One-step synthesis of carbon-supported Pd–Pt alloy electrocatalysts for methanol tolerant oxygen reduction

A facile, one-step reduction route was developed to synthesize Pd-rich carbon-supported Pd–Pt alloy electrocatalysts of different Pd/Pt atomic ratios. As-prepared Pd–Pt/C catalysts exhibit a single phase fcc structure and an expansion lattice parameter. Comparison of the oxygen reduction reaction (ORR) on the Pd–Pt/C alloy catalysts indicates that the Pd₃Pt₁/C bimetallic catalyst exhibits the highest ORR activity among all the Pd–Pt alloy catalysts and shows a comparative ORR activity with the commercial Pt/C catalyst. Moreover, all the Pd–Pt alloy catalysts exhibited much higher methanol tolerance during the ORR than the commercial Pt/C catalyst. High methanol tolerance of the Pd–Pt alloy catalysts could be attributed to the weak adsorption of methanol induced by the composition effect, to the presence of Pd atoms and to the formation of Pd-based alloys.     

Electrochemical characteristics of platinum-based binary catalysts for middle-temperature hydrogen-air fuel cells with phosphoric acid electrolyte

The high-temperature synthesis based on commercial catalyst E-TEK (40% Pt) using cobalt, chromium, and iron organic precursors as well as d-metal salts yielded PtM (1:1) catalysts (PtCo, PtCr, PtMn, PtNi, PtFe, and PtV) for electroreduction of molecular oxygen in concentrated H₃PO₄ at the temperature of 160°C. The phase composition of the synthesized catalysts was studied by powder diffraction. The electrochemical measurements were carried out in 15 M H₃PO₄ at 20 and 160°C using a model gas diffusion electrode. An assumption was made that close charging curves recorded for synthesized PtM catalysts in both hydrogen and oxygen adsorption ranges were due to formation of the core-shell structure: alloy core and surface layers enriched with platinum. The Tafel curves of molecular oxygen reduction in 15 M H₃PO₄ at 160°C were characterized with the sole slope of 0.10 to 0.11 V. The catalytic activity in the range of potentials from 0.8 to 0.9 V (RHE) was shown approximately twice as that of pure platinum catalyst. The highest activity was recorded for PtCo and PtCr binary catalysts. Their use in middle-temperature hydrogen-air fuel cells with solid polymeric electrolyte based on polybenzimidazole doped with phosphoric acid enabled 2- to 3-fold decrease of the platinum share in the cathode.     

Preparation and surface characterization of Pt–Au/C cathode catalysts with ceria modification for oxygen reduction reaction

Alloy catalysts of Pt₅₀Au₅₀/Ce_xC with various Ce additions (x) were prepared for the oxygen reduction reaction (ORR). The characterization of the alloy structures, surface species, and electro-catalytic activities of prepared alloy catalysts were performed by XRD, temperature-programmed reduction (TPR), and rotating disc electrode (RDE) technique, respectively. The ORR activity of Pt₅₀Au₅₀/C alloy catalyst with a promotion of 15% CeO₂ was enhanced significantly in comparison to the commercial Pt/C catalyst within the mixed kinetic-diffusion control region. The addition of CeO₂ decreased the particle sizes, increased the dispersion and enhanced the surface segregation of Pt which resulting in an alloy surface with a moderate oxophilicity on alloy catalysts.     

Synthesis of Pt3Ni-based functionalized MWCNTs to enhance electrocatalysis for PEM fuel cells

Nanoscale Pt₃Ni/functionalized multiwalled carbon nanotubes (FMWCNTs) catalysts, successfully synthesized by anchoring nickel–platinum alloy nanoparticles on FMWCNTs, are presented in this paper. Compared with conventional commercial Pt/C catalysts, the preliminary results revealed that the Pt₃Ni/FMWCNTs catalysts demonstrated not only higher specific activity for oxygen reduction reaction (ORR) but also outstanding stability. The enhancement in the stability of the Pt₃Ni/FMWCNTs catalysts is believed to be due to the anchor effects in Pt₃Ni alloy structure, the stronger interaction between Pt₃Ni alloy nanoparticles and FMWCNTs, and the “π sites” anchoring centers for metal nanoparticles from CNTs with high graphite.     

Tungsten‐Doped L10‐PtCo Ultrasmall Nanoparticles as a High‐Performance Fuel Cell Cathode

The commercialization of proton exchange membrane fuel cells (PEMFCs) relies on highly active and stable electrocatalysts for oxygen reduction reaction (ORR) in acid media. The most successful catalysts for this reaction are nanostructured Pt‐alloy with a Pt‐skin. The synthesis of ultrasmall and ordered L1₀‐PtCo nanoparticle ORR catalysts further doped with a few percent of metals (W, Ga, Zn) is reported. Compared to commercial Pt/C catalyst, the L1₀‐W‐PtCo/C catalyst shows significant improvement in both initial activity and high‐temperature stability. The L1₀‐W‐PtCo/C catalyst achieves high activity and stability in the PEMFC after 50 000 voltage cycles at 80 °C, which is superior to the DOE 2020 targets. EXAFS analysis and density functional theory calculations reveal that W doping not only stabilizes the ordered intermetallic structure, but also tunes the Pt‐Pt distances in such a way to optimize the binding energy between Pt and O intermediates on the surface.     

Composition,surface segregation,and electrochemical properties of binary PtM/C (M = Co,Ni, Cr) catalysts

The effect of the nature of transient metal and chemical treatment of binary cathodic PtM/C (M = Co, Ni, Cr) catalysts, which were prepared by high-temperature synthesis, on their structure, surface segregation, and characteristic properties (activity and stability) is studied. It is shown that, in the course of treatment in 0.5 M H₂SO₄ at the elevated temperature (60°C), the surface of nanoparticles becomes enriched in platinum with the formation of core-shell structures. The PtCo/C catalyst is the most efficient one. In this case, a compromise between the corrosion resistance and electrocatalytic activity is reached due to a higher, as compared with PtNi/C and PtCr/C, degree of alloy formation and enriching of surface in platinum in the course of corrosive attack. Thereby, the properties of platinum on the core surface change as a result of a pronounced ligand effect of the core. Thus, depending on the nature of transient metal, the binary cathodic PtM/C catalysts differ in their activity and stability, which depend on the degree of alloy formation and a possibility of formation of core-shell structure as a result of surface segregation in the course of synthesis and chemical treatment.     

Electrochemical processes on multi-component cathodic catalysts PtM and PtM<Subscript>1</Subscript>M<Subscript>2</Subscript> (M = Co,Ni, Cr): the effect of surface composition on the catalyst stability and its activity in O<Subscript>2</Subscript> reduction

The multi-component nanocatalysts based on platinum-transient metals alloys applied onto dispersed carbon material are considered as the most promising catalysts, which can be substituted for platinum in the fuel cell cathodes. The electrocatalytic activity of platinum in the PtM₁/C and PtM₁M₂/C alloys increases by several times with simultaneous increase in the stability. From the results obtained by structural and electrochemical methods, it is found that the synthesized binary and ternary catalysts are the metal alloys, whose surface is enriched in platinum as a result of surface segregation and subsequent chemical or electrochemical treatment. Under the corrosive attack, the less-noble metal, which has not entered into the alloy, dissolves, and the core-shell structures form. The properties of platinum in the shell differ from its properties in Pt/C due to the ligand effect of the core (metal alloy). As a result, the surface coverage with oxygen chemisorbed from water decreases in the binary and ternary systems. This causes an increase of the catalytic activity in the O₂ reduction reaction due to a decline in the effect of surface blocking against molecular oxygen adsorption and a decrease in the platinum dissolution rate, because the oxidation of platinum by water is the onset of corrosion process. For the catalytic systems studied, the mass activity decreases in the following order: 20% Pt in PtCoCr/C > 7.3% Pt in PtCo/C ≥ 7.3% Pt in PtCr/C and PtNi/C ≥ 40% Pt/C. The application of PtCoCr/C catalyst as the cathode in a low-temperature hydrogen-air fuel cell enabled one to reduce the platinum consumption by one half on retention of its performance.     

Electrocatalytic oxidation of methanol on Pt-Pd nanoparticles supported on honeycomb-like porous carbons in alkaline media

Honeycomb-like porous carbons (PCs) were synthesized using a facile self-assembly method with phenolic resin as the carbon source and tetraethyl orthosilicate (TEOS) as the silica source. The PCs were found to have a large BET surface area of 458 m² g^?1 and a partially graphitized structure. The obtained PCs were used as a support for various Pt-Pd bimetallic alloy catalysts employed for methanol oxidation in alkaline media. Compared with Pt supported on commercial Vulcan XC-72R carbon (Pt/C) and with the other Pt-Pd bimetallic alloy catalysts on PCs, Pt₃Pd₁ on PCs displayed the most negative onset potential for methanol oxidation and the highest steady-state current (2.04 mA cm^?2). This may be because the Pt₃Pd₁/PCs catalyst has the largest electrochemical active surface area (ESA), and because adding Pd to the catalyst improves the ability of the intermediate species to tolerate oxidation. The results show that the prepared Pt-Pd/PCs is a potential candidate for application as a catalyst in alkaline direct methanol fuel cells.     

Chemically dealloyed Pt–Au–Cu ternary electrocatalysts with enhanced stability in electrochemical oxygen reduction

We report simple synthesis of ternary Pt–Au–Cu catalysts consisting of active Pt-rich shell and Pt transition-metal alloy core for use as highly active and durable electrocatalysts in oxygen reduction reactions. The ternary Pt–Au–Cu catalysts were synthesized by chemical coreduction followed by thermal treatment and chemical dealloying. During synthesis, thermal treatment formed metal particles into high-degree alloys, and chemical dealloying led to selective dissolution of soluble Cu species from the outer surface layer of the thermally treated alloy particles, resulting in Pt-based alloys@Pt-rich surface core–shell configuration. Compared with a commercial Pt/C catalyst, our Pt_1?xAu _x Cu₃/C-AT catalysts exhibited approximately 2.4-fold enhanced performance in oxygen reduction reactions. Among the catalysts employed in this work, Pt_0.97Au_0.3Cu₃/C-AT showed the highest performance in terms of mass activity, specific activity, and electrochemically active surface area loss with negligible change during 10,000 potential cycles. The synthesis details, electrochemical characteristics, oxygen reduction reaction performance, and durability of the chemically dealloyed ternary Pt–Au–Cu catalysts are presented and discussed.     

氧-硼共修饰多壁碳纳米管载铂催化剂的制备及氧还原活性

采用一种简便的方法,合成了氧-硼共修饰的多壁碳纳米管材料,以此为载体制备的铂基催化剂具有更小的铂粒径、更高的电化学表面积(40 m²·g_Pt^-1)和更高的氧还原活性(0.3 A·mg_Pt^-1)。氧、硼在提高碳纳米管的载体分散性、控制铂颗粒的均匀性和粒径、促进氧还原反应的氧吸附/解离方面发挥着重要的作用。     

氧-硼共修饰多壁碳纳米管载铂催化剂的制备及氧还原活性

采用一种简便的方法,合成了氧-硼共修饰的多壁碳纳米管材料,以此为载体制备的铂基催化剂具有更小的铂粒径、更高的电化学表面积(40 m²·g_Pt^-1)和更高的氧还原活性(0.3 A·mg_Pt^-1)。氧、硼在提高碳纳米管的载体分散性、控制铂颗粒的均匀性和粒径、促进氧还原反应的氧吸附/解离方面发挥着重要的作用。     

Electrochemical characteristics of PdCoPt/C catalysts synthesized under different conditions

Kinetics of oxygen reduction is studied on PdCoPt/C catalysts with different platinum contents in the metal phase. Catalytic systems are synthesized by the high-temperature method. According to XRD analysis, as the contents of metallic Pd and Co in the catalysts increase, the degree of formation of the alloy between them also increase, which however is accompanied by a considerable growth of metal phase particles. To minimize this adverse effect, a method of sequential metal deposition is put forward. This approach makes it possible to considerably decrease the catalyst grain size as compared the single-step deposition for high metal phase contents in the catalytic system. The kinetics of oxygen reduction on the PdCoPt/C catalysts is studied on the rotating disk electrode. Under model conditions (0.5 M H₂SO₄, 60°C, O₂), the 20Pd13Co5Pt/C catalyst exhibited the highest activity per mass unit (0.5 M H₂SO₄, 60°C, O₂), namely, 9 A/g_{Pd + Pt} at 0.9 V.     

Platinum Oxide Nanoparticles for Electrochemical Hydrogen Evolution: Influence of Platinum Valence State

Electrochemical hydrogen generation is a rising prospect for future renewable energy storage and conversion. Platinum remains a leading choice of catalyst, but because of its high cost and low natural abundance, it is critical to optimize its use. In the present study, platinum oxide nanoparticles of approximately 2 nm in diameter are deposited on carbon nitride (C3N4) nanosheets by thermal refluxing of C3N4 and PtCl₂ or PtCl₄ in water. These nanoparticles exhibit apparent electrocatalytic activity toward the hydrogen evolution reaction (HER) in acid. Interestingly, the HER activity increases with increasing Pt⁴⁺ concentration in the nanoparticles, and the optimized catalyst even outperforms commercial Pt/C, exhibiting an overpotential of only −7.7 mV to reach the current density of 10 mA cm⁻² and a Tafel slope of −26.3 mV dec⁻¹. The results from this study suggest that the future design of platinum oxide catalysts should strive to maximize the Pt⁴⁺ sites and minimize the formation of the less active Pt²⁺ species.     

Oxidation of carbon monoxide and formic acid on bulk and nanosized Pt–Co alloys

Bulk Pt₃Co and nanosized Pt₃Co and PtCo alloys supported on high area carbon were investigated as the electrocatalysts for the CO_ads and HCOOH oxidation. Pt₃Co alloy with Co electrochemically leached from the surface (Pt skeleton) was employed to separate electronic from ensemble and bifunctional effects of Co. Cyclic voltammetry in 0.1 M HClO₄ showed reduced amount of adsorbed hydrogen on Pt sites on Pt₃Co alloy compared to pure Pt. However, no significant difference in hydrogen adsorption/desorption and Pt-oxide reduction features between Pt₃Co with Pt skeleton structure and bulk Pt was observed. The oxidation of CO_ads on Pt₃Co alloy commenced earlier than on Pt, but this effect on Pt₃Co with Pt skeleton structure was minor indicating that bifunctional mechanism is stronger than the electronic modification of Pt by Co. The HCOOH oxidation rate on Pt₃Co alloy was about seven times higher than on bulk Pt when the reaction rates were compared at 0.4 V, i.e., in the middle of the potential range for the HCOOH oxidation. Like in the case of CO_ads oxidation, Pt skeleton showed similar activity as bulk Pt indicating that the ensemble effect is responsible for the enhanced activity of Pt₃Co alloy toward HCOOH oxidation. The comparison of CO_ads and HCOOH oxidation on Pt₃Co/C and PtCo/C with the same reaction on Pt/C were qualitatively the same as on bulk materials.     

Promotional effect of Snad on the ethanol oxidation at Pt3Sn/C catalyst

Oxidation of ethanol was studied at Sn_ad modified and unmodified Pt₃Sn/C and Pt/C catalysts. Pt₃Sn/C and Pt/C catalysts were characterized by XRD. Potentiodynamic and chronoamperometric measurements were used to establish catalytic activity and stability. High activity achieved at Sn_ad modified Pt₃Sn/C catalyst has not been observed at any bimetallic catalyst so far. Promotional effect of Sn_ad on the ethanol oxidation was related to the enhancement of CO oxidation rate in bifunctional mechanism. It was shown that electrodeposited Sn exhibited different effect on the catalytic activity compared to Sn in alloy.     

The structure and characteristics of a PtCoCr nanosized polymetallic cathode catalyst on a carbon carrier

The paper presents X-ray and transmission electron microscopy data characterizing the structure of trimetallic PtCoCr catalysts synthesized on a disperse carbon carrier (carbon black KhS 72) and the influence of the structure on electrocatalytic activity in the reduction of oxygen in 0.5 M H₂SO₄. The mechanisms of oxygen reduction on platinum and trimetallic catalysts were shown to be similar. A higher activity of platinum contained in the trimetallic catalyst was caused by smaller PtCoCr/C catalyst surface coverage by oxygen-containing particles formed from water and interfering with the adsorption of molecular oxygen, which was, in turn, determined by the electronic structure of trimetallic system nanoparticles.     

Bimetallic Pd—Pt/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for complete methane oxidation: the effect of the Pt: Pd ratio

Alumina-supported bimetallic Pt—Pd catalysts proved to be more active in the complete oxidation of methane than monometallic systems (Pt/Al₂O₃, Pd/Al₂O₃). The maximum activity of the bimetallic catalysts was achieved at ~40 at.% Pt in Pd on the catalyst surface. After the oxidation reaction, redistribution of platinum and palladium was observed in the active component of the catalysts with the degree of redistribution depending on the initial Pt: Pd ratio.     

Revealing the Effect of Surface Composition on Multiwalled Carbon Nanotubes Supported Pt-Fe Alloy Electrocatalysts for Methanol Oxidation Performance

The designs of efficient and inexpensive Pt-based catalysts for methanol oxidation reaction (MOR) are essential to boost the commercialization of direct methanol fuel cells. Here, the highly catalytic performance PtFe alloys supported on multiwalled carbon nanotubes (MWCNTs) decorating nitrogen-doped carbon (NC) have been successfully prepared via co-engineering of the surface composition and electronic structure. The Pt₁Fe₃@NC/MWCNTs catalyst with moderate Fe³⁺ feeding content (0.86 mA/mg_Pt) exhibits 2.26-fold enhancement in MOR mass activity compared to pristine Pt/C catalyst (0.38 mA/mg_Pt). Furthermore, the CO oxidation initial potential of Pt₁Fe₃@NC/MWCNTs catalyst is lower relative to Pt/C catalyst (0.71 V and 0.80 V). Benefited from the optimal surface compositions, the anti-corrosion ability of MWCNT, strong electron interaction between PtFe alloys and MWCNTs and the N-doped carbon (NC) layer, the Pt₁Fe₃@NC/MWCNTs catalyst presents an improved MOR performance and anti-CO poisoning ability. This study would open up new perspective for designing efficient electrocatalysts for the DMFCs field.     

Inducing Covalent Atomic Interaction in Intermetallic Pt Alloy Nanocatalysts for High-Performance Fuel Cells

The harsh working environments of proton exchange membrane fuel cells (PEMFCs) pose huge challenges to the stability of Pt-based alloy catalysts. The widespread presence of metallic bonds with significantly delocalized electron distribution often lead to component segregation and rapid performance decay. Here we report L1₀−Pt₂CuGa intermetallic nanoparticles with a unique covalent atomic interaction between Pt−Ga as high-performance PEMFC cathode catalysts. The L1₀−Pt₂CuGa/C catalyst shows superb oxygen reduction reaction (ORR) activity and stability in fuel cell cathode (mass activity=0.57 A mg_Pt⁻¹ at 0.9 V, peak power density=2.60/1.24 W cm⁻² in H₂-O₂/air, 28 mV voltage loss at 0.8 A cm⁻² after 30 000 cycles). Theoretical calculations reveal the optimized adsorption of oxygen intermediates via the formed biaxial strain on L1₀−Pt₂CuGa surface, and the durability enhancement stems from the stronger Pt−M bonds than those in L1₁−PtCu resulted from Pt−Ga covalent interactions.     

In situ Spectroscopic Insight into the Origin of the Enhanced Performance of Bimetallic Nanocatalysts towards the Oxygen Reduction Reaction (ORR)

It is vital to understand the oxygen reduction reaction (ORR) mechanism at the molecular level for the rational design and synthesis of high activity fuel‐cell catalysts. Surface enhanced Raman spectroscopy (SERS) is a powerful technique capable of detecting the bond vibrations of surface species in the low wavenumber range, however, using it to probe practical nanocatalysts remains extremely challenging. Herein, shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) was used to investigate ORR processes on the surface of bimetallic Pt₃Co nanocatalyst structures. Direct spectroscopic evidence of *OOH suggests that ORR undergoes an associative mechanism on Pt₃Co in both acidic and basic environments. Density functional theory (DFT) calculations show that the weak *O adsorption arise from electronic effect on the Pt₃Co surface accounts for enhanced ORR activity. This work shows SHINERS is a promising technique for the real‐time observation of catalytic processes.