MXene supported rhodium nanocrystals for efficient electrocatalysts towards methanol oxidation

Since conventional Pt/carbon catalysts usually suffer from CO poisoning as well as carbon corrosion issues during the methanol oxidation reaction, it is essential to explore high-efficiency Pt-alternative electrocatalysts supported by a robust matrix in the direct methanol fuel cells. Herein, we report a convenient low-temperature approach to the controllable fabrication of well-dispersive Rh nanocrystals in situ grown on Ti₃C₂T_x MXene nanosheets. The ultrathin lamellar MXene structure reveals unique superiorities on the construction of advanced Rh-based hybrid catalysts, which can not only provide a large number of efficient anchoring sites for immobilizing small-sized Rh nanocrystals with abundant exposed catalytic crystal planes, but also enable direct electronic interaction with Rh for strong synergistic effects and facilitate the fast charge transportation during the catalytic process. As a consequence, the resulting Rh/Ti₃C₂T_x hybrid exhibits prominent electrocatalytic properties towards methanol oxidation reaction, such as a large electrochemical active surface area of 71.6 m² g^?1, a high mass activity of 600.2 mA mg^?1, and good long-term stability, all of which are much better than those of conventional carbon-supported Rh as well as Pt/C and Pd/C catalysts.     

Effect of heat treatment on the performance of TiO2-Pt/CNT catalysts for methanol electro-oxidation

TiO₂-Pt/CNT catalysts before and after heat treatment were prepared. Their catalytic activities for methanol and CO electro-oxidation were studied in detail. The results showed that the proper amount of hydrous TiO₂ in TiO₂-Pt/CNTs (e.g. heated at 200 °C for 2 h) was favorable for enhancing the catalytic activity of Pt/CNTs, which provided evidence for bi-functional mechanism. The studies on the catalysts with different TiO₂/Pt molar ratio displayed that the optimum molar ratio varied with the increase of heat treatment temperature. It was found that the optimum molar ratio of TiO₂/Pt was at 1:2 for the catalysts without heat treatment and was at 1:1 for the catalysts by heat treatment at 500 °C. This fact was ascribed to the difference in compact degree between TiO₂ and Pt/CNTs before and after heat treatment. Considering the influence of heating temperature, it was found that TiO₂-Pt/CNT catalyst heated at 200 °C for 2 h had better catalytic activity for methanol oxidation.     

Synthesis and characterization of MoOx-Pt/C and TiOx-Pt/C nano-catalysts for oxygen reduction

The oxygen reduction reaction (ORR) was studied at carbon supported MoO_x-Pt/C and TiO_x-Pt nanocatalysts in 0.5 mol dm⁻³ HClO₄ solution, at 25 °C. The MoO_x-Pt/C and TiO_x-Pt/C catalysts were prepared by the polyole method combined by MoO_x or TiO_x post-deposition. Home made catalysts were characterized by TEM and EDX techniques. It was found that catalyst nanoparticles were homogenously distributed over the carbon support with a mean particle size about 2.5 nm. Quite similar distribution and particle size was previously obtained for Pt/C catalyst. Results confirmed that MoO_x and TiO_x post-deposition did not lead to a significant growth of the Pt nanoparticles.The ORR kinetics was investigated by cyclic voltammetry and linear sweep voltammetry at the rotating disc electrode. These results showed the existence of two E − log j regions, usually observed with polycrystalline Pt in acid solution. It was proposed that the main path in the ORR mechanism on MoO_x-Pt/C and TiO_x-Pt/C catalysts was the direct four-electron process with the transfer of the first electron as the rate-determining step. The increase in catalytic activity for ORR on MoO_x-Pt/C and TiO_x-Pt/C catalysts, in comparison with Pt/C catalyst, was explained by synergetic effects due to the formation of the interface between the platinum and oxide materials and by spillover due to the surface diffusion of oxygen reaction intermediates.     

Synthesis of well-dispersed PtRuSnOx by ultrasonic-assisted chemical reduction and its property for methanol electrooxidation

PtRuSnO_x supported on multi-wall carbon nanotubes (MWCNTs) was prepared by ultrasonic-assisted chemical reduction method. The as-prepared catalyst was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns indicate that Pt exists as the face-centered cubic structure, Ru is alloyed with platinum, while non-noble metal oxide SnO_x exists as an amorphous state. From TEM observation, PtRuSnO_x is well dispersed on the surface of MWCNTs with the particle size of several nanometers. The electrochemical properties of the as-prepared catalyst for methanol electrooxidation were studied by cyclic voltammetry (CV) and chronoamperometry (CA). The onset potential of methanol oxidation on PtRuSnO_x and PtRu catalysts is much more negative than that on Pt catalyst, shifting negatively by about 0.20 V, while the peak current density of methanol oxidation on PtRuSnO_x is higher than that on PtRu. Electrochemical impedance spectroscopy (EIS) studies also show that the reaction kinetics of methanol oxidation is improved with the presence of SnO_x. The addition of non-noble metal oxide SnO_x to PtRu promotes the catalytic activity for methanol electrooxidation and the possible reaction mechanism is proposed.     

CoPdx oxygen reduction electrocatalysts for polymer electrolyte membrane and direct methanol fuel cells

The electrochemical activity of carbon-supported cobalt-palladium alloy electrocatalysts of various compositions have been investigated for the oxygen reduction reaction in a 5 cm² single cell polymer electrolyte membrane fuel cell. The polarization experiments have been conducted at various temperatures between 30 and 60 °C and the reduction performance compared with data from a commercial Pt catalyst under identical conditions. Investigation of the catalytic activity of the CoPd_x PEMFC system with varying composition reveals that a nominal cobalt-palladium atomic ratio of 1:3, CoPd₃, exhibits the best performance of all studied catalysts, exhibiting a catalytic activity comparable to the commercial Pt catalyst. The ORR on CoPd₃ has a low activation energy, 52 kJ/mol, and a Tafel slope of approximately 60 mV/decade, indicating that the rate-determining step is a chemical step following the first electron transfer step and may involve the breaking of the oxygen bond. The CoPd₃ catalyst also exhibits excellent chemical stability, with the open circuit cell voltage decreasing by only 3% and the observed current decreasing by only 10% at 0.8 V over 25 h. The CoPd₃ catalyst also exhibits superior tolerance to methanol crossover poisoning than Pt.     

Preparation and Characterization of Pt/C and Pt/TiO2 Electrocatalysts by Liquid Phase Photodeposition

The preparation of carbon and titanium dioxide supported Pt catalysts through a photochemical and photocatalytic routes were investigated. The catalysts were prepared by irradiation with UV-light (365 nm) at room temperature using H₂PtCl₆ and C₁₀H₁₄O₄Pt (Pt(acac)₂) as platinum precursors. The kinetic studies revealed that H₂PtCl₆ produced metallic platinum faster than Pt(acac)₂ and also showed that the amount of platinum deposited on TiO₂ was higher than on carbon. The samples were characterized by X-ray diffraction, SEM/EDS and cyclic voltammetry. X-ray diffraction permitted to identify the crystallographic (111) and (200) planes from platinum metal on the catalysts synthesized, the intensity of peaks depends of the amount of platinum deposited. SEM/EDS test confirmed what it was found by the kinetics studies. The electrocatalytic activity was compared with a commercial Pt E-Tek catalyst (10 wt%). The electrochemical results showed that Pt/C-AA catalyst synthesized by liquid phase photo-deposition method has stability in acid media and high distribution of the actives sites on the electrode surfaces. It could be considered as a candidate for electro-catalyst for polymer electrolyte fuel cell. The Pt/TiO₂ catalysts did not present electrochemical activity.     

The effect of plasma pre-treatment of carbon used as a Pt catalyst support for methanol electrooxidation

Vulcan XC-72 carbon black for use as a catalyst support was treated in three different plasma atmospheres, H₂, Ar and O₂. The results showed that the microstructure and surface functional groups were significantly changed after plasma treatment. Pt/C catalysts were prepared by chemical reduction of H₂PtCl₆ with HCHO and those with untreated and plasma treated carbon black supports were characterized and tested for methanol electrooxidation. TEM showed that the platinum nanoparticles on H₂ and Ar plasma treated carbon were uniform and well distributed. Those on untreated carbon were uniform in most regions but coalesced in others. On O₂ plasma treated carbon agglomeration of the platinum nanoparticles was significant. XRD showed that the catalysts were composed of face-centered cubic Pt nanoparticles and XPS showed that they were metallic with no oxides present. Cyclic voltammetry and chronoamperometry were used to study methanol electrooxidation on the Pt/C catalysts in a solution of 0.5 M H₂SO₄ + 0.5 M CH₃OH, and showed that the catalytic activity those using H₂ and Ar plasma treated carbon was higher than for the untreated one. Catalysts supported by O₂ plasma treated carbon showed no catalytic activity. The treatment atmosphere of carbon therefore had a large effect on the catalyst performance, with the H₂ plasma being the best.     

High activity PtRu/C catalysts synthesized by a modified impregnation method for methanol electro-oxidation

A modified impregnation method was used to prepare highly dispersive carbon-supported PtRu catalyst (PtRu/C). Two modifications to the conventional impregnation method were performed: one was to precipitate the precursors ((NH₄)₂PtCl₆ and Ru(OH)₃) on the carbon support before metal reduction; the other was to add a buffer into the synthetic solution to stabilize the pH. The prepared catalyst showed a much higher activity for methanol electro-oxidation than a catalyst prepared by the conventional impregnation method, even higher than that of current commercially available, state-of-the-art catalysts. The morphology of the prepared catalyst was characterized using TEM and XRD measurements to determine particle sizes, alloying degree, and lattice parameters. Electrochemical methods were also used to ascertain the electrochemical active surface area and the specific activity of the catalyst. Based on XPS measurements, the high activity of this catalyst was found to originate from both metallic Ru (Ru⁰) and hydrous ruthenium oxides (RuO_xH_y) species on the catalyst surface. However, RuO_xH_y was found to be more active than metallic Ru. In addition, the anhydrous ruthenium oxide (RuO₂) species on the catalyst surface was found to be less active.     

Water-gas shift reaction over supported Pt and Pt-CeOx catalysts

A comparison study was performed of the water-gas shift (WGS) reaction over Pt and ceria-promoted Pt catalysts supported on CeO₂, ZrO₂, and TiO₂ under rather severe reaction conditions: 6.7 mol% CO, 6.7 mol% CO₂, and 33.2 mol% H₂O in H₂. Several techniques—CO chemisorption, temperature-programmed reduction (TPR), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES)—were employed to characterize the catalysts. The WGS reaction rate increased with increasing amount of chemisorbed CO over Pt/ZrO₂, Pt/TiO₂, and Pt-CeO _x /ZrO₂, whereas no such correlation was found over Pt/CeO₂, Pt-CeO _x /CeO₂, and Pt-CeO _x /TiO₂. For these catalysts in the absence of any impurities such as Na⁺, the WGS activity increased with increasing surface area of the support, showed a maximum value, and then decreased as the surface area of the support was further increased. An adverse effect of Na⁺ on the amount of chemisorbed CO and the WGS activity was observed over Pt/CeO₂. Pt-CeO _x /TiO₂ (51) showed the highest WGS activity among the tested supported Pt and Pt-CeO_x catalysts. The close contact between Pt and the support or between Pt and CeO _x , as monitored by H₂-TPR, is closely related to the WGS activity. The catalytic stability at 583K improved with increasing surface area of the support over the CeO₂- and ZrO₂-supported Pt and Pt-CeO _x catalysts.     

Electrochemical effect of gold nanoparticles on Pt/α-Fe2O3/C for use in methanol oxidation in alkaline solution

A catalyst containing gold nanoparticles with Pt/α-Fe₂O₃/C was prepared by a co-precipitation method and its catalytic activity for the oxidation of methanol, formaldehyde, and formic acid in alkaline solutions was evaluated by an electrochemical method and high-performance liquid chromatography (HPLC). The addition of gold nanoparticles improved catalytic activity only for the oxidation of methanol and formaldehyde, and not for the oxidation of formic acid. HPLC analysis was performed for methanol oxidation to detect the oxidative products. In HPLC analysis, only formate anion could be detected in the electrolyte solution and the ratio of formate anion obtained to the total passed charge in Pt/nano-Au/α-Fe₂O₃/C was less than that in Pt/C, indicating that formic acid is not the final product of methanol oxidation. These results show that gold nanoparticles promoted methanol oxidation up to CO₂.     

掺杂元素对TiO2/SO2-4固体酸特性的影响

为了进行掺杂元素对超强酸特性的影响研究,采用均匀沉淀法合成了Fe、Si、Al和Zr氧化物掺杂的TiO2/SO2-4的固体酸(TiO2-MrOy),采用XRD、FTIR、NH3-TPD以及H2-FPR等分析方法对催化剂进行表征.以大豆油和甲醇的酯交换反应为活性评价反应,比较了各催化剂的催化活性.研究发现,除了Al外掺杂元...     

Electroreduction of dioxygen (ORR) in alkaline medium on Ag/C and Pt/C nanostructured catalysts—effect of the presence of methanol

Ag/C catalysts with different loading were prepared using a colloidal route to obtain well dispersed catalysts on carbon, with a particle size close to 15 nm. An amount of 20 wt.% Ag on carbon was found to be the best loading in terms of current density and mass activity. The 20 wt.% Ag/C catalyst was then studied and the kinetics towards ORR was determined and compared with that of a 20 wt.% Pt/C catalyst. The number of exchanged electrons for the ORR was found to be close to four with the rotating disk electrode (RDE) as well as with the rotating ring disc electrode (RRDE) techniques. From the RDE results, the Tafel slopes b, the diffusion limiting current density inside the catalytic film (j_l^film) and the exchange current density (j₀) were evaluated. The Tafel slopes b and diffusion limiting current densities inside the catalytic film (j_l^film) were found to be in the same order for both catalysts, whereas the exchange current density (j₀), which is a suitable estimation of the activity of the catalyst, was at least 10 times higher at the Pt/C catalyst than at the Ag/C catalyst. The behavior of both catalysts in methanol containing electrolyte was investigated and it was found that at a low methanol concentration, the Pt/C catalyst was quasi-tolerant to methanol. But, at a high methanol concentration, the ORR at a Pt/C was affected. However, the Pt/C catalyst showed in each case better activity towards ORR than the Ag/C catalyst, even if the latter one was less affected by the presence of methanol than the former one.     

Novel dynamic effects in electrocatalysis of methanol oxidation on supported nanoporous TiO2 bimetallic nanocatalysts

New dynamic aspects of the catalysis of methanol oxidation reaction (MOR) have been studied using quantum mechanical calculations applied to the support-catalyst cluster interactions and surface diffusivity of adsorbed intermediates. For very small catalyst-support clusters, we have found a strong enhancement of the ligand effect for bimetallic catalysts of the type Pt_nM_m attributed to the decreased local density of states near the Fermi level of Pt atoms neighboring the additive metal atom M. This enhancement results in a decreased barrier for surface diffusion of adsorbed CO_ad through the cooperative diffusion mechanism, based on structural relaxation of the catalyst-support cluster, proposed in this work. The strong ligand effect dominates over the Schwoebel potential and trapping well effects, being responsible for accumulation of poisoning intermediates at step sites on the catalyst surface and gradual decrease of catalytic activity with decreasing size of catalyst nanoparticles. The lattice relaxation and strong ligand effects in small catalyst-support clusters lead to lower adsorption energy for CO_ad and thus, to higher reactivity and mobility of reactants and intermediates. The experimental investigations included submonolayer films of bi-functional catalysts (PtRu, PtFe) deposited on novel nanostructured supporting materials, designed with the goal of achieving high variability of their electronic and chemical properties to influence the catalytic activity of sub-monolayer catalyst. The mesoscopic TiO₂ supporting film formation was investigated using EQCN, pulse voltammetric and AFM techniques. The conditions for the formation of monodispersed TiO₂ nanoparticles with regular nanopores (nanotubes), 20-80 nm in diameter, were described. It follows from EQCN and voltammetric measurements and AFM image analysis that the nanopores are formed by a dissolution-precipitation mechanism. The catalysts, Pt and PtRu, deposited on supporting nanoporous TiO_2−x films, were used to study MOR. A lower poisoning effect for cluster PtRu on a TiO_2−x support film than that for unsupported PtRu or bare Pt catalysts has been observed. These effects have been attributed to differences in CO_ad binding energy and lowering of activation energy for surface mobility leading to a more facile 2D diffusion of CO_ad from Pt sites to Ru and the supporting TiO_2−x. The substrate-catalyst interactions were further investigated using quantum mechanical calculations performed for a model TiO₂ nano-ring (representing an orifice of a TiO_2−x nanotube studied experimentally) with adlayers of Pt, Ru and Fe catalysts. We have found unusually strong electron delocalization effects for Pt₂Fe₂ clusters on (TiO₂)₄ as compared to (TiO_2−x)₄Pt₂Ru₂. We have also analyzed various states in surface diffusion of CO_ad on bimetal clusters supported on (TiO₂)_n and observed considerable dynamic widening of metal-to-metal atom distances induced by CO adsorption (up to 9% for Pt-Pt distance and up to 15% for Fe-Fe distance). We propose that this new dynamic effect leading to cooperative surface diffusion may be further explored in designing novel nanoparticle catalysts.     

Novel methanol electro-oxidation catalyst assisting with functional phthalocyanine supports

Novel electro-catalyst based on phthalocyanine stabilized Pt colloids has been developed for methanol electro-oxidation. Water soluble Cu²⁺ phthalocyanine functioned with sulfonic groups were selected as catalyst supports because of the relatively high catalytic activity of Pt catalyst and nearly the same catalytic selectivity complex with Cu-phthalocyanine, compared to others that chelated with Fe, Co and Ni ions. The as-resulting Pt-CuTsPc catalysts have average particle size of 2 nm and narrow size distribution. With the assistance of CuTsPc supports, the methanol electro-oxidation activity and poison tolerance of Pt catalyst have a significant increase. I_f/I_b ratio (anodic peak current density, forward to backward) of the Pt-CuTsPc/C catalysts also has obvious increase to 2.5, from value of 0.8 for pure Pt/C catalyst. The reaction Tafel slope of Pt-CuTsPc/C catalysts is 56.6 mV dec⁻¹, much smaller than that of the Pt/C catalyst. The transient current density on Pt-CuTsPc/C at 0.60 V is enhanced to 650% of that on the Pt/C catalyst while the enhancement factor R for comparison of steady-state current obtained on Pt-CuTsPc/C and Pt/C catalyst varies between 111% and 534% in the potential region of 0.3-0.75 V.     

Fabrication of Pt–Cu/RGO hybrids and their electrochemical performance for the oxidation of methanol and formic acid in acid media

Pt–Cu/reduced graphene oxide (Pt–Cu/RGO) hybrids with different Pt/Cu ratios were prepared by the reduction of H₂PtCl₆ and CuSO₄ by NaBH₄ in the presence of graphene oxide (GO). The Pt–Cu nanoparticles were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The reduction of GO was verified by ultraviolet–visible absorption spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Compared to Pt/RGO, the Pt–Cu/RGO hybrids have superior electrocatalytic activity and stability for the oxidation of methanol and formic acid. Thus they should have potential applications in direct methanol and formic acid fuel cells.     

Graphene-modified carbon fiber mats used to improve the activity and stability of Pt catalyst for methanol electrochemical oxidation

Graphene-modified carbon fiber mats (GCFMs) with high conductivity of about 65 S cm⁻¹ and good flexibility have been fabricated by thermally treating electrospun polyacrylonitrile fibers decorated with graphene oxide. Pt particles were then deposited on the GCFM by using formaldehyde vapor as a reducer to react with H₂PtCl₆·6H₂O adsorbed on the GCFM. The obtained electro-catalytic electrodes were characterized and evaluated. The results show that the Pt catalyst loaded on GCFM exhibits high electro-catalytic activity, good tolerance towards reaction intermediates and unusually high stability towards methanol electrochemical oxidation because the special structure of GCFM can stabilize the Pt particles, and that the charge transfer resistance between the methanol and the catalytic electrode is as small as 15.7 Ωcm². An electrochemical catalyst with high activity and stability can be developed by using GCFM as a supporting material.     

A novel nanocomposite catalytic cathode for direct methanol fuel cells

We report a new nanocomposite catalytic cathode composed of iron phthalocyanine, platinum, carbon black and Nafion^® (FePc-Pt/C-Nafion^®) which exhibited enhanced catalytic activity for the oxygen reduction reaction (ORR) in the presence of methanol compared with usual Pt/C based electrodes. The catalytic cathode was prepared by depositing Pt colloidal nanoparticles (d_av = 2.2 nm) on a FePc/C support to form a FePc-Pt/C powder and ultrasonically treating a mixture of Nafion^® and the FePc-Pt/C powder in ethanol, followed by loading the mixture on a glassy carbon electrode and drying at 120 °C. In an O₂-saturated H₂SO₄ solution (0.5 M) with methanol (0.5 M), the onset potential (0.92 V vs RHE) over the FePc-Pt/C-Nafion^® electrode shifted by more than 240 mV toward positive relative to that over an electrode prepared with a commercial Pt/C catalyst and Nafion^®. A new kind of catalytic sites constructed by FePc nanocrystals and Pt nanoparticles was found in the FePc-Pt/C-Nafion^® electrode for the first time, which exhibited higher specific activity for ORR than Pt as calculated based on the hydrogen desorption charge.     

Ethanol electrooxidation on novel carbon supported Pt/SnOx/C catalysts with varied Pt:Sn ratio

Novel carbon supported Pt/SnO_x/C catalysts with Pt:Sn atomic ratios of 5:5, 6:4, 7:3 and 8:2 were prepared by a modified polyol method and characterized with respect to their structural properties (X-ray diffraction (XRD) and transmission electron microscopy (TEM)), chemical composition (XPS), their electrochemical properties (base voltammetry, CO_ad stripping) and their electrocatalytic activity and selectivity for ethanol oxidation (ethanol oxidation reaction (EOR)). The data show that the Pt/SnO_x/C catalysts are composed of Pt and tin oxide nanoparticles with an average Pt particle diameter of about 2 nm. The steady-state activity of the Pt/SnO_x/C catalysts towards the EOR decreases with tin content at room temperature, but increases at 80 °C. On all Pt/SnO_x/C catalysts, acetic acid and acetaldehyde represent dominant products, CO₂ formation contributes 1-3% for both potentiostatic and potentiodynamic reaction conditions. With increasing potential, the acetaldehyde yield decreases and the acetic acid yield increases. The apparent activation energies of the EOR increase with tin content (19-29 kJ mol⁻¹), but are lower than on Pt/C (32 kJ mol⁻¹). The somewhat better performance of the Pt/SnO_x/C catalysts compared to alloyed PtSn_x/C catalysts is attributed to the presence of both sufficiently large Pt ensembles for ethanol dehydrogenation and C-C bond splitting and of tin oxide for OH generation. Fuel cell measurements performed for comparison largely confirm the results obtained in model studies.     

Preparation and electrochemical characteristics of CoTMPP-TiO2NT/BP composite electrocatalyst for oxygen reduction reaction

CoTMPP-TiO₂NT/BP composites have been synthesized by preparing CoTMPP and depositing CoTMPP on carbon-supported titania nanotube (TiO₂NT/BP) using microwave irradiation method at the same time, followed by heat-treatment from 300 to 900 °C in N₂ atmosphere. The catalytic activity for oxygen reduction was evaluated by rotating disc electrode technique in half cells with 0.5 M H₂SO₄. The number of electrons exchanged during ORR and the percentage of peroxide (%H₂O₂) produced by the reaction were evaluated for catalysts by rotating ring disk electrode (RRDE) measurements. The influences of TiO₂NT doping, the heat-treating temperature and the different ratios of BP:TiO₂NT on the activity of electrocatalysts for oxygen reduction were investigated. The stability of the CoTMPP-TiO₂NT/BP electrocatalysts was studied with potentialstatic-polarization measurements in 0.5 M H₂SO₄ + 0.5 M CH₃OH. CoTMPP-TiO₂NT/BP composites show higher catalytic activity and better stability than CoTMPP/BP. The mechanism for the enhanced catalytic activity of CoTMPP-TiO₂NT/BP is discussed.     

Characterization of methanol-tolerant Pd–WO3 and Pd–SnO2 electrocatalysts for the oxygen reduction reaction in direct methanol fuel cells

Palladium (Pd) catalysts containing nanosized metal oxides, tungsten oxide (WO₃) and tin oxide (SnO₂), supported on carbon black (Pd–MO_x/C) were synthesized, and the effect of the metal oxide on the oxygen reduction reaction (ORR) in a direct methanol fuel cell (DMFC) was investigated. The SEM images showed that the Pd nanoparticles were highly dispersed on the carbon black, and the metal oxide particles were also distributed well. Pd/C and Pd–WO₃/C catalysts as cathode materials for the ORR in DMFCs showed activity similar to or better than that of Pt/C, whereas Pd–SnO₂/C showed no improvement in catalytic activity.