Activity For Ethanol Oxidation Reaction Research Articles

Monodispersed silver-palladium nanoparticles for ethanol oxidation reaction achieved by controllable electrochemical synthesis from ionic liquid microemulsions

Alloyed nanoparticles are promising electrocatalysts for electrochemical energy storage and conversion devices. However, syntheses of alloyed nanoparticles with controllable size and stoichiometry remain challenging. In this study, continuous, uniform and monodispersed bimetallic AgPd nanoparticles (NPs) with diameters ∼10 nm are achieved by electrochemical synthesis from quaternary ionic liquid microemulsion (ILM) for use as electrocatalysts for ethanol oxidation reaction (EOR). It is found that the ionic liquid, 1-butyl-3-methyl-imidazolium chloride ([BMIM]Cl), acts not only as a soft template and co-surfactant for the formation of micro-reactors, but also as an electrolyte for enhancing conductivity. The stoichiometry (AgxPdy), size and size distribution of AgPd NPs can be accurately tuned by varying electrolyte composition, electrodeposition conditions, and ionic liquids concentrations. Attributed to the high surface area, optimal stoichiometric ratio, and strong attachment onto substrates without using organic binders, the as-deposited AgxPdy NPs exhibit extraordinary electrocatalytic activity and stability for EOR. It is found that the mass activity of Ag49Pd51 NPs/Pt electrode reaches 3360 mA mg−1 for EOR in 1.0 M ethanol and 1.0 M KOH aqueous solution, which is much higher than commercial Pd/C catalyst (210.5 mA mg−1) and also the highest among state-of-the-art AgPd NPs electrocatalysts reported to date for EOR in alkaline media.

A metal–organic framework derived PtCo/C electrocatalyst for ethanol electro-oxidation

Abstract Currently, designing and preparing low-cost and high-efficiency electrocatalysts still remains of huge impediment for direct ethanol fuel cells (DEFCs). In this work, by leveraging the unique superiority of Co3[Co(CN)6]2 (Prussian blue analogues, PBA) precursor, we used Pt4+ to replace partial dispersed Co2+ in Co3[Co(CN)6]2 and a metal–organic framework (MOF) derived PtCo electrocatalyst (MD-PtCo/C) was successfully fabricated. Notably, as-obtained MD-PtCo/C (Pt, 0.9532 wt.%) electrocatalyst achieves high utilization rate of ultra-low Pt load and exhibits favorable electrocatalytic performance with lower onset potential, higher EOR activity, less activation energy (Ea) value and better stability compared to commercial Pt/C for ethanol oxidation reaction (EOR). Moreover, the consequence of concentrations (KOH, C2H5OH) and temperatures on electrocatalytic activity of EOR have also been studied. This study would be supportive of developing highly active and low-cost electrocatalysts for other catalytic applications.

Surface Structure Effects of High-Index Faceted Pd Nanocrystals Decorated by Au Submonolayer in Enhancing the Catalytic Activity for Ethanol Oxidation Reaction

Pd-based nanoparticles are considered as the most promising electrocatalysts for ethanol oxidation reaction (EOR) in alkaline direct ethanol fuel cells (DEFCs). However, the existing catalysts stil...

Ni(OH)2 Decorated Pt-Cu Octahedra for Ethanol Electrooxidation Reaction.

Here we report the synthesis of 9 nm Ni(OH)2 decorated Pt-Cu octahedra (Ni(OH)2-PtCu) in one-pot synthesis for ethanol oxidation reaction (EOR) electrocatalysis in acidic electrolyte. To prepare Ni(OH)2-PtCu octahedra, CO gas was directly introduced in a reaction process as selective capping agents on the PtCu(111) facet. Ni(OH)2 was naturally deposited on the Pt-Cu octahedra during the synthesis. Carbon supported Ni(OH)2-PtCu (Ni(OH)2-PtCu/C) as an EOR catalyst showed enhanced CO tolerance due to the existence of oxophilic Ni(OH)2 on the surface of Pt-Cu, facilitating water dissolution to produce OH adsorption and to promote complete CO oxidation to CO2. In addition, Pt-Cu alloy composition also showed improvement of CO tolerance because of modified d-band structure of the Pt atoms, thereby weakening the binding strength of CO on the catalysts. Therefore, the Ni(OH)2-PtCu/C showed enhanced EOR activity and durability compared to the Pt-Cu octahedra and commercial Pt/C counterparts.

A novel catalyst for efficient electrooxidation of ethanol enabled by 3D open-structured PdCu nanocages

Mastery over the structure at nanoscale can efficiently tune the catalytic properties of catalysts, enabling great enhancement in electrocatalytic performance toward liquid fuel electrooxidation reactions. Herein, we demonstrate a facile one-pot method for the successful fabrication of binary PdCu nanocatalysts bounded with 3D open-structured nanocages, which show the advantages of high surface areas, facile mass/electron transport, and strong synergistic effect. Impressively, the resultant 3D open-structured PdCu nanocages (NCs) show large promotion in electrocatalytic performance toward ethanol oxidation reaction (EOR) with the mass activity of 1790.8 mA mg−1, being 3.3 times higher than that of commercial Pd/C (536.2 mA mg−1). Besides, the specific activity for EOR on PdCu NCs (7.7 mA cm−2) is also comparable to many Pt-based electrocatalysts, suggesting the dramatically improved electrocatalytic activity. The outstanding electrocatalytic performance of binary PdCu catalysts is attributed to the highly open 3D nanocage structure and strong electronic effect of Pd and Cu.

Bi(OH)3/PdBi Composite Nanochains as Highly Active and Durable Electrocatalysts for Ethanol Oxidation.

Developing high-performance electrocatalysts for the ethanol oxidation reaction (EOR) is critical to the commercialization of direct ethanol fuel cells. However, current EOR catalysts suffer from high cost, low activity, and poor durability. Here we report the preparation of PdBi-Bi(OH)3 composite nanochains with outstanding EOR activity and durability. The incorporation of Bi can tune the electronic structure and downshift the d-band center of Pd while the surface decoration of Bi(OH)3 can facilitate the oxidative removal of CO and other carbonaceous intermediates. As a result, the nanochains manifest an exceptional mass activity (5.30 A mgPd-1, 4.6-fold higher than that of commercial Pd/C) and outstanding durability (with a retained current density of ∼1.00 A mgPd-1 after operating for 20 000 s). More importantly, the nanochain catalyst can be reactivated, and negligible activity loss has been observed after operating for 200 000 s with periodic reactivation, making it one of the best EOR catalysts.

Reduced Graphene Oxide-Supported Nickel(II)-Bis(1,10-Phenanthroline) Complex as a Highly Active Electrocatalyst for Ethanol Oxidation Reaction

The reduced graphene oxide (rGO) is used to support nickel(II)-bis(1,10-phenanthroline) complex (Ni(II)(Phen)2), forming a catalyst Ni(II)(Phen)2/rGO for ethanol oxidation reaction (EOR). A pyrolytic graphite electrode modified by this catalyst shows excellent electrocatalytic EOR activity, characterized by physical and electrochemical methods. The electrocatalytic activity of the material was evaluated by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). The significant increase in EOR currents compared to the electrode modified with only (Ni(II)(Phen)2 complex demonstrates the promotion role of the rGO. It is believed that the interaction between Ni(II)(Phen)2 and rGO to create a synergistic effect of Ni(II)(Phen)2/rGO catalyst should be responsible for the observed enhancement of the catalytic EOR performance. Using the Laviron theory, the charge transfer rate constant (ks) and the electron transfer coefficient (α) of the electrode reaction are calculated to be 0.60 s−1 and 0.61, respectively. Both the effects of OH− and ethanol concentration on the catalyst EOR activity are also studied to obtain the diffusion coefficient of ethanol (D = 4.7 × 10−6 cm2 s−1) and the catalytic rate constant (kcat = 1.26 × 107 cm3 mol−1 s−1). Based on the experimental results, an EOR mechanism catalyzed by Ni(II)(Phen)2/rGO is proposed. The catalytic EOR peak currents exhibit a linear growth (behavior) with increasing ethanol concentration, suggesting the possible use of this catalyst material as a sensor for ethanol analysis. In addition, the obtained chronoamperometric curves confirm the stability of the catalyst. It is believed that this Ni(II)(Phen)2/rGO catalyst is a promising cost-effective alternative for ethanol oxidation reaction in direct ethanol fuel cells.

Shape-controlled PdSn alloy as superior electrocatalysts for alcohol oxidation reactions

Abstract At present, it is still a great challenge to control the morphology and size of nanoparticles for obtaining more efficient and stable catalysts for direct fuel cell reactions. Herein, we have synthesized a series of Pd3Sn bimetallic catalysts with different morphologies that transitioned from nanonetwork to nanostrips and then to nanodots by altering the varieties of reducing agents and the amount of surfactant. And the formation mechanisms of nanocatalysts were also investigated. It is worth noting that Pd3Sn-dots, due to the unique structure, uniform dispersion and ultra-small size, exhibit excellent electrocatalytic activity for ethanol oxidation reaction and ethylene glycol oxidation reaction, which distinctly higher than the other Pd3Sn catalysts and commercial Pd/C catalysts. Moreover, the as-prepared Pd3Sn catalysts also performed greater long-term durability due to the electronic and synergistic effects. This work provides guidance on the morphology-dependent nanocrystals, which will show a great potential as anodic catalysts in direct fuel cell applications.

(Invited) Challenges and Opportunities in Developing Anode Catalysts for Direct Ethanol and Ammonia Fuel Cells

Direct liquid fuel cells (DLFC) are attractive alternatives of batteries and hydrogen fuel cells for applications where high energy density and easy to refill are critical. For example, in powering a 200W-1kWh drone, a DLFC system can weigh only 1/10 of a battery and refill is simpler than hydrogen and faster than battery recharging. Among liquid fuels, ethanol stands out for its high energy density and ammonia is carbon free. A drawback is the lack of anode catalysts for complete oxidation of ethanol and ammonia at low potentials with sufficient activity per mass of platinum group metals (PGM). Dr. Shimshon Gottesfeld is currently leading an ARPA-E project on “Direct ammonia hydroxide exchange membrane fuel cells”, and I am in the team to develop high performance catalysts for ammonia oxidation reaction (AOR) with low PGM contents. While I learned from reading his papers on a wide range of topics and talking with him at conferences in many years, working under his leadership made me further appreciate his contribution in advancing fuel cell technologies. Inspired by his sharp and open mind in choosing and solving technical issues and in pursuing deep fundamental understandings, I’d like to discuss the challenges in developing anode catalysts for ethanol and ammonia oxidation and to illustrate promising directions and opportunities based on new insights in reaction mechanisms and material/structure/performance correlations. The performances of ethanol oxidation reaction (EOR) and AOR in alkaline media on the best catalysts that we recently developed will be presented and compared. The results show that facile EOR is possible at ambient temperature when a direct 12-electron EOR pathway is activated. Analyses of in situ infrared reflection absorption spectra indicate that the C-C bond splits via ethanol dissociation and full oxidation completes without CO as poisoning intermediate. However, carbonate formation in alkaline media lowers pH and reduces EOR activity. Carbon-free ammonia circumvents this issue, but AOR activity needs enhancement from elevated temperature due to the high activation barrier for N-N bond formation. Most studies so far focused on Pt-based catalysts and the polarization curves were measured at ambient temperature. Our study of temperature-dependent AOR kinetics found that activity enhancement from 25 to 60 oC is in the order of Ir (5.5) > IrPt (4.2) > Pt (2.0).1 For both EOR and AOR, Ir is effective in promoting dehydrogenation, and thus, in lowering the onset potentials. Thus, Ir-based catalysts are more promising than Pt-based catalysts for AOR. I’ll also show that the C-C bond cleavage in EOR and the N-N bond formation in AOR prefer distinctly different atomic structures. The new insights point out opportunities and directions for future studies. Acknowledgements The author thanks Zhixiu Liang, Liang Song, Jingyi Chen, Shiqing Deng, and Eli Stavitski for their collaborations. The work was funded by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000805 and by the Division of Chemical Sciences, Geosciences and Biosciences Division, US Department of Energy under contract DE-SC0012704. References Song, L. et al. Temperature-Dependent Kinetics and Reaction Mechanism of Ammonia Oxidation on Pt, Ir, and PtIr Alloy Catalysts. J. Electrochem. Soc. 165, J3095–J3100 (2018).

Effects of Incorporated Iron or Cobalt on the Ethanol Oxidation Activity of Nickel (Oxy)Hydroxides in Alkaline Media

Nickel (oxy)hydroxides (NiOxHy) are promising cost-effective materials that exhibit a fair catalytic activity for the ethanol oxidation reaction (EOR) and could be used for sustainable energy conversion. Doping the NiOxHy structure with other metals could lead to enhanced catalytic properties but more research needs to be done to understand the role of the doping metal on the EOR. We prepared NiOxHy films doped with Fe or Co with different metallic ratios by electrodeposition and evaluated the EOR. We found a positive and negative effect on the catalytic activity after the incorporation of Co and Fe, respectively. Our results suggest that Ni atoms are the active sites for the EOR since Tafel slopes were similar on the binary and pristine nickel (oxy)hydroxides and that the formal potential of the Ni(II)/Ni(III) redox couple is a good descriptor for the EOR activity. This work also highlights the importance of controlled metal doping on catalysts and may help in the design and development of improved materials for the EOR.Graphical Ethanol oxidation reaction was studied on different electrodeposited nickel (oxy)hydroxides modified with iron or cobalt. Enhanced activity was observed for the materials modified with cobalt, while iron doping had a negative influence. Results also suggest that nickel atoms are the active sites in the bimetallic materials.

1D-2D integrated hybrid carbon nanostructure supported bimetallic alloy catalyst for ethanol oxidation and oxygen reduction reactions

Herein, 1-D carbon nanotubes and 2-D graphene hybrid carbon hetero-structure is employed as the catalyst support material for low temperature fuel cell. Partial unraveling of carbon nanotubes results in 1D-2D hybrid hetero-structure with enhanced surface area, while the intact inner tubes result in good electrical conductivity. Platinum-tin alloy decorated on partially exfoliated carbon nanotubes (Pt–Sn/PCNT) were prepared by ethylene glycol reduction method and investigated its electrocatalytic activity towards ethanol oxidation reaction (EOR) for direct ethanol fuel cell (DEFC) and oxygen reduction reaction (ORR) for hydrogen fuelled polymer electrolyte membrane fuel cell (PEMFC). Along with the intrinsic properties of carbon nanotubes, PCNT provides more anchoring sites, thereby facilitates complete utilization of catalysts. The electrochemical EOR studies reveal that Pt–Sn/PCNT has better tolerance to the accumulation of intermediate species than Pt–Sn/CNT. Besides, as-synthesized electrocatalysts exhibit good ORR activity with four-electron pathway. The enhanced EOR and ORR activity of as prepared electrocatalysts is attributed to the high dispersion of catalyst nanoparticles on PCNT along with the inhibition of production of intermediate species on the Pt surface by alloying. Further, the practical suitability of PCNT supported Pt–Sn nanocatalysts as EOR and ORR electrocatalysts has been examined by performing the full fuel cell measurements.

Novel highly active carbon supported ternary PdNiBi nanoparticles as anode catalyst for the alkaline direct ethanol fuel cell

The study focuses on the influence of Ni and Bi on alkaline ethanol oxidation reaction (EOR) activities, stabilities and structure characteristics of carbon supported Pd-based nanocatalysts (Pd/C, Pd60Ni40/C, Pd60Bi40/C, Pd60Ni20Bi20/C) by cyclic voltammetry/chronoamperometry using rotating disk electrode and various physico-chemical methods such as X-ray powder diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy coupled with energy dispersive X-ray spectroscopy and inductively coupled plasma optical emission spectrometry. Nickel generates more adsorbed OH on the Pd catalyst surface than Bi and promotes the oxidation of adsorbed ethanol species. This results in a low onset potential toward ethanol oxidation with high current density. The presence of Bi facilitates high tolerance toward various reaction intermediates resulting from the incomplete ethanol oxidation, but might also initiate the agglomeration of Pd nanoparticles. The novel Pd60Ni20Bi20/C nanocatalyst displays exceptional byproduct tolerance, but only satisfying catalytic activity toward ethanol oxidation in an alkaline medium. Therefore, the EOR performance of the novel carbon supported ternary PdxNiyBiz anode catalyst with various atomic variations (Pd70Ni25Bi5/C, Pd70Ni20Bi10/C, Pd80Ni10Bi10/C and Pd40Ni20Bi40/C) using the common instant reduction synthesis method was further optimized for the alkaline direct ethanol fuel cell. The carbon supported Pd:Ni:Bi nanocatalyst with atomic ratio of 70:20:10 displays outstanding catalytic activity for the alkaline EOR compared to the other PdxNiyBiz/C nanocatalysts as well as to the benchmarks Pd/C, Pd60Ni40/C and Pd60Bi40/C. The synergy and the optimal content in consideration of the oxide species of Pd, Ni and Bi are crucial for the EOR kinetic enhancement in alkaline medium.

Synthesis and facile structure-adjusting of Pd–Pt nanocrystal electrocatalysts with improved activity for ethanol oxidation reaction

Illustration of the synthesis of the nanospheroid-, nanoflower- and nanoworm-Pd–Pt NCs and their electrocatalytic activity for ethanol oxidation.

Monodisperse ordered indium-palladium nanoparticles: synthesis and role of indium for boosting superior electrocatalytic activity for ethanol oxidation reaction.

The slow kinetics of ethanol oxidation reaction (EOR) has limited its widespread use for fuel cells. Bimetallic catalysts with optimized surface compositions can considerably govern rate-determining steps through selectivity for CH3COOH formation or by facilitating the adsorption of OHadsvia the bifunctional effect of an alloy to increase the EOR's kinetic rates. Here, we reported monodisperse ordered In-Pd nanoparticles as new bimetallic high-performance catalysts for EOR. In-Pd nanoparticles, i.e., In3Pd2 and In3Pd5 were prepared using arrested precipitation in solution, and their composition, structures, phase and crystallinity were confirmed using a variety of analyses including TEM, XPS, EDS and XRD. In-Pd nanoparticles were loaded on carbon black (Vulcan XC-72) as electrocatalysts for EOR in alkaline media. In3Pd2 and In3Pd5 nanoparticles exhibited 5.8 times and 4.0 times higher mass activities than commercial Pd/C, which showed that the presence of indium greatly boosts electrocatalytic reactivity for EOR of Pd catalysts. This performance is the best among those of bimetallic nanoparticles reported to date. Such high performance of In-Pd nanoparticles may be attributed to the following two reasons. First, In-Pd nanoparticles exhibited excellent CO anti-poison ability, as confirmed by CO striping experiments. Second, as revealed by DFT calculations of metals with OHads adsorption, In atoms on In3Pd2 surface exhibited the lowest energy (-1.659 eV) for OHads adsorption as compared to other common oxophilic metals including Sn, SnPt, Ag, Ge, Co, Pb, and Cu. We propose that the presence of indium sites promoted efficient free OH radical adsorption on indium sites and resulted in a faster reaction rate of acetate formation from acetaldehyde (the rate determining step for EOR on Pd sites). Finally, a single direct ethanol fuel cell (DEFC) with Pd/C anode was prepared. Compared to the results for a commercial Pd/C anode, the open circuit voltage (OCV) of In3Pd2/C improved by 0.25 V (from 0.64 to 0.89 V) and the power density improved by ∼80% (from 3.7 to 6.7 mW cm-2), demonstrating its practical uses as Pt or Pd catalyst alternatives for DEFC.

Hydrogenated graphene as support of Pd nanoparticles with improved electrocatalytic activity for ethanol oxidation reaction in alkaline media

A new class of ethanol electrooxidation catalyst was developed based on Pd nanoparticles supported by hydrogenated graphene (HG). The catalytic activities of Pd/HG with different hydrogenation degree (annealed at 60, 300, 800 °C respectively) were also carefully studied. Test results suggested that Pd/HG-60 exhibited super activity for electrocatalytic ethanol oxidation to Pd/HG-300 and Pd/HG-800. Moreover, Pd/HG-60 showed the highest electrochemically active surface area (EASA) among these obtained catalysts. The characterization data indicated that hydrogenated graphene with high hydrogenation degree was more favorable to promote the formation and dispersion of small Pd nanoparticles. In turn, highly dispersed Pd nanoparticles have strong electronic interaction with graphene support, which contributes to high EASA resulting in better electrocatalytic activity for ethanol oxidation reaction in alkaline media.

A perspective on the promoting effect of Ir and Au on Pd toward the ethanol oxidation reaction in alkaline media

There remain great challenges in developing highly efficient electrocatalysts with both high activity and good stability for the ethanol oxidation reaction in alkaline media. Herein, two architectures of tri-metallic PdIrAu/C electrocatalysts are designed and the promoting effect of Au and Ir on Pd toward the ethanol oxidation reaction (EOR) in alkaline media is investigated in detail. On the one hand, the tri-metallic Pd7Au7Ir/C electrocatalyst with a solid solution alloy architecture is less active relative to Pd7Ir/C and Pd/C while the stabilizing effect of Au leads to both a higher activity and a lower degradation percentage after 3000 cycles of the accelerated degradation test (ADT) on Pd7Au7Ir/C than those on Pd7Ir/C. On the other hand, the tri-metallic Pd7Ir@(1/3Au)/C electrocatalyst with a near surface alloy architecture delivers a much higher activity with an improvement up to 50.4% compared to Pd7Ir/C. It is speculated that for the tri-metallic Pd7Ir@(1/3Au)/C electrocatalyst, certain Au atoms are well designed on surfaces to introduce an electronic modification, thus leading to an anti-poisoning effect and improving the EOR activity.

Performance and In‐Situ FTIR Evaluation of Pt−Sn/C Electrocatalysts with Several Pt : Sn Atomic Ratios for the Ethanol Oxidation Reaction in Acidic Media

AbstractPt−Sn/C electrocatalysts with nominal Pt : Sn atomic ratios of 1 : 1, 2 : 1 and 3 : 1 were synthesized via the polyol method. The effects of the atomic ratios on their catalytic activity for the ethanol oxidation reaction (EOR) in acidic media was evaluated and compared to a Pt/C electrocatalyst obtained by the same procedure. The differences in reaction mechanism between the alloys and Pt/C were elucidated by in‐situ FTIR measurements. XRD characterization of the Pt−Sn/C electrocatalysts showed a degree of alloying ranging between 27 and 54 % (from Vegard's law), while crystallite sizes close to 2.2 nm were determined with the Scherrer equation. Pt : Sn atomic ratios of 1 : 1, 1.6 : 1 and 2.4 : 1 were found experimentally via EDS analysis, fairly close to the nominally expected values. Electrochemical evaluation indicated that the alloy having a 1 : 1 ratio has the highest electrocatalytic activity for EOR. In‐situ FTIR characterization showed that the Pt−Sn/C alloys promote the oxidation of ethanol via a triple parallel pathway: one path involving the directly conversion of COL (linearly‐bonded CO) to CO2, while the second proceeds via the reaction of AAL (acetaldehyde) into COL and later to CO2, and the third involves the formation of AA (acetic acid) from adsorbed acetate that may be produced from AAL. Such mechanism promoted the EOR at more negative potentials at the alloys, also delivering higher current densities, relative to Pt/C. Thus, the inclusion of Sn in the Pt structure enhanced the catalytic activity for the EOR in acidic media.

(Invited) Gold Nanoparticles Modified with Platinum and Palladium As Electrocatalysts for Ethanol Oxidation Reactions

Electrooxidation of ethanol on noble metals, such as Pt in acidic and Pd in alkaline solutions is of particular interest due to its potential application in low-temperature direct ethanol fuel cells (DEFCs). The slow, incomplete oxidation of ethanol as well as the high price of Pt and Pd has impeded the wide application of DEFCs. In response to these challenges, several resembling core-shell electrocatalysts using Au nanoparticles were synthesized and evaluated for ethanol oxidation reaction (EOR). It was found that the Pd shell is not uniform consisting of tiny Pd clusters with a coverage of 0.5-0.6. The EOR activity of this kind of structure is much higher than Pd/C in an alkaline solution. The forward peak current density of was 5 times higher than that of Pd/C. Furthermore, the onset potential for EOR of the former was ~100 mV more negative. An interesting particle size dependent EOR activity was also observed. With increasing the Au particle size (2.9 to 5.8 and 6.5 nm), the EOR activity increases. The strain and ligand effects from the Au core, together with the bifunctional mechanism from the core and shell can explain the observed activity trend. Similar core-shell catalysts with a Pt shell were also synthesized and evaluated for EOR in acidic electrolytes. In a further study, the core-shell particles were modified with Ru and SnO2, which showed enhanced activities. In situ spectroscopic studies were conducted to reveal the reaction intermediates and products of various catalysts to give more insights into the reaction pathway and activity enhancement mechanisms.

Pt-modified TaC as an efficient electrocatalyst for ethanol oxidation in acid and alkaline electrolytes

Ethanol is an ideal fuel in low-temperature fuel cells. The ethanol oxidation reaction (EOR) on platinum-modified tantalum carbide (TaC) has been investigated using both model thin films and powder catalysts. The results demonstrate that the 1.5 wt% Pt-modified TaC catalyst shows enhanced EOR activity compared to Pt. In-situ infrared reflection absorption spectroscopy (IRRAS) study reveals that the Pt surface is less poisoned by EOR intermediates and a higher CO2 selectivity (7∼9%) is achieved on the 1.5 wt% Pt/TaC catalyst, compared to the 40 wt% Pt/C. Density functional theory (DFT) calculations reveal that the binding energies of EOR intermediates on the Pt/TaC(111) surface are weaker than on Pt(111), suggesting an enhanced poison-tolerance from the adsorption of these intermediates. The combined experimental and theoretical investigations indicate that Pt/TaC is a promising electrocatalyst for EOR.

(Invited) Pt/Rh/SnO2 Catalysts for Selective Ethanol Oxidation Reaction to CO2

Introduction Direct ethanol fuel cells (DEFCs) using bioethanol are eco-friendly devices like polymer electrolyte fuel cells because they do not increase CO2. Ethanol is nontoxic, and superior in transportation, storage, and handling to hydrogen. However, ethanol is slowly and incompletely oxidized due to the hardness of C-C bond cleavage. Binary PtSn alloy and Pt/SnOx catalysts are known to be the best anode catalysts for ethanol oxidation reaction (EOR). In these catalysts Pt facilitated the adsorption and dissociation of ethanol, while Sn provided OH species for the oxidation of CO on Pt. The main product, however, was not CO2, but acetaldehyde and acetic acid, the partial EOR products. PtRh was effective for the C-C bond cleavage to form CO2, although its EOR activity was low. The combination of Pt, Rh and Sn can enhance the EOR activity in addition to the merit of the PtRh catalyst. The improvement of EOR activity and CO2 selectivity with ternary Pt-Rh-Sn catalysts has been reported so far. The atomic arrangement at active sites, however, has not been discussed except for only a few papers. In this study we used a Pt electrode modified partly with SnO2, and preferentially deposited Rh on Pt adjacent to SnO2 by a limited CO stripping technique to realize selective EOR to CO2. Moreover, based on the results with the model electrodes, we prepared Pt/Rh/SnO2 nanoparticle catalysts, in which the position of the Rh atoms was controlled, and evaluated the CO2 selectivity. Experimental The ternary Pt/Rh/SnO2 electrode was prepared as follows.1 Sn was deposited on a Pt disk electrode at -0.2 V vs. RHE for 30 s in an Ar-saturated 0.2 mM SnCl2/0.1 M H2SO4 solution. The resultant Sn-deposited Pt (Pt/SnO2) electrode was moved into a CO-saturated 0.1 M H2SO4, to adsorb CO on the exposed Pt surface. After removing dissolved CO by Ar bubbling, CO on the exposed Pt atoms adjacent to SnO2 was removed by a potential sweep from 0.05 to 0.5 V. After that, an aliquot of 50 mM RhCl3/0.1 M H2SO4 was added to the solution, following by depositing Rh on the exposed Pt atoms at -0.2 V for 30 s. The resultant Rh-deposited Pt/SnO2 (Pt/Rh/SnO2) electrode was thoroughly washed with ultrapure water. Pt/SnO2(3:1) nanoparticle-loaded carbon black was prepared according to ref. 2. The Pt/SnO2/C powder was sonicated in an Ar-saturated 0.5 M H2SO4 solution at 30 oC for 1 h to get the well-dispersed suspension. CO was adsorbed on the Pt surface of the Pt/SnO2 nanoparticles. Then the adsorbed CO on Pt neighboring to Sn was selectively desorbed while the potential was set at 0.5 V vs. RHE for 15 min. After adding 0.1 mM RhCl3 solution, Rh was deposited on the exposed Pt surface of the Pt/SnO2 nanoparticles with hydrogen.3 Results and Discussion The X-ray photoelectron spectroscopy showed the main valence of Sn for the Pt/Rh/SnO2 electrode was IV (SnO2), whereas the valences of Pt and Rh were 0 (metallic). Cyclic voltammograms exhibited that the Pt/Rh/SnO2 electrode was about 4 and 1.5 times higher in EOR activity than the Pt and Pt/SnO2 electrode, respectively. In-situ infrared refraction-absorption spectroscopy (IRAS) elucidated that CO2 was selectively formed on Pt/Rh/SnO2, and acetaldehyde and acetic acid, which were mainly produced on Pt/SnO2, were scarcely formed, demonstrating that the arrangement of Rh atoms separating Pt and SnO2 is important for selective CO2 formation. For the Pt/Rh/SnO2/C nanoparticle catalyst, the mean particle size was 2.8 nm, which is a little bit larger than that of Pt/SnO2C (2.5 nm). For EOR activity, the former was higher than the latter. In-situ IRAS CO2 and acetaldehyde were main products although acetic acid was the main product for the Pt/SnO2/C. The CO2 production increased with potential from 0.2 V, whereas the acetaldehyde did not depend on potential. References M. P. Tu, M. Chiku, E. Higuchi, and H. Inoue, J. Electrochem. Soc., 164, F1011 (2017).E. Higuchi, K. Miyata, T. Takase, and H. Inoue, J. Power Sources, 196, 1730 (2011).M. P. Tu, M. Chiku, E. Higuchi, and H. Inoue, ECS Trans., 77(11), 1937 (2017).