Mass Catalytic Activity Research Articles

Organometallic synthesis of a high-density Pt single atom catalyst on nickel for the alkaline hydrogen evolution reaction

Single atom platinum catalysts, characterized by isolated Pt atoms dispersed on suitable supports, exhibit high hydrogen evolution catalytic mass activity.

Integrating PtCo nanoparticles on N, S doped pore carbon nanosheets as high-performance bifunctional catalysts for oxygen reduction and hydrogen evolution reactions

The development of low-Pt bifunctional electrocatalysts with excellent performance for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is critical for the advancement of the hydrogen economy. Here, we have integrated low-loading Pt and Co metals into N, S doped porous carbon nanosheets to obtain composite catalysts encapsulating PtCo alloy nanoparticles (PtCo2@Co9S8/N-CNS and PtCo2@N-CNS). The acquired PtCo nanoparticles, with dimensions of about 2.5 nm, are uniformly distributed and firmly anchored in N, S doped carbon nanosheets with large specific surface areas and rich pore structure, forming multiple active centers and effectively preventing the aggregation of metal nanoparticles. The PtCo2@Co9S8/N-CNS and PtCo2@N-CNS display high ORR catalytic mass activity of 1.65 A mgPt-1 and 1.01 A mgPt-1 in 0.1 M HClO4. The PtCo2@N-CNS catalyst exhibits excellent HER performance in 0.5 M H2SO4, with a mass activity (at 50 mV) 4.3 times higher than that of Pt/C. The PtCo2@Co9S8/N-CNS and PtCo2@N-CNS also exhibit stronger ORR and HER stability than Pt/C after accelerated durability tests. The superior catalytic activity performance of catalysts can be attributed to the synergistic effect of multiple active centers of PtCo, Co9S8 and Co-N in the catalysts. The confinement of PtCo nanoparticles by Co metal and N, S doped porous nanosheets derived from graphitic carbon nitride (g-C3N4) as the template, which can effectively prevent the corrosion and migration of the catalysts under acidic conditions, enhances the catalytic stability of the materials. This study provides a new perspective for the development of economical and efficient bifunctional low-Pt catalysts.

Single-Atom Cr-N4 Sites with High Oxophilicity Interfaced with Pt Atomic Clusters for Practical Alkaline Hydrogen Evolution Catalysis.

Although dispersing Pt atomic clusters (ACs) on a conducting support is a promising way to minimize the Pt amount required in hydrogen evolution reaction (HER), the catalytic mass activity and durability of Pt ACs are often unsatisfactory for alkaline HER due to their unfavorable water dissociation and challenges in stabilizing them against agglomeration and detachment. Herein, we report a class of single-atom Cr-N4 sites with high oxophilicity interfaced with Pt ACs on mesoporous carbon for achieving a highly active and stable alkaline HER in an anion-exchange-membrane water electrolyzer (AEMWE). The as-made catalyst achieves the highest reported Pt mass activity (37.6 times higher than commercial Pt/C) and outstanding operational stability. Experimental and theoretical studies elucidate that the formation of a unique Pt-Cr quasi-covalent bonding interaction at the interface of Cr-N4 sites and Pt ACs effectively suppresses the migration and thermal vibration of Pt atoms to stabilize Pt ACs and contributes to the greatly enhanced catalytic stability. Moreover, oxophilic Cr-N4 sites adjacent to Pt ACs with favorable adsorption of hydroxyl species facilitate nearly barrierless water dissociation and thus enhance the HER activity. An AEMWE using this catalyst (with only 50 μgPt cm-2) can operate stably at an industrial-level current density of 500 mA cm-2 at 1.8 V for >100 h with a small degradation rate of 90 μV h-1.

Monodispersed ultrathin twisty PdBi alloys nanowires assemblies with tensile strain enhance C2+ alcohols electrooxidation

Direct alcohol fuel cells (DAFCs) are powered by the alcohol electro-oxidation reaction (AOR), where an electrocatalyst with an optimal electronic structure can accelerate the sluggish AOR. Interestingly, strain engineering in hetero-catalysis offers a promising route to boost their catalytic activity. Herein, we report on a class of monodispersed ultrathin twisty PdBi alloy nanowires (TNWs) assemblies with face-centered structures that drive AORs. These thin nanowire structures expose a large number of reactive sites. Strikingly, Pd6Bi1 TNWs show an excellent current density of 2066, 3047, and 1231 mA mgPd−1 for oxidation of ethanol, ethylene glycol, and glycerol, respectively. The “volcano-like” behaviors observed on PdBi TNWs for AORs indicate that the maximum catalytic mass activity is a well balance between active intermediates and blocking species at the interface. This study offers an effective and universal method to build novel nanocatalysts in various applications by rationally designing highly efficient catalysts with specific strain.

PtFeCoNiCu high-entropy solid solution alloy as highly efficient electrocatalyst for the oxygen reduction reaction

Searching for an efficient, durable, and low cost catalyst toward oxygen reduction reaction (ORR) is of paramount importance for the application of fuel cell technology. Herein, PtFeCoNiCu high-entropy alloy nanoparticles (PFCNC-HEA) is reported as electrocatalyst toward ORR. It shows remarkable ORR catalytic mass activity of 1.738 A mg-1 Pt at 0.90V, which is 15.8 times higher than that of the state-of-art commercial Pt/C catalyst. It also exhibits outstanding stability with negligible voltage decay (3mV) after 10k cycles accelerated durability test. High ORR activity is ascribed to the ligand effect caused by polymetallic elements, the optimization of the surface electronic structure, and the formation of multiple active sites on the surface. In the proton exchange membrane fuel cell setup, this cell delivers a power density of up to 1.380Wcm-2 with a cathodic Pt loading of 0.03mgPt cm-2, demonstrating a promising catalyst design direction for highly efficient ORR.

Molecule-Enhanced Electrocatalysis of Sustainable Oxygen Evolution Using Organoselenium Functionalized Metal-Organic Nanosheets.

Remolding the reactivity of metal active sites is critical to facilitate renewable electricity-powered water electrolysis. Doping heteroatoms, such as Se, into a metal crystal lattice has been considered an effective approach, yet usually suffers from loss of functional heteroatoms during harsh electrocatalytic conditions, thus leading to the gradual inactivation of the catalysts. Here, we report a new heteroatom-containing molecule-enhanced strategy toward sustainable oxygen evolution improvement. An organoselenium ligand, bis(3,5-dimethyl-1H-pyrazol-4-yl)selenide containing robust C-Se-C covalent bonds equipped in the precatalyst of ultrathin metal-organic nanosheets Co-SeMON, is revealed to significantly enhance the catalytic mass activity of the cobalt site by 25 times, as well as extend the catalyst operation time in alkaline conditions by 1 or 2 orders of magnitude compared with these reported metal selenides. A combination of various in situ/ex situ spectroscopic techniques, ab initio molecular dynamics, and density functional theory calculations unveiled the organoselenium intensified mechanism, in which the nonclassical bonding of Se to O-containing intermediates endows adsorption-energy regulation beyond the conventional scaling relationship. Our results showcase the great potential of molecule-enhanced catalysts for highly efficient and economical water oxidation.

First-principle-data-integrated machine-learning approach for high-throughput searching of ternary electrocatalyst toward oxygen reduction reaction

Platinum (Pt) alloys are expected to overcome long-standing issues of Pt/C electrocatalysts for oxygen reduction reaction (ORR). Entangled with serious uncertainty in configurational and compositional information, the design of a promising multi-component electrocatalyst, however, has been delayed. Here, we demonstrate that a first-principle database-driven machine-learning approach is extremely useful for the purpose via exploring materials beyond the regime of pure quantum mechanical calculations. Guided by a computational ternary phase diagram we indeed experimentally synthesized a PtFeCu nanocatalyst with 2 g per batch capacity and measured its catalytic performance for ORR. Both our computation and experiment consistently demonstrate that PtFeCu is highly active due to the atomic distribution of Cu leading to beneficial modulation of surface strain and segregation. Strikingly, PtFe high Cu low (776 μA cm −2 Pt and 0.67 A mg −1 Pt ) exhibits not only 3-fold better specific and mass activities than Pt/C but also little performance degradation over the accelerated stress test. • First-principle establishment of catalytic property data for ternary nanoparticles • Parametrization of atomistic interaction into neural network potentials • A striking consistency between computational prediction and experimental validation • Exceptional catalytic mass activity of PtFeCu 3-fold higher than that of Pt/C One of the challenging issues in nanocatalyst design for catalysis applications is to introduce the atomic-level functionalities of nanoparticles, determining the activity and stability. Multi-component systems can be promising, but the enormous configurational degrees of freedom and optimization routes for a target reaction remained unsolved. We demonstrate the combination of a machine-learning approach and experimental tests of PtFeCu nanoparticles for oxygen reduction reaction. Promising candidates were efficiently screened theoretically and successfully validated by the experiments. Both our computational and experimental outcomes indicate that the highly active electrocatalytic performance of PtFeCu originates from Cu atomic distribution. Our study suggests that first-principle calculations combined with machine-learning technology can be a promising approach in design of nanocatalysts to reduce the gap between the simulations and experiments. To efficiently design the Pt-based alloy nanocatalysts for oxygen reduction reaction, we utilized first-principle data integrated with machine learning to search for PtFeCu configurational spaces. We identified the promising candidates and revealed the atomic-level understanding via first-principle calculations. Cu atomic distribution remarkably modulated surface strain energies and segregation of the alloying components toward better oxygen reduction reaction performance. Tuning of Cu contents led to the high electrochemical performance of PtFeCu nanocatalysts, which was successfully validated by experiments.

Defects induced growth of Pt on the heterojunction of TaON|N-rGO as highly CO-tolerant electrocatalyst for ethylene glycol oxidation

For platinum (Pt) composite electrocatalysts formed by multiple components, the selective growth of Pt on oxygen-containing species can maximize the CO-resistance and durability, which is a big challenge in interfacial science. In this paper, Pt/TaON|N-rGO composite was obtained by an in-situ calcination of a layered supramolecule self-assembled by TaCl5, urea and n-butanol, followed with the targeted growth of Pt nanoparticles induced by the defects at the junction of TaON|N-rGO. As a result, Pt/TaON|N-rGO electrode with the ideal ternary interface of Pt|TaON|N-rGO exhibited exceptionally high catalytic mass activity (250.6 mA·mg−1Pt), excellent CO-tolerance (If/Ib = 1.6 normalized to Pt/C) and long-term durability (136.4 mA·mg−1Pt after continuous 1200 min operation) for EG oxidation in acid, compared to commercial Pt/C (57.8 mA·mg−1Pt). The promoted performance was attributed to the synergies at ternary interface of Pt|TaON|N-rGO, and the boosting CO-tolerance was achieved by the shortened L-H pathway ascribed to the selective growth of Pt nanoparticles on the heterojunction of TaON|N-rGO.

Ternary Interface of Pt|Few‐Layered N‐rGO|TiN for the Boasting Electrocatalytic Activity in Ethylene Glycol Oxidation

AbstractThe efficient electrochemical oxidation of ethylene glycol (EG) requires the superior synergism of platinum (Pt) based composites, which depends on the formation of effective interface between the components. In this paper, Pt loaded on co‐supporter of TiN and N‐doped reduced graphene oxide (Pt/TiN @ N‐rGO) composite is obtained by an in situ calcination of TiN @ N‐rGO followed with the targeted growth of Pt nanoparticles at the junction of TiN|N‐rGO. As a result, Pt/TiN @ N‐rGO electrode with medium molar ratio of urea to TiCl4 (R =10) and the ideal ternary interface of Pt|few layered N‐rGO|TiN exhibited exceptionally high catalytic mass activity (343.9 mA mg−1 Pt) and long‐term durability (117 mA mg−1 Pt after continuous 1200 min operation) for EG oxidation in acid, compared to other Pt/TiN @ N‐rGO composites and commercial Pt/C (41.1 mA mg−1 Pt). The promoted performance is attributed to the synergies at ternary interface, involving the highest electrochemically active surface areas due to more exposed active sites of Pt nanoparticles, the best electrical conductivity ascribed to the incorporation of few layered N‐rGO, and excellent CO tolerance with the assistance of TiN.

Metal and Metal Oxide Interaction in Hollow CuO/Pd Catalyst Boosting Ethanol Electrooxidation

A low Pd-loaded lychee-nut-like catalysts of CuO/Pd with hollow nanostructure are prepared by electrochemical displacement reaction, in which a Cu2O mesoporous sphere is as a sacrificial template in the presence of triblock copolymers Pluronic P123 (EO20PO70EO20). Furthermore, the feeding molar ratio of Cu2O and Na2PdCl4 is found to be critical factor for preparing well-defined hollow lychee-nut-like (HLN) CuO/Pd. Morphology, composition and crystal structure of the optimal HLN CuO/Pd catalysts are sufficiently characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy. The as-synthesized HLN CuO/Pd catalysts show high catalytic activity for ethanol oxidation in alkaline medium and the catalytic mass activity of the HLN CuO/Pd is 5.9-fold of commercial Pd/C and 10.8-fold of Pd black. In turn, HLN CuO/Pd catalysts possess outstanding stability and superior tolerance to CO species. The remarkably electrochemical catalysis performance of HLN CuO/Pd catalysts is attributed to the unique lychee-nut–like open nanostructures and the mutual interaction between Pd and CuO support, which optimizing the electronic structure.

AuPd/C core–shell and alloy nanoparticles with enhanced catalytic activity toward the electro-oxidation of ethanol in alkaline media

Carbon-supported Pd, Au@Pd core–shell and Au1–xPdx-alloyed nanoparticles were prepared by a chemical reduction method and characterized by different experimental techniques, including X-ray powder diffraction, transmission electron microscopy, scanning-transmission electron microscopy using bright-field and high-angle annular dark field detectors and X-ray energy dispersive spectroscopy. The catalytic mass activity toward ethanol oxidation was assessed by cyclic voltammetry and chronoamperometry at room temperature. The measurements showed that the addition of Au enhances remarkably the electrocatalytic activity of the material, due to the bifunctional effect of Au1–xPdx/C alloys, and the synergetic effect on Au@Pd/C, resulting in a dissolution resistance of core–shell catalysts at potentials of 1.5 V versus reversible hydrogen electrode. In situ Fourier transform infrared spectroscopy measurements showed that the mechanism for ethanol oxidation depends on the electrocatalyst structure and morphology. Acetate was identified as the main product of ethanol electro-oxidation on the studied electrocatalysts. However, the presence of a core–shell structure on Au@Pd/C resulted in enhanced ethanol oxidation selectivity toward CO2. The improvement of activity is attributed to the interaction between Pd shell and Au core.

SOFC anodes impregnated with noble metal catalyst nanoparticles for high fuel utilization

Redox-stable solid oxide fuel cell (SOFC) anodes are developed in order to improve durability at higher fuel utilization, as a possible alternative to conventional Ni-zirconia cermet anodes. Ce0.9Gd0.1O2 (GDC) is utilized as a mixed ionic and electronic conductor (MIEC), in combination with Sr0.9La0.1TiO3 (LST) as an electronic conductor. The stability of noble metals (Rh, Pt, and Pd) is analyzed via thermochemical calculation of stable phases. Noble metal catalyst nanoparticles are incorporated via co-impregnation with GDC. The electrochemical characteristics of SOFC single cells using these anode materials are investigated in highly-humidified H2 at 800 °C. Their stability at high fuel utilization is analyzed. These co-impregnated anodes with highly dispersed noble metal catalysts on the LST-GDC conducting backbones, achieve high IV performance comparable to conventional Ni-cermet anodes. The co-impregnated anodes also achieve considerably high catalytic mass activity. At higher oxygen partial pressure, where the Ni catalyst can be deactivated by oxidation, these noble catalysts are thermochemically stable in the metallic state, and tolerant against oxidation. This class of alternative catalyst, impregnated with low-loading of noble metals could contribute to stable operation in the downstream region of SOFC systems. A simple cost analysis indicates a tolerance of using noble metals, provided their loading is sufficiently low.

Employing iron and nickel to enhance ethanol oxidation of Pd-based anodes in alkaline medium

We report the addition of Fe or Ni to Pd:M electrocatalysts supported on Vulcan carbon XC-72 with 20 wt% metal loading to activate ethanol electrooxidation reaction in alkaline medium. Experimental bulk compositions of nanoparticles were very close to the nominal one. All the catalysts display the fcc crystalline structure of palladium with crystallite sizes ranging from 2.5 nm to 5.4 nm. Electrochemical tests in the presence of ethanol shows that the addition of Fe and Ni to Pd catalysts enhances ethanol electrooxidation. Ni-containing compositions such as Pd(56)Ni(44) and Pd(71)Ni(29) exhibit excellent catalytic mass activity (30 A gPd−1) at 0.5 V vs. RHE showing that they are promising anode electrocatalysts for direct ethanol alkaline fuel cells.

Dentritic CuPtPd Catalyst for Enhanced Electrochemical Oxidation of Methanol.

The CuPtPd catalyst is designed and synthesized successfully via directly reducing metal ions. The composition, morphology, and structure of the as-prepared CuPtPd nanohybrids are characterized by scanning electron microscopy and transmission electron microscopy, energy-dispersive spectrometry, selected-area electron diffraction, X-ray diffraction, and inductively coupled plasma atomic emission spectrometry. By comparison of the electrocatalytic properties of the ternary CuPtPd catalyst with bimetallic catalysts, we find that ternary nanocomposites perform better electrocatalytic and antipoisoning activity toward oxidation of methanol. The catalytic mass activity of the CuPtPd nanoparticles is 5.51-fold of commercial Pd black and 12.1-fold of Pt black.

Degradation of Pt/C catalysts in start-stop cycling tests

The stability of highly disperse 50 wt % Pt catalysts deposited on carbon supports with various porosity and morphology is tested in accelerated oxidative experiments in the potential range of 1–1.5 V (RHE) in 0.1 M HClO4 solution. The electrochemically active surface area of platinum (S Pt) is determined based on the charge of adsorbed hydrogen by the cyclic voltammetry (CVA) method. The specific activity per mass unit (the mass catalytic activity (MCA)) and the electrochemically active surface area of the active component (surface catalytic activity (SCA)) are determined in the oxygen electroreduction reaction (OERR) by the method of rotating disk electrode (RDE). It is shown that the catalyst degradation is mainly due to the growth of Pt particles and the corrosion of the carbon support. It is found that under these cycling conditions, the rate of the S Pt decline depends inversely on the cycle number throughout the cycling interval (up to 60000 cycles) for all catalysts, which points to the quadratic dependence of the degradation rate on S Pt. Two regions are revealed in the MCA and SCA dependences on the cycle number, In the first region (from 0 to 8–10 thousand cycles), a sharp decrease in MCA and SCA is observed for all catalysts, which can be associated with the restructuring or passivation of the Pt particle surface due to the oxide formation on oxidative cycling. In the second region, the relative stabilization of MCA and the linear increase in SCA are observed for all catalysts without exception. The linear increase in SCA is due to the growth of Pt particles and the size effect. It is shown that carbonization of the carbon support leads to enhancement of its cycling stability.

Ethylene Glycol Oxidation at Pt/TiO2/Carbon Hybrid Catalysts Modified Glassy Carbon Electrodes in Alkaline Media

Biomass-based fuels in conjunction with direct alcohol alkaline fuel cells are an emerging technology that may be able to wean us of our dependency of fossil fuels. However, their adoption is stalled by their high production costs (i.e., precious metal loading) and low electrocatalytic efficiencies. In this study, the platinum loading of 20 % Pt/C catalyst for use in ethylene glycol electrooxidation was reduced by mixing with TiO2 nanopowder in different mass ratios. This was followed by surface activation and cyclic voltammograms of the hydrogen adsorption and Pt oxide potential regions in 0.1 M KOH showed peak potential changes that are attributed to platinum interactions with TiO2. The catalysts were further tested for the electrochemical oxidation of ethylene glycol in alkaline media, where the titanium-modified catalysts showed a maximum increase in peak current density by 91 %, when compared to the commercial Pt/C catalyst. When the peak current was normalized by Pt surface area and mass, a maximum increase of 322 % was found. Tafel plot analysis showed increased exchange currents for the rate determining step of ethylene glycol oxidation at Pt/TiO2/C hybrid catalysts up to 7.35 × 10−7A/cm2. This is nearly 8.7 times larger than, 8.47 × 10-8A/cm2, the ethylene glycol exchange current density for the rate determining step in commercial Pt/C catalysts. Finally, chronoamperometric studies showed that the hybrid catalysts possessed increased stability and activity for ethylene glycol electrooxidation in 0.1 M ethylene glycol in 0.1 M KOH at an applied potential of −0.350 V vs. Ag/AgCl. This study shows that TiO2 can modify the platinum surface catalyst activity without the need of a TiO2 support. This avoids loss in electrical conductivity of the catalyst and lowers the total catalyst mass without sacrificing catalytic mass activity.

Rapid Microwave Synthesis of CO Tolerant Reduced Graphene Oxide-Supported Platinum Electrocatalysts for Oxidation of Methanol

Reduced graphene oxide/platinum supported electrocatalysts (Pt/RGO) were synthesized by employing a fast and eco-friendly microwave-assisted polyol process, which facilitated the simultaneous reduction of graphene oxide and formation of Pt nanocrystals. This system was tested for potential use as an anode material through the electrooxidation of methanol. Compared to the commercial carbon-supported Pt electrocatalysts, the Pt/RGO showed an unprecedented CO poisoning tolerance, high electrochemical active surface area, and high catalytic mass activity for methanol oxidation reaction, demonstrated by increases of 110, 134, and 60%, respectively. We found that the high concentration of oxygen functional groups on reduced graphene oxide plays a major role on the removal of carbonaceous species on the adjacent Pt sites, underlining a synergetic effect between the oxygen moieties on graphene support and Pt nanoparticles. The present microwave assisted synthesis of Pt/RGO provides a new path to prepare electroca...

Synthesis of High‐Surface‐Area Platinum Nanotubes Using a Viral Template

AbstractA novel method for the synthesis of high‐active‐surface‐area, platinum–tobacco mosaic virus (Pt–TMV) nanotubes is presented. A platinum salt is reduced to its metallic form on the external surface of a rod‐shaped TMV by methanol, which serves as a solvent and reductant simultaneously. It was found that for the same Pt loading the Pt–TMV nanotubes had an electrochemically active surface area between 4 to 8 times larger than similarly sized Pt nanoparticles. A Pt–TMV catalyst displays greater stability in acidic conditions than those based on nanoparticles. When used as a catalyst for methanol oxidation, these Pt nanotubes display a 65% increase in catalytic mass activity compared to that based on Pt nanoparticles.

Electrospun bimetallic nanowires of PtRh and PtRu with compositional variation for methanol electrooxidation

Binary metallic nanowires (NWs) of PtRh and PtRu were synthesized by electrospinning method with compositional variation from 1:3 to 2:1. The electrospun bimetallic NWs were highly alloyed with diameters smaller than 60 nm and lengths up to hundreds of micrometers. The PtRh and PtRu NWs with 1:1 atomic ratio resulted in the higher catalytic mass activity over the methanol electrooxidation than those with the different atomic ratios, and the mass activity of Pt 1Ru 1 NWs was superior to the other NWs and even better than the commercial catalyst of the highly dispersed Pt 1Ru 1 nanoparticles on carbon. Moreover, the bimetallic NW electrocatalysts showed the better stability than the bimetallic nanoparticles. The enhancements of electrocatalytic properties for the Pt 1Rh 1 and Pt 1Ru 1 NWs could be attributed to their one-dimensional features, which can outperform on the electro-oxidations over the fuel cell electrodes.

A polyoxometalate-deposited Pt/CNT electrocatalyst via chemical synthesis for methanol electrooxidation

Polyoxometalate anion PMo 12O 40 3− (POM) is chemically impregnated into a Pt-supported carbon nanotubes (Pt/CNTs) catalyst that is prepared via a colloidal method. The POM-impregnated Pt/CNTs catalyst system (Pt/CNTs-POM) shows at least 50% higher catalytic mass activity with improved stability for the electrooxidation of methanol than Pt/CNTs or POM-impregnated Pt/C (Pt/C-POM) catalyst systems. The enhancement in electrochemical performance of the Pt/CNTs-POM catalyst system can be attributed to the combined beneficial effects of improved electrical conductivity due to the CNTs support, highly dispersed Pt nanoparticles on the CNTs, and increased oxidation power of the polyoxometalate that can assist oxidative removal of reaction intermediates adsorbed on the Pt catalyst surface.