Enhancement of the Catalytic Activity and Load Cycle Durability of a PtCo Alloy Cathode Catalyst Supported on Ta-Doped SnO<sub>2</sub> with a Unique Fused Aggregated Network Microstructure for Polymer Electrolyte Fuel Cells

Kakinuma, Katsuyoshi; Hayashi, Mizuki; Hashimoto, Takuma; Iiyama, Akihiro; Uchida, Makoto

doi:10.1021/acsaem.0c00993

Cited by 19 publications

(14 citation statements)

References 51 publications

(101 reference statements)

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“…TEM images show that the oxide catalysts comprise interconnected nanoparticles with sizes between 20 and 100 nm. Each nanoparticle was necked with nearest neighbors and constructed a fused-aggregate network structure (see also Figure S2), which would be favorable to construct both electronic conduction pathways and gas diffusion pathways . Elemental mapping analysis of STEM-EDX provides an elemental distribution of the catalysts and proves the presence of Ni, Co, and O in all of the samples.…”

Section: Resultsmentioning

confidence: 99%

“…The electrochemical measurements were performed with rotating disk electrode (RDE) using an HZ-5000 potentiostat (Hokuto Denko Co., Japan). − The electrochemical cell was equipped with a water bath whose temperature variation against the set temperature was controlled within ±1 °C by a hot water circulation system (HS-1000, Tokyo Rikakikai Co., Ltd., Japan). The catalysts were coated onto a glassy carbon (GC) substrate (diameter 5 mm, Hokuto Denko, Co., Japan) with a constant loading of 40 μg cm –2 .…”

Section: Methodsmentioning

confidence: 99%

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Temperature Dependence of Oxygen Evolution Reaction Activity in Alkaline Solution at Ni–Co Oxide Catalysts with Amorphous/Crystalline Surfaces

et al. 2022

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The development of high-performance oxygen evolution reaction (OER) catalysts based on earth-abundant transition metal oxides as alternatives to precious metal oxides is being pursued intensively for the large-scale application of alkaline water electrolysis for hydrogen production. Active OER electrocatalysts can be designed on the basis of fundamental insights into the catalytic phenomena occurring on surfaces. In particular, the temperature dependence of OER activity as a measure of reaction energies/barriers needs to be characterized by taking into account the operating temperature (60−80 °C) of a practical water electrolyzer. In this work, we synthesized Ni−Co oxide solid solution catalysts by the flame pyrolysis method, with particular emphasis on the temperature dependence of the OER catalysis, as a way to elucidate the catalytic reactions, from both experimental and theoretical perspectives. The as-prepared catalysts structured with conductive Ni−Co alloys were heat-treated at different temperatures in the presence of O 2 to regulate the crystallinity of the oxide surfaces. The OER activity has been evaluated from 20 to 80 °C in 1 M KOH, and the OER kinetic current density was found to increase with increasing temperature for all catalysts obtained. Interestingly, the Ni−Co/oxide materials with amorphous or poorly crystalline oxide surfaces showed superior activity (3−8 times higher surface-specific activity at 1.55 V vs reversible hydrogen electrode (RHE)) than their crystalline counterparts at all temperatures. The OER activation energy also decreased with decrease of the crystalline oxide phases. It was demonstrated that the catalyst with amorphous Ni−Co oxide surfaces could be readily activated to form active oxyhydroxides under alkaline OER conditions. The amorphous or disordered structure of the surface oxide with low-coordinated sites is proposed to render the surface geometry energetically favorable for the rate-determining step O + OH → OOH, which accelerates the reaction kinetics and thus improves the OER activity, as explained by density functional theory calculations.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Temperature Dependence of Oxygen Evolution Reaction Activity in Alkaline Solution at Ni–Co Oxide Catalysts with Amorphous/Crystalline Surfaces

et al. 2022

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“…The effect of Pt loading is proposed to involve a specific ORR mechanism that helps to rationalize both the kinetic results and the involvement of the (111) facets based on DFT calculations. A preliminary durability test by potential-step cycling (0.6 ↔ 1.0 V) was also conducted for the most active catalyst (34.2 wt %) in an O 2 -saturated 0.1 M HClO 4 solution at 80 °C, which simulates load changes in the drive cycle of fuel cell vehicles (FCVs). , An encouragingly high durability of Pt/Nb-SnO 2 subjected to 3000 cycles has been demonstrated in comparison to that of a commercial Pt/C catalyst.…”

Section: Introductionmentioning

confidence: 99%

Temperature Dependence of Oxygen Reduction Activity at Pt/Nb-Doped SnO₂ Catalysts with Varied Pt Loading

et al. 2021

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We have examined the temperature dependence of the activities for the oxygen reduction reaction (ORR) at Pt catalysts supported on Nb-doped SnO2 (Pt/Nb-SnO2) in 0.1 M HClO4. The apparent rate constants (k app) for the ORR have been evaluated from 20 to 80 °C. The k app values increased with increasing temperature, and at each temperature, k app was also observed to increase with a higher loading amount of Pt on the Nb-SnO2 support (from 17.4 to 34.2 wt %). The Pt particles tended to coalesce and form nanorods with preferential growth of (111) planes when the Pt loading was increased. This is proposed to render the surface geometry favorable for the ORR, as explained by density functional theory (DFT) calculations. The high-weight-percent catalyst also showed higher Pt mass activity, making it possible to reduce the cathode Pt loading while maintaining high fuel cell performance. The apparent activation energy of the ORR was found to be virtually independent of Pt loading on the Nb-SnO2, with values of 15–19 kJ mol–1. The activity enhancement is explained by an increase in the pre-exponential factor of the Arrhenius equation, which could be related to the increased exposure of the (111)-like facets, which provide an optimum platform for O2 adsorption, together with facile desorption of OHad. The durability was assessed in a high-temperature acid electrolyte, similar to that in an actual fuel cell. The test involved potential steps between 0.6 and 1.0 V in O2-saturated 0.1 M HClO4 at 80 °C. The ORR mass activity (@0.9 V) of Pt/Nb-SnO2 (34.2 wt %-Pt) after 3000 cycles showed only a small loss, 13%, and the retained value was 2.6 times higher than that of a commercial Pt/C catalyst, which experienced a much larger loss of 41%.

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“…The constructed three-dimensional structure allows us to calculate the physical properties of the system, for example the transport coefficient of gas diffusion and the thermal conductivity of an aerogel. Similar complex systems such as catalysts and catalytic supports (Kakinuma et al, 2020) and mesoporous polymers (Samitsu et al, 2013) have also been extensively studied. We believe the present SAXS-RMC method could allow the evaluation of various critical characteristics of these materials.…”

Section: Discussionmentioning

confidence: 99%

Real-space modeling for complex structures based on small-angle X-ray scattering

Omote

Iwata

2021

J Appl Cryst

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A three-dimensional real-space model has been created for hierarchical materials by matching observed and simulated small-angle X-ray scattering patterns. The simulation is performed by arranging the positions of small primary particles and constructing an aggregate structure in a finite-sized cell. In order to avoid the effect of the finite size of the cell, the cell size is extended to infinity by introducing an asymptotic form of the long-range correlations among the primary particles. As a result, simulations for small-angle X-ray scattering patterns can be performed correctly in the low-wavenumber regime (<0.1 nm−1), allowing the model to handle hundred-nanometre-scale structures composed of primary particles of a few nanometres in size. An aerogel structure was determined using this model, resulting in an excellent match with the experimental scattering pattern. The resultant three-dimensional model can generate cross-sectional images similar to those obtained by transmission electron microscopy, and the calculated pore-size distribution is in accord with that derived from the gas adsorption method.

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Enhancement of the Catalytic Activity and Load Cycle Durability of a PtCo Alloy Cathode Catalyst Supported on Ta-Doped SnO₂ with a Unique Fused Aggregated Network Microstructure for Polymer Electrolyte Fuel Cells

Cited by 19 publications

References 51 publications

Temperature Dependence of Oxygen Evolution Reaction Activity in Alkaline Solution at Ni–Co Oxide Catalysts with Amorphous/Crystalline Surfaces

Temperature Dependence of Oxygen Evolution Reaction Activity in Alkaline Solution at Ni–Co Oxide Catalysts with Amorphous/Crystalline Surfaces

Temperature Dependence of Oxygen Reduction Activity at Pt/Nb-Doped SnO₂ Catalysts with Varied Pt Loading

Real-space modeling for complex structures based on small-angle X-ray scattering

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Enhancement of the Catalytic Activity and Load Cycle Durability of a PtCo Alloy Cathode Catalyst Supported on Ta-Doped SnO2 with a Unique Fused Aggregated Network Microstructure for Polymer Electrolyte Fuel Cells

Cited by 19 publications

References 51 publications

Temperature Dependence of Oxygen Evolution Reaction Activity in Alkaline Solution at Ni–Co Oxide Catalysts with Amorphous/Crystalline Surfaces

Temperature Dependence of Oxygen Evolution Reaction Activity in Alkaline Solution at Ni–Co Oxide Catalysts with Amorphous/Crystalline Surfaces

Temperature Dependence of Oxygen Reduction Activity at Pt/Nb-Doped SnO2 Catalysts with Varied Pt Loading

Real-space modeling for complex structures based on small-angle X-ray scattering

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Enhancement of the Catalytic Activity and Load Cycle Durability of a PtCo Alloy Cathode Catalyst Supported on Ta-Doped SnO₂ with a Unique Fused Aggregated Network Microstructure for Polymer Electrolyte Fuel Cells

Temperature Dependence of Oxygen Reduction Activity at Pt/Nb-Doped SnO₂ Catalysts with Varied Pt Loading