Electrooxidation of Ammonia at Tuned (100)Pt Surfaces by using Epitaxial Thin Films

Abstract

PtxNi100−x thin films (72≤x≤100, 10–25 nm thick) were deposited on MgO (100) substrates by using pulsed laser deposition. As shown from X‐ray diffraction analysis, the formation of a Pt(Ni) solid solution was observed over the Ni range investigated. All PtNi‐based films showed epitaxial growth in the (100) direction at 350 °C, which is in contrast to pure Pt films, where a Ni seeding layer was required to obtain epitaxial deposits at this temperature. X‐ray photoelectron spectroscopy depth‐profile analyses showed a Ni enrichment at the PtNi/MgO interface, which may be at the origin of the epitaxial growth in the alloys. After immersion in acidic media, Ni atoms are totally dissolved from the first ten atomic layers of the PtNi films, forming pure Pt electrodes. On the basis of underpotential‐deposited hydrogen electrochemical analyses, a (100) preferential surface orientation of the crystallites originating from epitaxial growth was confirmed on both Ptseeded and PtxNi100−x films. It was shown that the fraction of (100) terraces and terrace edge sites are a determining factor in the electrooxidation of NH3. The highest electrocatalytic activity was observed with the Ptseeded film.

Enhanced Catalysis of Pt 3 Clusters Supported on Graphene for N–H Bond Dissociation

“…4,5 The polycrystalline surfaces of Pt, including (100), (111), and (533), have been employed as active substrates for ammonia decomposition to produce N 2 and H 2 . [6][7][8][9][10] However, the Pt catalysts for ammonia decomposition, including the use of doped Pt, 11 are to the best of our knowledge still not sufficiently effective at low temperatures (e.g., <350°C) and thus are not economically viable for large-scale applications. In view of this, there are ongoing efforts devoted to improving the Pt catalysis for ammonia decomposition.…”

Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering

“…MgO is chosen as a substrate because it is transparent, refractive, insulating, and does not react with Pt or Au, forming a clean atomically flat interface. Interface mixing reactions are a common problem with metal deposition on Si, which can form silicide precipitates at the interface and impact the epitaxial relationship 3 . MgO is also well lattice matched to many metals with face-centered-cubic symmetry and can grow biaxially textured on amorphous substrates, providing a path for large-area deposition of oriented films on amorphous substrates 4 .…”

“…MgO is also well lattice matched to many metals with face-centered-cubic symmetry and can grow biaxially textured on amorphous substrates, providing a path for large-area deposition of oriented films on amorphous substrates 4 . The use of Fe or Ni layers to seed cube-on-cube epitaxy of Pt (100) on MgO (100) has been studied for catalysis applications 3 , however, these transition metals create deep level electronic defects in many semiconductors, and so are of less interest for photovoltaic film applications.…”

Pt Monolayers on Electrodeposited Nanoparticles of Different Compositions for Ammonia Electro-Oxidation

“…Only for Ir nanoparticles did the CV curve exhibited an anodic current peak at 0.59 V (vs. RHE) ( Figure 3d). Such an oxidation current peak has been extensively reported on pure Ir and also Pt electrodes and is ascribed to the electro-oxidation of ammonia to N 2 [12,13,37]. Previous work performed CV measurements in the absence of ammonia and found that a such characteristic current peak did not appear [13,37,38].…”

“…On the other hand, ammonia is an environmental pollutant and a toxic gas. Therefore, the electro-oxidation of ammonia has important applications in direct fuel cells [8][9][10], hydrogen production [1,11,12], ammonia decomposition in wastewaters [8,13] and electrochemical sensors for detecting ammonia [14]. Since ammonia electro-oxidation is a sluggish reaction, electrocatalysts are required to catalyze the oxidation of ammonia to N 2 .…”