Pt In Acidic Media Research Articles

Electro‐Oxidation of Polyols on Bi‐Modified Pt in Acidic Media (HClO4). Understanding Activity and Selectivity Trends

AbstractHerein we show that Pt(111) and Pt(100) can produce the ketone through the oxidation of the secondary carbon of the polyols. After the Bi modification, the selectivity for the ketone formation increases. On the other hand, we observe that pure and Bi‐modified Pt(110) only produced the C3 molecules oxidized in the primary carbon, and it is the only facet that shows an enhancement in the activity due to the modification. In line with these findings, small Pt nanoparticles are not selective for ketone formation. Finally, based on data obtained through DFT calculations, we suggest that positively charged Bi adatoms interact with the OH‐ groups of the enediol‐like intermediate (believed to be the precursor for the ketone/aldehyde production), facilitating the oxidation of the secondary carbon to produce DHA.

The Synergistic Effects of Alloying on the Performance and Stability of Co3Mo and Co7Mo6 for the Electrocatalytic Hydrogen Evolution Reaction

Metal alloys have become a ubiquitous choice as catalysts for electrochemical hydrogen evolution in alkaline media. However, scarce and expensive Pt remains the key electrocatalyst in acidic electrolytes, making the search for earth-abundant and cheaper alternatives important. Herein, we present a facile and efficient synthetic route towards polycrystalline Co3Mo and Co7Mo6 alloys. The single-phased nature of the alloys is confirmed by X-ray diffraction and electron microscopy. When electrochemically tested, they achieve competitively low overpotentials of 115 mV (Co3Mo) and 160 mV (Co7Mo6) at 10 mA cm−2 in 0.5 M H2SO4, and 120 mV (Co3Mo) and 160 mV (Co7Mo6) at 10 mA cm−2 in 1 M KOH. Both alloys outperform Co and Mo metals, which showed significantly higher overpotentials and lower current densities when tested under identical conditions, confirming the synergistic effect of the alloying. However, the low overpotential in Co3Mo comes at the price of stability. It rapidly becomes inactive when tested under applied potential bias. On the other hand, Co7Mo6 retains the current density over time without evidence of current decay. The findings demonstrate that even in free-standing form and without nanostructuring, polycrystalline bimetallic electrocatalysts could challenge the dominance of Pt in acidic media if ways for improving their stability were found.

Au Nanoparticles Modified with Pt, Ru and SnO2 as Electrocatalysts for Ethanol Oxidation Reaction in Acids.

The anodic reaction in direct ethanol fuel cells (DEFCs), ethanol oxidation reaction (EOR) faces challenges, such as incomplete electrooxidation of ethanol and high cost of the most efficient electrocatalyst, Pt in acidic media at low temperature. In this study, core-shell electrocatalysts with an Au core and Pt-based shell (Au@Pt) are developed. The Au core size and Pt shell thickness play an important role in the EOR activity. The Au size of 2.8 nm and one layer of Pt provide the most optimized performance, having 6 times higher peak current density in contrast to commercial Pt/C. SnO2 as a support also enhances the EOR activity of Au@Pt by 1.73 times. Further modifying the Pt shell with Ru atoms achieve the highest EOR current density that is 15 and 2.5 times of Pt/C and Au@Pt. Our results suggest the importance of surface modification in rational design of advanced electrocatalysts.

Extracting the kinetic parameters of the hydrogen evolution reaction at Pt in acidic media by means of dynamic multi-frequency analysis

Herein, we use dynamic multi-frequency analysis (DMFA) to investigate the reaction kinetics of a paradigm electro-catalytic reaction, i.e. the hydrogen evolution reaction (HER) at polycrystalline Pt electrodes in acidic media. DMFA allows measuring dynamic impedance spectra under non-steady state conditions, as it is the case to avoid the formation of hydrogen bubbles. The extracted impedance spectra were fitted using electrical equivalent circuits (EECs) based on an analytical model, which took into account a Volmer-Tafel mechanism for hydrogen evolution. We found that the EECs based on this model can serve as suitable electrical analog in order to describe the physico-electrochemical processes that govern the different stages of the HER.

Thermodynamic analysis of electrodeposition of copper from copper sulphate

The free energy of activation of copper electrodeposition from copper sulphate solution is derived in terms of the dehydration energy of copper sulphate, hydration number of copper sulphate, solvated work function of the host metal and coordination number of the host metal on which the copper deposition is carried out. The free energy of activation for copper electrodeposition on 31 different host metals had been evaluated. The trend in the free energy of activation on different metals is studied and feasible electrodeposition of copper for appropriate applications had been suggested. The methodology is extended to obtain the exchange current densities for copper electrodeposition on different surfaces of Pt in acid medium and compared with the existing literature.

Effect of trifluoromethanesulfonic acid on the ORR activity of Pt in acid medium

Effect of trifluoromethanesulfonic acid on the ORR activity of Pt in acid medium

Preparation and electrocatalytic characteristics of the Pt-based anode catalysts for ethanol oxidation in acid and alkaline media

The current study reports the preparation and investigation of several Pt-based anode catalysts loaded on reduced graphene oxide (rGO) as electrocatalysts in both acid and alkaline media for ethanol electrooxidation. The synthesized catalysts are evaluated by the method of XRD, Raman spectroscopy, XPS and TEM. Electrocatalytic properties of these catalysts for ethanol oxidation were investigated by cyclic voltammetry and chronoamperometry. It was found that the as-prepared nanocatalysts doped by metals and oxide metals showed the improvement of catalytic performance compared to Pt-only supported on graphene catalyst. The results indicated that the presence of Al favoured Pt nanoparticles dispersing on the surface of rGO sheets. Indeed, the PAG catalyst exhibits the highest mass activity for the ethanol oxidation of 1194 mA mg−1Pt in acid medium and 3691 mA mg−1Pt in alkaline medium. In addition, the PAG catalyst also shows good antipoisoning ability for ethanol electrooxidation in both media. This catalyst could be a potential catalyst for direct ethanol fuel cell (DEFC).

N-doped carbon nanotubes containing a high concentration of single iron atoms for efficient oxygen reduction

Fe-N-C has emerged as a promising noble-metal-free catalyst for the oxygen reduction reaction (ORR). However, achieving a catalytic activity comparable to that of Pt in acidic medium remains a great challenge. Here we report a N-doped carbon nanotube (CNT) catalyst in which a high concentration of single Fe atoms has been dispersed (CNT@Fe-N-PC). The catalyst was prepared by a simple and scalable atomic isolation method, in which a metal isolation agent was introduced to isolate Fe atoms and was then evaporated to produce abundant micropores that host single Fe atom active sites. The CNT@Fe-N-PC catalyst contained a high concentration of single Fe atom active sites and exhibited ultrahigh ORR activity with a half-wave potential of 0.82 V, comparable to that of Pt/C in an acidic medium. A high concentration of Fe-Nx active sites was created on a flexible single-wall CNT film and carbon cloth using this technique, and these materials showed even better ORR performance, that is, 40–60 mV more positive onset potentials than those of a commercial Pt/C catalyst. These catalysts exhibit excellent catalytic activity, good durability and low cost, and show great potential for commercial use as substitutes for current Pt-based catalysts.

Facile synthesis of high performance non-noble-metal electrocatalyst Fe–N–S/C for oxygen reduction reaction in acidic solutions

The development of non-noble metal catalysts is of great interest due to their significant potential application in both fuel cell system and metal-air batteries, particularly when considering long term commercial deployment. Fe/N/C is a promising non-Pt electrocatalyst for the oxygen reduction reaction (ORR), but its catalytic activity is considerably inferior to that of Pt in acidic medium. In this paper, an improved Fe/N/S/C catalyst (denoted as Fe–N–S/C) is presented. Nitrogen-sulfur-iron-doped porous carbon material is synthesized by the pyrolysis of dicyandiamide, a kind of abundant and inexpensive compound, with thiourea as additional sulfur source in argon atmosphere. The Fe–N–S/C shows excellent performance for the ORR with the onset and half-wave potential at 0.89 and 0.78 V (vs.RHE) in 0.1 M H2SO4 solution, respectively, which are significantly higher compared to those of the catalysts derived from only dicyandiamide (0.85 and 0.75 V). Our results indicate that as compared to the commercial 20 % Pt/C catalyst, the synthesized catalyst exhibits not only higher current density and long-term durability but also higher tolerance to methanol poisoning. More importantly, the synthetic method is simple and inexpensive.

S-Doping of an Fe/N/C ORR Catalyst for Polymer Electrolyte Membrane Fuel Cells with High Power Density.

Fe/N/C is a promising non-Pt electrocatalyst for the oxygen reduction reaction (ORR), but its catalytic activity is considerably inferior to that of Pt in acidic medium, the environment of polymer electrolyte membrane fuel cells (PEMFCs). An improved Fe/N/C catalyst (denoted as Fe/N/C-SCN) derived from Fe(SCN)3, poly-m-phenylenediamine, and carbon black is presented. The advantage of using Fe(SCN)3 as iron source is that the obtained catalyst has a high level of S doping and high surface area, and thus exhibits excellent ORR activity (23 A g(-1) at 0.80 V) in 0.1 M H2SO4 solution. When the Fe/N/C-SCN was applied in a PEMFC as cathode catalyst, the maximal power density could exceed 1 W cm(-2).

S‐Doping of an Fe/N/C ORR Catalyst for Polymer Electrolyte Membrane Fuel Cells with High Power Density

AbstractFe/N/C is a promising non‐Pt electrocatalyst for the oxygen reduction reaction (ORR), but its catalytic activity is considerably inferior to that of Pt in acidic medium, the environment of polymer electrolyte membrane fuel cells (PEMFCs). An improved Fe/N/C catalyst (denoted as Fe/N/C‐SCN) derived from Fe(SCN)3, poly‐m‐phenylenediamine, and carbon black is presented. The advantage of using Fe(SCN)3 as iron source is that the obtained catalyst has a high level of S doping and high surface area, and thus exhibits excellent ORR activity (23 A g−1 at 0.80 V) in 0.1 M H2SO4 solution. When the Fe/N/C‐SCN was applied in a PEMFC as cathode catalyst, the maximal power density could exceed 1 W cm−2.

Reactivity of Alcohols with Three-Carbon Atom Chain on Pt in Acidic Medium

n-Propanol, 2-propanol, 1,2-propanediol, 1,3-propanediol, and glycerol are all saturated alcohols with a three-carbon atom chain. The difference between them is the number of hydroxyl groups and their positions in these molecules. The interaction between alcohols with a three-carbon atom chain and model surfaces and the further reaction have been widely investigated in the last three decades. In this short review, we will concentrate our attention on the reactivity of n-propanol, 2-propanol, 1,2-propanediol, 1,3-propanediol, and glycerol on smooth Pt in acidic medium. We will present the most important results reported in the literature in this field, highlighting the main particularities related to their reactions, addressing key points such as the impact of the position of the OH group in the molecule, number of OH groups in the molecule, and presence of vicinal OH groups in the molecule on the reactivity of these alcohols over Pt. Finally, we will present some perspectives concerning the application of alcohols with a three-carbon atom chain, mainly glycerol, in fuel cells.

Resolving the H UPD and H OPD by DEMS to determine the ECSA of Pt electrodes in PEM fuel cells

Overpotential deposited hydrogen (H OPD) and underpotential deposited hydrogen (H UPD) are produced together on Pt in acidic media between 0 and 110 mV vs. SHE and cannot be resolved by cyclic voltammetry alone. Differential electrochemical mass spectrometry was demonstrated for the first time to resolve H OPD and H UPD by measuring the H 2 evolved from water by the hydrogen evolution reaction at the cathode (a Pt electrode) of a proton exchange membrane fuel cell (PEMFC). The H UPD at the cathode was thus quantified and determined to form a saturated layer on the Pt surface when the lower potential limit of cyclic voltammetry is below about 70 mV vs. the anode, a dynamic hydrogen electrode. This amount of H UPD can be used to measure the ECSA of a Pt electrode in PEMFC and avoid the error from including H OPD.

Alkylidynes-modified Pt nanoparticles: A spectroelectrochemical (SERS) and electrocatalytic study

Alkylidyne-modified (propylidyne or ethylidyne) Pt nanoparticles were electrochemically prepared and characterised by Surface Enhanced Raman Spectroscopy (SERS) and cyclic voltammetry. Formic acid oxidation on alkylidyne-modified Pt nanoparticles was used as probe reaction to evaluate their electrocatalytic properties. SERS spectra show that, in the presence of propylidyne, the observed frequency of ν[CO] is red-shifted with respect to the typical values on polycrystalline Pt in acidic medium, which suggests the existence of an instabilization of the carbon monoxide poisonous species, what contributes to the enhanced electrocatalytic activity. Similar electrooxidation current densities were obtained for both propylidyne and ethylidyne surface modifiers suggesting that the instabilization of the CO ads seems to be non-dependant of the nature of the alkylidyne intermediates, and that the enhanced mechanism is similar in both cases. The present paper shows how in situ spectroscopic measurements can help to understand the effect of the surface modifiers on the electrocatalytic properties of Pt nanoparticles, which can be effectively applied in real applications. Thus, this experimental methodology will allow selecting those modified-electrocatalysts with better properties.

Hydrogen Oxidation Reaction on Pt in Acidic Media: Adsorption Isotherm and Activation Free Energies

We present a method for quantifying the kinetic current of the hydrogen oxidation reaction (HOR) on Pt in acidic media using the adsorption and activation free energies as the intrinsic kinetic parameters. Our approach involves deriving the HOR intermediate's adsorption isotherm based on the same dual-pathway reaction model as for the kinetic equation. Coupled with density functional theory calculations of the coverage- and site-dependent hydrogen dissociation free energies, we analyzed the adsorption isotherms for H on atop (HAtop) sites and in hollow/bridge (HH/B) sites obtained respectively from infrared spectroscopic and electrochemical measurements. Although the hydrogen dissociative adsorption energy is not site-sensitive on Pt, HAtop has an order of magnitude lower coverage and higher activity than HH/B. We attributed this distinction to their different entropies; HH/B is less accessible to water than HAtop, and the formation of a hydrogen bond is essential in the oxidative generation of H3O+. Usin...

Acetaldehyde electrooxidation: The influence of concentration on the yields of parallel pathways

Parallel pathways forming CO2 and acetic acid occur during the electrooxidation of acetaldehyde at Pt in acid medium. The yields of products depend on potential and acetaldehyde concentration. In the whole range of concentrations investigated (2.5 × 10−3 – 0.5 M) and at potentials below 0.6 V, CO2 is the only product of acetaldehyde oxidation. Acetic acid is detected at potentials higher than 0.7 V. According to the analysis of products using FTIR spectroscopy, a maximum yield of CO2 production is obtained for an acetaldehyde concentration of 0.01 M at 0.6 V. The pathway forming CO2 is strongly inhibited for 0.5 M of acetaldehyde. It is suggested that, at high concentrations, a competition with water for active sites occurs, which inhibits the oxidation of adsorbed species, which probably follow a Langmuir–Hinshelwood mechanism.

Adsorption, oxidation and reduction of crotyl alcohol on platinum

Abstract The electrochemical reactivity of crotyl alcohol (CA) on Pt in acid media has been studied applying electrochemical methods combined with in situ Fourier transform IR spectroscopy (FTIRS) and on-line mass spectrometry (DEMS). Mass spectrometric cyclic voltammograms (MSCVs) and IR spectra, acquired with the alcohol in the solution, point out the formation of CO 2 and crotonaldehyde as oxidation products. On the other hand, spectra recorded during the electroreduction display negative features at 2964, 2934 and 2875 cm −1 , which are assigned to the CH 3 and CH 2 asymmetric stretchings and the CH 2 symmetric stretching, respectively. The intensity of these signals confirms that a massive hydrogenation process occurs at E V RHE with a strong production of hydrocarbons. Accordingly, several reduction compounds (2-butene, butane, propane, propene, ethane and methane) were detected by DEMS. The same products, with the exception of the aldehyde, were established from CA adsorbed species, isolated applying an electrolyte exchange procedure. A feature at 2020 cm −1 due to lineal adsorbed CO develops in the IR spectra. These results allow us to propose a general overview of the electrochemical reactions of CA at Pt.

A voltammetric and nanogravimetric study of Te underpotential deposition on Pt in perchloric acid medium

This work describes the study of Te underpotential deposition on Pt in acid media using cyclic voltammetry, rotating ring-disc electrode and electrochemical quartz crystal microbalance techniques. The voltammetric results indicate the presence of two dissolution peaks in the positive scan with a total charge density of 420 μC cm −2. These phenomena are attributed to the deposition of one Te monolayer with the occupancy of two active Pt sites by each ad-atom. This is confirmed by rotating ring-disc electrode results. The electrochemical quartz crystal microbalance (EQCM) experiments yielded the small mass variation of −32 ng cm −2 (while the theoretical one is −140.4 ng cm −2 for a complete Te monolayer). This low value can be attributed to the simultaneous adsorption of water, perchlorate anions and the formation of platinum oxide.

A model for the flux of the species generated during the electrodissolution of a copper–nickel alloy on Pt in acidic media

This paper describes a new model to calculate the fluxes of the species generated during the electrodeposition of Cu–Ni alloys on Pt in acidic media. Measurements were carried out using linear sweep voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. The alloy electrodeposition was performed between +1.0 and −0.9 V versus SCE in a bath containing 0.04 M CuCl 2·2H 2O+0.04 M NiCl 2·6H 2O+0.32 M H 3BO 3+1 M NH 4Cl. Following this, a sweep in the positive direction (between −0.3 and +1.0 V) to dissolve the alloy was performed using a blank solution (1 M NH 4Cl+0.32 M H 3BO 3). The fluxes of the species versus the potential (Ni 2+ (desorption) and Cl − (adsorption on the top of Cu +)) generated during the alloy dissolution were calculated using the current and mass responses. In fact, it was observed that the electrodissolution obeys Faraday's law. The flux calculated (considering a transference of two electrons in the case of Ni and one electron in the case of Cu) multiplied by the Faraday constant and plotted against E ( i calculated) presents the same profile as the experimental results for the alloy dissolution.

Hydroxylamine electrochemistry at polycrystalline platinum in acidic media: a voltammetric, DEMS and FTIR study

The electrochemical activity of hydroxylamine on polycrystalline Pt in acidic media has been characterized using cyclic voltammetry, on-line differential electrochemical mass spectrometry (DEMS) and in situ FTIR. The electrochemistry of hydroxylamine (HAM) is essentially controlled by other species that interact strongly with the electrode surface. Therefore, quite moderate current densities, both in oxidation and reduction, are observed in a wide potential window between ca 0 and 1 V. The HAM electroreduction is a slow process and is masked by the H upd. No formation of gaseous products was detected in this region; hence, ammonia must be the main product of HAM reduction. The HAM electro-oxidation is strongly influenced by the adsorption of its products, as well as their chemical transformations in solution. The key intermediate in HAM oxidation is NO, based both on voltammetric and spectroscopic evidence. Nitric oxide forms an adsorbed layer, stable over a wide potential region between ca. 0.55 and 0.75 V. At higher potentials NO ads is oxidized to form (adsorbed) HNO 2. At potentials above ca. 0.9 V the accumulation of HNO 2 in solution, accompanied by its partial oxidation to NO 2, is postulated. N 2O formation, observed in the potential region between ca. 0.5 and 1 V, has multiple sources. The most important source of N 2O is a homogeneous reaction between HNO 2 and HAM. The Tafel slope analysis suggests the second electron transfer to be the rate-determining step in HAM oxidation to NO ads. A tentative mechanism for this reaction is proposed.