High Activity For Methanol Oxidation Reaction Research Articles

Thermal Radiation Synthesis of Ultrafine Platinum Nanoclusters toward Methanol Oxidation

AbstractDirect methanol fuel cells (DMFCs) are considered as a promising candidate for portable electronic devices and small electric vehicles due to their high gravimetric and volumetric energy densities. The operation of DMFCs requires efficient catalysts, especially on the anode to promote methanol oxidation reaction (MOR). To date, platinum has emerged as a chief contender for MOR. Unfortunately, most catalysts suffer from severe CO poisoning, which can passivate the catalytic surface and decrease the activity over time. Herein, a transient, thermal radiation method to synthesize ultrafine platinum nanoclusters (0.68 ± 0.13 nm) supported on carbon black (Pt NC/CB) is demonstrated. The sample demonstrates a great CO poisoning resistance and excellent activity toward MOR. The ultrafine platinum nanoclusters with increased active sites can promote the oxidation of CO at potential as low as 0.4 V. The Pt NC/CB displays an onset potential of 0.4 V and a peak current density of 1.30 mA cm−2ECSA (electrochemical active surface area), which is superior than that of reported catalysts (0.57–1.06 mA cm−2ECSA), while many of the catalysts are alloys involving noble metals. This work showcases an efficient method to prepare Pt nanoclusters with high MOR activity and great CO poisoning resistance.

Quatermetallic Pt-based ultrathin nanowires intensified by Rh enable highly active and robust electrocatalysts for methanol oxidation

Inferior stability and anti-poisoning capacity of Pt-based ultrathin nanowires (NWs) are critical weaknesses under detrimental acidic running conditions for proton-exchange membrane fuel cell applications due to their energetic surface. Here 1.5-nm-thin quatermetallic PtCoNiRh NWs with high atomic-exposure are fabricated to serve as robust electrocatalysts for acidic methanol oxidation reaction (MOR). Surpassing Rh-free PtCoNi NWs and most of state-of-the-art catalysts, the PtCoNiRh NWs achieve extremely high MOR activity (1.36 A·mg−1Pt and 2.08 mA cm−2) with substantially lowered onset-potential and improved CO-tolerance. The anticorrosion effect of incorporated-Rh can effectively stabilize the PtCoNiRh NWs in the corrosive MOR. Electrochemical in situ Fourier transform infrared spectroscopy and density functional theory simulation cooperatively reveal that the methanol dehydrogenation is inclined to occur at the interatomic Pt–Rh sites, where the intermediate COads prefers bridge binding mode rather than linear mode with facilitated removal. Integratedly, the complete 6e−-transferred MOR process is reliably accelerated and stays efficient on the quaternary PtCoNiRh NWs.

In Situ Growth of BiOI/MoS2 Heterostructure as Pt Supports for Visible Light‐Assisted Electrocatalytic Methanol Oxidation Reaction

A two‐dimensional BiOI/MoS2 heterojunction is fabricated by in situ growth of MoS2 on BiOI nanosheets through a hydrothermal method and then as a carrier for loading on Pt nanoparticles. Transmission electron microscopy shows that Pt nanoparticles are decorated uniformly on the surface of BiOI/MoS2 nanosheets. The obtained Pt‐BiOI/MoS2 is utilized as an electrocatalyst for the methanol oxidation reaction in alkaline conditions under visible light irradiation. Electrochemical evaluations indicate that as‐prepared Pt‐BiOI/MoS2 expresses the highest methanol oxidation reaction activity and stability, and the maximum current density reaches 1007.2 mA mg−1Pt under visible light irradiation, which is 12 and 3.5 times higher compared with Pt‐BiOI and commercial Pt/C electrodes, respectively, in the traditional electrocatalytic process. The results suggest that a synergy of photo‐ and electro‐processes improves the photoelectrocatalytic performance of Pt‐BiOI/MoS2 in the methanol oxidation reaction.

Editors' Choice—Methanol Electrooxidation with Platinum Decorated Hematene Nanosheet

Developing a durable electrocatalyst with a high methanol oxidation reaction activity is highly important for anode design in direct methanol fuel cells. To that end, Pt-hematene sheets have been successfully synthesized by ultrasonic exfoliation followed by a double pulse deposition strategy to adjust the Pt loading. The morphology, structure, and composition of this new class of Pt decorated metal oxide nanosheet have been characterized by transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. Electrocatalytic characteristics have been systematically investigated by cyclic voltammetry and compared with commercial Pt/C catalyst. The novel Pt-hematene sheets exhibit a good mass activity with a low peak potential but most of all show an enhanced tolerance to the intermediates of methanol oxidation.

Investigation of oxygen reduction and methanol oxidation reaction activity of PtAu nano-alloy on surface modified porous hybrid nanocarbon supports

We investigate the electrocatalytic activity of PtAu alloy nanoparticles supported on various chemically modified carbon morphologies towards oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). The surface-modification of graphene nanosheets (f-G), multi-walled carbon nanotubes (f-MWNTs) and (graphene nanosheets-carbon nanotubes) hybrid support (f-G-MWNTs) were carried out by soft functionalization method using a cationic polyelectrolyte poly-(diallyldimethyl ammonium chloride). The Pt and PtAu alloy nanoparticles were dispersed over chemically modified carbon supports by sodium-borohydride assisted modified polyol reduction method. The electrochemical performance of all electrocatalysts were studied by half- and full-cell proton exchange membrane fuel cell (PEMFC) measurements and PtAu/f-G-MWNTs catalyst comparatively yielded the best catalytic performance. PEMFC full cell measurements of PtAu/f-G-MWNTs cathode electrocatalyst yield a maximum power density of 319 mW cm−2 at 60 °C without any back pressure,which is 2.1 times higher than that of cathode electrocatalyst Pt on graphene support. The high ORR and MOR activity of PtAu/f-G-MWNTs electrocatalyst is due to the alloying effect and inherent beneficial properties of porous hybrid nanocarbon support.

Synergistic Electronic Pull of Graphene Oxide Supported Pd Nanoparticles on Enhancing Catalytic Activity of Electro Deposited Pt Nanoparticles for Methanol Oxidation Reaction

Graphene oxide supported clean Pd nanoparticles were synthesized by using CO as a reducing agent. Pt film was deposited on Pd NPs through electrochemical potential cycling method. The as-developed catalyst, which exhibits higher catalytic performance for electro oxidation of methanol and better tolerance to the CO poisoning effect suffered during methanol oxidation reaction (MOR). The higher performance of catalyst attribute towards the long chain organic capping agent free formation process of clean PdPt nanocomposite. This facile and effective route is of great significance for the synthesis of Pd-based catalysts on electrode surface directly with highest MOR activity. The synergistic electronic pull provided by graphene oxide supported Pd nanoparticles to Pt in the composite material highly enhanced the electro catalytic activity.

Uniform Pt Nanoparticles Incorporated into Reduced Graphene Oxides with MoO3 as Advanced Anode Catalysts for Methanol Electro-oxidation

Pt nanoparticles (NPs) were uniformly deposited on the reduced graphene oxides (RGOs) by one-pot thermoreduction strategy with assist of MoO3. MoO3 can significantly reduce the size of Pt NPs on RGOs. These Pt NPs can be averaged to be 3.0 to 4.1nm with MoO3 loading from 27.4 to 8.8%. Without MoO3, the size of Pt NPs can reach up to 15.2nm. In addition, MoO3 in Pt-MoO3/RGO catalysts conducts a surface-confined reversible electron transfer. And the Pt-MoO3/RGO catalysts show strong resistance to CO poisoning and high activity towards methanol oxidation reaction (MOR). Among these Pt-based catalysts, Pt-MoO3/RGO catalysts with 16.5% MoO3 loading possess a largest MOR current up to 610mAmg−1 Pt with a smallest deteriorate rate of 0.000425s−1 polarizing for 5000s at 0.65V. These results demonstrate commercial feasibility for Pt catalysts to reduce significantly the amount of precious metals Pt in parallel to maintain a high MOR activity and CO tolerance.

Alloyed Pt–Ru Nanoparticles Immobilized on Mesostructured Nitrogen-Doped Carbon Nanocages for Efficient Methanol Electrooxidation

Direct methanol fuel cells (DMFC) have attracted extensive attention as ideal candidates for automotive and portable applications owing to the fascinating advantages such as high conversion efficiency, environmental friendliness, safety, wide sources of methanol, and simple cell structure. Electrocatalysts are one of crucial factors limiting the performance of DMFC. Nowadays, precious Pt-based catalyst, in spite of costliness and scarcity, is the most popular catalyst for methanol oxidation reaction (MOR) at anode due to the much better performances than those of the non-Pt catalysts. But there exists some shortcomings such as poor CO-tolerance and durability. Pt alloying with other metals, e.g. Ru, is an effective strategy to improve the catalytic performance. In addition, the support with a large specific surface area (SSA), high conductivity and suitable porous structure, such as sp carbon, could lead to high dispersion, high utilization and stability of Pt-based nanoparticles, also favorable for MOR. Recently, by in situ MgO template method, we reported the unique 3D hierarchical carbon-based nanocages featured with ultrahigh SSA, micro-meso-macro-pore coexistence, good conductivity and easy doping, which exhibited excellent electrochemical performances. Herein, taking the advantages of nitrogen-dopant anchoring function and unique mesostructures of hierarchical N-doped carbon nanocages (hNCNC), we report the Pt-Ru electrocatalysts immobilized on hNCNC (Pt-Ru/hNCNC) prepared via modified microwave-assisted ethylene glycol (EG) reduction method. The so-constructed Pt-Ru/hNCNC catalysts with ca. 30 wt% loading and tunable atomic ratio of Pt to Ru have a highly homogeneous dispersion of metal nanoparticles with the average size of ca. 3 nm. The alloying Pt-Ru/hNCNC catalysts demonstrate good CO-tolerance, high MOR activity and durability, superior to those of the counterparts of Pt/hNCNC and commercial PtRu/C. The good electrochemical performance can be ascribed to the synergistic effects of the bifunctional effect due to introduction of Ru, small size and high dispersion of metal nanoparticles induced by the large SSA and nitrogen participation of hNCNC, and multi-scaled hierarchical pore structures beneficial to the mass transportation. These results proposed a potential strategy to develop the high-performance Pt-based MOR catalysts based on the novel mesostructured hNCNC.

Influence of pH on Morphology and Electro-Activity of Ternary Pt-Co-P/MWCNT Electro-Catalysts Towards Methanol Electro-Oxidation

Methanol is widely investigated as anodic reactant in direct methanol fuel cell (DMFC) for its character of clean, convenient, and high theoretical density when compared with traditional fossil fuel and hydrogen. However, the sluggish kinetics of the methanol oxidation reaction (MOR) promotes the investigation of electrocatalysts to improve the reaction efficiency of the MOR process. Platinum is developed as the best catalysts for the MOR process, but poor anti-poisoning ability and the high cost severely limit its applications. Recent studies show that the amorphous metallic nanoparticles hold much promise for use as catalyst because of the surface-rich low-coordinate site, which could act as active site for catalyst [1].it was found that the incorporation of P into metallic alloy could form amorphous structure and lower the size of the nanoparticles, both of which are in favor of high electro-catalytic efficiency. Besides, the abundant valence electrons of phosphorous shows influence on magnetic and electro-catalytic properties of the metallic nanoparticles [2]. In this abstract, four supported Pt-based electro-catalysts prepared through impregnation method at different pH values were introduced for MOR. The difference of pH values for composition and crystallization of each electro-catalysts and their electro-catalytic activity was investigated through analyzing X-ray diffraction spectra (XRD), high-resolution transmittance electron micrograph (HRTEM), and cyclic voltammetry curves (CV). The XRD patterns show four obvious widening of diffraction peaks with the increase of pH value which indicates the decrement of particle size and the results are in accordance with our previous investigation. The CV tests show that the electro-catalyst prepared in high pH value perform a relatively high MOR activity comparing with others prepared in lower pH. The promotion of electro-catalytic activity for MOR is mainly due to the diminish of the particle size of electro-catalyst in high pH value which produce low-coordinate site on the surface of nanoparticle. The low-coordination sites show stronger adsorption towards small molecules which facilitate electro-oxidation of methanol on Pt-Co-P electro-catalyst. Figure 1

Platinum–Ruthenium Nanotubes and Platinum–Ruthenium Coated Copper Nanowires As Efficient Catalysts for Electro-Oxidation of Methanol

The sluggish kinetics of methanol oxidation reaction (MOR) is a major barrier to the commercialization of direct methanol fuel cells (DMFCs). In this work, we report a facile synthesis of platinum–ruthenium nanotubes (PtRuNTs) and platinum–ruthenium-coated copper nanowires (PtRu/CuNWs) by galvanic displacement reaction using copper nanowires as a template. The PtRu compositional effect on MOR is investigated; the optimum Pt/Ru bulk atomic ratio is about 4 and surface atomic ratio about 1 for both PtRuNTs and PtRu/CuNWs. Enhanced specific MOR activities are observed on both PtRuNTs and PtRu/CuNWs compared with the benchmark commercial carbon-supported PtRu catalyst (PtRu/C, Hispec 12100). X-ray photoelectron spectroscopy (XPS) reveals a larger extent of electron transfer from Ru to Pt on PtRu/CuNWs, which may lead to a modification of the d-band center of Pt and consequently a weaker bonding of CO (the poisoning intermediate) on Pt and a higher MOR activity on PtRu/CuNWs.

Core–Shell Structured PtRuCox Nanoparticles on Carbon Nanotubes as Highly Active and Durable Electrocatalysts for Direct Methanol Fuel Cells

Ternary alloy PtRuCox nanoparticles (NPs) with Co-rich core and PtRu skinned shell on carbon nanotubes (CNTs) have been successfully synthesized as electrocatalysts for methanol oxidation reaction (MOR) of direct methanol fuel cells (DMFCs) via a successive dealloying and annealing treatment of PtRuCo alloy particles. The best results were obtained on dealloyed PtRuCox NPs annealed at 450°C in argon with x=0.48, characterizing by a ∼1nm thick Co-free PtRu shell. The core–shell structured PtRuCox catalysts exhibit a high activity for MOR, 400Ag−1pt measured at 0.40V (vs Ag/AgCl), almost 4 times higher than 104Ag−1Pt for the reaction on the PtRuCo alloy before deallaying and annealing treatment. The core–shell structured PtRuCox NPs also show excellent structural stability; maintaining 74% of the activity after 1000 cycle between −0.2 to 1.0V (vs. Ag/AgCl), significantly higher than 49% for PtRuCo and 25% for the conventional PtRu/C catalysts. The results demonstrate that the successive dealloying and annealing treatment is very effective to synthesize core–shell structured PtRuCox ternary alloy electrocatalysts with high activity and durability for DMFCs.

Electrodeposited Pt-Ir Thin Films as DMFC Anode Materials

Pt-Ir alloys have been reported previously to be very good catalysts towards the methanol oxidation reaction (MOR), although the composition of these films was not known with certainty. In the present work, thin Pt-Ir films of varying, but controlled, composition were fabricated using electrodeposition, with a charge efficiency of close to 100%. X-ray photoelectron spectroscopy (XPS) analysis showed that the film composition is fully homogeneous with depth into the film and that it matches very closely with the metal molar ratio in the deposition solution. The Pt-Ir film composition with the highest MOR activity was found to have a 2:1 Pt:Ir mass ratio and 1:1 surface composition ratio, based on measurements of the underpotentially deposited adsorbed hydrogen charge.

Bulk and Surface Compositions of PtRu Catalysts and Their Methanol Oxidation Activity and Durability

A controlled synthetic scheme of PtRu catalyst for methanol oxidation reaction is reported. PtRu catalyst was obtained by using an electroless plating method with chelate ligands. The well-mixed PtRu catalyst synthesized with chelate ligands (PtRu/C WCL) showed higher methanol oxidation reaction activity and stability relative to those of PtRu catalyst synthesized without chelate ligands (PtRu/C WOCL).

Methanol Oxidation Activity of Nanosized PtRu Catalysts and Their Microstructures

The nanosized PtRu catalyst was synthesized via the polyol process and electroless plating method. The size of the catalyst was decreased to 2 nm with the addition of phosphorus (P) in order to improve the methanol oxidation reaction (MOR) activity. The highest MOR activity was obtained with the bulk and surface compositions of Pt 73 Ru 27 and Pt 53 Ru 47 , respectively. The XRF, Cu under potential deposition/Cu stripping and EXAFS analyses revealed that the Pt-enriched core/Ru-enriched shell microstructure was formed in the PtRuP catalyst with the particle size of 2 nm. This Pt-dominant bulk composition, Pt 73 Ru 27 , was required to make the surface composition close to the active composition of Pt 50 Ru 50 due to the preferential reduction of Pt cation. The difference in the reduction potential of Pt and Ru cations was decreased from 0.42 V to 0.31 V with the addition of the chelating ligand. This decrease advanced the mixing state of the Pt and Ru atoms in the whole region of the catalyst, resulting in the higher MOR activity.

Improved methanol oxidation activity and stability of well-mixed PtRu catalysts synthesized by electroless plating method with addition of chelate ligands

A new synthetic scheme of PtRu catalysts for methanol oxidation reaction is reported. P containing PtRu nanoparticles 2 nm in size were synthesized by electroless plating method using phosphinic acid as a reducing agent as well as the source of P. Chelate ligands were added in the synthetic system to decrease the difference of effective reduction potentials between Pt 4+ and Ru 3+ cations in their chloride precursors. Coordination ability of the chelate ligands with the cations was evaluated using UV–vis spectroscopy. It was found that dl-tartaric acid has the highest coordination ability with the cations and that the difference decreases from 0.4 to 0.19 V with addition of dl-tartaric acid. Microstructure, bulk and surface compositions of the PtRu catalysts were analyzed by means of XRD, XRF and Cu stripping voltammetry techniques, respectively. Results revealed that Pt and Ru atoms are well mixed and that both bulk and surface compositions are close to Pt 50Ru 50 in PtRu catalyst synthesized with dl-tartaric acid. The well-mixed PtRu catalyst synthesized with dl-tartaric acid showed higher methanol oxidation reaction activity and stability values relative to those of PtRu catalyst synthesized without dl-tartaric acid.

Investigation of methanol oxidation on unsupported platinum electrodes in strong alkali and strong acid

Abstract Porous unsupported electrodes are made from platinum powder prepared by a room-temperature NaBH4 reduction method. Cyclic voltammograms (CVs) are recorded in different electrolytes of high and low pH in the presence and the absence of different concentrations of methanol. Various electrochemical processes occurring in different potential regions of the CVs are discussed. Steady-state galvanostatic polarisation measurements for the methanol oxidation reaction (MOR) on these electrodes in different electrolyte/methanol mixtures are also carried out. The MOR performance increases from a highly acidic range to a highly alkaline range. On increasing the KOH concentration above 6 M, however, the activity declines. Also, the MOR performance changes on changing the methanol concentration in a solution of a given pH. The highest MOR activity is obtained in a 6 M KOH+6 M CH3OH mixture. It is concluded that by choosing the proper ratio of OH− ions and CH3OH in solution, it is possible to remove completely the intermediate organic species and/or poisonous species that retard the MOR rate on the electrode surface.