Ethanol electrooxidation on novel carbon supported Pt/SnOx/C catalysts with varied Pt:Sn ratio

Advanced Pt/Ti(1-x)SnxO2-C Composite Supported Electrocatalyst with Functionalized Carbon for Sustainable Energy Conversion Technologies

Sn-doped TiO2-carbon composites were identified as promising multifunctional supports for Pt electrocatalysts, in which the oxide component enhances resistance against corrosion and strong metal-support interactions at the Pt-oxide boundary ensure high stability for the Pt nanoparticles. This work is devoted to the study of the influence of preliminary functionalization of the carbon on the properties of Pt/Ti0.9Sn0.1O2-C catalysts. The structural, compositional and morphological differences between the samples prepared using functionalized or unmodified carbon, as well as the effect of carbon pre-modification on the electrocatalytic behavior of the synthesized Pt catalysts, were investigated using TEM, XRD, XPS, nitrogen adsorption and electrochemical measurements. The presence of oxygen-containing functional groups on carbon treated with HNO3 and glucose leads to the formation of a homogeneous coating of the carbon with dispersed crystallites of mixed oxide. Elemental mapping revealed the proximity of Sn species with highly dispersed (2-3 nm) Pt particles. Notably, the electrochemical results indicated enhanced activity in CO electrooxidation for both functionalized and unmodified carbon-containing catalysts. An improvement in the 10,000-cycle long-term stability of the catalyst prepared using functionalized carbon was evident compared to the catalyst with untreated carbon or reference Pt/C.

Electrocatalysis: From Planar Surfaces to Nanostructured Interfaces

The reactions critical for the energy transition center on the chemistry of hydrogen, oxygen, carbon, and the heterogeneous catalyst surfaces that make up electrochemical energy conversion systems. Together, the surface-adsorbate interactions constitute the electrochemical interphase and define reaction kinetics of many clean energy technologies. Practical devices introduce high levels of complexity where surface roughness, structure, composition, and morphology combine with electrolyte, pH, diffusion, and system level limitations to challenge our ability to deconvolute underlying phenomena. To make significant strides in materials design, a structured approach based on well-defined surfaces is necessary to selectively control distinct parameters, while complexity is added sequentially through careful application of nanostructured surfaces. In this review, we cover advances made through this approach for key elements in the field, beginning with the simplest hydrogen oxidation and evolution reactions and concluding with more complex organic molecules. In each case, we offer a unique perspective on the contribution of well-defined systems to our understanding of electrochemical energy conversion technologies and how wider deployment can aid intelligent materials design.

Tailor-designed nanoparticle-based PdNiSn catalyst as a potential anode for glycerol fuel cells

In order to effectively use glycerol as a fuel in direct glycerol fuel cells, a catalyst that can break the C-C bond and enhance the electro-oxidation of glycerol to CO2 is necessary. In this particular investigation, a palladium-nickel-tin nanocomposite electrodeposited on a glassy carbon electrode (PdNiSn/GC) exhibited excellent activity towards the electro-oxidation of glycerol, thanks to the synergistic effect of the catalyst composition. The PdNiSn/GC surface generated a peak current (Ip) that was 2.5 times higher than that obtained at a Pd/GC electrode, with a cathodic shift in the onset potential (Eonset) of approximately 300 mV. Additionally, the current obtained at the PdNiSn/GC surface remained stable during continuous electrolysis. Capacitance measurements were used to interpret the results of the electrocatalytic activity, and high-performance liquid chromatography indicated that the products of the glycerol electro-oxidation reaction were oxalic acid and formic acid, which were subsequently oxidized to CO2, as revealed by the charge calculations. The results depict that the synergy between Pd, β-Ni(OH)2, and SnO2 is crucial for boosting GEOR through enhancing the C-C bond cleavage and completely oxidize the reaction intermediates to CO2.

Reductive Treatment of Pt Supported on Ti0.8Sn0.2O2-C Composite: A Route for Modulating the Sn-Pt Interactions

The composites of transition metal-doped titania and carbon have emerged as promising supports for Pt electrocatalysts in PEM fuel cells. In these multifunctional supports, the oxide component stabilizes the Pt particles, while the dopant provides a co-catalytic function. Among other elements, Sn is a valuable additive. Stong metal-support interaction (SMSI), i.e., the migration of a partially reduced oxide species from the support to the surface of Pt during reductive treatment is a general feature of TiO2-supported Pt catalysts. In order to explore the influence of SMSI on the stability and performance of Pt/Ti0.8Sn0.2O2-C catalysts, the structural and catalytic properties of the as prepared samples measured using XRD, TEM, XPS and electrochemical investigations were compared to those obtained from catalysts reduced in hydrogen at elevated temperatures. According to the observations, the uniform oxide coverage of the carbon backbone facilitated the formation of Pt-oxide-C triple junctions at a high density. The electrocatalytic behavior of the as prepared catalysts was determined by the atomic closeness of Sn to Pt, while even a low temperature reductive treatment resulted in Sn-Pt alloying. The segregation of tin oxide on the surface of the alloy particles, a characteristic material transport process in Sn-Pt alloys after oxygen exposure, contributed to a better stability of the reduced catalysts.

Synthesis of free-standing ternary Rh-Pt-SnO2-carbon nanotube nanostructures as a highly active and robust catalyst for ethanol oxidation

The rational design of durable materials is an important issue for improving the performance of electrocatalysts towards the ethanol oxidation reaction (EOR). In this work, binderless thin nanostructured layers of SnO2, Pt, Rh, bilayers of Pt/SnO2, Rh/Pt and tri-layers of Rh (ca. 10 nm thickness)/PtSnO2 are directly grown by pulsed laser deposition onto carbon nanotubes (CNTs). SEM analysis shows that CNTs are perfectly coated with the catalysts. The onset potentials of the CO stripping and EOR indicate that Rh/Pt/SnO2 is the most active for the CO and the EOR. The incorporation of the CNTs in the catalyst layer is outstandingly beneficial to both the catalytic current activity and the durability. Indeed Rh/Pt/SnO2/CNT delivers mass activity as high as 213.42 mA mg-1 Pt. Moreover, Rh/Pt/SnO2/CNT demonstrates not only the lowest poisoning rate (by intermediate species, such as adsorbed CO) but also the highest durability current of 132.17 mA mg-1 Pt far superior to CNT-free Rh/Pt/SnO2/CP (58.33 mA mg-1 Pt). XPS shows that SnO2, Pt and Rh are all present at the surface of Rh/Pt/SnO2/CNT, the presence of two oxophilic materials like SnO2 and Rh, implies an earlier source of OHads-species, which facilitates the oxidation of CO and assuming a second contribution from Rh is to enhance the cleavage of the C-C bond for the complete oxidation of ethanol. The 3D porous and binderless structure, the low amount of the noble catalyst, the excellent electroactivity and durability of the Rh5/PtSnO2/CNT/CP composite represents an important step in advancing its use as an anode in commercial applications in DEFC.

Ethanol Electrooxidation on Rhodium-Lead Catalysts in Alkaline Media: High Mass Activity, Long-Term Durability, and Considerable CO2 Selectivity

Rhodium (Rh)-based catalysts may solve the long-standing inefficient oxidation of ethanol for direct ethanol fuel cells (DEFCs); however, the performance of ethanol oxidation reaction (EOR) on existing Rh-based catalysts are far limited. Herein, the Rh-Pb catalysts are synthesized by building Pb and Pb oxide around Rh nanodomain, which shows highly efficient splitting CC bond and facile further oxidation of as-generated C1 intermediates (CO_ad and CH_x fragments). It exhibits an ever-highest EOR peak mass activity of ≈2636 mA mg^-1 _Rh among Rh-based catalysts in alkaline media. Meanwhile, its anodic current remains ≈50% even after a 4 h durability test at 0.53 V versus RHE. As for the C1-pathway selectivity, in situ infrared adsorption spectral (IRAS) results demonstrate that it could significantly improve the production of CO₂ . More directly, the apparent faraday efficiency of EOR C1 pathway is estimated to be as high as 20% (at 0.53 V versus RHE). This Rh-Pb catalyst could hold great promise for developing the commercial DEFCs.

Electrochemical Studies of Pd-Based Anode Catalysts in Alkaline Medium for Direct Glycerol Fuel Cells

This study investigates the most effective electrocatalyst for glycerol oxidation reaction (GOR) in alkaline medium for five synthesized electrocatalysts, Pd, PdNi, PdNiO, PdMn3O4 and PdMn3O4NiO, supported on multi-walled carbon nanotubes (MWCNTs) prepared using the polyol method. The particle size and crystalline size of the electrocatalysts were determined using HR-TEM and XRD techniques, respectively, while EDS was used to determine the elemental composition. XRD showed crystalline sizes ranging from 3.4 to 10.1 nm, while HR-TEM revealed particle sizes within the range of 3.4 and 7.2 nm. The electroactivity, electron kinetics and stability of the electrocatalysts towards glycerol in alkaline medium was evaluated using linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA), respectively, while the electroactive surface area (ECSA) of the electrocatalysts was determined using cyclic voltammetry (CV). The metal oxide-based Pd electrocatalysts PdNiO and PdMn3O4 were the most electrochemically active, while the addition of the second metal oxide to the Pd electrocatalyst PdMn3O4NiO did not show any improvement. This was associated with this electrocatalyst having the highest particle and crystalline sizes.

On the Influence of Composition and Structure of Carbon-Supported Pt-SnO2 Hetero-Clusters onto Their Electrocatalytic Activity and Durability in PEMFC

A detailed study of the structure, morphology and electrochemical properties of Pt/C and Pt/x-SnO2/C catalysts synthesized using a polyol method has been provided. A series of catalysts supported on the SnO2-modified carbon was synthesized and studied by various methods including transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electrochemical methods, and fuel cell testing. The SnO2 content varies from 5 to 40 wt %. The TEM images, XRD and XPS analysis suggested the Pt-SnO2 hetero-clusters formation. The SnO2 content of ca. 10% ensures an optimal catalytic layer structure and morphology providing uniform distribution of Pt-SnO2 clusters over the carbon support surface. Pt/10wt %-SnO2/C catalyst demonstrates increased activity and durability toward the oxygen reduction reaction (ORR) in course of accelerated stress testing due to the high stability of SnO2 and its interaction with Pt. The polymer electrolyte membrane fuel cell current–voltage performance of the Pt/10wt %-SnO2/C is comparable with those of Pt/C, however, higher durability is expected.

Pt-Based Catalysts for Electrochemical Oxidation of Ethanol

Despite its attractive features as a power source for direct alcohol fuel cells, utilization of ethanol is still hampered by both fundamental and technical challenges. The rationale behind the slow and incomplete ethanol oxidation reaction (EOR) with low selectivity towards CO₂ on most Pt-based catalysts is still far from being understood, and a number of practical problems need to be addressed before an efficient and low-cost catalyst is designed. Some recent achievements towards solving these problems are presented. Pt film electrodes and Pt monolayer (Pt_ML) electrodes on various single crystal substrates showed that EOR follows the partial oxidation pathway without C-C bond cleavage, with acetic acid and acetaldehyde as the final products. The role of the substrate lattice on the catalytic properties of Pt_ML was proven by the choice of appropriate M(111) structure (M = Pd, Ir, Rh, Ru and Au) showing enhanced kinetics when Pt_ML is under tensile strain on Au(111) electrode. Nanostructured electrocatalysts containing Pt-Rh solid solution on SnO₂ and Pt monolayer on non-noble metals are shown, optimized, and characterized by in situ methods. Electrochemical, in situ Fourier transform infrared (FTIR) and X-ray absorption spectroscopy (XAS) techniques highlighted the effect of Rh in facilitating C-C bond splitting in the ternary PtRh/SnO₂ catalyst. In situ FTIR proved quantitatively the enhancement in the total oxidation pathway to CO₂, and in situ XAS confirmed that Pt and Rh form a solid solution that remains in metallic form through a wide range of potentials due to the presence of SnO₂. Combination of these findings with density functional theory calculations revealed the EOR reaction pathway and the role of each constituent of the ternary PtRh/SnO₂ catalyst. The optimal Pt:Rh:Sn atomic ratio was found by the two in situ techniques. Attempts to replace Rh with cost-effective alternatives for commercially viable catalysts has shown that Ir can also split the C-C bond in ethanol, but the performance of optimized Pt-Rh-SnO₂ is still higher than that of the Pt-Ir-SnO₂ catalyst.

Pt/C and Pt/SnOx/C Catalysts for Ethanol Electrooxidation: Rotating Disk Electrode Study

Pt/C and Pt/SnOx/C catalysts were synthesized using the polyol method. Their structure, morphology and chemical composition were studied using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer, transition electron microscope and X-ray photoelectron spectroscope. Electrochemical measurements were based on the results of rotating disk electrode (RDE) experiments applied to ethanol electrooxidation. The quick evaluation of catalyst activity, electrochemical behavior, and an average number of transferred electrons were made using the RDE technique. The usage of SnOx (through the carbon support modification) in a binary system together with Pt causes a significant increase of the catalyst activity in ethanol oxidation reaction and the utilization of ethanol.

Promoting Effect of Ni(OH)2 on Palladium Nanocrystals Leads to Greatly Improved Operation Durability for Electrocatalytic Ethanol Oxidation in Alkaline Solution

Most electrocatalysts for the ethanol oxidation reaction suffer from extremely limited operational durability and poor selectivity toward the CC bond cleavage. In spite of tremendous efforts over the past several decades, little progress has been made in this regard. This study reports the remarkable promoting effect of Ni(OH)₂ on Pd nanocrystals for electrocatalytic ethanol oxidation reaction in alkaline solution. A hybrid electrocatalyst consisting of intimately mixed nanosized Pd particles, defective Ni(OH)₂ nanoflakes, and a graphene support is prepared via a two-step solution method. The optimal product exhibits a high mass-specific peak current of >1500 mA mg^-1_Pd , and excellent operational durability forms both cycling and chronoamperometric measurements in alkaline solution. Most impressively, this hybrid catalyst retains a mass-specific current of 440 mA mg^-1 even after 20 000 s of chronoamperometric testing, and its original activity can be regenerated via simple cyclic voltammetry cycles in clean KOH. This great catalyst durability is understood based on both CO stripping and in situ attenuated total reflection infrared experiments suggesting that the presence of Ni(OH)₂ alleviates the poisoning of Pd nanocrystals by carbonaceous intermediates. The incorporation of Ni(OH)₂ also markedly shifts the reaction selectivity from the originally predominant C2 pathway toward the more desirable C1 pathway, even at room temperature.

Ethanol Oxidation Reaction on Tandem Pt/Rh/SnOx Catalyst

To elucidate the atomic arrangement of a Pt-Rh-Sn ternary catalyst with a high catalytic activity for ethanol oxidation reaction (EOR) and high CO2 selectivity, we prepared a tandem Pt/Rh/SnOx, in which a Rh adlayer was deposited on a Pt substrate (Rh coverage: 0.28), followed by depositing several layers of SnOx only on the Rh surface (Sn coverage: 0.07). For reference, Sn was randomly deposited on the Rh-modified Pt (Pt/Rh) electrode whose Rh and Sn coverages were 0.22 and 0.36 (random Pt/Rh/SnOx). X-ray photoelectron spectroscopy demonstrated that Pt and Rh were metallic, and Sn was largely oxidized. Both Pt/Rh/SnOx electrodes were less positive in onset potential of EOR current density and higher in EOR current density than Pt and Rh/Pt electrodes. In situ infrared reflection-absorption spectroscopy demonstrated that the tandem Pt/Rh/SnOx electrode did not produce acetic acid, but produced CO2 in contrast to the random Pt/Rh/SnOx, suggesting that a tandem arrangement of Pt, Rh and SnOx, in which the Pt and SnOx sites were separated by the Rh sites, was effective for selective CO2 production. In the electrostatic electrolysis at 0.5 V vs. RHE, the tandem Pt/Rh/SnOx electrode exhibited higher EOR current density than the Pt and Pt/Rh electrodes after 1.5 h.

Influence of H- and OH-adsorbates on the ethanol oxidation reaction--a DEMS study

The ethanol oxidation reaction (EOR) was investigated by potentiodynamic techniques on Pt/C, Rh/C, Pt-Rh/C, Pt-SnO2/C and Pt-Rh-SnO2/C by differential electrochemical mass spectrometry (DEMS) in a flow cell system. Prior to the cyclic voltammetries, adsorption of H- and OH-species was carried out by chronoamperometry at Ead = 0.05 and 1 V vs. RHE, respectively, in order to examine their influence on the EOR on the different electrocatalysts. For the sake of comparison, another adsorption potential was chosen at Ead = 0.3 V vs. RHE, in the double layer region (i.e. in the absence of such adsorbates). For this study, 20 wt% electrocatalysts were synthesized using a modified polyol method and were physically characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD) and transmission electron microscopy (TEM). When comparing the first and second cycles of the cyclic voltammograms (CVs) on Pt/C and Pt-SnO2/C, the presence of Had on the electrocatalyst surface seems to hinder the initiation of the ethanol electrooxidation, whereas the reaction onset potential is shifted negatively with the presence of OH-adsorbates. In contrast to them, the EOR on Rh/C is enhanced when the electrocatalyst surface is covered with Had and is inhibited after adsorption at Ead = 0.3 and 1 V vs. RHE. Finally, on Pt-Rh/C and Pt-Rh-SnO2/C, neither the H- nor OH-adsorbates do impact the EOR initiation. The lowest EOR onset was recorded on Pt-SnO2/C and Pt-Rh-SnO2/C electrocatalysts. The CO2 currency efficiency (CCE) was also determined for each electrocatalyst and demonstrated higher values on Pt-Rh-SnO2/C.

Activity of platinum/carbon and palladium/carbon catalysts promoted by Ni2 P in direct ethanol fuel cells

Ethanol is an alternative fuel for direct alcohol fuel cells, in which the electrode materials are commonly based on Pt or Pd. Owing to the excellent promotion effect of Ni2 P that was found in methanol oxidation, we extended the catalyst system of Pt or Pd modified by Ni2 P in direct ethanol fuel cells. The Ni2 P-promoted catalysts were compared to commercial catalysts as well as to reference catalysts promoted with only Ni or only P. Among the studied catalysts, Pt/C and Pd/C modified by Ni2 P (30 wt %) showed both the highest activity and stability. Upon integration into the anode of a homemade direct ethanol fuel cell, the Pt-Ni2 P/C-30 % catalyst showed a maximum power density of 21 mW cm(-2) , which is approximately two times higher than that of a commercial Pt/C catalyst. The Pd-Ni2 P/C-30 % catalyst exhibited a maximum power density of 90 mW cm(-2) . This is approximately 1.5 times higher than that of a commercial Pd/C catalyst. The discharge stability on both two catalysts was also greatly improved over a 12 h discharge operation.

PtIr-WO3 nanostructured alloy for electrocatalytic oxidation of ethylene glycol and ethanol

In this article, we characterized tungsten oxide-decorated carbon-supported PtIr nanoparticles and tested it for the electrooxidation reactions of ethylene glycol and ethanol. Phase and morphological evaluation of the proposed electrocatalytic materials are investigated employing various characterization techniques including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrochemical diagnostic measurements such as cyclic voltammetry, chronoamperometry, and linear sweep voltammetry revealed that the tungsten oxide-modified PtIr/Vulcan nanoparticles have higher catalytic activity for ethylene glycol and ethanol electrooxidation than that of PtIr/Vulcan. A significant enhancement for electrooxidation of CO-adsorbate monolayers occurred in the presence of a transition metal oxide relative to that of pure PtIr/Vulcan electrocatalyst. The likely reasons for this are modification on the Pt center electronic structure and/or increasing the population of reactive oxo groups at the PtIr/Vulcan electrocatalytic interface in different potential regions.

Small-sized PdCu nanocapsules on 3D graphene for high-performance ethanol oxidation

A one-pot solvothermal process has been developed for direct preparation of PdCu nanocapsules (with a size of ca. 10 nm) on three-dimensional (3D) graphene. Due to the 3D pore-rich network of graphene and the unique hollow structure of PdCu nanocapsules with a wall thickness of ca. 3 nm, the newly-prepared PdCu/3D graphene hybrids activated electrochemically have great electrocatalytic activity towards ethanol oxidation in alkaline media, much better than single-phase Pd and commercial E-TEK 20% Pt/C catalysts promising for application in direct ethanol fuel cells.

The origin of high activity but low CO2 selectivity on binary PtSn in the direct ethanol fuel cell

Combined electrochemical in situ FTIR and DFT study provides an insight into ethanol fuel cell catalysis on the most active binary catalyst, PtSn, at the atomic and molecular levels.

Carbon supported Pt–Sn/SnO2 anode catalyst for direct ethanol fuel cells

Steady-state performance data of DEFCs (CH₃CH₂OH and O₂) comprising the MEA containing Pt–Sn/SnO₂(33 : 7)–C anode catalyst prepared using the decal transfer method.

Pt nanoparticles supported on Sb-doped SnO2 porous structures: developments and issues

Control of the metal oxide surface properties leads in the case of Sb–SnO₂ to a support material for Pt nanoparticles with tailored catalyst corrosion stability and activity.

Improved electrocatalytic ethanol oxidation activity in acidic and alkaline electrolytes using size-controlled Pt-Sn nanoparticles

The promotion of the electrocatalytic ethanol oxidation reaction (EOR) on extended single-crystal Pt surfaces and dispersed Pt nanoparticles by Sn under acidic conditions is well known. However, the correlation of Sn coverage on Pt nanoparticle electrocatalysts to their size has proven difficult. The reason is that previous investigations have typically relied on commercially difficult to reproduce electrochemical treatments of prepared macroscopic electrodes to adsorb Sn onto exposed Pt surfaces. We demonstrate here how independent control over both Sn coverage and particle size can yield a significant enhancement in EOR activity in an acidic electrolyte relative to previously reported electrocatalysts. Our novel approach uses electroless nanoparticle synthesis where surface-adsorbed Sn is intrinsic to Pt particle formation. Sn serves as both a reducing agent and stabilizing ligand, producing particles with a narrow particle size distribution in a size range where the mass-specific electrocatalytic activity can be maximized (ca. 1-4 nm) as a result of the formation of a fully developed Sn shell. The extent of fractional Sn surface coverage on carbon-supported Pt nanoparticles can be systematically varied through wet-chemical treatment subsequent to nanoparticle formation but prior to incorporation into macroscopic electrodes. EOR activity for Pt nanoparticles is found to be optimum at a fractional Sn surface coverage of ca. 0.6. Furthermore, the EOR activity is shown to increase with Pt particle size and correlate with the active area of available Pt (110) surface sites for the corresponding Sn-free nanoparticles. The maximum area- and mass-specific EOR activities for the most active catalyst investigated were 17.9 μA/cm(2)Pt and 12.5 A/gPt, respectively, after 1 h of use at 0.42 V versus RHE in an acidic electrolyte. Such activity is a substantial improvement over that of commercially available Pt, Pt-Sn, and Pt-Ru alloy catalysts under either acidic or alkaline conditions.