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Palladium has attracted significant attention as a catalyst or co-catalyst 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 VRHE, while AST2 was performed between 0.05 and 1.4 VRHE. 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.

Electrochemical stability of a commercial Au/C catalyst in an acidic electrolyte has been investigated by an accelerated stress test (AST), which consisted of 10,000 voltammetric scans (1 V/s) in the potential range between 0.58 and 1.41 VRHE. Loss of Au electrochemical surface area (ESA) during the AST pointed out to the degradation of Au/C. Coupling of an electrochemical flow cell with ICP-MS showed that only a minor amount of gold is dissolved despite the substantial loss of gold ESA during the AST (∼35% of initial value remains at the end of the AST). According to the electrochemical mass spectrometry experiments, carbon corrosion occurs during the AST but to a minor extent. By using identical location scanning electron microscopy and identical location transmission electron microscopy, it was possible to discern that the dissolution of small Au particles (

Oxidation of methanol was studied in alkaline solution on bimetallic Ir/Pt(poly) catalysts prepared by the spontaneous deposition of Ir on polycrystalline Pt. Nano-scale surface properties of Ir/Pt(poly) catalysts were revealed by ex situ Atomic Force Microscopy imaging. Modified electrodes were characterized in situ electrochemically by cyclic voltammetry in 0.1 M KOH. Investigations of the methanol oxidation in the same alkaline solution showed that Ir/Pt(poly) electrode obtained after 1 minute Ir deposition, which is equivalent to 80% Ir coverage, showed improved activity with respect to both constitutive metals. The observed synergism on the methanol oxidation activity was ascribed to both bifunctional and electronic effects that are induced by the presence of spontaneously deposited Ir. The origin of the synergism and the possible methanol oxidation pathways were discussed on the basis of the activities of the Ir/Pt(poly) electrodes for the oxidation of the most probable reaction intermediates, CO and formaldehyde, in the same alkaline solution.

Developing a Pt-based electrocatalytic material able to selectively catalyze hydrogen oxidation (HOR) while supressing oxygen reduction (ORR) is beneficial for durability of the fuel cells. Namely, degradation of carbon supported Pt particles is dramatically influenced by the unwanted ORR enrolling at the anode due to the air penetration during start-up/shut-down events. We present an organic matrix tris(aza)pentacene (TAP), which belongs to π-functional materials with ladder-like conjugated nitrogen-containing units, as the support for Pt to form a “smart” fuel cell anode able to selectively catalyze HOR and to suppress ORR. “Switching-on/off” of the composite material activity is provided by reversible reduction/oxidation of the TAP in the low potential region which provokes TAP - HxTAP transition. Conductivity of the reduced HxTAP enables supported Pt particles to effectively run HOR. In contrast, restricted conductivity of oxidized TAP analogue leads to the substantial drop in the ORR activity with respect to benchmark Pt/C catalyst., This work was supported by the Ministry of Education, Science and Sport of the Republic of Slovenia through Raziskovalci-2.1-KI-952007 and by Slovenian Research Agency through the research programs P1-0034 and P2-0393 and project N2-0106.

To date, copper is the only monometallic catalyst that can electrochemically reduce CO

Hydrogen evolution reaction (HER) was explored on tri-metallic Rh@Pd/Au(poly) and bimetallic Pd/Au(poly) and Rh/Au(poly) electrodes in alkaline solution. Electrodes were prepared by the spontaneous deposition of either Pd or Rh and by co-deposition of both Rh and Pd on polycrystalline gold electrode. Characterization of modified electrodes was performed by cyclic voltammetry in alkaline solution, while additional information about phase analysis, chemical composition and surface morphology of tri-metallic Rh@Pd/Au(poly) electrode were acquired using X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy and atomic force microscopy. Investigations of HER catalysis have shown that the activity of tri-metallic Rh@Pd/Au(poly) electrode exceeds the activities of both Pd/Au(poly) and Rh/Au(poly) electrodes, meaning that the synergism between co-deposited Pd and Rh islands is achieved. Moreover, Rh@Pd/Au(poly) electrode showed significant approach to the activities of bulk Pd and Rh electrodes for HER, especially when taking into account low activity of bare Au substrate. Synergistic effect of co-deposited Pd and Rh islands is a consequence of the strong electronic interaction between three metals in a close contact, which promotes the activity for HER by lowering the adsorption energy of Hads intermediate. © 2018 Hydrogen Energy Publications LLC

A comprehensive experimental investigation of the influence of the chain length on the electric field induced proton transfer at α,ω-mercaptoalkanecarboxylic acids self-assembled monolayers (SAMs) is conducted by means of voltammetric and electrochemical impedance spectroscopic measurements. The chain length has a significant impact on the total protonation/deprotonation charge and on the kinetics of the phenomenon. The results are discussed in light of existing theoretical models describing this electric field driven protonation/deprotonation process. Characteristic proton transfer frequencies were independently determined by impedance spectroscopy and by scan rate dependent voltammetric analyses. The two types of measurements are in mutual agreement and show that the protonation/deprotonation slows down as the chain length increases.

Rh/Au(100) and Rh/Au(111) electrodes with Rh coverage below a monolayer are prepared by a spontaneous deposition method. Electrodes are characterized by AFM and XPS. Hydrogen evolution reaction (HER) is studied by linear sweep voltammetry in 0.1 M HClO4 solution. Results for gold single crystals with 50% Rh coverage, which have shown the best catalytic activity for HER are presented in this work. Enhanced catalytic activity of such bimetallic electrodes compared to the ones with higher Rh coverage is ascribed to the presence of smaller Rh islands, which provide suitable active surface sites. Rather strong electronic interaction between Rh deposit and gold substrates, which is manifested by the upshift of Rh3d5/2 photoelectron line, also contributes to their activity. Structural effect is manifested through a higher activity of 50% Rh/Au(111) than 50% Rh/Au(100), which is consistent with the difference in activity of respective bare gold single crystals.

Electrochemical stability of a commercial Rh/C catalyst has been studied in an acidic electrolyte by accelerated degradation protocols (ADP) which involved 5000 rapid voltammetric scans (1 V/s) in two potential regions: ADP1 was performed between 0.4 VRHE and 1.4 VRHE, while ADP2 was performed between 0.05 VRHE and 1.4 VRHE. Degradation of Rh/C was monitored by the changes in Rh electrochemical surface area (ECSA) and electrocatalytic activity for hydrogen evolution (HER) and oxygen reduction (ORR). Rh/C catalyst was particularly stable during ADP1 showing only a minor loss of ECSA, while its electrocatalytic activity for HER and ORR was practically unaffected, which was further corroborated with identical location SEM (IL-SEM) imaging. In the case of ADP2, severe degradation of Rh/C occurred followed by substantial decay in its electrocatalytic activity. Coupling of the electrochemical flow cell (EFC) with ICP-MS revealed much higher Rh dissolution in ADP2 than in ADP1. IL-SEM in combination with ex-situ TEM imaging showed that degradation of the Rh/C sample is not homogeneous during ADP2, as dissolution prevails on certain locations, while dissolution followed by re-deposition occurs on others. According to the results obtained in this work, Rh/C catalysts are exceptionally sensitive to the sudden potential jumps between particularly low and high values.

Hydrogen evolution reaction (HER) was studied in alkaline solution on Pt(poly) electrode modified by spontaneously deposited Ir nanoislands. Comprehensive insight into the characteristics of the bimetallic Ir/Pt(poly) catalysts was obtained by a combination of Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), X-ray Photoelectron Spectroscopy (XPS) and classical electrochemical techniques. HER investigations have shown that the presence of spontaneously deposited Ir enhances the activity of bare Pt(poly) in alkaline solution. This was attributed to the heterogeneity of the active surface sites and to the electronic interaction between two metals in close contact which together facilitated the adsorption of the H intermediate species. This is peer-reviewed version of the article: Svetlana Štrbac, Milutin Smiljanić, Thomas Wakelin, Jelena Potočnik, Zlatko Rakočević, Hydrogen evolution reaction on bimetallic Ir/Pt(poly) electrodes in alkaline solution, Electrochimica Acta (2019), [https://dx.doi.org/10.1016/j.electacta.2019.03.100] [http://cer.ihtm.bg.ac.rs/handle/123456789/2951]

Hydrogen evolution reaction (HER) was investigated in alkaline solution on tri-metallic Rh@Pd/Pt(poly) electrode, prepared by spontaneous deposition of Rh on top of Pd/Pt(poly) electrode with intermediate Pd coverage of 35%. Characterization of tri-metallic catalyst was performed by electrochemical methods of cyclic voltammetry and CO stripping voltammetry, while its activity for HER was tested by linear sweep voltammetry in 0.1 M NaOH. Rh@Pd/Pt(poly) catalyst has shown superior catalytic activity for HER with respect to initial Pt(poly) and both corresponding bimetallic Pd/Pt(poly) and Rh/Pt(poly) electrodes. This was explained by a strong synergistic electronic interaction between three metals in close contact induced at a number of different active sites across the surface of tri-metallic catalyst, which results with lowering of the binding energy for the adsorption of H intermediate species. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

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 voltammetry 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. (C) 2013 Elsevier Ltd. All rights reserved.

Hydrogen 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 center dot 2H(2)O 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. (C) 2012 Elsevier Ltd. All rights reserved.

Rhodium nanoislands were spontaneously deposited on Au(111) up to a full coverage. Obtained Rh/Au(111) bimetallic surface was characterized ex situ by Atomic Force Microscopy imaging and by X-Ray Photoelectron Microscopy, while in situ characterization was performed by Cyclic Voltammetry in 0.1 M NaOH solution. Pronounced catalysis of hydrogen evolution reaction has been observed on Rh modified Au(111) surface compared to bare Au(111). This is ascribed to the suitable geometry of obtained Rh/Au(111) nanostructured electrode surface providing large number of active sites and to the electronic interaction between Au(111) substrate and Rh deposit. (C) 2016 The Electrochemical Society. All rights reserved.

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. (C) 2016 Elsevier Ltd. All rights reserved.

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 voltammetry. 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). (C) 2015 Elsevier B.V. All rights reserved.

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. (C) 2014 Elsevier B.V. All rights reserved.

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. Keywords: Au(111), Rhodium, Spontaneous deposition, AFM, Hydrogen evolution

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. (C) 2013 Elsevier B.V. All rights reserved.

Oxygen reduction reaction (ORR) was studied on polycrystalline gold, Au(poly), modified by nanosized palladium islands in 0.1 M HClO4 solution using rotating disc electrode technique. Paladium was spontaneously deposited from 1 mM PdSO4 center dot 2H(2)O + 0.5 M H2SO4 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. (C) 2012 Elsevier Ltd. All rights reserved.

Hydrogen evolution reaction was studied on Au(111) modified by palladium spontaneously deposited on the Au(111) surface from (1 mM PdSO4 center dot 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.

The oxygen reduction reaction (ORR) was studied on the polycrystalline Pt electrode in 0.1 M NaCl electrolyte containing various amounts of acetonitrile (AcN). The state of the electrode surface was characterized by the cyclic voltammetry in oxygen free electrolytes, while ORR studies were performed on the polycrystalline Pt rotating disc electrode by the 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. 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 (0.1 M NaCl + 1 M AcN) solution.

To date, copper is the only monometallic catalyst that can electrochemically reduce CO2 into high value and energy-dense products, such as hydrocarbons and alcohols. In recent years, great efforts have been directed towards understanding how its nanoscale structure affects activity and selectivity for the electrochemical CO2 reduction reaction (CO2 RR). Furthermore, many attempts have been made to improve these two properties. Nevertheless, to advance towards applied systems, the stability of the catalysts during electrolysis is of great significance. This aspect, however, remains less investigated and discussed across the CO2 RR literature. In this Minireview, the recent progress on understanding the stability of copper-based catalysts is summarized, along with the very few proposed degradation mechanisms. Finally, our perspective on the topic is given.

The commercialization of acidic proton exchange membrane water electrolyzers (PEMWE) is heavily hindered by the price and scarcity of oxygen evolution reaction (OER) catalyst, i. e. iridium and its oxides. One of the solutions to enhance the utilization of this precious metal is to use a support to distribute well dispersed Ir nanoparticles. In addition, adequately chosen support can also impact the activity and stability of the catalyst. However, not many materials can sustain the oxidative and acidic conditions of OER in PEMWE. Hereby, we critically and extensively review the different materials proposed as possible supports for OER in acidic media and the effect they have on iridium performances.