Commercial Platinum Catalyst Research Articles

CATALYST BASED ON PALLADIUM‐MODIFIED MIL‐53(AL) PYROLYSATE FOR ORR IN ALKALINE MEDIA

A catalyst for the oxygen reduction reaction (ORR) based on the metal‐organic framework material MIL‐53(Al) modified with palladium was synthesized. Its textural and morphological characteristics were studied using the method of adsorption porosimetry, SEM, TEM, energy dispersive X‐ray analysis (EDAX) , X‐ray diffraction (XRD), Raman –spectroscopy, X‐ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA‐DSC). The electrocatalytic properties of the synthesized material in ORR were studied by voltammetry using a rotating disk electrode. Corrosion resistance was studied in the CV mode. It was found that the synthesized catalyst is characterized by high corrosion resistance. The tolerance of synthetized catalyst Pyr_MIL‐53(Al)_Pd to the methanol was studied. The obtained catalyst was studied in a membrane electrode assembly (MEA) formed by spraying an ionomer suspension onto a gas diffusion layer (GDL). The synthesized Pyr‐MIL‐53 (Al)_Pd and commercial platinum (60% Pt) (HiSPEC 9100) catalysts were compared in the cathode composition, and 10% PtM (M = Ni, Mo)/CNT catalysts were used on the anode. The power density of the FC (P) was calculated based on the obtained current‐voltage curves. Based on the set of characteristics, the synthesized catalyst based on MIL‐53 (AL) doped with palladium is superior in efficiency to the commercial platinum catalyst.

Mo-modified Pt/C electrocatalyst prepared by the catalytic decomposition of molybdenum peroxo-complexes for the hydrogen oxidation reaction with enhanced CO tolerance

Commercial 20 % Pt/C catalyst was modified by molybdenum via catalytic decomposition of peroxocomplexes of molybdenum with the subsequent reduction of the Pt2Mo1/C precursor in H2 flow at 600 °C. The detailed HRTEM, EDX, XRD and XPS studies showed that amorphous molybdenum oxide was deposited on Pt particles surface and partially on carbon support. After reduction of the Pt2Mo1/C precursor, the substantial Mo fraction merges the structure of Pt particles thus forming PtMo alloy with reduced lattice parameter, while the rest of molybdenum covers the surface of PtMo particles as MoO3. The presented method of Mo-modification of Pt-based catalysts provides rather simple way to vary Pt:Mo molar ratio. Electrochemical study revealed that the amount of the surface MoO3 plays a key role in the CO tolerance of the PtMo/C catalyst. As prepared Pt2Mo1/C precursor is 15 times superior to the Pt/C catalyst in the CO-tolerance. After reduction, the Pt2Mo1/C electrocatalyst exhibits extremely high CO-tolerance, more than 100 times higher than that of the pristine commercial platinum catalyst.

Electrochemical Ethylamine Dehydrogenation to Acetonitrile on Platinum-Based Catalysts

Hydrogen storage is a crucial link between green hydrogen generation by water electrolysis and hydrogen application in fuel cells. We very recently reported a new, electrochemical ethylamine/acetonitrile redox method for hydrogen storage [1]. This method realizes hydrogen uptake by pairing acetonitrile hydrogenation to ethylamine reaction (AHR) on cathode and hydrogen oxidation reaction (HOR) on anode, and realizes hydrogen release by pairing ethylamine dehydrogenation to acetonitrile reaction (EDR) on anode and hydrogen evolution reaction (HER) on cathode. With 8.9 wt.% theoretical storage capacity and ambient reaction conditions being demonstrated in the study, this method shows a great potential to advance hydrogen storage technology and meet the DOE target. One remaining challenge of this method was a rapid activity decay of the used commercial platinum catalyst (Pt/C) in the EDR, which caused a long-term durability issue.In this work, we report our fundamental study of Pt catalyst deactivation mechanism in EDR and the discovery of new Pt-based catalysts. Attenuated total reflection infrared spectroscopy (ATR-IR) was employed for characterizing working catalyst surface under reactive conditions. Partially dehydrogenated intermediate species were observed to generate on Pt surface, which strongly adsorbed and caused an accumulation and blockage of the active sites. Interestingly, the catalyst showed a self-cleaning property where the intermediates can be hydrogenated back to ethylamine and released from Pt surface below 0 V vs. RHE. A group of Pt-Ni alloy catalysts were prepared and investigated the composition effect in this reaction, among which Pt3Ni exhibited 75% higher activity and significantly improved stability compared to Pt. ATR-IR experiments showed that the accumulation of intermediates on the Pt3Ni surface was much slower than that on the Pt, attributed to weakened adsorption. This work provides mechanistic insights into EDR reaction pathways and the cause of Pt catalyst deactivation and offers a Pt alloy strategy for active and stable catalyst design.[1] Wu, D.; Li, J.; Yao, L.; Xie, R.; Peng, Z. ACS Appl. Mater. Interfaces 13, 55292 (2021).

High dispersion Pd nanoclusters modified sulfur-rich vacancies ZnIn2S4 for high-performance hydrogen evolution

Hydrogen energy is regarded as the clean energy alternative for fossil energy. Hydrogen evolution reaction (HER) is a sustainable way for the production of hydrogen energy. However, commercial platinum (Pt) catalysts for HER are expensive and scarce, which will not fully meet the demand of the future market. Therefore, scientists have been actively exploring alternatives to Pt-based catalysts. Studies have shown that palladium (Pd) and Pt have similar catalytic activity in HER. Small molecular Pd nanoclusters can be used as a perfect HER activity center. Herein, anchoring of Pd nanoclusters (Pd NCs) on sulfur-vacancy-enriched ZnIn2S4 nanosheets (Pd/ZIS-T) has been successfully achieved. The zeta potential value for ZnIn2S4 is −59.9 mV, indicating that the surface of ZnIn2S4 is abundant negatively charged in deionized water, thus providing plentiful anchoring sites to absorb Pd2+. The results show that the synergistic effect of Pd NCs and sulfur vacancies will endow the obtained catalyst with excellent electrocatalytic activity and stability. It also managed to reducing costs by reducing noble metal content. In particular, the Pd/ZIS-T electrocatalyst with excellent performance delivered low overpotential of 25 mV at 10 mA cm−2 and small Tafel slope of 33 mV dec-1 in acidic electrolyte.

Double Riveting and Steric Hindrance Strategy for Ultrahigh‐Loading Atomically Dispersed Iron Catalysts Toward Oxygen Reduction

Atomically dispersed iron on nitrogen doped carbon displays high intrinsic activity toward oxygen reduction reaction, and has been identified as an attractive candidate to precious platinum catalysts. However, the loading of atomic iron sites is generally limited to below 4 wt% due to the undesired formation of iron-related particles at higher contents. Herein, this work overcomes this limit by a double riveting and steric hindrance strategy to achieve monodispersed iron with a high-loading of 12.8 wt%. Systematic study reveals that chemical riveting of atomic iron in ZIF-8 framework, chelation of Fe ions with interconfined 1,4-phenylenebisboronic, and physical hindrance are essential to obtain high-loading monodispersed Fe moieties. Resultantly, designed Fe-N-C-PDBA exhibits superior catalytic activity and excellent stability over commercial platinum catalysts toward oxygen reduction reaction in both half-cells and zinc-air fuel cells (ZAFCs). This provides an avenue for developing high-loading single-atom catalysts (SACs) for energy devices.

Preparation of ruthenium oxide catalyst for oxygen evolution reaction in HT-PAWE by pulsed electrodeposition

Despite the fact that the technique of proton exchange membrane water electrolysis (PEMWE) dominates the market because of its low temperature of operation, platinum as a catalyst renders it relatively expensive. In this work, we demonstrated a recyclable ruthenium catalyst with high stability, high oxygen evolution reaction (OER) performance and low onset potential. In particular, instead of PEMWE, the technique of high temperature phosphoric acid water electrolysis (HT-PAWE) was used, with ruthenium oxide as its anode catalyst and a high operation temperature to decrease the amount of noble metals being used. Ruthenium was chosen in this study due to its excellent catalytic activity. The possibility of recycling and reusing noble metals would ease the problem of high cost. Homemade ruthenium catalyst in this study exhibited an outstanding OER performance including high stability and high current density than those of commercial platinum catalyst. Linear sweep voltammetry (LSV) test results showed that a maximum current density of 190 mA/cm2 was reached at only 1.5VSCE.For this experiment, ruthenium (III) chloride hydrate (RuCl3·3H2O) was used as the precursor, and potassium chloride (KCl) and hydrochloric acid (HCl) acted as the supporting electrolyte. Pulsed electrodeposition was chosen to achieve a better control in particle size and distribution of the catalyst over selected specimens. After electrodeposition, the specimens underwent thermal treatment for increasing stability in catalyst particles. Scanning electron microscopy (SEM), linear sweep voltammetry (LSV) and cyclic voltammetry (CV) were used to observe the morphology and to analyze the OER performance of the specimens, respectively. Types of catalyst carrier, electrodeposition potential and duration, and thermal treatment temperature were studied. As a result, all four parameters affected the morphologies and electrochemical performances of the tested specimens.

PtRuFe/Carbon Nanotube Composites as Bifunctional Catalysts for Efficient Methanol Oxidation and Oxygen Reduction.

The design of bifunctional catalysts with high performance and low platinum for the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) is of significant implication to promote the industrialization of fuel cells. In our work, Pt/carbon nanotube (CNT), Pt3Ru/CNT, and PtRu/CNT catalysts were synthesized by plasma heat treatment, in which the pyrolysis reduction of organometallic salts and the dispersion of CNTs were achieved simultaneously, and catalytic nanoparticles with uniform particle size were anchored on the dispersed CNT surface. Later, Fe was further introduced, and PtFe/CNT, Pt3RuFe/CNT, and PtRuFe/CNT catalysts were synthesized by calcination, and the structure and electrochemical properties in both MOR and ORR of all as-synthesized catalysts were investigated. The results indicated that plasma thermal treatment has the advantage of rapidness and immediacy in the synthesis of catalysts, and the Pt/CNT, Pt3Ru/CNT, and PtRu/CNT catalysts exhibited better electrocatalytic properties than commercial platinum (JM-Pt/C) catalysts. Meanwhile, the introduction of Fe during the calcination further changed the surface electronic properties of catalytic nanoparticles and enhanced the graphitization degree of catalysts; the PtRuFe/CNT catalyst exhibited outstanding electrocatalytic properties with a mass activity of 834.3 mA mg-1 for MOR and a half-wave potential of 0.928 V in alkaline media for ORR. The combination of plasma thermal treatment and calcination puts forward a novel strategy for the optimization of catalysts, and the synthesis method based on plasma dispersion needs to be further optimized to achieve its large-scale promotion.

Pt-Bi on carbon aerogels as efficient electrocatalysts for ethanol oxidation reaction in alkaline medium

Platinum-containing multimetallic catalysts supported on carbon materials have become one of the main choices for direct ethanol fuel cells (DEFCs) due to their high catalytic activity for the ethanol oxidation reaction (EOR). In this study, a platinum-bismuth alloy catalyst (PtBi@CA) with uniform distribution and small particles was provided by a one-step reduction method without the addition of structure directing agents and stabilizers. In the half-cell test, PtBi@CA(50−50) with the smallest crystallite size has high peak current density and pseudo-steady current density of 64.336 mA/cm2 and 0.096 mA/cm2, respectively, which is 11.22 times and 1.85 times the high of the most advanced commercial carbon-supported platinum catalysts (Pt/C). The method is simple and feasible, greatly reduces the amounts of precious metals, and has broad application prospects in the synthesis of anode electrocatalysts for direct ethanol fuel cells.

Multi-sites synergistic modulation in oxygen reduction electrocatalysis

Revealing the types of and interplays among multiple active-sites in iron-nitrogen-carbon (FeNC) materials is of great significance for developing high-performance, Fe-based non-precious metal catalysts for oxygen reduction reaction (ORR). In this paper, a single-atom FeNC catalyst is prepared through high-temperature pyrolyzing of melamine foam (MF), iron phthalocyanine (FePc), phthalocyanine (Pc), and zinc (Zn)-salts composite. The catalyst is found to contain a variety of active-sites, including carbon atom next to pyridinic-N (pyridinicNC), Fe-N4 and pore defect. It is shown that MF with high N-content is responsible for the formation of the main pyridinicNC sites and in the meantime acts as the self-sacrificed template for framework of the catalyst. The presence of Pc can facilitate the formation of the predominant Fe-N4 sites, since the interplay between Pc and FePc results in a confinement of Fe-N4. Zn-salts serve as the pore-forming additives to create sufficient pore defects which can also anchor pyridinicNC and Fe-N4 structures. The results of density functional theory (DFT) calculations suggest that the multiple active-sites function synergistically to enable high-efficiency ORR electrocatalysis. The optimal FeNC catalyst shows superior ORR activity with a half-wave potential of ∼0.88 V (vs. RHE), as well as high methanol tolerance and electrochemical stability compared to the commercial carbon-supported platinum (Pt/C) catalyst.

Correlating Surface Strain with Activity in Commercial Platinum Catalysts

Correlating Surface Strain with Activity in Commercial Platinum Catalysts

Investigation of the hydroisomerization of diesel fractions with different concentration of nitrogen-containing compounds on bifunctional catalysts based on ZSM-23 and non-noble metals

Bifunctional catalysts based on NiMo(W) sulfides and a ZSM-23-Al2O3 composite support have been synthesized. Their properties were studied in the transformations of diesel fractions with different nitrogen content (< 1, 10 and 20 ppm). It was demonstrated that the synthesized catalysts could be used to obtain hydrogenizates with the limiting filterability temperature  –38 °C, which comply with the requirements of GOST R 55475-2013 to the content of gasoline fraction and aromatic compounds, and the derived cetane number. Properties of the developed catalysts based on NiMo and NiW sulfides and characteristics of the corresponding hydrogenizates were compared with each other. In addition, properties of the developed samples were compared with the properties of a foreign commercial platinum catalyst for isodeparaffinization. The synthesized catalysts were found to be less selective than the reference sample, but more stable to N-containing compounds in the feedstock.

Decomposition studies of NH3 and ND3 in presence of H2 and D2 with Pt/Al2O3 and Ru/Al2O3 catalysts

In the fusion reactor ITER, ammonia will be produced as a result of the interaction between the hydrogen isotopes used as fuel and nitrogen used to spread the power loads of a larger area. As part of the fuel management in ITER, NQ3 (NQ3, Q = H, D, T) will have to be decomposed using a palladium membrane reactor. The decomposition of pure NH3 and ND3 was studied in this work using commercial platinum (Pt) and ruthenium (Ru) catalysts on alumina (0.5 wt% loading), in a conventional reactor configuration (i.e., without a palladium membrane). With Pt/Al2O3, decomposition fractions larger than 90% were achieved with NH3 above 800 K using the lowest flow-to-mass ratio (FNH3/g-cat) of 0.015 sccm g−1. However, with the increase of FNH3/g-cat to 0.220 sccm g−1, similar decompositions were achieved only at ≈1000 K. In contrast, with Ru/Al2O3 decomposition fractions above 90% were attained already below 700 K, regardless of FNH3/g-cat. With both catalysts the decomposition of NH3 was found to be more efficient than that of ND3 at a wide range of temperatures, thus evidencing the existence of isotopic effect. A strong inhibition of both NH3 and ND3 in presence of, respectively, H2 and D2 with Pt/Al2O3 was observed. This effect was stronger at lower temperatures and larger hydrogen partial pressures. The inhibition effect with Ru/Al2O3 was less pronounced and it was suppressed at 629 K. Isotopic exchange reactions with equimolar mixtures of NH3-D2 and ND3-H2 revealed that the most and least abundant isotopologue are, respectively, NH2D and ND3. At the relevant temperature window in which the PMR will be operated (673–823 K), the Ru-based catalyst exhibits superior performances in terms of decomposition rates, negligible isotopic and inhibition effects. A slight reduction of the performances with this catalyst was observed with 0.200 sccm g−1. This work suggests that 0.5 wt% Ru/Al2O3 is the most suitable catalyst to be used during ITER operation.

Cerium Catalysts in Steam-Assisted Pyrolysis of -Dodecane for Hypersonic Thermal Management

Cerium was used as a catalyst for cracking in a cylindrical packed bed reactor, alone and then in conjunction with a commercially available platinum catalyst. The objective was to examine its suitability for use in potential thermal management systems. Cracking product distribution, fuel endotherm, and carbon deposition results for the cerium catalyst were compared to those reported previously for the commercial platinum catalyst in a similar packed bed reactor configuration. For some experiments, water was added to the fuel for steam assistance to the pyrolysis reactions in order to examine the effect of water on carbon production and endotherm. The cerium catalysts outperformed the platinum catalyst in terms of both increased endotherm and decreased carbon deposition. Steam assistance proved beneficial in decreasing carbon deposition, although at the cost of decreased endotherm. No appreciable product selectivity was observed for steam assistance with either catalyst. Finally, the overall reaction constant for each catalyst-steam addition case was compared to dodecane conversion in order to determine a relationship that can be applied in designing a reactor for use in a thermal management system.

Electrospun Carbon Nanofibers Loaded with Atomic FeNx/Fe2O3 Active Sites for Efficient Oxygen Reduction Reaction in Both Acidic and Alkaline Media

AbstractRenewable energy storage systems based on oxygen reduction reaction (ORR) call for high‐performance, durable, and low‐cost electrocatalysts. However, practical applications of ORR catalysts available today are hampered by the inability to load accessible catalytic sites efficiently. Herein, a novel and efficient ORR electrocatalyst (Fe2O3/FeNx@CNF) with atomic FeNx sites and neighboring Fe2O3 nanoparticles embedded in interconnected carbon nanofibers prepared via electrospinning is reported. Detailed material characterizations confirm that the as‐prepared catalysts possess a well‐defined fibrous structure with hierarchical pores, large specific surface area, and uniformly distributed Fe2O3/FeNx active sites. Further, it exhibits excellent ORR performance with high onset potential, half‐wave potential, and current density in both alkaline and acidic media. And these electrocatalysts show excellent long‐term performance and tolerance to methanol, exceeding the properties of commercial platinum catalysts. Additionally, the Fe2O3/FeNx@CNF electrocatalyst prepared in this study exhibits high discharge voltage, excellent power density, and cycling durability in Zn–air batteries. Notably, the detailed analyses demonstrate the co‐existence of Fe2O3 nanoparticles and FeNx active sites boost the ORR catalytic activity of the hybrid catalyst. These new findings, particularly the enhancement of intrinsic activity of FeNx sites brought about by Fe2O3 nanoparticles, provide insights into the rational design of hybrid single‐atom ORR electrocatalysts.

Elucidating the Critical Role of Ruthenium Single Atom Sites in Water Dissociation and Dehydrogenation Behaviors for Robust Hydrazine Oxidation‐Boosted Alkaline Hydrogen Evolution

AbstractHydrazine oxidation (HzOR)‐assisted overall water splitting (OWS) provides a unique approach to energy‐efficient hydrogen production (HER). However, there are still major challenges in the design of bifunctional catalysts and gain deep insight into the mechanism of both water dissociation and dehydrogenation kinetics triggered by the same active species during HzOR‐assisted OWS. Here, ruthenium single atoms (Ru SAs) anchored onto sulphur‐vacancies of tungsten disulphide (WS2) are prepared by a sulfidation and facile galvanostatic deposition strategy. The WS2/Ru SAs act as a bifunctional catalyst and outperforms commercial platinum (Pt) catalysts for both HzOR and HER. Ultralow potentials of −74 and −32.1 mV at 10 mA cm−2 are achieved for HzOR and HER, respectively. Two‐electrode electrolyzer using WS2/Ru SAs as both anode and cathode reaches 10 mA cm−2 with cell voltage of only 15.4 mV, which is far below that of most electrocatalysts including commercial Pt. Density functional theory calculations unravel the critical role of Ru SAs in WS2, where the sluggish dissociation of water in HER can be promoted on Ru sites, and the sulfur sites of WS2 exhibit a more thermoneutral behavior for hydrogen intermediate adsorption. Moreover, Ru sites are also active centers for stepwise hydrazine dehydrogenation during HzOR.

Pt–Cu nanoalloy catalysts: compositional dependence and selectivity for direct electrochemical oxidation of formic acid

A PtCu3 nanoalloy catalyst showed much enhanced catalytic activity for the direct electrochemical oxidation of formic acid compared to a commercial platinum catalyst.

Dual-layer catalyst layers for increased proton exchange membrane fuel cell performance

The use of a dual-layer cathode catalyst layer improves the performance of proton exchange membrane fuel cells. To generate single and dual-layer catalyst layers between the gas diffusion media and proton exchange membrane electrolyte, two commercial carbon-supported platinum catalysts with either a high microporosity carbon (Ketjen Black EC-300J) or a low porosity carbon (XC-72 Vulcan carbon) are utilized. We discovered that dual-layer cathode catalyst layers boost maximum power of fuel cells regardless of carbon porosity directionality, with either high surface area carbon at the proton exchange membrane electrolyte or gas diffusion media interface. At 25% relative humidity, a condition that generally inhibits fuel cell performance, a 20% performance boost is realized when using dual-layer cathode CLs. The electrochemical impedance spectroscopy results indicate that cathodes with dual-layer catalyst layer aid in water management due to lower kinetic activity losses of the Pt and improved hydration of the proton exchange membrane electrolyte.

Tuning the Intrinsic Activity and Electrochemical Surface Area of MoS2 via Tiny Zn Doping: Toward an Efficient Hydrogen Evolution Reaction (HER) Catalyst.

Molybdenum sulfide (MoS2 ) is considered as an alternative material for commercial platinum catalysts for electrocatalytic hydrogen evolution reaction (HER). Improving the apparent HER activity of MoS2 to a level comparable to that of Pt is an essential premise for the commercial use of MoS2 . In this work, a Zn-doping strategy is proposed to enhance the HER performance of MoS2 . It is shown that tiny Zn doping into MoS2 leads to the enhancement of the electrochemical surface area, increases in proportion of HER active 1T phase in the material and formation of catalytic sites of higher intrinsic activity. These benefits result in a high-performance HER electrocatalyst with a low overpotential of 190 mV(@10 mA cm-2 ) and a low Tafel slope of 58 mV dec-1 . The origin for the excellent electrochemical performance of the doped MoS2 is rationalized with both experimental and theoretical investigations.

Crystalline carbon modified hierarchical porous iron and nitrogen co-doped carbon for efficient electrocatalytic oxygen reduction

Hierarchical porous iron and nitrogen co-doped carbon (Fe-N/C) materials have been considered as an appealing non-noble metal-based catalyst in oxygen reduction reactions (ORR). However, the conductivity loss caused by the scattering of electrons on pores and defects markedly limits their catalytic activity, which attracted seldom attention in this area. Herein, a novel crystalline carbon modified hierarchical porous Fe-N/C electrocatalyst with enhanced electronic conductivity is designed and prepared via a two-step calcination-catalysis process. The resistivity of hierarchical porous Fe-N/C is decreased from 2.123 Ω cm to 0.479 Ω cm after crystalline carbon introduction. The electrocatalyst annealed at 800 °C (Fe-N/C-800) exhibits a superior activity with the half-wave potential (E1/2) of 0.89 V, which outperforms the commercial carbon-supported platinum (Pt/C) catalyst (0.85 V). The strategy of crystalline carbon modification provides a fresh approach to improve the electronic conductivity of porous carbon-based materials.

Systematic study of iridium-based catalysts derived from Ir4(CO)12, capable to perform the ORR and HOR

In this work, we used Ir4(CO)12 as precursor compound in order to obtain different Ir-based materials by two different thermal processes: pyrolysis and thermolysis. All materials were studied as catalysts for the ORR and HOR in the absence and presence of contaminants (methanol and carbon monoxide, respectively). These studies indicate that only two catalysts performed the ORR in the presence of methanol, since most of them present activity for the methanol oxidation reaction, due to the presence of Ir° particles. However, all synthesized materials performed the HOR even in the presence of CO in different concentrations. Some catalysts, were also evaluated directly as cathodes and anodes in a single PEM Fuel Cell even using a H2/CO mixture gas as fuel, corroborating its acceptable performance compared with commercial platinum catalyst, which are easily deactivated by traces of CO. The products were characterized structural and morphologically by different analytical techniques. The results show that hydrogen atmosphere stimulates the decarbonylation process of the precursor and produces metallic-iridium nanoparticles with a different chemistry nature compared with the materials obtained in nitrogen. In general, results show that these Ir-based materials are a good alternative to be used as both cathodes/anodes in a PEMFC.