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Papers by Milutin Smiljanic

Research paper thumbnail of Electrochemical Stability and Degradation of Commercial Pd/C Catalyst in Acidic Media

The Journal of Physical Chemistry C, 2021

Palladium has attracted significant attention as a catalyst or cocatalyst for many electrochemica... more Palladium has attracted significant attention as a catalyst or cocatalyst for many electrochemical reactions in energy conversion devices. We have studied electrochemical stability of a commercial Pd/C sample in an acidic electrolyte by exposing it to an accelerated stress test (AST) to mimic potential spikes in fuel cells and electrolyzers during start/stop events. AST consisted of extensive rapid potential cycling (5000 cycles, 1 V/s) in two potential regions, namely AST1 was performed between 0.4 and 1.4 V RHE , while AST2 was performed between 0.05 and 1.4 V RHE. Degradation of Pd/C was monitored by the changes in Pd electrochemical surface area, while the hydrogen evolution reaction (HER) was used as a test reaction to observe the corresponding impact of the degradation on the activity of Pd/C. Significant Pd/C degradation and HER activity loss were observed in both potential regions. Coupling of the electrochemical flow cell with an inductively coupled plasma mass spectrometry device showed substantial Pd dissolution during both ASTs. Identical location scanning electron microscopy revealed that Pd dissolution is followed by redeposition during both ASTs, resulting in particle size growth. Particle size growth was seen as especially dramatic in the case of AST2, when particularly large Pd nanostructures were obtained on top of the catalyst layer. According to the results presented in this work, (in)stability of Pd/C and other Pd-based nanocatalysts should be studied systematically as it may present a key factor limiting their application in energy conversion devices.

Research paper thumbnail of Electrocatalysis of hydrogen evolution on polycrystalline palladium by rhodium nanoislands in alkaline solution

Hydrogen evolution reaction (HER) was investigated on bimetallic Rh/Pd(poly) electrodes in alkali... more Hydrogen evolution reaction (HER) was investigated on bimetallic Rh/Pd(poly) electrodes in alkaline solution. Bimetallic electrodes were obtained by a spontaneous deposition of rhodium on polycrystalline Pd. Characterization of obtained electrodes was performed ex situ by atomic force microscopy and by spectroscopic ellipsometry. The results have shown that the coverage of palladium substrate with the deposited Rh nanoislands was up to 50%, depending on the chosen deposition time. Electrochemical properties and catalytic activity of Rh/Pd(poly) nanostructures for HER were examined in 0.1 M NaOH solution by cyclic voltammetry and linear sweep volt-ammetry. Rh/Pd(poly) electrodes have shown an enhanced activity for HER with respect to bare Pd(poly), which was ascribed to the strong electronic interaction between palladium substrate and the deposited rhodium islands. The enhanced catalytic activity of 50% Rh/Pd(poly) for HER in alkaline solution is comparable to that of bare Pt(poly).

Research paper thumbnail of Ethanol Oxidation on Rh/Pd(poly) in Alkaline Solution

A B S T R A C T Bimetallic electrodes prepared by Rh nanoislands spontaneously deposited on polyc... more A B S T R A C T Bimetallic electrodes prepared by Rh nanoislands spontaneously deposited on polycrystalline palladium, Pd(poly), at submonolayer coverage were explored for ethanol oxidation in alkaline media. Characterization of obtained Rh/Pd(poly) nanostructures was performed ex situ by AFM imaging and by X-ray photoelectron spectroscopy. In situ characterization of the obtained electrodes and subsequent ethanol oxidation measurements were performed by cyclic voltammetry in 0.1 M KOH. Palladium surface with 50% Rh coverage exhibited the highest catalytic activity for ethanol oxidation in alkaline media. The origin of the enhanced catalysis of Rh/Pd(poly) surfaces with respect to bare Pd was explained by the electronic effect. Possible reaction pathways for ethanol oxidation were discussed taking into account the activity of obtained bimetallic electrodes for the oxidation of CO and acetaldehyde, as the most probable reaction intermediates.

Research paper thumbnail of Hydrogen Evolution Reaction on Platinum Catalyzed by Palladium and Rhodium Nanoislands

Pd/Pt(poly) and Rh/Pt(poly) bimetallic electrodes prepared by spontaneous deposition of Pd and Rh... more Pd/Pt(poly) and Rh/Pt(poly) bimetallic electrodes prepared by spontaneous deposition of Pd and Rh nanoislands on Pt(poly) at submonolayer coverage were explored as catalysts for hydrogen evolution reaction (HER) in alkaline media. Characterization of bimetallic surfaces was performed ex situ by height and phase AFM imaging and in situ by cyclic voltammetry. HER was investigated by linear sweep voltam-metry in 0.1 M NaOH. Both Pd/Pt(poly) and Rh/Pt(poly) surfaces exhibited an enhanced catalysis for HER with respect to bare Pt(poly), which is explained by a strong synergistic electronic effect of platinum substrate on the deposited Pd or Rh nanoislands. This electronic effect leads to the lowering of a binding energy of adsorbed hydrogen intermediate and consequently to the lowering of the overpotential for HER.

Research paper thumbnail of Methanol oxidation on Pd/Pt(poly) in alkaline solution

Journal of Power Sources, 2015

ABSTRACT Bimetallic electrodes prepared by Pd nanoislands spontaneously deposited on polycrystall... more ABSTRACT Bimetallic electrodes prepared by Pd nanoislands spontaneously deposited on polycrystalline platinum, Pt(poly), at submonolayer coverage were explored for methanol oxidation in alkaline media. Characterization of obtained Pd/Pt(poly) nanostructures was performed ex situ by AFM imaging, spectroscopic ellipsometry and by X-ray photoelectron spectroscopy. In situ characterization of the obtained electrodes and subsequent methanol oxidation measurements were performed by cyclic voltammetry in 0.1 M KOH. Platinum surface with 35% Pd coverage exhibited the highest catalytic activity for methanol oxidation in alkaline media, exceeding those of bare Pt and Pd. Both synergistic and electronic effects are responsible for such enhanced catalysis. The origin of the synergistic effect and possible reaction pathways for methanol oxidation were discussed taking into account the activity of obtained bimetallic electrodes for the oxidation of CO and formaldehyde, as the most probable reaction intermediates.

Research paper thumbnail of Oxygen Reduction on Polycrystalline Pt and Au Electrodes in Perchloric Acid Solution in the Presence of Acetonitrile

International journal of electrochemical science

Oxygen reduction reaction (ORR) was studied on polycrystalline Pt and Au electrodes in 0.1 M HClO... more Oxygen reduction reaction (ORR) was studied on polycrystalline Pt and Au electrodes in 0.1 M HClO4 solutions containing various amounts of acetonitrile (AcN). The state of the electrode surface was characterized by cyclic voltammetry in oxygen free electrolytes, while ORR studies were performed on polycrystalline Pt and Au rotating disc electrodes by a linear sweep voltammetry in oxygen saturated electrolytes. Acetonitrile is chemisorbed on Pt over a wide potential range inhibiting both H adsorption and oxide formation. The extent of AcN chemisorption depends on its concentration in the solution. Initial potential of oxygen reduction is shifted negatively, while the kinetics of ORR is increasingly hindered with the increase of AcN concentration. Inhibiting effect of acetonitrile on ORR is pronounced on both Pt(poly) and Au(poly). Complete inhibition of ORR in the potential range of AcN chemisorptions is achieved for 0.1 M HClO4 solution containing 1 M AcN on Au(poly) and 3 M AcN on ...

Research paper thumbnail of Ethanol Oxidation on Pd/Au(111) Bimetallic Surfaces in Alkaline Solution

International journal of electrochemical science

Catalytic properties of Pd/Au(111) nanostructures obtained by spontaneous palladium deposition us... more Catalytic properties of Pd/Au(111) nanostructures obtained by spontaneous palladium deposition using PdSO4 and PdCl2 salts were examined for the oxidation of ethanol in alkaline media. Atomic force microscopy has shown that counter anions in Pd salts are responsible for the differences in surface topography. In both cases the oxidation of ethanol is characterized by the rise of a new peak at approximately the same potential for the same coverage, indicating similar electronic modification of Pd islands by the Au(111) substrate. Pd/Au(111) nanostructures obtained using PdCl2 salt have shown higher ethanol oxidation current densities, which can be ascribed to the surface structure consisting of thinner and smoother Pd deposit providing more convenient sites for the adsorption of ethanol and its subsequent oxidation.

Research paper thumbnail of Catalysis of Hydrogen Evolution on Au(111) Modified by Spontaneously Deposited Pd Nanoislands

Electrocatalysis, 2012

ABSTRACT Hydrogen evolution reaction was studied on Au(111) modified by palladium spontaneously d... more ABSTRACT Hydrogen evolution reaction was studied on Au(111) modified by palladium spontaneously deposited on the Au(111) surface from (1 mM PdSO4·2 H2O + 0.5 M H2SO4) solution at a submonolayer coverage. Number and size of Pd islands increased with the increase of the deposition time as observed by ex situ surface topography atomic force microscopy (AFM). The overall coverage of the underlying Au(111) surface by the deposited Pd islands was estimated from simultaneously acquired phase AFM images, which provided a clear contrast between different materials. The obtained Pd/Au(111) surfaces have shown a significant catalytic activity toward hydrogen evolution reaction in 0.5 M H2SO4 solution. This is discussed with respect to Pd islands size and coverage and to the influence of an electronic effect induced in Pd islands by the underlying Au(111) substrate.

Research paper thumbnail of Inhibiting effect of acetonitrile on oxygen reduction on polycrystalline pt electrode in sodium chloride solution | Inhibirajući efekat acetonitrila na redukciju kiseonika na polikristalnoj pt elektrodi u rastvoru natrijum-hlorida

The oxygen reduction reaction (ORR) was studied on a polycrystalline Pt electrode in 0.1 M NaCl e... more The oxygen reduction reaction (ORR) was studied on a polycrystalline Pt electrode in 0.1 M NaCl electrolyte containing various amounts of acetonitrile (AcN). The state of the electrode surface was characterized by cyclic voltammetry in oxygen free electrolytes, while ORR studies were performed on a polycrystalline Pt rotating disc electrode by linear sweep voltammetry in oxygen saturated electrolytes. The acetonitrile is chemisorbed on Pt over a wide potential range, inhibiting both hydrogen adsorption and oxide formation. The extent of AcN chemisorption depends on its concentration in the solution. The initial potential of oxygen reduction is shifted negatively, while the ORR current is increasingly reduced with the increase of AcN concentration. Complete inhibition of ORR in the potential range of AcN and Cl anion coadsorption is achieved for a 0.1 M NaCl + 1 M AcN solution.

Research paper thumbnail of The effect of rhodium nanoislands on the electrocatalytic activity of gold for oxygen reduction in perchloric acid solution

Journal of Electroanalytical Chemistry, 2013

ABSTRACT The effect of spontaneously deposited rhodium nanoislands on the electrocatalytic activi... more ABSTRACT The effect of spontaneously deposited rhodium nanoislands on the electrocatalytic activity of polycrystalline gold, Au(poly), for oxygen reduction reaction (ORR) was studied using rotating disc electrode technique in 0.1 M HClO4 solution. Surface topography atomic force microscopy (AFM) images of obtained Rh/Au(poly) surfaces revealed that both the size and coverage of rhodium nanoislands increase with the deposition time, for a given depositing conditions. The exact values of rhodium coverage ranging from 50% to the full coverage, and the qualitative changes in the surface chemical composition with respect to bare gold were estimated from phase AFM images. Deposited Rh was also identified by the changes in cyclic voltammetry (CV) profiles from which potential limits for ORR were determined. Obtained Rh/Au(poly) surfaces have shown a significant shift of the initial potential for ORR to the more positive potentials with respect to pure gold already for 50% Rh coverage, indicating that a pronounced electronic effect is responsible for the lowering of the activation energy for oxygen adsorption. The initial potential increases only slightly with the further increase of Rh coverage. Reaction pathway changes from 2e− reduction at lower overpotentials to a partial 4e− reduction at higher overpotentials. The later is attributed to the increased activity of obtained Rh/Au(poly) surfaces towards hydrogen peroxide reduction (HPRR), which appear as an intermediate during ORR. The fraction of 4e− reduction slightly increases with the increase of Rh coverage.

Research paper thumbnail of Catalysis of hydrogen evolution on different Pd/Au(111) nanostructures in alkaline solution

Electrochimica Acta, 2013

ABSTRACT ydrogen evolution reaction (HER) was studied on Pd/Au(1 1 1) bimetallic surfaces in alka... more ABSTRACT ydrogen evolution reaction (HER) was studied on Pd/Au(1 1 1) bimetallic surfaces in alkaline solution. Au(1 1 1) was modified by palladium nanoislands spontaneously deposited using PdSO4·2H2O and PdCl2 salts. As revealed from both surface topography Atomic Force Microscopy (AFM) and phase AFM images, for the same deposition conditions, the obtained Pd/Au(1 1 1) nanostructures differ depending on the counter anion in the depositing palladium salt. These differences are reflected on their catalytic activity toward HER, which occurs between the potentials for pure consisting metals. HER proceeded with the same mechanism, but it is shifted to more positive potentials for Pd/Au(1 1 1) nanostructures obtained using PdCl2 salt with respect to ones obtained using PdSO4 salt. Better catalytic activity of Pd/Au(1 1 1) nanostructures obtained using PdCl2 salt can be explained by their surface structure consisting of smaller and thinner Pd nanoislands, preferentially deposited at steps, which provides more Pd and Pd/Au sites suitable for hydrogen evolution reaction.

Research paper thumbnail of Catalysis of oxygen reduction on Au modified by Pd nanoislands in perchloric acid solution

Electrochimica Acta, 2012

Oxygen reduction reaction (ORR) was studied on polycrystalline gold, Au(poly), modified by nanosi... more Oxygen reduction reaction (ORR) was studied on polycrystalline gold, Au(poly), modified by nanosized palladium islands in 0.1 M HClO 4 solution using rotating disc electrode technique. Paladium was spontaneously deposited from 1 mM PdSO 4 ·2H 2 O + 0.5 M H 2 SO 4 solution for various deposition times at a submonolayer coverage. Topography of obtained Pd/Au(poly) surfaces was observed by tapping mode atomic force microscopy (AFM), while chemical surface composition changes were detected by simultaneously performed phase AFM. Deposited Pd islands were nonuniform in size and randomly distributed over the gold substrate. Size and number of Pd islands increase with the increase of the deposition time, and consequently surface coverage increases too. Deposited Pd was also identified by the changes in cyclic voltammetry (CV) profiles from which an active surface area was estimated. Obtained Pd/Au(poly) surfaces have shown a significant catalytic activity towards oxygen reduction reaction which increases with the increase of Pd islands coverage. The initial potential of ORR was shifted positively, while reaction pathway changes from 2e-reduction on pure gold to 4e-reduction on Pd modified gold. Additionally, obtained Pd/Au(poly) surfaces have shown a significant activity towards hydrogen peroxide reduction (HPRR), which appear as an intermediate during ORR. This supports the assumption that ORR on Pd/Au(poly) occurs partly through 4e-series reduction pathway, the fraction of which increases with the increase of Pd coverage.

Research paper thumbnail of Hydrogen evolution on Au(111) catalyzed by rhodium nanoislands

Electrochemistry Communications, 2013

ABSTRACT Pronounced catalysis of hydrogen evolution reaction (HER) by rhodium nanoislands spontan... more ABSTRACT Pronounced catalysis of hydrogen evolution reaction (HER) by rhodium nanoislands spontaneously deposited on Au(111) has been observed. Different Rh/Au(111) nanostructures were characterized ex situ by both height and phase imaging AFM. The most pronounced catalytic activity for HER in 0.5 M H2SO4 was obtained for 50% Rh coverage. This is ascribed to the suitable size of Rh nanoislands and to the electronic modification of Rh deposit by Au(111) substrate.

Research paper thumbnail of Electrochemical Stability and Degradation of Commercial Pd/C Catalyst in Acidic Media

The Journal of Physical Chemistry C, 2021

Palladium has attracted significant attention as a catalyst or cocatalyst for many electrochemica... more Palladium has attracted significant attention as a catalyst or cocatalyst for many electrochemical reactions in energy conversion devices. We have studied electrochemical stability of a commercial Pd/C sample in an acidic electrolyte by exposing it to an accelerated stress test (AST) to mimic potential spikes in fuel cells and electrolyzers during start/stop events. AST consisted of extensive rapid potential cycling (5000 cycles, 1 V/s) in two potential regions, namely AST1 was performed between 0.4 and 1.4 V RHE , while AST2 was performed between 0.05 and 1.4 V RHE. Degradation of Pd/C was monitored by the changes in Pd electrochemical surface area, while the hydrogen evolution reaction (HER) was used as a test reaction to observe the corresponding impact of the degradation on the activity of Pd/C. Significant Pd/C degradation and HER activity loss were observed in both potential regions. Coupling of the electrochemical flow cell with an inductively coupled plasma mass spectrometry device showed substantial Pd dissolution during both ASTs. Identical location scanning electron microscopy revealed that Pd dissolution is followed by redeposition during both ASTs, resulting in particle size growth. Particle size growth was seen as especially dramatic in the case of AST2, when particularly large Pd nanostructures were obtained on top of the catalyst layer. According to the results presented in this work, (in)stability of Pd/C and other Pd-based nanocatalysts should be studied systematically as it may present a key factor limiting their application in energy conversion devices.

Research paper thumbnail of Electrocatalysis of hydrogen evolution on polycrystalline palladium by rhodium nanoislands in alkaline solution

Hydrogen evolution reaction (HER) was investigated on bimetallic Rh/Pd(poly) electrodes in alkali... more Hydrogen evolution reaction (HER) was investigated on bimetallic Rh/Pd(poly) electrodes in alkaline solution. Bimetallic electrodes were obtained by a spontaneous deposition of rhodium on polycrystalline Pd. Characterization of obtained electrodes was performed ex situ by atomic force microscopy and by spectroscopic ellipsometry. The results have shown that the coverage of palladium substrate with the deposited Rh nanoislands was up to 50%, depending on the chosen deposition time. Electrochemical properties and catalytic activity of Rh/Pd(poly) nanostructures for HER were examined in 0.1 M NaOH solution by cyclic voltammetry and linear sweep volt-ammetry. Rh/Pd(poly) electrodes have shown an enhanced activity for HER with respect to bare Pd(poly), which was ascribed to the strong electronic interaction between palladium substrate and the deposited rhodium islands. The enhanced catalytic activity of 50% Rh/Pd(poly) for HER in alkaline solution is comparable to that of bare Pt(poly).

Research paper thumbnail of Ethanol Oxidation on Rh/Pd(poly) in Alkaline Solution

A B S T R A C T Bimetallic electrodes prepared by Rh nanoislands spontaneously deposited on polyc... more A B S T R A C T Bimetallic electrodes prepared by Rh nanoislands spontaneously deposited on polycrystalline palladium, Pd(poly), at submonolayer coverage were explored for ethanol oxidation in alkaline media. Characterization of obtained Rh/Pd(poly) nanostructures was performed ex situ by AFM imaging and by X-ray photoelectron spectroscopy. In situ characterization of the obtained electrodes and subsequent ethanol oxidation measurements were performed by cyclic voltammetry in 0.1 M KOH. Palladium surface with 50% Rh coverage exhibited the highest catalytic activity for ethanol oxidation in alkaline media. The origin of the enhanced catalysis of Rh/Pd(poly) surfaces with respect to bare Pd was explained by the electronic effect. Possible reaction pathways for ethanol oxidation were discussed taking into account the activity of obtained bimetallic electrodes for the oxidation of CO and acetaldehyde, as the most probable reaction intermediates.

Research paper thumbnail of Hydrogen Evolution Reaction on Platinum Catalyzed by Palladium and Rhodium Nanoislands

Pd/Pt(poly) and Rh/Pt(poly) bimetallic electrodes prepared by spontaneous deposition of Pd and Rh... more Pd/Pt(poly) and Rh/Pt(poly) bimetallic electrodes prepared by spontaneous deposition of Pd and Rh nanoislands on Pt(poly) at submonolayer coverage were explored as catalysts for hydrogen evolution reaction (HER) in alkaline media. Characterization of bimetallic surfaces was performed ex situ by height and phase AFM imaging and in situ by cyclic voltammetry. HER was investigated by linear sweep voltam-metry in 0.1 M NaOH. Both Pd/Pt(poly) and Rh/Pt(poly) surfaces exhibited an enhanced catalysis for HER with respect to bare Pt(poly), which is explained by a strong synergistic electronic effect of platinum substrate on the deposited Pd or Rh nanoislands. This electronic effect leads to the lowering of a binding energy of adsorbed hydrogen intermediate and consequently to the lowering of the overpotential for HER.

Research paper thumbnail of Methanol oxidation on Pd/Pt(poly) in alkaline solution

Journal of Power Sources, 2015

ABSTRACT Bimetallic electrodes prepared by Pd nanoislands spontaneously deposited on polycrystall... more ABSTRACT Bimetallic electrodes prepared by Pd nanoislands spontaneously deposited on polycrystalline platinum, Pt(poly), at submonolayer coverage were explored for methanol oxidation in alkaline media. Characterization of obtained Pd/Pt(poly) nanostructures was performed ex situ by AFM imaging, spectroscopic ellipsometry and by X-ray photoelectron spectroscopy. In situ characterization of the obtained electrodes and subsequent methanol oxidation measurements were performed by cyclic voltammetry in 0.1 M KOH. Platinum surface with 35% Pd coverage exhibited the highest catalytic activity for methanol oxidation in alkaline media, exceeding those of bare Pt and Pd. Both synergistic and electronic effects are responsible for such enhanced catalysis. The origin of the synergistic effect and possible reaction pathways for methanol oxidation were discussed taking into account the activity of obtained bimetallic electrodes for the oxidation of CO and formaldehyde, as the most probable reaction intermediates.

Research paper thumbnail of Oxygen Reduction on Polycrystalline Pt and Au Electrodes in Perchloric Acid Solution in the Presence of Acetonitrile

International journal of electrochemical science

Oxygen reduction reaction (ORR) was studied on polycrystalline Pt and Au electrodes in 0.1 M HClO... more Oxygen reduction reaction (ORR) was studied on polycrystalline Pt and Au electrodes in 0.1 M HClO4 solutions containing various amounts of acetonitrile (AcN). The state of the electrode surface was characterized by cyclic voltammetry in oxygen free electrolytes, while ORR studies were performed on polycrystalline Pt and Au rotating disc electrodes by a linear sweep voltammetry in oxygen saturated electrolytes. Acetonitrile is chemisorbed on Pt over a wide potential range inhibiting both H adsorption and oxide formation. The extent of AcN chemisorption depends on its concentration in the solution. Initial potential of oxygen reduction is shifted negatively, while the kinetics of ORR is increasingly hindered with the increase of AcN concentration. Inhibiting effect of acetonitrile on ORR is pronounced on both Pt(poly) and Au(poly). Complete inhibition of ORR in the potential range of AcN chemisorptions is achieved for 0.1 M HClO4 solution containing 1 M AcN on Au(poly) and 3 M AcN on ...

Research paper thumbnail of Ethanol Oxidation on Pd/Au(111) Bimetallic Surfaces in Alkaline Solution

International journal of electrochemical science

Catalytic properties of Pd/Au(111) nanostructures obtained by spontaneous palladium deposition us... more Catalytic properties of Pd/Au(111) nanostructures obtained by spontaneous palladium deposition using PdSO4 and PdCl2 salts were examined for the oxidation of ethanol in alkaline media. Atomic force microscopy has shown that counter anions in Pd salts are responsible for the differences in surface topography. In both cases the oxidation of ethanol is characterized by the rise of a new peak at approximately the same potential for the same coverage, indicating similar electronic modification of Pd islands by the Au(111) substrate. Pd/Au(111) nanostructures obtained using PdCl2 salt have shown higher ethanol oxidation current densities, which can be ascribed to the surface structure consisting of thinner and smoother Pd deposit providing more convenient sites for the adsorption of ethanol and its subsequent oxidation.

Research paper thumbnail of Catalysis of Hydrogen Evolution on Au(111) Modified by Spontaneously Deposited Pd Nanoislands

Electrocatalysis, 2012

ABSTRACT Hydrogen evolution reaction was studied on Au(111) modified by palladium spontaneously d... more ABSTRACT Hydrogen evolution reaction was studied on Au(111) modified by palladium spontaneously deposited on the Au(111) surface from (1 mM PdSO4·2 H2O + 0.5 M H2SO4) solution at a submonolayer coverage. Number and size of Pd islands increased with the increase of the deposition time as observed by ex situ surface topography atomic force microscopy (AFM). The overall coverage of the underlying Au(111) surface by the deposited Pd islands was estimated from simultaneously acquired phase AFM images, which provided a clear contrast between different materials. The obtained Pd/Au(111) surfaces have shown a significant catalytic activity toward hydrogen evolution reaction in 0.5 M H2SO4 solution. This is discussed with respect to Pd islands size and coverage and to the influence of an electronic effect induced in Pd islands by the underlying Au(111) substrate.

Research paper thumbnail of Inhibiting effect of acetonitrile on oxygen reduction on polycrystalline pt electrode in sodium chloride solution | Inhibirajući efekat acetonitrila na redukciju kiseonika na polikristalnoj pt elektrodi u rastvoru natrijum-hlorida

The oxygen reduction reaction (ORR) was studied on a polycrystalline Pt electrode in 0.1 M NaCl e... more The oxygen reduction reaction (ORR) was studied on a polycrystalline Pt electrode in 0.1 M NaCl electrolyte containing various amounts of acetonitrile (AcN). The state of the electrode surface was characterized by cyclic voltammetry in oxygen free electrolytes, while ORR studies were performed on a polycrystalline Pt rotating disc electrode by linear sweep voltammetry in oxygen saturated electrolytes. The acetonitrile is chemisorbed on Pt over a wide potential range, inhibiting both hydrogen adsorption and oxide formation. The extent of AcN chemisorption depends on its concentration in the solution. The initial potential of oxygen reduction is shifted negatively, while the ORR current is increasingly reduced with the increase of AcN concentration. Complete inhibition of ORR in the potential range of AcN and Cl anion coadsorption is achieved for a 0.1 M NaCl + 1 M AcN solution.

Research paper thumbnail of The effect of rhodium nanoislands on the electrocatalytic activity of gold for oxygen reduction in perchloric acid solution

Journal of Electroanalytical Chemistry, 2013

ABSTRACT The effect of spontaneously deposited rhodium nanoislands on the electrocatalytic activi... more ABSTRACT The effect of spontaneously deposited rhodium nanoislands on the electrocatalytic activity of polycrystalline gold, Au(poly), for oxygen reduction reaction (ORR) was studied using rotating disc electrode technique in 0.1 M HClO4 solution. Surface topography atomic force microscopy (AFM) images of obtained Rh/Au(poly) surfaces revealed that both the size and coverage of rhodium nanoislands increase with the deposition time, for a given depositing conditions. The exact values of rhodium coverage ranging from 50% to the full coverage, and the qualitative changes in the surface chemical composition with respect to bare gold were estimated from phase AFM images. Deposited Rh was also identified by the changes in cyclic voltammetry (CV) profiles from which potential limits for ORR were determined. Obtained Rh/Au(poly) surfaces have shown a significant shift of the initial potential for ORR to the more positive potentials with respect to pure gold already for 50% Rh coverage, indicating that a pronounced electronic effect is responsible for the lowering of the activation energy for oxygen adsorption. The initial potential increases only slightly with the further increase of Rh coverage. Reaction pathway changes from 2e− reduction at lower overpotentials to a partial 4e− reduction at higher overpotentials. The later is attributed to the increased activity of obtained Rh/Au(poly) surfaces towards hydrogen peroxide reduction (HPRR), which appear as an intermediate during ORR. The fraction of 4e− reduction slightly increases with the increase of Rh coverage.

Research paper thumbnail of Catalysis of hydrogen evolution on different Pd/Au(111) nanostructures in alkaline solution

Electrochimica Acta, 2013

ABSTRACT ydrogen evolution reaction (HER) was studied on Pd/Au(1 1 1) bimetallic surfaces in alka... more ABSTRACT ydrogen evolution reaction (HER) was studied on Pd/Au(1 1 1) bimetallic surfaces in alkaline solution. Au(1 1 1) was modified by palladium nanoislands spontaneously deposited using PdSO4·2H2O and PdCl2 salts. As revealed from both surface topography Atomic Force Microscopy (AFM) and phase AFM images, for the same deposition conditions, the obtained Pd/Au(1 1 1) nanostructures differ depending on the counter anion in the depositing palladium salt. These differences are reflected on their catalytic activity toward HER, which occurs between the potentials for pure consisting metals. HER proceeded with the same mechanism, but it is shifted to more positive potentials for Pd/Au(1 1 1) nanostructures obtained using PdCl2 salt with respect to ones obtained using PdSO4 salt. Better catalytic activity of Pd/Au(1 1 1) nanostructures obtained using PdCl2 salt can be explained by their surface structure consisting of smaller and thinner Pd nanoislands, preferentially deposited at steps, which provides more Pd and Pd/Au sites suitable for hydrogen evolution reaction.

Research paper thumbnail of Catalysis of oxygen reduction on Au modified by Pd nanoislands in perchloric acid solution

Electrochimica Acta, 2012

Oxygen reduction reaction (ORR) was studied on polycrystalline gold, Au(poly), modified by nanosi... more Oxygen reduction reaction (ORR) was studied on polycrystalline gold, Au(poly), modified by nanosized palladium islands in 0.1 M HClO 4 solution using rotating disc electrode technique. Paladium was spontaneously deposited from 1 mM PdSO 4 ·2H 2 O + 0.5 M H 2 SO 4 solution for various deposition times at a submonolayer coverage. Topography of obtained Pd/Au(poly) surfaces was observed by tapping mode atomic force microscopy (AFM), while chemical surface composition changes were detected by simultaneously performed phase AFM. Deposited Pd islands were nonuniform in size and randomly distributed over the gold substrate. Size and number of Pd islands increase with the increase of the deposition time, and consequently surface coverage increases too. Deposited Pd was also identified by the changes in cyclic voltammetry (CV) profiles from which an active surface area was estimated. Obtained Pd/Au(poly) surfaces have shown a significant catalytic activity towards oxygen reduction reaction which increases with the increase of Pd islands coverage. The initial potential of ORR was shifted positively, while reaction pathway changes from 2e-reduction on pure gold to 4e-reduction on Pd modified gold. Additionally, obtained Pd/Au(poly) surfaces have shown a significant activity towards hydrogen peroxide reduction (HPRR), which appear as an intermediate during ORR. This supports the assumption that ORR on Pd/Au(poly) occurs partly through 4e-series reduction pathway, the fraction of which increases with the increase of Pd coverage.

Research paper thumbnail of Hydrogen evolution on Au(111) catalyzed by rhodium nanoislands

Electrochemistry Communications, 2013

ABSTRACT Pronounced catalysis of hydrogen evolution reaction (HER) by rhodium nanoislands spontan... more ABSTRACT Pronounced catalysis of hydrogen evolution reaction (HER) by rhodium nanoislands spontaneously deposited on Au(111) has been observed. Different Rh/Au(111) nanostructures were characterized ex situ by both height and phase imaging AFM. The most pronounced catalytic activity for HER in 0.5 M H2SO4 was obtained for 50% Rh coverage. This is ascribed to the suitable size of Rh nanoislands and to the electronic modification of Rh deposit by Au(111) substrate.