Fe loading of a carbon-supported Fe–N electrocatalyst and its effect on the oxygen reduction reaction

Carbon-supported non-noble metal catalysts with Fe as the metal and tripyridyl triazine (TPTZ) as the ligand (Fe-TPTZ/C) were synthesized using a simple chemical method. How the Fe loading in this Fe-TPTZ/C catalyst affected the ORR activity was investigated using several Fe loadings: 0.2, 0.4, 0.7, 2.7, 4.7, 5.8 and 7.8 wt%. The as-prepared catalysts were then heat-treated at 800 °C in an N₂ environment to obtain catalysts of Fe–N/C. Energy dispersive X-ray spectroscopy (EDX) was used to identify the Fe–N/C catalysts. These Fe–N/C catalysts showed significant ORR activity improvement over the as-prepared Fe-TPTZ/C catalysts. The kinetics of the ORR catalyzed by the catalysts with different Fe loadings was studied using the rotating disk electrode technique. It was observed that a 4.7 wt% Fe loading yielded the best catalytic ORR activity. Regarding the overall ORR electron transfer number, it was found that as the catalyst's Fe loading increased, the overall ORR electron transfer number changed from 2.9 to 3.9, suggesting that increasing the Fe loading could alter the ORR mechanism from a 2-electron to a 4-electron transfer dominated process. The Tafel method was also used to obtain one important kinetic parameter: the exchange current density. A fuel cell was assembled using a membrane electrode assembly with 4.7 wt% Fe loaded Fe–N/C as the cathode catalyst, and the cell was tested for both performance and durability, yielding a 1000-h lifetime.     

Novel carbon-supported Fe-N electrocatalysts synthesized through heat treatment of iron tripyridyl triazine complexes for the PEM fuel cell oxygen reduction reaction

2,4,6-Tris(2-pyridyl)-1,3,5-triazine (TPTZ) was used as a ligand to prepare iron-TPTZ (Fe-TPTZ) complexes for the development of a new oxygen reduction reaction (ORR) catalyst. The prepared Fe-TPTZ complexes were then heat-treated at temperatures ranging from 400 °C to 1100 °C to obtain carbon-supported Fe-N catalysts (Fe-N/C). These catalysts were characterized in terms of catalyst composition, structure, and morphology by several instrumental methods such as energy dispersive X-ray, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. With respect to the ORR activity, the Fe-N/C catalysts were also evaluated by cyclic voltammetry, as well as rotating disk and ring-disk electrodes. The results showed that among the heat-treated catalysts, that obtained at a heat-treatment temperature of 800 °C is the most active ORR catalyst. The overall electron transfer number for the catalyzed ORR was determined to be between 3.5 and 3.8, with 10-30% H₂O₂ production. The ORR catalytic activity of this catalyst was also tested in a hydrogen-air proton exchange membrane (PEM) fuel cell. At a cell voltage of 0.30 V, this fuel cell can give a current density of 0.23 A cm⁻² with a maximum MEA power density of 0.070 W cm⁻² indicating that this catalyst has potential to be used as a non-noble catalyst in PEM fuel cells.     

Fe–Nx/C electrocatalysts synthesized by pyrolysis of Fe(II)–2,3,5,6-tetra(2-pyridyl)pyrazine complex for PEM fuel cell oxygen reduction reaction

2,3,5,6-Tetra(2-pyridyl)pyrazine (TPPZ) was employed as a ligand to prepare an iron(II) complex (Fe–TPPZ) that served as a precursor to synthesize carbon-supported catalysts (Fe–N_x/C) through heat-treatment at 600, 700, 800 and 900 °C under N₂ atmosphere. Both the structure and composition of the synthesized Fe–N_x/C were analyzed by X-ray diffraction and energy-dispersive X-ray microanalysis, respectively. The rotating disk and ring-disk electrode measurements showed that these catalysts have strong ORR activity with an overall 4-electron transfer process through a (2 + 2)-electron transfer mechanism, which was assigned to the catalytic function of the Fe–N_x center. A study on the heat-treatment temperature on the ORR activity showed that 800 °C is the optimal temperature for the synthesized catalysts. Furthermore, the effect of both catalyst and Nafion^® ionomer loadings in the catalyst layer on the corresponding ORR activity was also investigated. The kinetic parameters such as the chemical reaction rate between O₂ and Fe–N_x/C (adduct formation reaction), the rate constant for the rate-determining step (RDS), and the electron numbers in the ORR, were obtained. The methanol tolerance of the catalyst was also tested. To validate the ORR activity, a membrane electrode assembly in which the cathode catalyst layer contained Fe–N_x/C was constructed and tested in a real fuel cell. The results obtained are encouraging when compared with similar non-noble catalysts.     

Synthesis of carbon-supported binary FeCo–N non-noble metal electrocatalysts for the oxygen reduction reaction

In this paper, a carbon-supported binary FeCo–N/C catalyst using tripyridyl triazine (TPTZ) as the complex ligand was successfully synthesized. The FeCo–TPTZ complex was then heat-treated at 600 °C, 700 °C, 800 °C, and 900 °C to optimize its oxygen reduction reaction (ORR) activity. It was found that the 700 °C heat-treatment yielded the most active FeCo–N/C catalyst for the ORR. XRD, EDX, TEM, XPS, and cyclic voltammetry techniques were used to characterize the structural changes in these catalysts after heat-treatment, including the total metal loading and the mole ratio of Fe to Co in the catalyst, the possible structures of the surface active sites, and the electrochemical activity. XPS analysis revealed that Co–N_x, Fe–N_x, and C–N were present on the catalyst particle surface. To assess catalyst ORR activity, quantitative evaluations using both RDE and RRDE techniques were carried out, and several kinetic parameters were obtained, including overall ORR electron transfer number, electron transfer coefficient in the rate-determining step (RDS), electron transfer rate constant in the RDS, exchange current density, and mole percentage of H₂O₂ produced in the catalyzed ORR. The overall electron transfer number for the catalyzed ORR was ～3.88, with H₂O₂ production under 10%, suggesting that the ORR catalyzed by FeCo–N/C catalyst is dominated by a 4-electron transfer pathway that produces H₂O. The stability of the binary FeCo–N/C catalyst was also tested using single Fe–N/C and Co–N/C catalysts as baselines. The experimental results clearly indicated that the binary FeCo–N/C catalyst had enhanced activity and stability towards the ORR. Based on the experimental results, a possible mechanism for ORR performance enhancement using a binary FeCo–N/C catalyst is proposed and discussed.     

Oxygen reduction reaction on carbon-supported CoSe2 nanoparticles in an acidic medium

We investigated the effect of CoSe₂/C nanoparticle loading rate on oxygen reduction reaction (ORR) activity and H₂O₂ production using the rotating disk electrode and the rotating ring-disk electrode techniques. We prepared carbon-supported CoSe₂ nanoparticles with different nominal loading rates and evaluated these samples by means of powder X-ray diffraction. All the catalysts had an OCP value of 0.81 V vs. RHE. H₂O₂ production during the ORR process decreased with an increase in catalytic layer thickness. This decrease was related to the CoSe₂ loading on the disk electrode. H₂O₂ production also decreased with increasing catalytic site density, a phenomenon related to the CoSe₂ loading rate on the carbon substrate. The cathodic current density significantly increased with increasing catalytic layer thickness, but decreased with increasing catalytic site density. In the case of 20 wt% CoSe₂/C nanoparticles at 22 μg cm⁻², we determined that the transfer process involves about 3.5 electrons.     

Nano-stuctured Pt-Fe/C as cathode catalyst in direct methanol fuel cell

Pt-Fe/C catalysts were prepared by a modified polyol synthesis method in an ethylene glycol (EG) solution, and then were heat-treated under H₂/Ar (10 vol.%) at moderate temperature (300 °C, Pt-Fe/C300) or high temperature (900 °C, Pt-Fe/C900). As comparison, Pt-Fe/C alloy catalyst was prepared by a two-step method (Pt-Fe/C900B). X-ray diffraction (XRD) and transmission electron microscopy (TEM) images show that particles size of the catalyst increases with the increase of treatment temperatures. Pt-Fe/C300 catalyst has a mean particle size of 2.8 nm (XRD), 3.6 nm (TEM) and some Pt-Fe alloy was partly formed in this sample. Pt-Fe/C900B catalyst has the biggest particle size of 6.2 nm (XRD) and the best Pt-Fe alloy form. Cyclicvoltammetry (CV) shows that Pt-Fe/C300 has larger electrochemical surface area than other Pt-Fe/C and the highest utilization ratio of 76% among these Pt-based catalysts. Rotating disk electrode (RDE) cathodic curves show that Pt-Fe/C300 has the highest oxygen reduction reaction (ORR) mass activity (MA) and specific activity (SA), as compared with Pt/C catalyst in 1.0 M HClO₄. However, Pt-Fe/C catalyst does not appears to be a more active catalyst than Pt/C for ORR in 1.0 M HClO₄ + 0.1 M CH₃OH. Pt-Fe/C300 exhibits higher ORR activity and better performance than other Pt-Fe/C or Pt/C catalysts when employed for cathode in direct methanol single cell test, the enhancement of the cell performance is logically attributed to its higher ORR activity, which is probably attributed to more Pt⁰ species existing and Fe ion corrosion from the catalyst.     

The effect of heat treatment on nanoparticle size and ORR activity for carbon-supported Pd-Co alloy electrocatalysts

Carbon-supported Pd-Co alloy electrocatalysts were synthesized and characterized for the purpose of the fuel cell cathode oxygen reduction reaction (ORR). An impregnation method was employed for the synthesis, in which sodium borohydride was used as a reducing agent. The synthesized catalysts were characterized in terms of structural morphology and catalytic activity by XRD, XPS and electrochemical measurements. Surface cyclic voltammetry was used to confirm the formation of the Pd-Co alloy. In order to improve activity and stability, the catalysts were heat-treated in the temperature range of 300 °C to 700 °C. The optimal heat-treatment temperature was found to be 300 °C, where the average particle size of 8.9 nm, and the highest ORR catalytic activity, were obtained. The catalyzed ORR kinetics were also studied using the rotating disk electrode (RDE) method. The kinetic parameters were then obtained. Electrocatalytic ORR activity was also examined in an acidic solution containing methanol. The results showed that the synthesized Pd-Co/C catalyst has methanol tolerant capabilities.     

The effect of boron doping into Co-C-N and Fe-C-N electrocatalysts on the oxygen reduction reaction

Co-C-N and Fe-C-N thin film catalysts have been modified by controlled doping with boron. Corresponding novel thin film catalysts Co-C-N-B and Fe-C-N-B were synthesized by combinatorial magnetron sputter deposition in an Ar/N₂ gas mixture followed by subsequent heat-treatment between 700 and 1000 °C in an argon atmosphere. The nitrogen content of the as-prepared thin film catalysts could be increased by the addition of boron. Furthermore, the amount of remaining nitrogen in heat-treated catalyst samples was significantly higher in case of boron containing samples. The thin film catalysts were characterized by means of X-ray diffraction (XRD) analysis, electron microprobe and electrochemical measurements. For electrochemical studies the activity as oxygen reduction reaction (ORR) catalyst was investigated using the rotating ring-disk electrode (RRDE) technique in 0.1 M HClO₄ solution at room temperature. The catalytic activity was found to decrease with the boron content in the thin film catalysts even though the N-content increased.     

Effect of synthetic reducing agents on morphology and ORR activity of carbon-supported nano-Pd–Co alloy electrocatalysts

Three different reducing agents, ethylene glycol (EG), formaldehyde (HCHO), and sodium borohydrate (NaBH₄), were used in the synthesis of carbon-supported Pd–Co catalysts (Pd–Co/C–EG, Pd–Co/C–HCHO, and Pd–Co/C–NaBH₄, respectively). The differences among these three catalysts in morphology and electrocatalytic activity for oxygen reduction reaction (ORR) were observed and characterized using X-ray diffraction, energy dispersive X-ray analysis, transmission electron microscope, Fourier transform infrared spectra, surface cyclic voltametry, and rotating disk electrode technique. It was observed that by using a mild reducing agent such as EG, well-controlled and homogenous nucleation and growth could be achieved during the catalyst synthesis. With respect to the morphology and ORR activity of synthesized catalysts, the order of preferred reducing agents was found to be EG > NaBH₄ > HCHO. In order to improve activity and stability, the catalysts were heat-treated at temperatures ranging from 300 °C to 700 °C. It was found that for all three Pd–Co/C catalysts, a temperature of 300 °C gave the best catalyst morphology and ORR activity. The investigation in ORR kinetics catalyzed by these three catalysts revealed that all three could catalyze a four-electron reduction of oxygen to produce water. The average Tafel slope of the catalyzed ORR was found to be 70 mV/dec, suggesting that the determining step in the mechanism is a one-electron transfer process. In an effort to validate the theoretical explanation, the ORR activity as a function of particle size, Pd lattice constant, and Pd–Pd bond distance of the three Pd–Co/C catalysts was also investigated. In addition, in the case of EG as reducing agent the impregnation–reduction method employed in this work was simplified, because the need for a stabilizing agent usage was removed and water was used as the solvent.     

Catalytic activity of titanium oxide for oxygen reduction reaction as a non-platinum catalyst for PEFC

A non-platinum cathode electrocatalyst must have the stability and catalytic activity for the oxygen reduction reaction (ORR) in order to be used in polymer electrolyte fuel cells (PEFCs). Titanium oxide catalysts as the non-platinum catalyst were prepared by the heat treatment of titanium sheets in the temperature range from 600 to 1000 °C. The prepared catalysts were chemically and electrochemically stable in 0.1 mol dm⁻³ H₂SO₄. The titanium oxide catalysts showed different catalytic activities for the ORR. The ORR of the catalysts heat-treated at around 900 °C occurred at the potential of about 0.65 V versus RHE. It is considered that the deference in the catalytic activity for the ORR of the heat-treated titanium oxide catalysts was due to the fact that the heat-treatment condition changed the material property of the catalyst surface. In particular, it was found that the catalytic activity for the ORR of the Ti oxide catalysts increased with the increase in the specific crystalline structure, such as the TiO₂ (rutile) (1 1 0) plane and the work function. It is considered that a surface state change, such as the crystalline structure and work function, might affect the catalytic activity for the ORR.     

Electrochemical behavior of nanostructured nickel phthalocyanine (NiPc/C) for oxygen reduction reaction in alkaline media

Carbon-supported nickel phthalocyanine (NiPc/C) nanoparticle catalysts have been synthesized by a simple solvent-impregnation and milling procedure, then heat-treated at 600, 700, 800 and 900?°C to optimize their activity for the oxygen reduction reaction (ORR). The electrocatalytic activity and electron transfer mechanism of NiPc/C catalysts were demonstrated in oxygen-saturated alkaline electrolyte by cyclic voltammetry, linear sweep voltammetry as well as rotating disk electrode techniques, respectively. The results show that the heat-treatment temperature has a remarkable impact on the ORR activity of NiPc/C. An onset potential of 0.05?V and a half-wave potential of ?0.15?V are achieved in 0.1?M KOH after the catalyst was heat-treated at 800?°C. In addition to an increase in ORR kinetics, the number of electrons transferred for ORR also increased from 2.2 to 2.8 with increasing heat-treatment temperature from 600 to 800?°C. To understand the heat-treatment effect, X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy (XPS) were used to identify the catalyst structure and composition. From XPS analysis, pyridinic-N and graphitic-N were clearly observed after the sample was heat-treated at 800?°C. Both of these species might be assigned to sites catalytically active toward the ORR leading to activity enhancement.     

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.     

High-surface-area CoTMPP/C synthesized by ultrasonic spray pyrolysis for PEM fuel cell electrocatalysts

Ultrasonic spray pyrolysis (USP) was used to synthesize a high-surface-area CoTMPP/C catalyst for oxygen reduction reaction (ORR). SEM micrographs showed that the USP-derived CoTMPP/C consists of spherical, porous and uniform particles with a diameter of 2-5 μm, which is superior to that with a random morphology and large particle sizes (up to 100 μm) synthesized by the conventional heat-treatment method. BET results revealed that the USP-derived catalyst had a higher specific surface area (834 m² g⁻¹) than the conventional one. Cyclic voltammetric, rotating ring-disk electrode (RRDE) and H₂-air PEM fuel cell testing were employed to evaluate the USP-derived CoTMPP/C. The kinetic current density of the USP-derived catalyst at 0.7 V versus NHE was two times higher than that of the conventional catalyst. Compared to Pt/C catalyst, the USP-derived CoTMPP/C catalyst showed a strong methanol tolerance and a higher ORR activity in the presence of methanol. In a H₂-air PEM fuel cell with USP-derived CoTMPP/C as the cathode catalyst, the cell performance was much higher than that with conventional heat-treated CoTMMP/C as the catalyst.     

Characterization and performances of cobalt-tungsten and molybdenum-tungsten carbides as anode catalyst for PEFC

The preparation of carbon-supported cobalt-tungsten and molybdenum-tungsten carbides and their activity as an anode catalyst for a polymer electrolyte fuel cell were investigated. The electrocatalytic activity for the hydrogen oxidation reaction over the catalysts was evaluated using a single-stack fuel cell and a rotating disk electrode. The characterization of the catalysts was performed by XRD, temperature-programmed carburization, temperature-programmed reduction and X-ray photoelectron spectroscopy. The maximum power densities of the 30 wt% 873 K-carburized cobalt-tungsten and molybdenum-tungsten mixed with Ketjen carbon (cobalt-tungsten carbide (CoWC)/Ketjen black (KB) and molybdenum-tungsten carbide (MoWC)/KB) were 15.7 and 12.0 mW cm⁻², respectively, which were 14 and 11%, compared to the in-house membrane electrode assembly (MEA) prepared from a 20 wt% Pt/C catalyst. The CoWC/KB catalyst exhibited the highest maximum power density compared to the MoWC/KB and WC/KB catalysts. The 873 K-carburized CoW/KB catalyst formed the oxycarbided and/or carbided CoW that are responsible for the excellent hydrogen oxygen reaction.     

Kinetics and electrocatalytic activity of nanostructured Ir-V/C for oxygen reduction reaction

Active, carbon-supported Ir-V nanoparticle catalysts have been synthesized by an ethylene glycol reduction method under controlled conditions at pH 10-13 and 120 °C, then further reduced at elevated temperature from 150 to 500 °C using IrCl₃ and NH₄VO₃ as the Ir and V precursors. The nanostructured catalysts have been characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM). Ir nanoparticles, after modification with V, show a narrow particle size distribution in the range 0.5-4.5 nm, centered at 1.8 nm, and are uniformly dispersed on Vulcan XC-72. No particle agglomeration was observed, not even at high V loadings (V:Ir = 4:1 in atomic ratio). Investigation of the catalytic activity of the Ir-V/C by means of cyclic voltammetry (CV) and linear sweep voltammetry (LSV) employing a rotating disk electrode (RDE) has revealed that the presence of V may suppress the electrochemical oxidation of Ir and stabilize the Ir active centers. About six times higher kinetic current density was obtained for Ir-V/C compared to that of the pure Ir/C catalyst at 0.8 V versus RHE for the oxygen reduction reaction (ORR). The ORR in acid solution proceeds by an approximately four-electron pathway, through which molecular oxygen is directly reduced to water. The performance of a membrane electrode assembly (MEA) prepared with the most active 40% Ir-10% V/C as the cathode catalyst in a single proton-exchange membrane fuel cell (PEMFC) generated a maximum power density of 517 mW cm⁻² at 0.431 V and 70 °C, and 100 h of stable cell operation due to no loss of catalyst sites on the cathode.     

Oxygen reduction reaction (ORR) catalyzed by carbon-supported cobalt polypyrrole (Co-PPy/C) electrocatalysts

This paper reports the experimental characterization of carbon-supported cobalt polypyrrole (Co-PPy/C) catalysts synthesized using a chemical method of polymerization synthesis. Both unpyrolyzed and pyrolyzed catalysts were characterized using electrochemical techniques such as cyclic voltammetry (CV), rotating disk electrode (RDE), as well as rotating ring disk electrode (RRDE) to quantitatively obtain the oxygen reduction reaction (ORR) kinetic constants and the reaction mechanisms. The pyrolyzed catalyst showed significantly improved ORR activity as well as different ORR mechanisms, suggesting that heat-treatment is a necessary step for catalyst activity improvement. To understand the heat-treatment effect, X-ray photoelectron spectroscopy (XPS) was used to detect surface structure changes. The XPS results showed that after the sample was heat-treated, new nitrogen peaks corresponding to pyrrolic (or pyridone) and graphitic (quaternary) type nitrogens could be observed. Both of these species may be assigned to sites catalytically active towards the ORR, resulting in activity enhancement as well as a mechanism change from a two-electron dominant to a four-electron dominant reduction process, when compared to that of the unpyrolyzed catalyst.     

Pt decorating of PdNi/C as electrocatalysts for oxygen reduction

A low-cost and high performance catalyst consisting of Pt decorating PdNi/C (Pt-PdNi/C) for oxygen reduction is prepared by a two-stage route. The characterization techniques considered are X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX) technique. The results show that the Pt-PdNi/C catalyst has an average diameter of ca. 5 nm. The electrochemical activity for the ORR is evaluated from steady state polarization measurements, which are carried out in an ultra-thin layer rotating disk electrode (RDE). The RDE tests show that the Pt-PdNi/C catalyst has the highest ORR activity compared to pure Pt/C, Pd/C and PdNi/C catalysts. High electrocatalytic activities could be attributed to the synergistic effect between Pt and PdNi.     

Oxygen reduction behavior of rutile-type iridium oxide in sulfuric acid solution

Two different forms of rutile-type iridium oxide catalysts were prepared: IrO₂-coated titanium plate electrocatalysts prepared by a dip-coating method (IrO₂/Ti) and iridium oxide nanoparticles (IrO₂) prepared by a wet method, the Adams fusion method. The catalytic behavior of the oxygen reduction reaction (ORR) was evaluated by cyclic voltammetry in 0.5 M H₂SO₄ at 60 °C. Both catalysts were found to exhibit considerable activity for the ORR; however, the former oxide electrodes showed higher activity than the latter ones. All the IrO₂/Ti catalyst electrodes heat-treated at a temperature between 400 °C and 550 °C showed ca. 0.84 V (vs. RHE) of the onset potential for the ORR, E_ORR, where the reduction current of oxygen had begun to be observed during the cathodic potential sweep of the test electrodes. It has been confirmed clearly that IrO₂, but neither metallic Ir nor the hydrated IrO₂, behaves as an active catalyst for the ORR in an acidic solution. It was also demonstrated that the enlargement of the surface area of the IrO₂/Ti with the help of lanthanum is effective for the enhancement of the catalytic activity in the reaction.     

Kinetics and PEMFC performance of RuxMoySez nanoparticles as a cathode catalyst

Kinetics of Ru_xMo_ySe_z nanoparticles dispersed on carbon powder was studied in 0.5 M H₂SO₄ electrolyte towards the oxygen reduction reaction (ORR) and as cathode catalysts for a proton exchange membrane fuel cell (PEMFC). Ru_xMo_ySe_z catalyst was synthesized by decarbonylation of transition-metal carbonyl compounds for 3 h in organic solvent. The powder was characterized by X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. Catalyst is composed of uniform agglomerates of nanocrystalline particles with an estimated composition of Ru₆Mo₁Se₃, embedded in an amorphous phase. The electrochemical activity was studied by rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. Tafel slopes for the ORR remain invariant with temperature at −0.116 V dec⁻¹ with an increase of the charge transfer coefficient in dα/dT = 1.6 × 10⁻³, attributed to an entropy turnover contribution to the electrocatalytic reaction. The effect of temperature on the ORR kinetics was analyzed resulting in an apparent activation energy of 45.6 ± 0.5 kJ mol⁻¹. The catalyst generates less than 2.5% hydrogen peroxide during oxygen reduction. The Ru_xMo_ySe_z nanoparticles dispersed on a carbon powder were tested as cathode electrocatalyst in a single fuel cell. The membrane-electrode assembly (MEA), included Nafion^® 112 as polymer electrolyte membrane and commercial carbon supported Pt (10 wt%Pt/C-Etek) as anode catalyst. It was found that the maximum performance achieved for the electro-reduction of oxygen was with a loading of 1.0 mg cm⁻² Ru_xMo_ySe_z 20 wt%/C, arriving to a power density of 240 mW cm⁻² at 0.3 V and 80 °C.     

Development of non-precious oxygen reduction reaction catalyst for polymer electrolyte membrane fuel cells based on substituted cobalt porphyrins

Active and stable cobalt-based non-precious metal catalysts for the oxygen reduction reaction (ORR) in PEM fuel cells were developed through high-temperature pyrolysis of metal-porphyrins supported on carbon. The roles of substituted porphyrins, carbon support, and catalyst loading on ORR activity were studied using rotating disc electrode (RDE) measurements. It was observed that the carbon support plays a major role in improving the catalytic activity. The results showed that among the supported catalysts, the homemade mesocarbon-supported cobalt-porphyrin catalyst with 20 wt% loading displayed higher ORR activity; the cell performance showed maximum current density of 1.1 A cm⁻² at 0.13 V in H₂/O₂ fuel cells.