本研究使用原子層沉積(Atomic layer deposition, ALD)製程,以 (methylcyclopentadienyl) trimethylplatinu (MeCpPtMe3)與氧氣(O2)為前驅物,製備奈米鉑觸媒金屬(ALD-Pt),並且結合氫氣熱還原處理程序,探討其電化學活性在甲酸及甲醇溶液中的影響。 由於鉑觸媒在甲酸及甲醇溶液中進行電化學反應時,會產生一氧化碳(CO)副產物,然而CO對於鉑觸媒有很強的吸附力,導致佔據觸媒的活性位置使觸媒失去催化能力,稱之為毒化作用。使用ALD製程製備出的鉑觸媒表面會包覆一層氧吸附層(Pt−Oads),以PtO與PtO2的形式存在,有助於甲酸及甲醇氧化反應所產生的CO吸附層進行脫附反應,釋出活性位置,提升觸媒的抗毒化能力。於是,本實驗使用150、300及450°C進行通氫熱還原處理,發現隨著熱處理溫度增加,Pt-Oads的含量會減少,但觸媒的粒徑大小也會隨之增加,在甲酸與甲醇的氧化反應中,活性衰退現象也更加明顯,此現象的發生一方面是因為粒徑增加導致活性面積降低,但最大的因素為毒化現象造成活性嚴重衰退,反而未經過通氫熱處理的樣品擁有良好的耐久性,由此證明ALD-Pt大量的氧吸附層對於抗毒化有正面的影響, 本研究藉由甲酸及甲醇的氧化反應機構得知,Pt-COads的脫附反應與Pt-(OH)ads有密切的關係,ALD-Pt所提供大量的Pt-Oads有助於Pt-COads的脫附進而增加Pt-(OH)ads的活性位置,加強觸媒抗毒耐性。
Atomic layer deposition (ALD) process of platinum (Pt) from (methylcyclopentadienyl) trimethylplatinum (MeCpPtMe3) and oxygen (O2) has been adopted for preparing electrocatalysts toward methanol and formic acid oxidation. The ALD-Pt catalysts were thermally treated in 5 vol% H2 atmosphere at different reduction temperatures of 150, 300, and 450°C. The reduction treatment enables the increase in Pt particle size but the decrease in amount of Pt oxide (Pt−O) species such as PtO and PtO2. The presence of Pt−O species in electrocatlyst facilitates not only the enhanced catalytic activity but also improved anti-poisoning ability in ethanol and formic acid oxidation. The improved performance is attributed to the fact that the Pt−O species, formed by the ALD route, provide a large number of Pt−Oads and Pt−(OH)ads active sites to strip the CO-adsorbed sites, leading to a high-level of CO tolerance. In addition, the presence of Pt−Oads sites significantly enhances the hydrophilic coverage on the Pt surface, creating more active sites (e.g., Pt−(OH)ads) toward the CO stripping. This work also proposes a stepwise reaction steps to shed some light on how the Pt−O species assist the catalytic activity.