oxidation. After grinding and polishing, the zinc foil was potentiodynamically polarized in alkaline solutions (i.e. 2 M NaOH) with and without 0.25 M Zn(NO3)2 and 0.25 M NaNO3. The polarization process was carried out using a potentiostat with sweeping potentials starting from 0.250 V below the open circuit potentials towards 2.000 V (vs. SHE) with a scan rate of 1 mV/s. Based on the polarization diagram, we chose four characteristic potentials (i.e., -0.5 V, -0.7 V, -0.9 V, and -1.1 V vs. SHE) at which potentiostatic polarizations were conducted on polished zinc plates (as the working electrodes) with respect to a counter electrode of 304 stainless steel and an Ag/AgClsat reference electrode. The potentiostatic experiments were carried out in 2 M NaOH solutions with 0.25 M Zn(NO3)2 for 1 hour and corresponding currents were measured. According to examinations via FE-SEM, we found that nano-wires of zinc oxide were produced at higher potentials (e.g., -0.5 V and -0.7 V) but nanoplates of zinc oxide formed at lower potentials (e.g., -0.9 V and -1.1 V). EDX analyses over the nano wires and the nano plates indicated an atomic ratio of Zn to O at almost one. In addition, the presence of Zn(2p3/2) at 1021.9 eV was confirmed by XPS, which ensured the oxide form of the nanostructures.