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Ternary PtIrNi Catalysts for Efficient Electrochemical Ammonia Oxidation
journal contribution
posted on 2020-03-12, 13:04 authored by Yi Li, Xing Li, Hemanth Somarajan Pillai, Judith Lattimer, Nadia Mohd Adli, Stavros Karakalos, Mengjie Chen, Lin Guo, Hui Xu, Juan Yang, Dong Su, Hongliang Xin, Gang WuAmmonia
(NH3) has proved to be an effective alternative
to hydrogen in low-temperature fuel cells via its
direct ammonia oxidation reaction (AOR). However, the kinetically
sluggish AOR has prohibitively hindered the attractive direct ammonia
fuel cell (DAFC) applications. Here, we report an efficient AOR catalyst,
in which ternary PtIrNi alloy nanoparticles well dispersed on a binary
composite support consisting of porous silicon dioxide (SiO2) and carboxyl-functionalized carbon nanotube (PtIrNi/SiO2-CNT-COOH) through a sonochemical-assisted synthesis method. The
PtIrNi alloy nanoparticles, with the aid of abundant OHad provided by porous SiO2 and the improved electrical conductivity
by CNTs, exhibit remarkable catalytic activity for the AOR in alkaline
media. It is evidenced by a lower onset potential (∼0.40 V vs reversible hydrogen electrode (RHE)) at room temperature
than that of commercial PtIr/C (ca. 0.43 V vs RHE). Increasing NH3 concentrations and operation
temperatures can significantly enhance AOR activity of this PtIrNi
nanoparticle catalyst. Specifically, the catalyst at the temperature
of 80 °C exhibits a much lower onset potential (∼0.32
V vs RHE) and a higher peak current density, indicating
that DAFCs operated at a higher temperature are favorable for increased
performance. Constant-potential density functional theory (DFT) calculations
showed that the Pt–Ir ensembles on {100}-terminated surfaces
serve as the active site. The introduction of Ni raises the center
energy of the density of states projected onto the group d-orbitals
of surface sites and thus lowers the theoretical onset potential for
*NH2 dehydrogenation to *NH compared to Pt and Pt3Ir alloy.
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Pt 3 Ir alloydensityAOROHammonia oxidation reactionCNT-COOHammonia fuel cellcarboxyl-functionalized carbon nanotubeTernary PtIrNi CatalystsNH 3 concentrationsternary PtIrNi alloy nanoparticles0.43 V vs RHENH 2 dehydrogenationDFTPtIrNi nanoparticle catalystDAFCPtIrNi alloy nanoparticlesexhibitsitesurfaceonsetCNTsonochemical-assisted synthesis methodSiO 2Efficient Electrochemical Ammonia Oxidation Ammonia
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