Influence of phosphoric anions on oxygen reduction reaction activity of platinum, and strategies to inhibit phosphoric anion adsorption

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• 作者：Yuping Li^a ; ^b ; Luhua Jiang^a ; ^{sunshine@dicp.ac.cn" class="auth_mail" title="E-mail the corresponding author} ; Suli Wang^a ; Gongquan Sun^a ; ^{gqsun@dicp.ac.cn" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Platinum ; Phosphoric anion poisoning ; Oxygen reduction reaction ; Modified electrode ; H3PO4-PBI based fuel cells
• 刊名：Chinese Journal of Catalysis
• 出版年：2016
• 出版时间：July 2016
• 年：2016
• 卷：37
• 期：7
• 页码：1134-1141
• 全文大小：1068 K

文摘

Nafion-membrane-based proton exchange fuel cells (PEMFCs) typically operate at below 100 °C. However, H₃PO₄-doped polybenzimidazole (PBI)-based PEMFCs can operate at 100–200 °C. This is advantageous because of accelerated reaction rates and enhanced tolerance to poisons such as CO and SO₂, which can arise from reformed gas or the atmosphere. However, the strong adsorption of phosphoric anions on the Pt surface dramatically decreases the electrocatalytic activity. This study exploits the “third-body effect”, in which a small amount of organic molecules are pre-adsorbed on the Pt surface to inhibit the adsorption of phosphoric anions. Pre-adsorbate species inhibit the adsorption of phosphoric anions, but can also partially occlude active sites. Thus, the optimum pre-adsorbate coverage is studied by correlating the oxygen reduction reaction (ORR) activity of Pt with pre-adsorbate coverage on the Pt surface. The influence of the pre-adsorbate molecule length is investigated using the organic amines, butylamine, octylamine, and dodecylamine, in both 0.1 mol/L HClO₄ and 0.1 mol/L H₃PO₄. Such amines readily bond to the Pt surface. In aqueous HClO₄ electrolyte, the ORR activity of Pt decreases monotonically with increasing pre-adsorbate coverage. In aqueous H₃PO₄ electrolyte, the ORR activity of Pt initially increases and then decreases with increasing pre-adsorbate coverage. The maximum ORR activity in H₃PO₄ occurs at a pre-adsorbate coverage of around 20%. The effect of molecular length of the pre-adsorbate is negligible, but its coverage strongly affects the degree to which phosphoric anion adsorption is inhibited. Butylamine adsorbs to Pt at partial active sites, which decreases the electrochemically active surface area. Adsorbed butylamine may also modify the electronic structure of the Pt surface. The ORR activity in the phosphoric acid electrolyte remains relatively low, even when using the pre-adsorbate modified Pt/C catalysts. Further development of the catalyst and electrolyte is required before the commercialization of H₃PO₄-PBI-based PEMFCs can be realized.