The role of adsorbates in the electrochemical oxidation of ammonia on noble and transition metal electrodes

Abstract The activity for ammonia oxidation and the intermediates formed during the reaction have been studied on platinum, palladium, rhodium, ruthenium, iridium, copper, silver and gold electrodes. The activity in the selective oxidation to N2 is related directly to the nature of the species at the surface: the electrode is active if NHads (or NH2,ads) is present and deactivates when Nads is present. The potential at which NHads or Nads is formed is metal dependent. The observed trend in the strength of adsorption of Nads is Ru>Rh>Pd>Ir>Pt ≫ Au, Ag, Cu . This trend corresponds well with the trend observed in the calculated heat of adsorption of atomic nitrogen, with iridium being an exception. Platinum is the best catalyst for this reaction because Nads is formed at high potential, compared to rhodium and palladium, but seems to stabilize NHads rather well. Gold, silver and copper do not form NHads or Nads, and show only an activity when the surface becomes oxidized. The metal electrodissolution is enhanced by ammonia under these conditions. Most metals produce oxygen-containing products, like NO and N2O, at potentials where the surface becomes oxidized.

[1]  K. Sasaki,et al.  Oxidation and Adsorption of Ammonia on a Platinized Platinum Electrode , 1970 .

[2]  H. Seki,et al.  Infrared photodesorption: Vibrational excitation and energy transfer processes on surfaces , 1985 .

[3]  Van Santen,et al.  A DEMS and cyclic voltammetry study of NH3 oxidation on platinized platinum , 1998 .

[4]  F. Mclarnon,et al.  Spectroscopic ellipsometry study of nickel oxidation in alkaline solution , 1997 .

[5]  W. Visscher,et al.  Electrochemical quartz crystal microbalance measurements of CO adsorption and oxidation on Pt in various electrolytes , 1998 .

[6]  S. H. Vosko,et al.  Accurate spin-dependent electron liquid correlation energies for local spin density calculations: a critical analysis , 1980 .

[7]  G. Kresse,et al.  Ab initio molecular dynamics for liquid metals. , 1993 .

[8]  H. Mishima,et al.  Electrochemical oxidation of ammonia in alkaline solutions : its application to an amperometric sensor , 1998 .

[9]  I. González,et al.  Temperature Effect on the Electrocrystallization Processes of Gold in Ammoniacal Medium , 1995 .

[10]  G. Kokkinidis.  The electrocatalytic influence of underpotential heavy metal adsorbates on the electrochemical behaviour of ammonia and hydroxylamine on platinum , 1985 .

[11]  Jackson,et al.  Atoms, molecules, solids, and surfaces: Applications of the generalized gradient approximation for exchange and correlation. , 1992, Physical review. B, Condensed matter.

[12]  Patricia A. Thiel,et al.  The interaction of water with solid surfaces: Fundamental aspects , 1987 .

[13]  D. King,et al.  Control of a Biphasic Surface Reaction by Oxygen Coverage: The Catalytic Oxidation of Ammonia over Pt{100} , 1995 .

[14]  R. Madix,et al.  Cleavage of N-H bonds by active oxygen on Ag(110): I. Ammonia , 1989 .

[15]  J. Niemantsverdriet,et al.  The adsorption of NH3 on Rh(111) , 1996 .

[16]  W. Vielstich,et al.  DEMS-cyclic voltammetry investigation of the electrochemistry of nitrogen compounds in 0.5 M potassium hydroxide , 1994 .

[17]  R. M. Lambert,et al.  Chemisorption and reactivity on supported clusters and thin films : towards an understanding of microscopic processes in catalysis , 1997 .

[18]  I. González,et al.  The role of pH and Cu(II) concentration in the electrodeposition of Cu(II) in NH4Cl solutions , 1996 .

[19]  F. Illas,et al.  Ab initio cluster model approach to the chemisorption of NH3 on Pt(111) , 1999 .

[20]  V. Grondelle,et al.  Determination of Surface Coverage of Catalysts: Temperature Programmed Experiments on Platinum and Iridium Sponge Catalysts after Low Temperature Ammonia Oxidation , 1999 .

[21]  Heinz Gerischer,et al.  Untersuchungen Zur anodischen Oxidation von Ammoniak an Platin-Elektroden , 1970 .

[22]  W. Ho,et al.  Thermally activated oxidation of NHs on Pt(111): intermediate species and reaction mechanisms , 1995 .

[23]  B. E. Nieuwenhuys,et al.  Synthesis of metastable surface complexes by chemical reactions N and NHx complexes on Pd(100), Rh(100) and Pt-Rh(100) , 1991 .

[24]  S. Remita,et al.  Reduction of AgI1(NH3)2+ to Ag01(NH3)2 in Solution. Redox Potential and Spectral Study , 1996 .

[25]  Eddie G. Baker,et al.  Chemical processing in high-pressure aqueous environments. 5. New processing concepts , 1996 .

[26]  P. Pickup,et al.  The Influence of the Aqueous Growth Medium on the Growth Rate, Composition, and Structure of Hydrous Iridium Oxide Films , 1988 .

[27]  D. King,et al.  A molecular beam study of ammonia adsorption on Pt{100} , 1997 .

[28]  D. Mckee,et al.  Improved Electrocatalysts for Ammonia Fuel Cell Anodes , 1969 .

[29]  M. Salomon,et al.  THE ANODIC OXIDATION OF AMMONIA AT PLATINUM BLACK ELECTRODES IN AQUEOUS KOH ELECTROLYTE , 1963 .

[30]  J. Willsau,et al.  Elementary steps of ethanol oxidation on Pt in sulfuric acid as evidenced by isotope labelling , 1985 .

[31]  Van Santen,et al.  Low temperature oxidation of ammonia to nitrogen in liquid phase , 1999 .

[32]  N. Marković,et al.  Hydrogen adsorption on single-crystal platinum electrodes in alkaline solutions , 1992 .