近年來，可逆式鋅-空氣電池因為具有高能量密度和經濟性而備受關注。在空氣電極端，需要雙功能觸媒於同一電極上進行充電(氧氣析出反應)和放電(氧氣還原反應)。常用的氧還原之觸媒 Pt/C和氧析出之觸媒 IrO2皆不具有雙功能特性且有成本及豐度問題，造成實際應用上的瓶頸。

本研究以鎳鐵層狀氫氧化物修飾銀奈米線作為用於鹼性電解質下氧氣還原反應和氧氣析出反應的雙功能觸媒。首先，以多元醇還原法合成奈米銀線，透過改變轉速和前驅物滴入速率來優化銀奈米線的線寬與形狀。接著利用水熱法將鎳鐵層狀氫氧化物成長在奈米銀線表面，並進行特性鑑定及電化學效能檢測。從表面形貌分析上得知銀奈米線線徑隨攪拌速度加快和前驅物的滴入速度增加而減少。紅外光譜分析結果可以發現銀線上仍有PVP的殘留以及Ni3Fe LDH層間的陰離子為CO32-和NO3-。XPS及XAS的結果說明銀奈米線對Ni3Fe LDH上Fe離子的影響較顯著，包含電子結構變化(正能量偏移)與Fe位置局域結構的變化(Fe-O和Fe-M鍵長縮短)。在氧氣析出反應的表現上，S-Ni3Fe LDH/Ag NWs-F(2:1)-10mL在1.53 VRHE的質量活性達432 mA mg-1LDH，明顯優於Ni3Fe LDH (121 mA mg-1LDH)和IrO2 (149 mA mg-1catalyst)，原因推測為攪拌後的Ni3Fe LDH活性位置數目大量增加，進而提升單位觸媒重量上的氧氣析出反應效能。但在氧氣還原反應的表現上，S-Ni3Fe LDH/Ag NWs-F(2:1)-10mL相較於純銀奈米線和商業化觸媒Pt/C，其催化能力不佳的原因推測與奈米銀線表面殘留PVP和鎳鐵層狀氫氧化物疊層太厚有關，阻礙氧氣擴散到觸媒表面。經過 24 小時氧氣析出反應的穩定性測試，結果顯示S-Ni3Fe LDH/Ag NWs-F(2:1)-10mL的電流保持率為92.6%，相較於純Ni3Fe LDH (76.3%)和商業化觸媒IrO2¬ (91.6%)，更適合作為氧氣析出反應觸媒。

Recently years, the rechargeable zinc-air batteries have its attracted much attention owing to high energy density and economic viability. In air electrode, a bifunctional electrocatalyst is desirable since the dual functionality of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are required on the same electrode under charging and discharging processes, respectively. Unfortunately, both commonly used catalysts: Pt/C in ORR and IrO2 in OER have no bifunctional property while the scarcity and cost of the metals limit its large-scale application for the electrolysis.

In this work, the NiFe layered double hydroxides (Ni3Fe LDH) decorated with Ag nanowires (Ag NWs), as a bifunctional catalyst, was applied in oxygen reduction reaction and oxygen evolution reaction under alkaline media. First, the Ag nanowires were prepared via a polyol reduction method, and to optimize their linewidth and shape by changing the stirring rate and the precursor dropping rate. The Ni3Fe LDH was then deposited on the Ag nanowires by a hydrothermal process. As the results in surface morphology, the linewidth of Ag NWs was shortened with increasing stirring rate and precursor dropping rate. In FTIR analysis, a few residual PVP was still observed on Ag NWs while the intercalation anions of CO32- and NO3- were identified. As characterized in XPS and XAS, it was found that Fe sites in decorated Ni3Fe LDH were strongly influenced by Ag NWs, including the electronic effect (binding energy positively shifts) and the local structure environment (shorter Fe-O and Fe-M bond length). In OER performance, a mass activity of 432 mA mg-1LDH was reached by S-Ni3Fe LDH/Ag NWs-F(2:1)-10mL, much better than Ni3Fe LDH (121 mA mg-1LDH) and IrO2 (149 mA mg-1catalyst), attributed to a large number of accessible active sites on the catalytic surface. However, the ORR activities of the Ni3Fe LDH/Ag NWs catalysts showed no advantage compared to as-synthesized Ag NWs and commercial Pt/C catalyst, which may be attributed to a few residual of PVP and too thick of LDH layer on Ag surface thereby inhibit O2 diffusion. In OER stability test, a chronoamperometric method was used for 24 hours, S-Ni3Fe LDH/Ag NWs-F(2:1)-10mL showed current retention by 92.6%, better than Ni3Fe LDH (76.3%) and IrO2 (91.6%), more suitable as an OER catalyst.

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