碳載體鉑鋨合金奈米顆粒觸媒應用於酸性燃料電池之氧氣還原反應

Abstract

本研究使用濕式回流化學合成法合成出附著在奈米碳球基材的Pt2Os 鉑鋨合金奈米顆粒觸媒，顆粒直徑為3.1 nm。之後沉積於旋轉電極上並在50 毫升，0.1 M 除氧的過氯酸水溶液中做電化學多圈循環掃描去合金處理，將表面的Os原子選擇性的移除，使更多的Pt原子裸露出來，形成表面Pt居多的顆粒觸媒。經過去合金處理的DA－Pt2Os合金觸媒，經X光繞射儀分析得知為Pt基的FCC單相合金，且經掃描穿透式電子顯微鏡元素分析結果顯現出經過去合金處理後，合金的元素組成為Pt4Os。 經過去合金處理的DA－Pt2Os/C觸媒具有很好的電化學活性，在氧氣飽合的0.1 M過氯酸水溶液中進行催化氧氣還原反應的測試，質量比活性值為0.29 mA μgPt-1`，比表面積活性值為1.03 mA cmPt-2，活性皆優於商用Pt/C觸媒的活性(0.17 mA μgPt-1，0.31 mA cmPt-2)。除此之外，經Koutecky-Levich plots的斜率計算，推算出氧氣是經由直接四電子的還原路徑被還原為水。另外在觸媒穩定性的測試中，將DA－Pt2Os/C觸媒置於0.1 M的過氯酸水溶液中進行10,000圈的電化學循環掃描加速觸媒的劣化，經測試後再以相同條件量測催化活性，假設電極上Pt乘載量並無改變的情形下，其電化學活性表面積下降了10.9 %，質量活性下降了11.1 %，結果還是優於Pt/C商用觸媒的14.7 %與24.6 %，可以見得此方法製備出的DA－Pt2Os/C鉑鋨合金觸媒在氧氣催化活性和觸媒耐久度方面，都有優於商用觸媒的表現。

Carbon-supported Pt2Os (Pt2Os/C) nanoparticles in 3.1 nm size are synthesized from a wet chemical reflux process. Subsequently, the Pt2Os/C undergoes a dealloying treatment in which multiple cyclic voltammetric scans are imposed in a 50 mL of deaerated 0.1 M aqueous HClO4 solution to dissolve the Os atoms selectively from the surface of the Pt2Os nanoparticles. X-ray diffraction signals from the dealloyed sample (DA－Pt2Os/C) indicate a fcc phase and composition analysis suggests Pt4Os. Line scans from the scanning transmission electron microscope confirm that the surface of Pt4Os is depleted with the Os atoms. The DA－Pt2Os/C shows impressive electrocatalytic behaviors (0.29 mA μgPt-1 in mass activity and 1.03 mA cmPt-2 in specific activity) for oxygen reduction reaction (ORR) in oxygen-saturated 0.1 M aqueous HClO4 solution, as compared to those of commercially available Pt/C and as-synthesized Pt2Os. In stability test, the DA－Pt2Os/C demonstrates better retention in ORR activities and smaller loss of electrochemical active surface area. In addition, a four-electron step is responsible for the ORR actions occurring on the DA－Pt2Os/C.