Efficient Phosphorus Doping into the Surface Oxide Layers on TiN to Enhance Oxygen Reduction Reaction Activity in Acidic Media
Efficient Phosphorus Doping into the Surface Oxide Layers on TiN to Enhance Oxygen Reduction Reaction Activity in Acidic Media
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DOI：
10.1021/acsaem.0c01576
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发表时间：
2020-10-26
影响因子：
6.4
通讯作者：
Daiguji, Hirofumi
中科院分区：
文献类型：
--
作者：
Chisaka, Mitsuharu;Xiang, Rong;Daiguji, Hirofumi
聚合物电解质燃料电池阴极中的氧化物催化剂已被开发出来，以取代铂族金属催化剂，同时保持适度的氧还原反应(ORR)活性。最近，在氮化钛(TiN)外表面形成的无碳载体的二氧化钛(TiN)催化剂被证明可以显著提高ORR活性。在本研究中，利用次磷酸作为磷源，通过增加无序TiO2层上的表面磷含量，进一步提高了ORR活性。在酸性介质中，半波电位和极限电流密度分别达到最大值0.66V和5.18 mA·cm~(-2)。此外，与车用关键的可逆氢电极相比，在1.0-1.5V之间的高电位循环的耐久性得到了提高。在5000次循环中，半波电位的下降被抑制到0.08V，比以前使用磷酸的研究低0.03V。此外，在NH3气流下对催化剂进行氮掺杂，提高了催化剂的4电子ORR选择性，使过氧化氢的产率降到了未掺杂催化剂的一半以下。尽管在高电势循环下，催化剂中的一些磷和氮原子被去除，但表面氧化物对内层锡的保护可持续5000次。在二氧化钛表面共掺杂大量的磷和氮原子是使用这种催化剂所必需的，而不需要依赖于将电位保持在1.0V以下的高成本系统。
Oxide catalysts have been developed in polymer electrolyte fuel cell cathodes to replace platinum-group-metal catalysts while retaining moderate oxygen reduction reaction (ORR) activity. Recently, carbon support-free titanium oxide (TiO2) catalysts formed on the outer surface of titanium nitride (TiN) have been shown to significantly increase ORR activity. In this study, ORR activity was further enhanced by increasing the surface phosphorus content on the disordered TiO2 layer by using hypophosphorous acid as a phosphorus source. Both the half-wave potential and limiting current density in acidic media were maximized to 0.66 V and 5.18 mA cm(-2), respectively. Besides, the durability against high potential cycles between 1.0 and 1.5 V versus the reversible hydrogen electrode, which is critical to be used in vehicles, was enhanced. The decrease in half-wave potential during the 5000 cycles was suppressed to 0.08 V, which is 0.03 V lower than that in a previous study in which phosphoric acid was used. Furthermore, nitrogen doping on the catalyst under an NH3 flow improved the 4-electron ORR selectivity and reduced the hydrogen peroxide yield to less than half of the value with undoped catalysts. Although some phosphorus and nitrogen atoms were removed from the catalyst under high potential cycles, the surface oxides protected inner TiN for 5000 cycles. Codoping the TiO2 surface with large amounts of both phosphorus and nitrogen atoms is necessary to use this catalyst without relying on a high-cost system in which the potential is kept below 1.0 V.