Temperature-Dependent Kinetics and Reaction Mechanism of Ammonia Oxidation on Pt, Ir, and PtIr Alloy Catalysts
Temperature-Dependent Kinetics and Reaction Mechanism of Ammonia Oxidation on Pt, Ir, and PtIr Alloy Catalysts
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DOI：
10.1149/2.0181815jes
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发表时间：
2018-09-20
影响因子：
3.9
通讯作者：
Wang, Jia X.
中科院分区：
文献类型：
--
作者：
Song, Liang;Liang, Zhixiu;Wang, Jia X.
本文报道了在1M KOH溶液中，采用气体扩散电极，在60 ℃以下的温度下，对碳载Pt，Ir和PtIr（1：1）合金催化剂上的氨氧化反应（AOR）进行了动力学研究。通过在Ar气进入电池之前使Ar气鼓泡通过浓氨溶液来保持氨浓度恒定。在0.5 V下，相对于可逆氢电极，电流归一化到铂族金属的质量的顺序为PtIr > Ir > Pt。与Pt相比，Ir具有更高的活性增强，随着温度的升高，较低的起始电位，和较低的峰电流。在与以前的理论研究的相关性，这些差异归因于Ir具有较低的激活势垒的第一个单电子去质子化NH3到NH2*，但较高的障碍二聚的两个NH2* N2H4*。AOR电流在高电位处达到峰值，因为该速率受到电位无关的二聚化和形成阻断活性表面的非活性N* 的限制。在峰值电位以下，由于NH* 的积累而发生逐渐失活，NH * 比NH 2 * 更难二聚。PtIr合金结合了Ir和Pt的优点，具有最宽的激活电位窗口和最高的峰值电流。(C)作者（S）2018由ECS发布。
We report here a kinetic study of ammonia oxidation reaction (AOR) on carbon supported Pt, Ir, and PtIr (1:1) alloy catalysts using gas diffusion electrodes in 1 M KOH solution at temperatures up to 60 degrees C. Ammonia concentration was kept constant by letting Ar gas bubbling through concentrated ammonia solution before entering the cell. At 0.5 V versus reversible hydrogen electrode, the currents normalized to the mass of platinum group metals are in the order of PtIr > Ir > Pt. Compared to Pt, Ir exhibited higher activity enhancement with increasing temperature, lower onset potential, and lower peak current. In correlation with previous theoretical studies, these differences are ascribed to Ir having lower activation barrier for the first one-electron deprotonation of NH3 to NH2*, but higher barrier for dimerization of two NH2* to N2H4*. The AOR current peaks at high potentials because the rate is limited by the potential-independent dimerization and formation of inactive N* that blocks the active surface. Below peak potentials, gradual deactivation occurs due to the accumulation of NH* that is harder to be dimerized than NH2*. PtIr alloy combines the virtues of Ir and Pt exhibiting the widest active potential window and the highest peak current. (C) The Author(s) 2018. Published by ECS.