Modification Of Pt Research Articles

Energy‐Saving Hydrogen Production from Methanol Electrocatalysis Catalyzed by Molybdenum Phosphide/Nitrogen‐Doped Carbon Polyhedrons Supported Pt Nanoparticles

Comprehensive SummaryImproving the catalytic efficiency and anti‐poisoning ability of Pt‐based catalysts is very critical in methanol electrolysis technology for high‐purity hydrogen generation. Herein, the nitrogen‐doped carbon polyhedrons‐encapsulated MoP (MoP@NC) supported Pt nanoparticles were demonstrated to be effective for methanol electrolysis resulting from the combined advantages. The nitrogen‐doped carbon polyhedrons not only greatly enhanced the conductivity but also effectively prevented the aggregation of MoP to offer Pt anchoring sites. The electronic structure modification of Pt from their interaction reduced the adsorption energy of CO*, resulting in good CO‐poisoning resistance and accelerated reaction kinetics. Specifically, Pt‐MoP@NC exhibited the highest peak current density of 106.4 mA·cm–2 for methanol oxidation and a lower overpotential of 28 mV at 10 mA·cm–2 for hydrogen evolution. Energy‐saving hydrogen production from methanol electrolysis was demonstrated in the two‐electrode systems assembled by Pt‐MoP@NC which required a low cell voltage of 0.65 V to reach a kinetic current density of 10 mA·cm–2 on the glass carbon system, about 1.02 V less than that of water electrolysis.

Insights into the roles of nitrogen and phosphorus co-doping for efficient methanol electrooxidation

Anchoring Pt onto multi-heteroatom doped carbon materials has been recognized as an effective approach to improve the performance of electrocatalytic methanol oxidation. However, distinct contributions and specific behavior mechanisms of different heteroatoms, notably N and P, the specific behavior mechanisms in synergistically promoting Pt NPs remain elusive. In this work, we construct 1D N and P co-doped carbon nanotube (N, P-CNTs) supports with abundant defect anchors for Pt. The as-prepared Pt/N, P-CNTs exhibit outstanding activity and exceptional stability in methanol oxidation reaction (MOR), achieving high mass activity up to 6481.3 mA mg−1Pt. Moreover, they can retain 90.5 % of their initial current density even after 800 cycles tests. Detailed characterizations and theoretical calculations indicate that the robust strong metal-support interactions (SMSI) effect caused by N doping within the unique N and P co-doped coordination structure controllably regulate the coordination environment of Pt, reduce the d-band center of Pt, thus promoting the adsorption and decomposition of CH3OH. However, P doping weakens the adsorption strength of CO on the Pt active site by sacrificing partial electron transfer, accelerating the oxidative conversion of the CO-like poisoning species (COads). Significantly, the synergistic mechanism of N and P species on the modification of Pt’s electronic structure and its subsequent impact on the electrocatalytic methanol oxidation behaviors on the Pt surface was thoroughly elucidated, providing a constructive route for designing robust MOR electrocatalysts with high MOR activity and durability.

Dissolution Stability of Graphene-Modified Pt(111)

Pt plays a leading role in electrocatalysis, being the best pure metal catalyst for the oxygen reduction reaction (ORR) taking place at the cathode of the commercial polymer electrolyte membrane fuel cells (PEMFCs). In addition, it is usually used in the cathode to catalyze the hydrogen evolution reaction (HER) in water electrolyzers for hydrogen production. Apart from activity, stability is another critical parameter to consider when evaluating the performance of electrochemical energy conversion devices. Even pure Pt catalysts degrade under real-life conditions due to electro-oxidation and dissolution processes. Fundamental studies with well-defined Pt surfaces are mandatory for understanding these phenomena and developing new electrocatalysts with improved activity and stability.1 Different types of protection on the surface of electrocatalysts, such as carbon layers or ceria surrounding metal nanoparticles,2-4 have been investigated to enhance their stability while maintaining or improving their activity towards a reaction of interest. Here, we propose the modification of Pt(111) single crystal electrode with an adlayer of graphene as a model system to evaluate the protection mechanism of carbon-capped catalysts.In this work, the stability of graphene-modified Pt(111) in 0.1 M HClO4 is studied by on-line inductively coupled plasma mass spectrometry (ICP-MS) measurements using an electrochemical scanning flow cell (SFC). The Pt(111) surface was modified by a fast and easy transfer method of a commercially available chemical vapor deposited (CVD) graphene single-layer. The cyclic voltammetry results are comparable to those previously reported for surfaces prepared by direct CVD on the Pt(111) electrode.5 To test the quality of the graphene adlayer we checked the electrocatalytic activities towards different reactions of interest, such as ORR, HER and hydrogen oxidation reaction (HOR), and compared the results with the previous works.6 The graphene-modified Pt(111) surface presents enhanced stability since no dissolution is detected for a cyclic voltammetry experiment at 10 mV s-1 with an upper potential limit (UPL) of 1.3 V vs. RHE. In contrast, evident Pt dissolution is observed for the unmodified surface. Different accelerated stress test (AST) protocols consisting in groups of 50 cyclic voltammetries at 200 mV s-1 were performed up to three different UPL, namely 1.3 V, 1.5 V and 1.7 V vs. RHE, showing almost no dissolution over the protocol when UPL = 1.3 V, while the integrity of the graphene adlayer was quickly compromised for UPL = 1.7 V as pointed out by the quick increase in Pt dissolution. The degradation of the graphene layer in the different conditions was additionally characterized by Raman spectroscopy and atomic force microscopy (AFM). The results from this work provide useful information about the behavior of carbon capping agents on Pt surfaces, which can help to design new electrocatalytic materials with improved stability. References (1) Fuchs, T.; Briega-Martos, V.; Drnec, J.; Stubb, N.; Martens, I.; Calle-Vallejo, F.; Harrington, D. A.; Cherevko, S.; Magnussen, O. M. Anodic and Cathodic Platinum Dissolution Processes Involve Different Oxide Species. Angew. Chem. Int. Edit. 2023, 62, e202304293.(2) Sgarbi, R.; Doan, H.; Martin, V.; Chatenet, M. Tailoring the Durability of Carbon-Coated Pd Catalysts Towards Hydrogen Oxidation Reaction (HOR) in Alkaline Media. Electrocatalysis 2023, 14 (2), 267-278.(3) Kim, H.; Kwon, G. H.; Han, S. O.; Robertson, A. Platinum Encapsulated within a Bacterial Nanocellulosic-Graphene Nanosandwich as a Durable Thin-Film Fuel Cell Catalyst. ACS Appl. Energy Mater. 2021, 4 (2), 1286-1293.(4) Miller, H. A.; Vizza, F.; Marelli, M.; Zadick, A.; Dubau, L.; Chatenet, M.; Geiger, S.; Cherevko, S.; Doan, H.; Pavlicek, R. K.; et al. Highly active nanostructured palladium-ceria electrocatalysts for the hydrogen oxidation reaction in alkaline medium. Nano Energy 2017, 33, 293-305.(5) Fu, Y. C.; Rudnev, A. V.; Wiberg, G. K. H.; Arenz, M. Single Graphene Layer on Pt(111) Creates Confined Electrochemical Environment via Selective Ion Transport. Angew. Chem. Int. Edit. 2017, 56 (42), 12883-12887.(6) Shih, A. J.; Arulmozhi, N.; Koper, M. T. M. Electrocatalysis under Cover: Enhanced Hydrogen Evolution via Defective Graphene-Covered Pt(111). ACS Catal. 2021, 11 (17), 10892-10901.

Modification of nickel wire electrodes with platinum in the presence of copper ions via galvanic replacement reactions

In the galvanic replacement reaction between Ni wire and PtCl42- in an aqueous solution, the deposition of Pt nanoparticles (PtNPs) on Ni wire is generally unfavorable. However, the addition of Cu2+ into an aqueous solution of PtCl42- was found to promote the deposition of PtNPs effectively for the immersion of Ni wire. This promoted deposition of PtNPs on Ni wire could be confirmed by observing the electrocatalytic responses for ethanol oxidation, electrochemical impedance and the surface images. In addition, the EDS analysis showed that the deposited PtNPs did not contain Cu. The formation of PtNPs without containing Cu was also verified by observing the electrocatalytic properties of other alcohols. Although we had previously reported the stepwise modification of Pt on Ag-deposited Ni wire, the Cu2O-modified Ni wire was useless to allow the deposition of PtNPs in a similar stepwise treatment. Hence, the simple preparation using aqueous solutions containing both PtCl42- and Cu2+ can be proposed as a useful approach to modify PtNPs on Ni materials via galvanic replacement reactions.

Oxaliplatin(IV) Prodrugs Functionalized with Gemcitabine and Capecitabine Induce Blockage of Colorectal Cancer Cell Growth-An Investigation of the Activation Mechanism and Their Nanoformulation.

The use of platinum-based anticancer drugs, such as cisplatin, oxaliplatin, and carboplatin, is a common frontline option in cancer management, but they have debilitating side effects and can lead to drug resistance. Combination therapy with other chemotherapeutic agents, such as capecitabine and gemcitabine, has been explored. One approach to overcome these limitations is the modification of traditional Pt(II) drugs to obtain new molecules with an improved pharmacological profile, such as Pt(IV) prodrugs. The design, synthesis, and characterization of two novel Pt(IV) prodrugs based on oxaliplatin bearing the anticancer drugs gemcitabine or capecitabine in the axial positions have been reported. These complexes were able to dissociate into their constituents to promote cell death and induce apoptosis and cell cycle blockade in a representative colorectal cancer cell model. Specifically, the complex bearing gemcitabine resulted in being the most active on the HCT116 colorectal cancer cell line with an IC50 value of 0.49 ± 0.04. A pilot study on the encapsulation of these complexes in biocompatible PLGA-PEG nanoparticles is also included to confirm the retention of the pharmacological properties and cellular drug uptake, opening up to the possible delivery of the studied complexes through their nanoformulation.

Selective Glycerol‐to‐glycerate Electro‐oxidation on Cerium‐modified Pt/C Nanocatalyst in an Alkaline Direct Alcohol Fuel Cell: Cogeneration of Energy and Value‐added Products

AbstractGlycerol electro‐oxidation reaction was performed in an alkaline environment with an anion exchange membrane fuel cell (AEMFC) operating in bath mode at low Pt‐loadings. BAE‐synthesized Pt/C and PtCe/C nanostructured catalysts were used as anode materials during 4‐hour operation to selectively obtain 65 % and 41 % of glycerate as main product, respectively. The modification of Pt with Ce improved the catalytic activity of the Pt/C catalyst generating 30 % more energy density after 4‐hour operation by achieving a higher degree of glycerol oxidation in cogeneration with added‐value products confirmed by spectroelectrochemical (in situ FTIR) and liquid chromatography coupled with mass spectrometry (LC–MS) analyses. The bifunctional mechanism generated by the presence of Ce is used to explain the improvement in the catalytic activity of Pt/C, due to the properties of this rare earth element to adsorb oxygenated species (OH−) and promote oxidation. The cathode material was a polyol‐synthesized PdFe/C electro‐catalyst for ORR that presented impressive stability and tolerance to glycerol.

(Poster Award - 2nd Place) Enhancement of ORR Activity of Pt Catalyst for PEFCs By Modification with Hydrogen-Bonded Organic Framework Composed of Melamine and Cyanuric Acid

Introduction Improvement in ORR activity of Pt and Pt-based catalysts used in PEFCs for FCEVs is crucial for cost reduction and widespread commercialization [1]. We have reported that surface modification of Pt and Pt-based catalysts with melamine and its derivatives enhance ORR activity [2, 3]. However, it is concerned that melamine is easily washed out by water generated at the cathode in PEFCs because melamine is soluble in water (3.1 g/L). In this study, a hydrogen-bonded organic framework (HOF) composed of melamine (MEL) and cyanuric acid (CA) [4] was prepared to suppress the washing-out problem and investigated as a modifier of Pt catalyst loaded on mesoporous carbon (MPC) support. Experimental MPC (CNovel MH-18, SBET 1,334 m2/g, TOYO TANSO) was used as a carbon support for Pt catalyst. Pt/MPC (50 wt%) was prepared by an impregnation-thermal decomposition method using Pt(NO2)2(NH3)2 as a Pt source. Pt/MPC was modified as the following procedure. First MEL was impregnated within the Pt/MPC by ultrasonically dispersing 100 mg Pt/MPC catalyst and 10 mg MEL (10 wt.% to the catalyst) in 100 mL pure water, followed by drying using a rotary evaporator (MEL-Pt/MPC). Then MEL-Pt/MPC (110 mg) was dispersed in 100 mL water containing 10 mg CA and dried to obtain HOF-Pt/MPC. The catalyst was loaded on a glassy carbon (GC) RDE. CV of the catalyst was recorded in Ar-saturated 0.1 M HClO4 at 25oC at a scan rate of 50 mV/s and ORR activity was evaluated by LSV performed at 25oC in O2-saturated 0.1 M HClO4 at a scan rate of 10 mV/s on the positive sweep while rotating the GC disk electrode at 1,600 rpm. To investigate the stability of MEL and HOF on the electrode, the GC electrode after the initial measurements was immersed in 0.1 M HClO4 at 80oC for 1 h, followed by washing with pure water, and CV and LSV were measured in the same manner at 25oC. Results and Discussion Figure 1 shows the molecular structure of MEL-CA HOF [4]. Figures 2 and 3 show CVs and LSVs, respectively, for bare, MEL-, and HOF-Pt/MPC before the stability tests. For bare Pt/MPC in Fig. 2, peaks were observed around 0.05−0.4 V and 0.6−1.0 V, which are assigned to the adsorption/desorption of underpotential deposited hydrogen (Hupd) and Pt-oxide species formation/reduction, respectively. For MEL- and HOF-Pt/MPC, the HUPD peak area decreased slightly, while the onset potential for Pt-oxide formation was shifted positively in Fig. 2. As a result, ORR activity of MEL- and HOF-Pt/MPC was improved remarkably as shown in Fig. 3 (mass activity: 894 and 829 A/g, respectively, at 0.9 V). These results indicate that HOF has an enhancement effect for ORR activity similar to that of MEL modification. Figure 4 shows CVs for bare, MEL-, and HOF-Pt/MPC after the stability tests at 80oC for 1 h. In Fig. 4, the waves of Hupd and Pt-oxide of MEL-Pt/MPC became similar to those of bare Pt/MPC after the stability test, which indicated that MEL was washed out in the electrolyte solution. On the contrary, the HOF-Pt/MPC catalyst substantially retained the waves shapes before the stability test shown in Fig. 2. These results indicate that the HOF has higher stability against washing-out than MEL owing to a much lower solubility at 80°C. Figure 5 shows LSVs after the stability tests. The loss of activity of HOF-Pt/MPC (639 A/g) was smaller than MEL-Pt/MPC (553 A/g) owing to the suppression of washing-out, which is consistent with the results in Fig. 4. The results of single cell tests using bare Pt/MPC, MEL-Pt/MPC and HOF-Pt/MPC cathode catalysts will be presented at the meeting.This study was partly supported by NEDO, Japan.

Ultrahigh-acetone-sensitivity sensor based on Pt-loaded TiO2 porous nanoparticles synthesized via a facile hydrothermal method

A simple hydrothermal method based on an orthogonal experimental design was used to synthesis Pt-loaded TiO2 mesoporous nanoparticles in one step. The successful synthesis of Pt-loaded TiO2 nanoparticles was demonstrated by various characterization methods. The effects of the modification of Pt and its explanation are described in detail by means of the test results. Through systematic gas-sensing tests, we found that the Pt-loaded TiO2 nanoparticles outperform pure TiO2 nanoparticles, with a high response value (S = 42.5) to 200 ppm acetone at 260 °C and with a film thickness of 0.45 mm, far superior to that of pure TiO2. The response time (8 s) and recovery time (11 s) of the material are also relatively good with excellent selectivity and long-term stability (30 days). The frequent use of acetone as an organic solution in factories and laboratories, as well as the possibility of making a preliminary diagnosis of diabetes by detecting acetone levels in exhaled gas, make this work promising for environmental monitoring and medical diagnosis.

Oxidative Desorption of Adsorbed Sulfur on Platinum Surfaces Modified with Cerium Species

In polymer electrolyte membrane fuel cells, hydrogen oxidation and oxygen reduction reaction occur at platinum (Pt) catalyst surface. Pollutants in air and hydrogen fuel, especially, sulfur (S) species, often strongly adsorb on the Pt surface, resulting in reduced electrochemically active surface area, namely poisoning effect. Because such poisoning causes the significant deterioration of cell performance and durability, understanding and control of adsorption behavior of S species are very important. Thus, it is necessary to develop a new method or material for recovery from S poisoning in anode.In this study, a Pt(111) single crystal electrode was modified with a Ce species and its electrochemical property was compared with a bare Pt electrode. The modification with Ce species was accomplished by immersion in a Ce (NO3)3 + HClO4 aqueous solution with bubbling Ar + H2 gas through the solution for 1 h or applying the potential at -0.2 V in a Ce (NO3)3 + HClO4 aqueous solution. The modification of Pt(111) electrode with Ce species drastically changed the electrochemical responses; hydrogen adsorption/desorption waves become smaller and adsorption/desorption waves of hydroxy group disappeared because of the presence of adsorbed Ce species. Adsorbed species was identified as a Ce3+ ion by XANES spectrum.After the bare Pt(111) electrode was immersed in an aqueous solution containing sodium sulfide, three types of adsorbed S species, HS and S/Sn were detected by XPS. HS was reductively desorbed from Pt electrode surface at potential cycling between 0.0 and 0.2 V vs. RHE (-0.2 and 0.0 V vs. Ag/AgCl). S/Sn species remained during this potential cycling but oxidatively desorbed when the positive limit of potential cycling was 0.6 V vs. RHE (0.8 V vs. Ag/AgCl). The hydrogen adsorption/desorption current gradually increased as repeating potential cycling between 0.0 and 1.0 V vs. RHE (-0.2 V and 0.8 V vs. Ag/AgCl).After the Ce-modified Pt(111) electrode was immersed in an aqueous solution containing sodium sulfide, an anodic current assignable to the oxidative desorption of S species appeared at 0.3 V. The peak current decreased as repeating potential cycling between 0.0 and 0.7 V vs. RHE (-0.2 V and 0.5 V vs. Ag/AgCl). After this potential cycling, the peak area of S2p region of XPS spectra decreased as well as Ce 3d peak. The oxidative desorption of S and Sn on the Ce-modified Pt(111) electrode took place at 0.5 V vs RHE (0.3 V vs. Ag/AgCl) which is much more negative than that of bare Pt(111) electrode (1.0 V vs. RHE (0.8 V vs. Ag/AgCl)). Thus, modification of Pt(111) electrode with Ce species promoted the oxidative desorption of S species.

Study on Catecholamine Sensors Based on Noble Metal Nanoparticles Modified Ti3C2 Mxene

Catecholamines are neurotransmitters in the peripheral and central nervous systems, which maintain the normal physiological state of the human body. Studies have shown that the occurrence of many diseases are often accompanied by changes in catecholamine levels. Clinically, the detection of catecholamine levels in human plasma or urine can assist in the diagnosis of endocrine-related diseases and neurological diseases. However, catecholamines are easily oxidized, and the content in human body is very low. So the rapid detection of catecholamines is very important for the prevention and diagnosis of related diseases. In this paper, the electrochemical response characteristics of Ti3C2Tx MXene and noble metal nanoparticles modified Ti3C2Tx to dopamine (one type of catecholamine) were explored. The results shown that Ti3C2Tx would undergo irreversible oxidation at the anode potential and the single Ti3C2Tx modified electrode was not suitable for the detection of dopamine. So we further explored the modification of Pt and Au nanoparticles on the Ti3C2Tx/GCE electrode, and the experimental results shown that Au/Ti3C2Tx/GCE had higher sensitivity for measuring dopamine, while Pt/Ti3C2Tx/GCE had a larger linear range. Both electrodes had good stability and repeatability and could be used for the detection of catecholamines.

High temperature performance and interface evolution of a NiCoCrAlY coating with Pt modification and Re-based diffusion barrier

The cyclic and early isothermal oxidation behaviors at 1050 °C of the NiCoCrAlY, Pt-modified NiCoCrAlY and Pt-modified NiCoCrAlY with Re-based diffusion barrier (DB) have been evaluated. The atomic immigration and electron location function (ELF) at the Ni-Re interface were simulated by density function theory (DFT) calculations. After isothermal oxidation for 1 h, island NiCoCrAlY particles with extremely poor Al were observed in the oxide scale of normal NiCoCrAlY coating, and then the oxide scale transformed into a double-layer structure after oxidation for 20 h. The initial “island-oxide” scale model was proposed to illustrate the oxidation mechanisms for normal NiCoCrAlY coating. The oxide scale of Pt-modified NiCoCrAlY coating was single-layer Al2O3 with rapid coverage at the surface, because the modification of Pt changed the initial oxidation mechanism by promoting the uphill diffusion of Al. The Re-based DB reduced the thickness of the secondary reaction zone (SRZ) by inhibiting the element interdiffusion between the NiCoCrAlY coating and the substrate, thus the Pt-modified NiCoCrAlY with Re-based DB exhibited the lowest interdiffusion extent. Interestingly, the thermal stability of Re-based DB in NiCoCrAlY coating system was poorer than that in NiCrAlY system. The DFT simulation shows that the incorporation of Co made the energy difference more negative, which confirmed that Co promoted the diffusion of Re in the NiCoCrAlY coating, thus accelerating the degradation of Re-based DB.

WO x /Pt(111) Prepared As PEFC Model Anode Catalyst: Surface Structure and Suppressed Hydrogen Peroxide Generation

Introduction To achieve prolonged lifetime of polymer electrolyte fuel cell (PEFC), hydrogen-peroxide (H2O2)-induced chemical degradation of polymer electrolyte membrane (PEM) is a crucial problem. In general, oxygen (O2) crossover from cathode to anode through the PEM yields H2O2 generation on Pt/C anode catalyst surface through 2-electron pathway of O2 reduction reaction. Thus, mitigation of H2O2 generation on Pt/C surface is a key to suppress the PEM degradation. Trogadas and Ramani reported tungsten trioxide (WO3) addition to Pt/C suppressed H2O2 generation.1 The results suggest that the cooperation of Pt nanoparticles and WO3 located near-by should be effective for suppression of H2O2 generation. However, influence of the oxidation states of tungsten oxide (WO x ) on H2O2 generation at the Pt surface is not fully resolved. Furthermore, it was reported that, although fully oxidized WO3 is stable in acid solution (pH < 2),2 sub-oxides of tungsten (WO x ) could dissolve in Pt-WO x electrochemical system.3 Thus, electrochemical dissolution behaviors of WO x located on Pt substrate surface should be investigated in detail. In this study, we prepare Pt(111) surface that modified by WO x having different oxidation states, and investigated the electrochemical H2O2 generations. Experimental Pt(111) single crystal substrate surface was cleaned by repeated cycles of Ar+ sputtering and annealing in an ultrahigh vacuum (UHV; ~10-8Pa). Subsequently, WO x was deposited on the cleaned Pt(111) via an arc-plasma deposition (APD) method using a W target under partial pressures of O2 (p(O2) = 1×10-1 or 1×10-3 Pa) at ca. 298 K. Deposition amounts of the WO x was estimated to be ca. 1.5 µg/(cm2 of substrate) by using a quartz crystal microbalance installed in the UHV chamber. Then, WO x -modified Pt(111) were annealed at 703 K for 10 min. in UHV. Hereafter, the fabricated samples are referred to as p(O2)-WO x /Pt(111). X-ray photoelectron spectroscopy (XPS) was conducted for the as-fabricated samples in situ in UHV.H2O2 generation amounts were evaluated by the tip generation/substrate collection mode of scanning electrochemical microscope (SECM)4 in O2-saturated 0.1 M HClO4. Generated H2O2 was detected by a Pt tip micro-electrode (diameter: ca. 20 µm, tip potential: 1.26 V vs. RHE) positioned ca. 50 µm at surface normal of the sample electrodes, with sweeping sample electrode potential (E S) at sweep rate of 2 mV/s in negative going direction. Thereafter, potential cycles (PCs: 0.05–1.0 V vs. RHE, sweep rate: 100 mV/s, 100 cycles) were applied to the sample surfaces; then, H2O2 generation was re-evaluated. Finally, the PCs-applied sample surfaces were re-introduced to the UHV chamber to perform XPS measurements. Results and Discussion XP spectra of W4f bands for the as-fabricated and PCs-applied sample surfaces are summarized in Figure. 1 (A). Considering peak areas of deconvoluted components (solid lines), the oxidation states of WO x as-fabricated can be judged mainly to be W6+ and Wx+ (x < 4) for 10-1 Pa-WO x /Pt(111) (a) and 10-3 Pa-WO x /Pt(111) (c), respectively.Figure. 1 (B) shows SECM-estimated H2O2 generations of the WO x /Pt(111) surfaces before (as-fabricated) and after the 100 PCs. As for the as-fabricated surfaces (solid lines), H2O2 detection current (i T) of the Pt tip micro-electrode normalized by respective sample electrode current (i S) is lower for 10-1 Pa-WO x /Pt(111) than 10-3 Pa-WO x /Pt(111), yet normalized i T/|i S|-values for both surfaces are smaller than that of clean Pt(111). The results show that surface modification of Pt(111) by the small amount of WO x , particularly with higher oxidation states, effectively suppressed H2O2 generations. However, the suppression effect degraded by the 100 PCs application for both the electrode surfaces (dotted lines). Compared of W4f bands for the PCs-applied surfaces (Figure. 1 (A) (b, d)) with corresponding as-fabricated ones (a, c), the bands shifted to negative- and positive-binding-energies for 10-1 Pa-WO x /Pt(111) and 10-3 Pa-WO x /Pt(111), respectively, indicating respective reduction and oxidation of the surface WO x by the PCs. In addition, W4f bands for both surfaces decreased in intensity by the PCs application, suggesting decrease in surface amount of the WO x , probably through electrochemical dissolution during the PCs. The PCs-induced changes in oxidation states and amounts of surface WO x should correlate to the degraded H2O2 generation suppressions. Acknowledgement This study was supported by the new energy and industrial technology development organization (NEDO) of Japan, JSPS KAKENHI Grant Number JP21H01645, and JST SPRING Grant Number JPMJSP2114. References P. Trogadas and V. Ramani, J. Electrochem. Soc., 155, B696–B703 (2008).M. Anik and K. Osseo-Asare, J. Electrochem. Soc., 149, B224 (2002).A. J. Martín, A. M. Chaparro, and L. Daza, J. Power Sources, 196, 4187–4192 (2011).C. M. Sánchez-Sánchez and A. J. Bard, Anal. Chem., 81, 8094–8100 (2009). Figure 1

Improvements in ORR Activity and Cell Performance of Pt-Based Catalysts for PEFCs By Modification with Protonated Melamine-Derivative Salts

1. Introduction Improvement in ORR activity of Pt-based catalysts for use in PEFCs of FCVs is crucial for cost reduction and widespread use [1]. We reported that surface modification of Pt and Pt-based catalysts with melamine molecules enhances ORR activity [2, 3]. However, it is predicted that the melamine is easily washed off by water generated at the cathode in PEFCs because melamine is soluble in water. In this study, organic salts composed of protonated melamine derivatives and bis(nonafluorobutanesulfonyl)imide were newly synthesized to suppress the washing-off effects. Pt and Pd@Pt core-shell catalysts were modified with the organic salts, and the ORR activity and the I-V performance were investigated. 2. Experimental Ketjen Black EC-600JD (KB, SBET: 1,345 m2/g, LION) and mesoporous carbon (MPC, CNovel MH-18®, SBET 1,334 m2/g, TOYO TANSO) were used as carbon supports for Pd@Pt core-shell and Pt catalysts, respectively. The Pt/Pd/KB core-shell catalyst was synthesized by a direct displacement reaction method [4] and the Pt/MPC catalyst was synthesized by an impregnation/thermal reduction method. The organic salts were synthesized by mixing equimolar melamine derivatives and Li bis(nonafluorobutanesulfonyl)imide in 0.1 M HNO3 aqueous solution at 80oC. Pt/Pd/KB catalyst was loaded onto a glassy carbon electrode and immersed in acetone containing 0.1 mM organic salts for 10 min. to modify the catalyst surface with the organic salts. CV of Pt/Pd/KB catalyst was recorded at 25oC in Ar-saturated 0.1 M HClO4 with a potential scan rate of 50 mV/s and LSV was measured by RDE method at 25oC in O2-saturated 0.1 M HClO4 with a potential scan rate of 10 mV/s at a rotation speed of 1,600 rpm.Pt/MPC catalyst was dispersed in acetone containing 20 wt.% organic salt and acetone was slowly evaporated by using an evaporator to modify the catalyst with organic salt, and used for 1 × 1 cm2 MEA tests. The MEA was fabricated by a decal method using Nafion® membrane (25 µm in thickness) and a GDL (SGL). Nafion® DE2020 was used as an ionomer for catalyst ink preparation (I/C: 0.83). The Pt loading of the cathode catalyst layer in the MEA was set to 0.1 mg-Pt/cm2. I-V performance of the MEA was evaluated at 80oC, 75% RH. H2 gas (418 NmL) and air (998 NmL) were supplied to the anode and the cathode, respectively, and the H2 gas was pressurized to 150 kPa (ambient + 50 kPa) at the gas-outlet (H2 utilization: 5% at a current density of 3.0 A/cm2). 3. Results and Discussion Figure 1 shows molecular structure of an organic salt of [diethylmelamine+H]+[bis(nonafluorobutanesulfonyl)imide]- ([DEM]+[NFSI]-). The salt was synthesized in 0.1 M HNO3 (pH 1) at 80oC and was obtained in a solid state in the solution with a yield > 90%. CVs of Pt/Pd/KB catalyst and after modification with [DEM]+[NFSI]- are depicted in Figure 2. Hydrogen adsorption/ desorption waves observed in the potential range of 0.05-0.4 V were slightly suppressed by the modification, indicating that surface Pt active sites were partially occupied by the salt. Simultaneously, the onset potential for Pt-OH formation was positively shifted and the formation of Pt-oxygenated species was suppressed in the high potential range of 0.7-1.2 V, showing that the modified Pt surface retained more metallic state at high potentials. Figure 3 demonstrates LSVs of the Pt/Pd/KB catalyst and after modification with [DEM]+[NFSI]-. The LSV of the catalyst positively shifted by the modification and the ORR mass activity was enhanced from 1,223 to 2,234 A/g-Pt at 0.9 V. These results indicated that the modification of the Pt/Pd/KB catalyst with [DEM]+[NFSI]- was effective in enhancing ORR activity and the results are almost the same as the activity enhancement observed by melamine modification [3].Figure 4 shows I-V performance of the MEA using Pt/MPC as the cathode catalyst. The cell voltage of the MEA using the modified Pt/MPC exceeded that using the unmodified catalyst in the whole current density region, indicating that ORR activity enhancement by the organic salt modification was also demonstrated in the MEA tests. Furthermore, the resistance and the diffusion overpotentials as well as the activation overpotential were all reduced by the modification with [DEM]+[NFSI]-. Thus, the organic salt could interact with ionomers or membrane and decrease the resistance and the diffusion overpotentials.This study was partly supported by NEDO, Japan.

Highly Selective and Humidity-Resistant Triethylamine Sensors Based on Pt and Cr2O3 Nanoparticles

A triethylamine gas sensor with humidity resistance, high selectivity, and high response is designed. Chromium oxide particles were prepared by heating them in a water bath at 80 °C. Pt/Cr2O3 nanoparticles were obtained by sodium borohydride reduction. The structure morphology of nanoparticles was characterized by some methods. The gas response test results showed that the modification of Pt improved the response value and selectivity of Cr2O3 to triethylamine. It was found that Cr2O3–2Pt nanoparticles had the best performance, and at the optimum operating temperature of 160 °C, its response value reached 200, 68 times that of Cr2O3 (S = 2.95). In addition, the modification of Pt made Cr2O3–2Pt nanoparticles had a wide range of humidity applications. The mechanism of gas response is explained by using the Schottky barrier and hole accumulation layer model of Pt and Cr2O3 contact and energy band theory.

Post-Functionalization of Organometallic Complexes via Click-Reaction

CuAAC (Cu catalyzed azide-alkyne cycloaddition) click-reaction is a simple and powerful method for the post-synthetic modification of organometallic complexes of transition metals. This approach allows the selective introduction of additional donor sites or functional groups to the periphery of the ligand environment. This is especially important if a metalloligand with free donor sites, which are of the same nature as the primary site for the coordination of the primary metal, has to be created. The concept of post-synthetic modification of organometallic complexes by click-reaction is relatively recent and the currently available experimental material does not yet allow us to identify trends and formulate recommendations to address specific problems. In the present study, we have applied the CuAAC reaction for the post-synthetic modification of diimine mononuclear complexes Re(I), Pt(II) and Ir(III) with C≡C bonds at the periphery of the ligand environment and demonstrated that click-chemistry is a powerful tool for the tunable chemical post-synthetic modification of coordination compounds.

Effect of CeO2 and Pt introduction on the structure and performance of Fe2O3 for Hg0 removal

In this work, the thermal stability and catalytic activity of Fe2O3 catalyst for Hg0 oxidation were improved by the introduction of CeO2 and Pt. During high-temperature calcination at 400 °C, the mesoporous structure of Pt/CeO2/Fe2O3 remained stable, and it also retained higher specific surface area and lower average pore size than Fe2O3. The X-ray diffraction, transmission electron microscopy, and thermal gravimetric-differential scanning calorimetry results revealed that the modification of CeO2 and Pt retarded the crystallization and growth of Fe2O3 grains during high-temperature calcination, limiting Fe2O3 particles to a smaller size. Temperature-programmed desorption experiments showed that Hg0 adsorption of Pt/CeO2/Fe2O3 was promoted. In addition, X-ray photoelectron spectroscopy spectra suggested that adding CeO2 and Pt also increased the content of chemisorbed oxygen and transformed Fe2O3 into an electron-rich state, which consequently improved its catalytic performance for Hg0 oxidation.

Non-oxidative dehydrogenation of propane to propene over Pt-Sn/Al2O3 catalysts: Identification of the nature of active site

Supported platinum-tin over various oxide supports have been widely recognized as the efficient propane dehydrogenation catalysts due to their excellent activity, C3H6 selectivity and stability after oxidative regeneration. The nature of the active species of the Pt-Sn catalysts is still under debate. Here, by controlling the formation of Pt-Sn chloride complexes during the impregnation stage, we managed to tune spatial distribution of Pt and Sn species over Al2O3 and further influence the degree of alloying between reduced Pt and Sn. The structure characterization revealed the co-impregnation method tend to generate PtSn alloy active site, while sequential impregnation of Pt on pre-synthesized Sn/Al2O3 tend to form Sn partially modification of Pt. Performance evaluation demonstrated that the Pt clusters partially modified by reduced Sn exhibited much higher activity and longer life-time than PtSn alloy counterparts under similar C3H6 selectivity. With further optimization, the Pt-Sn/Al2O3 prepared by sequential impregnation method achieved over 64.1 μmol/gcat/h propylene formation rate at the 30% propane conversion with the C3H6 selectivity exceeding 99%.

New insights into methanol and formic acid electro-oxidation on Pt: Simultaneous DEMS and ATR-SEIRAS study under well-defined flow conditions and simulations of CO spectra.

Methanol and formic acid electro-oxidation on Pt has been studied under well-defined flow conditions by a spectroscopic platform that combines differential electrochemical mass spectrometry (DEMS) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. The volatile soluble products from methanol and formic acid oxidation on Pt have been detected by DEMS, while adsorbed intermediates have been identified with ATR-FTIR spectroscopy. Besides CO2 and methylformate, which were detected by DEMS, other non-volatile soluble intermediates such as formaldehyde and formic acid were also generated during methanol oxidation on Pt. Besides water adsorption bands, linearly bonded CO, bridge-bonded CO, adsorbed formate, adsorbed formic acid, and adsorbed CHO bands were observed by ATR-FTIR spectroscopy during methanol and formic acid oxidation on Pt. Formic acid adsorption suppressed the formate and water adsorption. Our results suggest that formate could be an inactive adsorbed species, rather than an active intermediate, for both methanol and formic acid oxidation. Pb modification of Pt significantly enhanced formic acid oxidation through the direct pathway due to the third-body effect and electronic effects. Formic acid oxidation took place mainly at Pb modified low-coordinated defect sites at low potentials. Formic acid decomposition to form adsorbed CO occurred only in the hydrogen region, and Pb modification also slightly enhanced the successive oxidation of adsorbed CO. A double-peak infrared band was observed for linearly bound CO on the Pt film and was simulated with the Fresnel equations and Bruggeman effective medium theory.

Constructing Co3O4/g-C3N4 Ultra-Thin Nanosheets with Z-Scheme Charge Transfer Pathway for Efficient Photocatalytic Water Splitting.

Photocatalytic water splitting for hydrogen generation is a significant pathway for sustainable energy conversion and production. The photocatalysts with a Z-scheme water splitting charge transfer pathway is superior due to the good separation and migration ability of photoexcited charge carriers. Herein, Co3O4/g-C3N4 photocatalysts with Z-scheme charge transfer pathway were successfully constructed by an electrostatic interaction-annealing method. The as-prepared Co3O4/g-C3N4 ultra-thin nanosheets were tested and analyzed by XRD, EA, ICP, SEM, TEM, AFM, XPS, UV-Vis DRS, PL and photoelectrochemical measurements. Moreover, the influences of fabrication parameters on performance of Co3O4/g-C3N4 catalysts were investigated, and 0.5% Co3O4/g-C3N4 exhibited the optimal activity. Based on the characterization and catalytic performance, the Z-scheme charge transfer pathway of Co3O4/g-C3N4 was established and put forward. To further improve the catalytic performance of Co3O4/g-C3N4, 0.5% Pt was added as a co-catalyst. The obtained Pt/0.5% Co3O4/g-C3N4 was recyclable and remained the original catalytic water splitting performance within 20 h. The modification of Co3O4 and Pt improved the separation and migration of e− and h+, and induced the increased hydrogen evolution rate of g-C3N4.

Electrochemical Toluene Hydrogenation Using Binary Platinum-Based Alloy Nanoparticle-Loaded Carbon Catalysts

A couple of toluene (TL) and its hydrogenation product, methylcyclohexane (MCH), are promising high-density hydrogen carriers to store and transport large amounts of hydrogen. Electrochemical hydrogenation of TL to MCH can achieve energy savings compared with hydrogenation using molecular hydrogen generated separately, and development of highly active catalysts for electrochemical TL hydrogenation is indispensable. In this study, binary Pt3M (M = Rh, Au, Pd, Ir, Cu and Ni) alloy nanoparticle-loaded carbon catalysts were prepared by a colloidal method, and their activity for electrochemical TL hydrogenation was evaluated by linear sweep voltammetry. Each Pt3M electrode was initially activated by 100 cycles of potential sweep over a potential range of 0–1.2 or 0.8 V vs. reversible hydrogen electrode (RHE). For all activated Pt3M electrodes, the cathodic current density for electrochemical TL hydrogenation was observed above 0 V, that is the standard potential of hydrogen evolution reaction. Both specific activity, cathodic current density per electrochemical surface area, and mass activity, cathodic current density per mass of Pt3M, at 0 V for the Pt3Rh/C electrode were the highest, and about 8- and 1.2-times as high as those of the commercial Pt/C electrode, respectively, which could mainly be attributed to electronic modification of Pt by alloying with Rh. The Tafel slope for each activated Pt3M/C electrode exhibited the alloying of Pt with the second metals did not change the electrochemical TL hydrogenation mechanism.