Effect of Nanoporous Structure on Enhanced Electrochemical Reaction

Han, Ji-Hyung; Lee, Eonji; Park, Se Jin; Chang, Rakwoo; Chung, Taek Dong

doi:10.1021/jp909382b

Cited by 81 publications

(92 citation statements)

References 30 publications

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“…Collection efficiency was obtained before and after measuring ORR by CV in order to confirm that H 2 O 2 was successfully detected during ORR. The tip potential was scanned from −0.3 V to −0.9 V at a scan rate 10 mV s −1 while a substrate potential was held at −0.3 V to re-oxidize [Ru(NH 3 …”

mentioning

confidence: 99%

Study of Porosity-Dependent Oxygen Reduction at Porous Platinum Tips Using Scanning Electrochemical Microscopy

Cho

Lee

2015

J. Electrochem. Soc.

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Tip-generation/substrate-collection mode (TG-SC) of scanning electrochemical microscopy (SECM) was used to study oxygen reduction reaction (ORR) at nanoporous Pt films depending on their pore characteristics. Nanoporous Pt films were electrodeposited in solutions containing Pt precursor, Triton X-100, and lead acetate. The varied composition of electroplating solutions could control the porosities of the deposited Pt films with three different degrees (denoted as npPt-I, npPt-II, and npPt-III): npPt-I had only nanoscale pores but npPt-II and npPt-III had both nanoscale and microscale pores; and npPt-III possessed additional microscale pores. Recessed Pt tips deposited with three different npPts were used to observe their ORR activities in TG-SC mode of SECM, considering its advantage of ∼100% collection efficiency for H 2 O 2 (2-e transfer product of ORR). The SECM results indicate that npPt-I is beneficial for the kinetic controlled potential region via the O 2 molecule confinement within npPt-I, while npPt-III is more advantageous in the mass-transport controlled region due to the more promoted O 2 influx through the microscale pores leading to the more efficient utilization of the electrode surface for ORR. The search for new catalyst materials for high-performance oxygen reduction reaction (ORR) is important due to the wide range of applications especially for polymer electrolyte membrane fuel cell. ORR, however, is a sluggish reaction and requires a high overpotential. In acidic media, ORR undergoes to produce H 2 O as a final product via either direct 4-electron transfer or stepwise 2-/2-electron transfer going through the formation of a 2-electron reduction product, H 2 O 2 (equations 1 and 2 shown below). In any of these pathways, total number of electrons transferred (n value) nearly 4 is desirable to attain efficient ORR. In the case of 2-/2-electron transfer, the intermediate product, H 2 O 2 , is required to stay at the electrode surface or thereabouts for a certain time in order to be further reduced to H 2 O as a final product. Otherwise, this stepwise pathway causes to lower the ORR efficiency with decreasing n value.The best ORR catalyst material today is platinum (Pt). Due to the high price and scarcity of Pt, there have been many efforts to develop efficient electrocatalysts by increasing its catalytic surface area. One of the strategies for enlarging active surface area is fabricating nanoporous structures. Owing to their high surface-to-volume ratios, nanoporous structures have been attracted showing their high catalytic activity. In recent years, improved catalytic activity at nanoporous structures started to be explained in terms of not only increased surface area but also their morphological features, namely, confinement effect.2 According to Han et al., the confined space in nanoporous structures enhances H 2 O 2 redox reaction and ORR increasing collision efficiency of reactants by trapping them within pores.3 This suggests that the particle-to-particle distance of the nanoporous catalys...

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confidence: 99%

Study of Porosity-Dependent Oxygen Reduction at Porous Platinum Tips Using Scanning Electrochemical Microscopy

Cho

Lee

2015

J. Electrochem. Soc.

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“…On the other hand, the convex surface of random pores, which are observed in experiments such as electro-deposited Pt microelectrodes, 30 gives the opposite effect. Second, this geometrical effect shows a nonmonotonic dependence on the gas-pore interaction strength D. For example, the concave pore surface such as in cylindrical pores enhances the relative gas adsorption up to D = 3-4 kcal/mol, but starts diminishing with higher interaction strength, where the crowding effect of gas molecules near the surface plays a dominant role.…”

Section: Resultsmentioning

confidence: 99%

Effect of Pore Geometry on Gas Adsorption: Grand Canonical Monte Carlo Simulation Studies

Lee¹,

Chang

Han³

et al. 2012

Bulletin of the Korean Chemical Society

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In this study, we investigated the pure geometrical effect of porous materials in gas adsorption using the grand canonical Monte Carlo simulations of primitive gas-pore models with various pore geometries such as planar, cylindrical, and random pore geometries. Although the model does not possess atomistic level details of porous materials, our simulation results provided many insightful information in the effect of pore geometry on the adsorption behavior of gas molecules. First, the surface curvature of porous materials plays a significant role in the amount of adsorbed gas molecules: the concave surface such as in cylindrical pores induces more attraction between gas molecules and pore, which results in the enhanced gas adsorption. On the contrary, the convex surface of random pores gives the opposite effect. Second, this geometrical effect shows a nonmonotonic dependence on the gas-pore interaction strength and length. Third, as the external gas pressure is increased, the change in the gas adsorption due to pore geometry is reduced. Finally, the pore geometry also affects the collision dynamics of gas molecules. Since our model is based on primitive description of fluid molecules, our conclusion can be applied to any fluidic systems including reactant-electrode systems.

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“…[107][108][109][110][111][112][113] Nevertheless, nanomaterials of Pd show ORR activity greater than bulk Pd. 114 Hence, nanoporous Pd and Pt, 115,116 which possess high surface to volume ratios and high chemical and thermal stability, have been studied for this reaction. Nanoporous Pd (PdNPore) films have been prepared by electroplating method as described for PtNPore.…”

Section: Electrocatalytic Activity Of Ptnpore and Pdnpore For Oxygen mentioning

confidence: 99%

Nanoporous Metals as Novel Catalysts for Chemical Transformations☆

Takale¹,

Bao²,

Yamamoto³

2015

Reference Module in Chemistry, Molecular Sciences and Chemical Engineering

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Effect of Nanoporous Structure on Enhanced Electrochemical Reaction

Cited by 81 publications

References 30 publications

Study of Porosity-Dependent Oxygen Reduction at Porous Platinum Tips Using Scanning Electrochemical Microscopy

Study of Porosity-Dependent Oxygen Reduction at Porous Platinum Tips Using Scanning Electrochemical Microscopy

Effect of Pore Geometry on Gas Adsorption: Grand Canonical Monte Carlo Simulation Studies

Nanoporous Metals as Novel Catalysts for Chemical Transformations☆

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