Oxygen Reduction Reaction Current Density Research Articles

Kinetic effect of the ionomer on the oxygen reduction in carbon-supported Pt electrocatalysts

The mechanism of the oxygen reduction reaction (ORR) on nanoparticulated Pt/C-Nafion electrodes prepared in one step has been studied to simulate the reaction in the cathode of a Polymer Electrolyte Fuel Cell (PEFC). The kinetic parameters have been obtained by hydrodynamic polarization in O2-saturated 0.01–1.00 M H2SO4 and temperatures in the range 25.0–50.0 °C. The ORR current density was maximum and practically independent of the ionomer fraction in the rage 10–55 wt% Nafion. The poorer proton conductivity for lower Nafion fractions and the formation of catalyst areas completely surrounded by Nafion together with adsorption of Pt sites by sulfonate groups for higher Nafion fractions, explain the minor ORR activity in these conditions. The ionomer influence on the O2 diffusion at high overpotentials for Pt/C-Nafion was negligible when the Nafion content was smaller than 20 wt%. The higher kinetic current density for Pt/C-Nafion (100 mA cm−2) with respect to smooth Pt-Nafion (40 mA cm−2), together with the smaller activation energy of the former (25 ± 4 kJ mol−1) with respect to the latter (42 ± 5 kJ mol−1) highlighted the better properties attained by the nanosize effect. A remarkable novel result is that the reaction order of H+ in HClO4 is close to unity, whereas in sulfuric acid it is significantly smaller and changes with potential, what has been related to the sulfate adsorption. The anomalous dependence of the charge transfer coefficient with temperature was then explained by the thermal change of the double layer structure and the variation of the coverage of adsorbed species on Pt. The more sensitive effect for Pt/C-Nafion than for smooth Pt-Nafion was ascribed to the stronger interaction between the components when the nanoparticles are involved.

Oxygen Reduction Electrocatalyst Based on Strongly Coupled Cobalt Oxide Nanocrystals and Carbon Nanotubes

Electrocatalyst for oxygen reduction reaction (ORR) is crucial for a variety of renewable energy applications and energy-intensive industries. The design and synthesis of highly active ORR catalysts with strong durability at low cost is extremely desirable but remains challenging. Here, we used a simple two-step method to synthesize cobalt oxide/carbon nanotube (CNT) strongly coupled hybrid as efficient ORR catalyst by directly growing nanocrystals on oxidized multiwalled CNTs. The mildly oxidized CNTs provided functional groups on the outer walls to nucleate and anchor nanocrystals, while retaining intact inner walls for highly conducting network. Cobalt oxide was in the form of CoO due to a gas-phase annealing step in NH(3). The resulting CoO/nitrogen-doped CNT (NCNT) hybrid showed high ORR current density that outperformed Co(3)O(4)/graphene hybrid and commercial Pt/C catalyst at medium overpotential, mainly through a 4e reduction pathway. The metal oxide/carbon nanotube hybrid was found to be advantageous over the graphene counterpart in terms of active sites and charge transport. Last, the CoO/NCNT hybrid showed high ORR activity and stability under a highly corrosive condition of 10 M NaOH at 80 °C, demonstrating the potential of strongly coupled inorganic/nanocarbon hybrid as a novel catalyst system in oxygen depolarized cathode for chlor-alkali electrolysis.

Advanced nanoelectrocatalyst for methanol oxidation and oxygen reduction reaction, fabricated as one-dimensional pt nanowires on nanostructured robust Ti0.7Ru0.3O2 support

We present a simple and facile approach to tackling many current fuel cell issues by exploiting the direct growth of 1D Pt nanowires on nanostructured multifunctional Ti0.7Ru0.3O2 that exploit various advantages conferred by the multifunctional Ti0.7Ru0.3O2 support when synergistically combined with 1D Pt nanowires. The robust non-carbon Ti0.7Ru0.3O2 not only plays an important role as a co-catalyst but also shows extremely high stability in acidic and oxidative environments. Furthermore, the unique 1D anisotropic morphology of the Pt nanostructures can improve mass transport and the preferential exposure of certain crystal facets so promoting the catalytic activity of Pt NW/Ti0.7Ru0.3O2 for both ORR and the Methanol Oxidation Reaction (MOR). We also show that the oxygen reduction reaction current densities at the half-wave potential (∼0.9V), generated using co-catalytic Pt NW/Ti0.7Ru0.3O2 are, respectively, ∼2-fold higher than those of commercial Pt/C (JM) catalyst or Pt NW on carbon. Additionally, Pt NW/Ti0.7Ru0.3O2 exhibited excellent electrocatalytic activity and CO-tolerance toward MOR. For example, at 600mV the polarization current density of Pt NW/Ti0.7Ru0.3O2 was ∼5 times and 8 times greater than for the Pt NW/C and Pt/C (JM) catalysts. Thus, Pt NW/Ti0.7Ru0.3O2 is a novel functionalised co-catalytic support that shows utility as an advanced nanoelectrocatalyst for both of anode and cathode fuel cell applications. This powerful approach opens a reliable path to the discovery of advanced multifunctional nanoelectrocatalysts that can replace the traditional catalytic structures and motivate further research in the field.

Polyaniline‐Modified Silver and Binary Silver‐Cobalt Catalysts for Oxygen Reduction Reaction

AbstractNovel dendrite‐like silver particles were electrodeposited on Ti substrates from a supporting electrolyte‐free 30 mmol L−1 Ag(NH3)2+ solution, to synthesize the den‐Ag/Ti electrode. Binary AgxCoy/Ti electrodes with different Ag:Co atomic ratios were further obtained by electrodeposition of Co particles on the den‐Ag/Ti electrode. Polyaniline (PANI) modified den‐Ag/Ti and AgxCoy/Ti electrodes, PANI(n)‐den‐Ag/Ti and PANI(n)‐AgxCoy/Ti, were also obtained by cyclic voltammetry at different numbers of cycles (n) in acidic and alkaline solutions containing aniline, respectively. All these electrodes exhibit high electroactivity for oxygen reduction reaction (ORR) in alkaline solution and their electroactivities follow the order: PANI(15)‐Ag31Co69/Ti>Ag31Co69/Ti>PANI(20)‐den‐Ag/Ti>den‐Ag/Ti. Among them, PANI(15)‐Ag31Co69/Ti displays the highest electrocatalytic activity for ORR with a much positive onset potential of 0 V (vs. Ag/AgCl) and a high ORR current density of 1.2 mA cm−2 at −0.12 V (vs. Ag/AgCl). The electrocatalysts are electrochemically insensitive to methanol and ethanol oxidation, and, as cathode electrocatalysts of direct alcohol fuel cells, can resist poisoning by the possible alcohol crossover from the anode.

Oxygen Reduction Reaction Activity of La-Based Perovskite Oxides in Alkaline Medium: A Thin-Film Rotating Ring-Disk Electrode Study

In this work, LaMO3 and LaNi0.5M0.5O3 (M = Ni, Co, Fe, Mn and Cr) perovskite oxide electrocatalysts were synthesized by a combined ethylenediaminetetraacetic acid-citrate complexation technique and subsequent calcinations at 1000 °C in air. Their powder X-ray diffraction patterns demonstrate the formation of a specific crystalline structure for each composition. The catalytic property of these materials toward the oxygen reduction reaction (ORR) was studied in alkaline potassium hydroxide solution using the rotating disk and rotating ring-disk electrode techniques. Carbon is considered to be a crucial additive component because its addition into perovskite oxide leads to optimized ORR current density. For LaMO3 (M = Ni, Co, Fe, Mn and Cr)), in terms of the ORR current densities, the performance is enhanced in the order of LaCrO3, LaFeO3, LaNiO3, LaMnO3, and LaCoO3. For LaNi0.5M0.5O3, the ORR current performance is enhanced in the order of LaNi0.5Fe0.5O3, LaNi0.5Co0.5O3, LaNi0.5Cr0.5O3, and LaNi0.5Mn0.5O3....

Covalent Hybrid of Spinel Manganese–Cobalt Oxide and Graphene as Advanced Oxygen Reduction Electrocatalysts

Through direct nanoparticle nucleation and growth on nitrogen doped, reduced graphene oxide sheets and cation substitution of spinel Co(3)O(4) nanoparticles, a manganese-cobalt spinel MnCo(2)O(4)/graphene hybrid was developed as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline conditions. Electrochemical and X-ray near-edge structure (XANES) investigations revealed that the nucleation and growth method for forming inorganic-nanocarbon hybrids results in covalent coupling between spinel oxide nanoparticles and N-doped reduced graphene oxide (N-rmGO) sheets. Carbon K-edge and nitrogen K-edge XANES showed strongly perturbed C-O and C-N bonding in the N-rmGO sheet, suggesting the formation of C-O-metal and C-N-metal bonds between N-doped graphene oxide and spinel oxide nanoparticles. Co L-edge and Mn L-edge XANES suggested substitution of Co(3+) sites by Mn(3+), which increased the activity of the catalytic sites in the hybrid materials, further boosting the ORR activity compared with the pure cobalt oxide hybrid. The covalently bonded hybrid afforded much greater activity and durability than the physical mixture of nanoparticles and carbon materials including N-rmGO. At the same mass loading, the MnCo(2)O(4)/N-graphene hybrid can outperform Pt/C in ORR current density at medium overpotentials with stability superior to Pt/C in alkaline solutions.

Preparation and properties of thin Pt–Ir films deposited by dc magnetron co-sputtering

A series of Pt–Ir thin films envisaged for application as fuel cell cathodic catalysts are deposited by dc co-sputtering from pure metal targets. To achieve different metal ratios, the sputtering power applied on the iridium target ( P Ir) is varied in the range 0–100 W at constant power of the Pt target ( P Pt). The influence of the sputtering power on the film composition, morphology, and surface structure is analysed by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The catalytic activity towards oxygen reduction reaction (ORR) is evaluated in sulphuric acid solutions applying the methods of cyclic voltammetry and potentiodynamic polarization curves. The performed morphological and electrochemical investigations reveal that catalytic efficiency of the co-sputtered Pt-Ir films is superior compared to pure Pt. The ORR is most intensive on the sample deposited at power ratio P Pt: P Ir = 100:30 W containing 11 at.% Ir that has also the most developed active surface. The ORR current density for this film achieved at 0.825 V in acid solution (4.1 mA cm −2) is about 6 times higher than for pure Pt (0.67 mA cm −2). The improved activity of the thin co-sputtered Pt-Ir over Pt allows for essential reduction of the catalyst loading at preserved performance.

Nanostructured Ti0.7Mo0.3O2 Support Enhances Electron Transfer to Pt: High-Performance Catalyst for Oxygen Reduction Reaction

The slow rate of the oxygen reduction reaction (ORR) and the instability of Pt-based catalysts are two of the most important issues that must be solved in order to make proton exchange membrane fuel cells (PEMFCs) a reality. Additionally, the serious carbon corrosion on the cathode side is a critical problem with respect to the durability of catalyst that limits its wide application. Here, we present a new approach by exploring robust noncarbon Ti(0.7)Mo(0.3)O(2) used as a novel functionalized cocatalytic support for Pt. This approach is based on the novel nanostructure Ti(0.7)Mo(0.3)O(2) support with "electronic transfer mechanism" from Ti(0.7)Mo(0.3)O(2) to Pt that can modify the surface electronic structure of Pt, owing to a shift in the d-band center of the surface Pt atoms. Furthermore, another benefit of Ti(0.7)Mo(0.3)O(2) is the extremely high stability of Pt/Ti(0.7)Mo(0.3)O(2) during potential cycling, which is attributable to the strong metal/support interaction (SMSI) between Pt and Ti(0.7)Mo(0.3)O(2). This also enhances the inherent structural and chemical stability and the corrosion resistance of the TiO(2)-based oxide in acidic and oxidative environments. We also demonstrate that the ORR current densities generated using cocatalytic Pt/Ti(0.7)Mo(0.3)O(2) are respectively ~7- and 2.6-fold higher than those of commercial Pt/C and PtCo/C catalysts with the same Pt loading. This new approach opens a reliable path to the discovery advanced concept in designing new catalysts that can replace the traditional catalytic structure and motivate further research in the field.

RDE Measurements of ORR Activity of Pt1 − xIrx ( 0 < x < 0.3 ) on High Surface Area NSTF-Coated Glassy Carbon Disks

Layered and Pt films were sputtered onto mirror-polished and nanostructured thin film (NSTF)-coated glassy carbon (GC) disks. Rotating disk electrode (RDE) studies of oxygen reduction reaction (ORR) activity were completed for all prepared disks. The film was prepared by depositing alternating layers of Pt (constant thickness) and Ir (gradient), finished with a Pt top layer. The NSTF-supported catalysts had much higher active surface areas and reached the diffusion-limited current at higher potentials than the bare GC supported catalysts. The surface enhancement factor (SEF) of Pt on NSTF-coated disks was approximately 14. The SEF increased (reaching a maximum of 22 at in ) as the Ir content increased for the samples on NSTF. The kinetic ORR current density also increased with increasing Ir content. A similar trend was not observed for the same catalyst coated onto bare GC disks. All of the catalyst/support combinations had identical Tafel slopes and area-specific current densities, suggesting that Pt is the active catalytic ingredient. Catalysts coated on NSTF-coated GC disks can be used to accurately examine both catalytic activities and the effects of high surface area supports in a single measurement.

Effect of oxide film on oxygen reduction current for the platinum–cobalt alloy electrodes in PEFC

Effect of surface oxide on Pt–Co alloy electrodes on the oxygen reduction reaction (ORR) was investigated in 0.5 M sulfuric acid solution by electrochemistry, ellipsometry, laser Raman scattering spectroscopy, and XPS. The oxide as thick as 1–2 nm increases the overpotential of ORR and falls down efficiency of PEFC. The thickness of the oxide films is precisely determined by ellipsometry. The oxide film 1.9 nm thick was formed on Pt–50 mol% Co electrode by constant potential oxidation at 1.20 V and the film 1.5 nm thick remains on the electrode at 0.6 V at which ORR already starts. The remaining oxide decreases the current density of ORR and increases the overpotential. On pure Pt electrode, the similar influence of the oxide film was observed.

Tantalum (oxy)nitrides prepared using reactive sputtering for new nonplatinum cathodes of polymer electrolyte fuel cell

Tantalum (oxy)nitrides (TaO x N y ) have been investigated as new cathodes for polymer electrolyte fuel cells without platinum. TaO x N y films were prepared using a radio frequency magnetron sputtering under Ar + O 2 + N 2 atmosphere at substrate temperatures from 50 to 800 °C. The effect of the substrate temperature on the catalytic activity for the oxygen reduction reaction (ORR) and properties of the TaO x N y films were examined. The catalytic activity of the TaO x N y for the ORR increased with the increasing substrate temperature. The ORR current density at 0.4 V vs. RHE on TaO x N y prepared at 800 °C was approximately 20 times larger than that on TaO x N y prepared at 50 °C. The onset potential of the TaO x N y for the ORR was obtained at the ORR current density of −0.2 μA cm −2. The onset potential of the TaO x N y prepared at 800 °C was ca. 0.75 V vs. RHE. The X-ray diffraction patterns revealed that Ta 3N 5 structure grew as the substrate temperature increased. While, the ionization potentials of all specimens were lower than that of Ta 3N 5, and decreased with the increasing substrate temperature. The TaO x N y which had Ta 3N 5 structure and lower ionization potential might have a definite catalytic activity for the ORR.

Preparation and oxygen reduction activity of BN-doped carbons

B-, N- and BN-doped carbons were prepared by the carbonization of poly(furfuryl alcohol) containing either BF 3–MeOH complex, melamine or both. Various characterization techniques were conducted in order to understand the controlling factors for the electrocatalytic activity of carbons for oxygen reduction reaction (ORR). Analytical inspections of the obtained XRD profiles, such as the Diamond and the Hirsch methods, revealed that the doping of boron and nitrogen broadened the graphene size distribution; while it did not influence the stacking manner of graphenes. All doped carbons showed reductions in electrical conductivity by the factors of a quarter to a hundredth of the pristine carbons. Development of porosity was observed for the doped carbons. B1s and N1s XPS analyses revealed the presences of B–C bonds and B–N–C moieties in the BN-doped carbons. The oxygen reductive activity, which was assessed by the ORR current density normalized by BET surface area, was increased by the factors of 4–5 for B-doped and N-doped carbons, while a factor of 20 was attained for the BN-doped carbons. The ORR activity of the prepared carbons was found to be controlled by the presence of both the edge-N and B–N–C moieties, which were distinguished by XPS.

Development of Zirconium Based Non-Platinum Cathode for Polymer Electrolyte Fuel Cell

Zirconium based compounds (ZrO x N y ) have been investigated as a new cathode of polymer electrolyte fuel cells without platinum. The ZrO x N y film were prepared by the radio frequency magnetron sputtering method under Ar + O 2 + N 2 atmosphere with heating the sputtered material. The effect of the heat treatment on both the catalytic activity for the oxygen reduction reaction (ORR) and the properties of ZrO x N y has been examined. The solubility of ZrO x Ny was less than 5x10 -8 mol dm -3 in 0.1 mol dm -3 sulfuric acid at 30 °C under atmospheric condition. This indicated that ZrO x N y had a high chemical stability in acidic media. The ORR current density on ZrO x N y which was heated at 800 °C was about 30 times larger than that on ZrO x N y deposited at 50 °C. It was found that heating the sputtered material during the deposition was very effective to increase the catalytic activity for ORR. The higher temperature of heat treatment caused the change of crystalline structure and the increase of the crystallinity of ZrO x N y .

Zirconium-Based Compounds for Cathode of Polymer Electrolyte Fuel Cell

Zirconium-based compounds, such as , have been investigated as a cathode of polymer electrolyte fuel cells. was prepared using radio-frequency (rf) magnetron sputtering under an with heating the substrate. The solubility of deposited at was less than in at under atmospheric condition, indicating that had a high chemical stability in acidic media. The effect of the heat-treatment during the film deposition on the catalytic activity for oxygen reduction reaction (ORR) and the properties of has been examined. The ORR current density on deposited at a substrate temperature of was times greater than that at . The dependence of both the ORR current density at and the apparent activation energy of the ORR at on the substrate temperature changed near . The crystalline structure of also changed near . In addition, the catalytic activity for the ORR increased with the increasing crystallinity and decreasing ionization potential of the specimens. Therefore, the crystalline structure, the crystallinity, and the ionization potential might affect the catalytic activity for the ORR.

Carbon-Supported Manganese Oxide Nanoparticles as Electrocatalysts for the Oxygen Reduction Reaction (ORR) in Alkaline Medium: Physical Characterizations and ORR Mechanism

MnOx/C and Me-MnOx/C (Me = Ni, Mg) electrocatalysts prepared by chemical deposition of manganese oxide nanoparticles on carbon have been characterized by Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), and chemical analysis. Their Oxygen Reduction Reaction (ORR) kinetics and mechanism have been investigated in alkaline KOH solutions by using the Rotating Disk Electrode (RDE) and the Rotating Ring-Disk Electrode (RRDE) setups. Doping the MnOx/C nanoparticles with nickel or magnesium divalent cations can considerably improve their oxygen reduction activity. As a result, the Me-MnOx/C electrocatalysts exhibit ORR specific or mass activities close to the benchmark 10 wt % Pt/C from E-TEK. At low ORR current densities, the undoped MnOx/C electrocatalyst displays a reaction order with respect to PO2 and OH- of 1 and −0.5, respectively, while ∂E/∂log i is ca. −59 mV dec-1. The ORR reaction order toward OH- is unchanged with the magnesium doping, while it becomes −2 with the nickel doping. RRDE d...

Tantalum Nitride and Oxynitride for New Cathode of Polymer Electrolyte Fuel Cell

Tantalum (oxy)nitrides (TaOxNy) have been investigated as a new cathode of polymer electrolyte fuel cells without platinum. TaOxNy films were prepared by radio frequency magnetron sputtering under Ar + O2 + N2 atmosphere with heating the substrate, and the effect of heat treatment on the catalytic activity for oxygen reduction reaction (ORR) and the properties of TaOxNy films were examined. The solubility of Ta in 0.1 mol dm-3 sulfuric acid at 30oC under atmospheric condition was about 2×10-7 mol dm-3, indicating that TaOxNy had high chemical stability. The ORR current density on TaOxNy deposited at 800oC was about 20 times larger than that on TaOxNy deposited at 50oC. Both the degree of crystallinity and the relative nitrogen content increased with increasing the heat treatment temperature.

Zirconium Nitride and Oxynitride for New Cathode of Polymer Electrolyte Fuel Cell

Zirconium compounds (ZrOxNy) have been investigated as a new cathode of polymer electrolyte fuel cells without platinum. The electrocatalysts of ZrOxNy were prepared by the radio frequency magnetron sputtering method under Ar + O2 + N2 atmosphere with heating the sputtered material. The effect of the heat treatment on the catalytic activity for the oxygen reduction reaction (ORR) and the properties of ZrOxNy has been examined. The solubility of ZrOxNy was less than 5×10-8 mol dm-3 in 0.1 mol dm-3 sulfuric acid at 30 oC under atmospheric condition. This indicated that ZrOxNy had a high chemical stability in acidic media. The ORR current density on ZrOxNy which was heated at 800 oC was about 30 times larger than that on ZrOxNy deposited at 50 oC. The higher heat treatment caused the change of crystalline structure and the increase of the crystallinity of ZrOxNy.