本研究旨在尋求一個合理的分析方法,以進行不同Pt觸媒對氧氣還原的電催化反應活性比較。以旋轉圓盤電極(RDE)與旋轉環盤電極(RRDE)分析發現,反應電流量測值除了受到電極轉數影響的液相質傳效應影響之外,還需考慮薄膜電極內部質傳效應的影響;扣除這些質傳效應後,分析發現Pt顆粒大小,在擔體上的分佈狀態以及Pt/C製備方法等因素,都不會影響Pt催化ORR的反應特性。 為了探討白金觸媒電催化氧氣還原反應的影響因素,本研究比較(1)相同觸媒但在電極上使用量不同,以建立ORR反應特性的分析方法,(2) Pt sol與Pt black兩種無擔體觸媒的反應特性,以比較顆粒大小的影響,(3)使用具有不同Pt顆粒分佈密度的Pt/C觸媒,以討論顆粒分佈密度對ORR活性的影響,(4) 利用Pt sol /C、商用Pt/C、沈澱法10%Pt/C及沈澱法10%Pt/WO3-C,討論觸媒製備程序對ORR活性的影響,(5)利用RRDE探討中間產物H2O2的生成。實驗結果發現上述因素對氧氣還原反應特性與活性影響皆不明顯,造成觸媒反應活性顯著差異的主要因素,可能為觸媒厚度造成的內部質傳效應;不受質傳效應影響的Pt催化ORR反應行為可以用實驗數據所整理的” E= -0.1×log (j) +0.64”方程式描述,而H2O2的生成分析顯示,不同觸媒的H2O2生成選擇率都在3%以下。
In this study, RDE (ring-disk electrode) or RRDE (rotating ring-disk electrode) analyses are used to study the oxygen reduction reaction over film electrodes prepared form different Pt catalysts. The measured current (reaction rate) is affected by electrode rotation speed, which is related to external mass transfer. Furthermore, The measured current is found also affected by internal mass transfer effect which is related to the catalyst loading of film electrodes. When both mass transfer effects are corrected, the specific activity was formed almost identical for all the different Pt catalysts tested. The effect of different Pt loadings、Pt particle size and Pt/C preparation method on the ORR specific activity is negligible. In this study, we use Pt sol and Pt black to compare the effect of Pt particle size on ORR activity. The Pt/C prepared form Pt sol is compared to a commercial Pt/C(E-TEK) catalysts to examined the effect of Pt distribution on carbon support. RRDE analyses are used to calculate the H2O2 selectivity from the disk current (ID) and the ring current (IR). The H2O2 selectivity of all the different Pt catalysts tested is below 3%. This indicates that the intermediate H2O2 formation is relatively insignificant.
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