Activity Of Pt Electrocatalysts Research Articles

Tuning Structure and Properties of Pt Catalysts Confined in Single‐Walled Carbon Nanotubes (SWNTs) for Electrocatalysis

AbstractNew approaches to enhance the activity of Pt electrocatalysts in the field of H2 energy are desirable, and recently Pt catalysts confined in SWNTs have been shown to possess an enhanced catalytic activity, but the way to control their structure and properties for optimized performance is still unexplored. Here, a facile two‐step process was developed to provide such control, in which Pt was firstly co‐filled with different ratio of Co in SWNTs and followed by acid treatment to remove Co. The resulting Pt catalysts (d‐Pt‐Co@SWNT) were appraised for two typical electrocatalytic applications with the correlation between structure and catalytic activity demonstrated: for amperometric hydrogen sensing, the d‐Pt90‐Co10@SWNT catalyst showed sensitivity 7 times higher than that of Pt100@SWNT; for hydrogen evolution, the d‐Pt10‐Co90@SWNT catalyst exhibited mass activity about 10 times higher than that of the commercial Pt‐C. Overall the approach provides a general route to tune structure and properties of metal catalyst confined in carbon nanotubes for different applications in many fields.

Metal Oxide Inclusion in Polycrystalline Pt-Based Electrocatalyst for an Ammonia Oxidation Reaction

In April 2021, an average daily amount of 421 ppm of carbon dioxide (CO2) was recorded in the atmosphere, CO2 has increased more than 100 ppm in the last 66 years. Fuel cells are a suitable option for addressing the major issues of meeting current and future energy demand while also reducing CO2 pollution. If the fuel source originates from renewable sources, this makes the overall process CO2-neutral. In the quest for sustainable fuels with high energy density, focus is currently on nitrogen-containing fuels, such as ammonia (NH3) since their oxidation will yield predominantly dinitrogen (N2). Different platinum precursors (K2PtCl6 and H2Pt(OH)6) were used to study the effect on the electrocatalytic activity of Pt for an ammonia oxidation reaction when different metal oxides are added to Pt particles. The metal oxides chosen are CeO2, Fe2O3, and Ag2O. The morphology and element distribution of the Pt catalyst was determined by SEM equipped with an EDS detector. The crystalline phase present in the samples was determined by X-ray diffraction. Cyclic voltammetry was used to characterize the particles and to study the catalytic activity of Pt electrocatalyst for ammonia oxidation. No significant difference was found (by student t-test) between the onset potential for ammonia electrooxidation of Pt particles and Pt precursor. Average onset potential for ammonia electrooxidation was -0.464 V vs Ag|AgCl. The highest average current peak densities were reported by catalyst from non-chlorinated precursor with addition of Fe2O3. Current densities of nanoparticles synthesized from the H2Pt(OH)6 precursor decreased to 24.9 x 10-2 mA/cm-2 with CeO2 addition, but increased to 28.2 x 10-2 mA/cm-2 when Fe2O3 was added. We are currently working on the electrochemical characterization and oxidation of ammonia with catalyst from Ag2O addition

Drop-casted Platinum Nanocube Catalysts for Hydrogen Evolution Reaction with Ultrahigh Mass Activity.

Platinum hydrogen evolution reaction (HER) electrocatalysts in the form of nanocubes (NCs) were synthesized at 50 °C by aqueous-based colloidal synthesis and were applied to electrochemical (EC) and photoelectrochemical (PEC) systems by a fast and simple drop-casting method. A remarkable Pt mass activity of 1.77 A mg-1 at -100 mV was achieved in EC systems (fluorine-doped tin oxide/Pt NC cathode) with neutral electrolyte while maintaining low overpotential and Tafel slope. In the Cu(In,Ga)(S,Se)2 (CIGS)-based PEC system, a carefully chosen amount of Pt NC loading to achieve a compromise between the catalytic activity (more Pt NCs) and better light transmittance (fewer Pt NCs) led to a maximum onset potential of 0.678 V against the reference hydrogen electrode. The photoelectrodes with Pt NCs also exhibited good long-term operational stability over 9.5 h with negligible degradation of the photocurrent. This study presents an effective strategy to greatly reduce the use of expensive Pt without compromising the catalytic performance because the drop-casting of Pt NC solutions to form electrocatalysts is expected to waste less raw material than vacuum deposition.

Nano-single crystal coalesced PtCu nanospheres as robust bifunctional catalyst for hydrogen evolution and oxygen reduction reactions

Because of high electrocatalytic activity, Pt based metal nanospheres (NSs) have attracted a lot of attention. Hence, multi-particle nano-single crystal coalesced PtCu NSs are designed and successfully synthesized by a cost-effective aqueous solution method. The formed PtCu NS catalyst exhibits a superior hydrogen evolution reaction (HER) electrocatalytic activity with an ultralow onset potential of 18 mV at the current density of 2 mA/cm2 and high mass activity of 1.08 A/mgPt (7.2 times higher than that of commercial Pt/C catalysts). Also, it shows an enhancement of 3.2 and 2.7 times in the mass and specific activities toward oxygen reduction reaction (ORR) compared to that of Pt/C. Moreover, it possesses an excellent catalytic durability for both ORR and HER. Even after 10,000 cycles, its ORR mass activity retains 87% of its initial value. The density functional theory (DFT) calculations demonstrate that by introducing Cu atoms into the Pt lattice, a downshift of the D-band center and favorable hydrogen adsorption free energy of approaching to zero (ΔG) occur, indicating the increased electrocatalytic activity of Pt electrocatalysts.

Investigating Catalyst-Electrolyte Interface By Microelectrode, Infrared Reflection Adsorption Spectroscopy and Neutron Reflectometry

Understanding of the catalyst-ionomer interfacial behavior is critically important for fuel cell research. In fact, alkaline membrane fuel cells (AMFCs) have shown limited performance compared to proton exchange membrane fuel cells due to relatively poor hydrogen oxidation reaction (HOR) kinetics [1]. Previous work has shown that cationic adsorption at the surface of the catalyst was closely related to the HOR activity [2, 3]. Here, we present the results of a study of the benzyltrimethyl ammonium electrolyte-Pt interface in hydrogen oxidation reaction (HOR). More specifically, we will discuss the adsorption of the cationic group that may inhibit the HOR activity of Pt electrocatalysts. Microelectrode, Infrared Reflection Adsorption Spectroscopy (IRRAS) and Neutron Reflectometry are complementary tools to investigate the catalyst-ionomer interface. Acknowledgement US department of Energy Fuel Cell Technologies Program (Program Manager: Nancy Garland) supports this research through Fuel Cell Incubator Project. We also wish to acknowledge Oak Ridge National Laboratory Spallation Neutron Source, the NIST Center for Neutron Research and the Los Alamos Neutron Science Center.

Graphitic mesoporous carbon based on aromatic polycondensation as catalyst support for oxygen reduction reaction

Mesoporous carbon is constructed by monolithic polyaromatic mesophase deriving from the hexane insoluble of coal-tar pitch. This carbon material exhibits spherical morphology and layered crystallite, and thereby can be graphitized at 900 °C without destroying the mesoporous structure. Electrochemical measurements indicate that graphitic mesoporous carbon (GMC) support not only improves the activity of Pt electrocatalyst to oxygen reduction reaction (ORR), but also shows higher corrosion resistance than commercial XC-72 carbon black in the acid cathode environment.

High stability and activity of Pt electrocatalyst on atomic layer deposited metal oxide/nitrogen-doped graphene hybrid support

A novel nanostructured support of ZrO2/nitrogen-doped graphene nanosheets (ZrO2/NGNs) hybrid was synthesized successfully by atomic layer deposition (ALD) technology to significantly improve the activity and stability of Pt electrocatalyst. Electrochemical test shows that Pt–ZrO2/NGNs catalyst has 2.1 times higher activity towards methanol oxidation reaction (MOR) than Pt/NGNs catalyst, due to the promotion by ZrO2 to the MOR on Pt surface. Pt–ZrO2/NGNs catalyst has higher electrochemical surface area (ECSA) and better oxygen reduction reaction (ORR) activity than Pt/NGNs catalyst. Pt–ZrO2/NGNs catalyst has also demonstrated 2.2 times higher durability than that of Pt/NGNs. The enhanced activity and durability were attributed to the unique triple-interaction of ZrO2–Pt–NGNs. These findings indicate that metal oxide-metal-support is a promising catalyst structure for low temperature fuel cells.

Highly catalytic activity of Pt electrocatalyst supported on sulphated SnO 2/multi-walled carbon nanotube composites for methanol electro-oxidation

Highly catalytic active platinum nanoparticles supported on sulphated SnO 2/multi-walled carbon nanotube composites (Pt–S–SnO 2/MWCNT) are reported. As a novel catalyst support, S–SnO 2/MWCNT composites with both electron and proton conductivity can improve the catalytic activity and utilization of Pt catalyst in direct methanol fuel cell. X-ray diffraction and transmission electron microscopy show that the sulphated SnO 2 and Pt nanoparticle is coexist in the Pt–S–SnO 2/MWCNT composites and coated uniformly on the surface of the MWCNTs. Fourier transform infrared spectroscopy analysis proves that the MWCNT surfaces are modified with sulphated SnO 2 and a high concentration of SO x , and adsorbed OH species exist on the surface of the sulphated SnO 2. Electrochemical studies are carried out using cyclic voltammetry, chronoamperometry and CO stripping voltammetry. The results indicate that Pt–S–SnO 2/MWCNT catalysts have much higher catalytic activity and CO tolerance for methanol electrooxidation than Pt-SnO 2/MWCNTs, commercial Pt/C and PtRu/C.

Carbon-Free Pt Electrocatalysts Supported on SnO2 for Polymer Electrolyte Fuel Cells: Electrocatalytic Activity and Durability

The use of SnO2 as an alternative electrocatalyst support improves durability against voltage cycling up to a high potential, corresponding to the start-up and shut-down situation of polymer electrolyte fuel cell (PEFC) systems. Electrochemical surface area (ECSA) and oxygen reduction reaction (ORR) activity of Pt electrocatalysts as well as electrical conductivity of the electrocatalyst layers increase by doping of SnO2 with Nb or Sb. The durability tests with voltage cycles between 0.9 and 1.3 V versus reversible hydrogen electrode (RHE) potential have revealed that the Pt electrocatalyst supported on SnO2 (Pt/SnO2) withstands 60,000 voltage cycles while maintaining its ECSA, which corresponds to a lifetime of more than 20 years with respect to the durability against voltage cycling. These results indicate that SnO2-supported carbon-free electrocatalysts can be alternatives to the conventional Pt/C electrocatalyst, as a fundamental solution against carbon support corrosion, to improve PEFC durability.

Synthesis of sulfated ZrO2/MWCNT composites as new supports of Pt catalysts for direct methanol fuel cell application

Sulfated zirconia supported on multi-walled carbon nanotubes as new supports of Pt catalyst (Pt–S-ZrO2/MWCNT) was synthesized with aims to enhance electron and proton conductivity and also catalytic activity of Pt electrocatalyst in terms of larger concentrations of ionizable OH groups on surfaces. Fourier transform infrared spectroscopy analysis shows that the sample surfaces were modified with sulfate. Transmission electron microscopy results show that the Pt and sulfated ZrO2 particles dispersed relatively uniformly on the surface of the multi-walled carbon nanotube. X-ray diffraction shows that S-ZrO2 and Pt coexist in the Pt–S-ZrO2/MWCNT composites and S-ZrO2 has no effect on the crystalline lattice of Pt. Pt–S-ZrO2/MWCNT catalyst was evaluated in terms of the electrochemical activity for methanol electro-oxidation using cyclic voltammetry, steady-state polarization experiments and electrochemical impedance spectroscopy technique at room temperature. Pt–S-ZrO2/MWCNT catalyst show higher catalytic activity for methanol electro-oxidation compared with Pt catalyst on non-sulfated ZrO2/MWCNT support and commercial Pt/C (E-TEK).