Jong-Sung Yu

Homogeneous Deposition of Platinum Nanoparticles on Carbon Black for Proton Exchange Membrane Fuel Cell

A simple and efficient approach has been developed for synthesis of carbon-supported Pt nanoparticles (NPs) that combines homogeneous deposition (HD) of Pt complex species through a gradual increase of pH realized by in situ hydrolysis of urea and subsequent uniform reduction by ethylene glycol (EG) in a polyol process, giving control over the size and dispersion of Pt NPs. With increasing amount of urea in the starting Pt salt aqueous solution, the size of Pt complex species decreases and so does that of the metallic Pt NPs. The decrease in size of the Pt species is likely attributable to two determining factors: the steric contraction effect and the electrostatic charge effect. The excellent electrocatalysis ability of the Pt catalysts produced by HD-EG is demonstrated through the determination of electrochemical surface area and fuel-cell polarization performance. The Pt NPs deposited on Vulcan XC-72 (VC) carbon black by the HD-EG strategy show smaller size with more uniform dispersion, higher Pt utilization efficiency, and considerably improved fuel-cell polarization performance compared with the Pt NPs prepared by conventional sodium borohydride reduction or by a microwave-assisted polyol approach. Particularly important and significant is that this HD-EG method is very efficient for the synthesis of high Pt loading catalysts with tunable NP size and uniform particle dispersion. A high metal loading catalyst such as Pt(60 wt %)/VC fabricated by the HD-EG method outperforms ones with mid-to-low metal loadings (i.e., 40 and 20 wt %), even at a very low catalyst loading of 0.2 mg of Pt cm(-2) at the cathode, which is for the first time reported for the VC-supported Pt catalysts.

Novel ordered nanoporous graphitic C3N4 as a support for Pt-Ru anode catalyst in direct methanol fuel cell

The fabrication of graphitic carbon nitride with 3-dimensionally extended highly ordered pore arrays is described, and the N-rich porous carbon was utilized for the first time as a support for Pt50–Ru50 alloy catalyst to study the support effect on the anodic performance in direct methanol fuel cells; it displays promising results as a catalyst support in the fuel cell.

Ordered multimodal porous carbon as highly efficient counter electrodes in dye-sensitized and quantum-dot solar cells.

Ordered multimodal porous carbon (OMPC) was explored as a counter electrode in ruthenium complex dye-sensitized solar cells (DSSCs) and CdSe quantum-dot solar cells (QDSCs). The unique structural characteristics such as large surface area and well-developed three-dimensional (3-D) interconnected ordered macropore framework with open mesopores embedded in the macropore walls make the OMPC electrodes have high catalytic activities and fast mass transfer kinetics toward both triiodide/iodide and polysulfide electrolytes. The efficiency (ca. 8.67%) of the OMPC based DSSC is close to that (ca. 9.34%) of the Pt based one. Most importantly, the QDSC employing OMPC material presents a high efficiency of up to 4.36%, which is significantly higher than those of Pt- and activated carbon based solar cells, ca. 2.29% and 3.30%, respectively.

Layer-by-Layer Films of Dual-Pore Carbon Capsules with Designable Selectivity of Gas Adsorption

Stable, homogeneous ultrathin films of uniformly dimensioned dual-pore carbon capsules with mesoporous walls and macroscopic empty cores were fabricated using layer-by-layer methods based on electrostatic interaction between a polyelectrolyte and a surfactant coating of the carbon capsules. The resulting dual-porous carbon capsule films were investigated as a sensor substrate for vapors of different organic solvents. The carbon capsule films have much higher adsorption capacities than conventional electrolyte films and even than noncapsular mesoporous carbon films. The dual-pore carbon capsules have greater affinities for aromatic volatiles over their aliphatic counterparts, probably due to stronger pi-pi interactions. Additionally, the adsorption selectivity can be designed. Impregnation of additional recognition components into the carbon capsules permits further control over adsorption selectivity between aromatic and nonaromatic substances and between acids and bases in the prevailing atmosphere. Therefore, it is anticipated that the dual-pore carbon capsule films developed in this work will find application in sensing and separation applications because of their designable selectivity.

Hierarchical nanostructured spherical carbon with hollow core/mesoporous shell as a highly efficient counter electrode in CdSe quantum-dot-sensitized solar cells

Hierarchical nanostructured spherical carbon with hollow core/mesoporous shell (HCMS) was explored as a counter electrode in CdSe quantum-dot-sensitized solar cells. Compared with conventional Pt electrodes and commercially available activated carbon, the HCMS carbon counter electrode exhibits a much larger fill factor due to the considerably decreased charge transfer resistance at the interface of the counter electrode/polysulfide electrolyte. Furthermore, a solar cell with the HCMS carbon counter electrode presents a high power conversion efficiency of up to 3.90% as well as an incident photon-to-current conversion efficiency peak of 80%.

Stimuli-free auto-modulated material release from mesoporous nanocompartment films

Mesoporous nanocompartment films composed of silica particles and hollow silica capsules were prepared by the layer-by-layer (LbL) technique. The resulting mesoporous nanocompartment films possess special molecular encapsulation and release capabilities so that stimuli-free auto-modulated stepwise release of water or drug molecules was achieved through the mesopore channels of robust silica capsule containers embedded in the film. Stepwise release of water was reproducibly observed that originates in the non-equilibrated rates between evaporation of water from the mesopore channels to the exterior and the capillary penetration of water from container interior to the mesopore channels. It was generalized to evaporation of other substances, fragrances, limonene. Application was also tested in the controlled release of the sunscreen UV-absorber (UV-S1) for circumvention of its rapid dissolution in water and prolongation of its prophylactic effect toward harmful ultraviolet radiation. UV-S1 was successfully entrapped within the mesoporous nanocompartment films and was released in a prolonged stepwise mode. The nanocompartment films developed in this research are promising materials for drug delivery since they allow gradual release of therapeutic agents with likely related improvements in their efficacy.

Synthesis of monodisperse spherical silica particles with solid core and mesoporous shell: mesopore channels perpendicular to the surface

Both particle monodispersity and mesopore orientation have been considered in this work. Monodisperse spherical silica particles with a solid core and a mesoporous shell featuring mesopore channels perpendicular to the core surface were synthesized for the first time by adopting silica particles as the core component and by employing Cn-TAB (n = 12, 14, 16, 18), the structure-directing agent for the mesoporous shell. Micelles on the surface of the silica particles are formed from the electrostatic interaction between the partially negatively charged silica particles and the positively charged surfactant molecules under basic conditions. The particles synthesized in this work have a uniformly coated thin mesoporous shell of about 28–61 nm in thickness over the silica core and possess a surface area of ca. 370–500 m2 g−1, pore volume of ca. 0.2–0.35 cc g−1, and narrow pore size distribution.

Ordered multimodal porous carbon with hierarchical nanostructure for high Li storage capacity and good cycling performance

Ordered multimodal porous carbon (OMPC) with a hierarchical nanostructure was prepared and explored as an anode for Li ion batteries. OMPC possesses unique structural characteristics, such as large surface area and mesopore volume, particularly the multimodal porosity composed of a well-developed 3D interconnected ordered macropore framework with open mesopores embedded in the macropore walls, which facilitate fast mass transport and charge transfer. Compared with ordered mesoporous carbon CMK-3, the OMPC not only demonstrates higher Li storage capacity, but also better cycling performance and rate capability. The enhancement in anode performance especially in cycling performance and rate capability is mainly attributable to the superb structural characteristics of the OMPC, particularly the open larger mesopores located in the ordered macropores, which act as efficient Li storage and buffer reservoirs to reduce volume change during the charge–discharge cycling especially at high rates.

Incorporating hierarchical nanostructured carbon counter electrode into metal-free organic dye-sensitized solar cell.

Hierarchical nanostructured carbon with a hollow macroporous core of ca. 60 nm in diameter in combination with mesoporous shell of ca. 30 nm in thickness has been explored as counter electrode in metal-free organic dye-sensitized solar cell. Compared with other porous carbon counterparts such as activated carbon and ordered mesoporous carbon CMK-3 and Pt counter electrode, the superior structural characteristics including large specific surface area and mesoporous volume and particularly the unique hierarchical core/shell nanostructure along with 3D large interconnected interstitial volume guarantee fast mass transport in hollow macroporous core/mesoporous shell carbon (HCMSC), and enable HCMSC to have highly enhanced catalytic activity toward the reduction of I(3)(-), and accordingly considerably improved photovoltaic performance. HCMSC exhibits a V(oc) of 0.74 V, which is 20 mV higher than that (i.e., 0.72 V) of Pt. In addition, it also demonstrates a fill factor of 0.67 and an energy conversion efficiency of 7.56%, which are markedly higher than those of its carbon counterparts and comparable to that of Pt (i.e., fill factor of 0.70 and conversion efficiency of 7.79%). Furthermore, HCMSC possesses excellent chemical stability in the liquid electrolyte containing I(-)/I(3)(-) redox couples, namely, after 60 days of aging, ca. 87% of its initial efficiency is still achieved by the solar cell based on HCMSC counter electrode.

Controllable Synthesis of Hierarchical Nanostructured Hollow Core/ Mesopore Shell Carbon for Electrochemical Hydrogen Storage

Hierarchical nanostructured hollow core/mesopore shell carbon (HN-HCMSC) represents an innovative concept in electrochemical hydrogen storage. This work deals with physical characteristics and electrochemical hydrogen storage behavior of the HN-HCMSCs, produced by a replica technique using solid core/mesopore shell (SCMS) silica as template. HN-HCMSCs with various core sizes and/or shell thicknesses have been fabricated through the independent control of the core sizes and/or shell thicknesses of the SCMS silica templates. The superb structural characteristics of the HN-HCMSCs including large specific surface area and micropore volume, and particularly well-developed three-dimensionally interconnected hierarchical nanostructure (hollow macroporous core in combination with meso-/microporous shell), provide them with great potential for electrochemical hydrogen storage. A discharge capacity up to 586 mAh/g, corresponding to 2.17 wt % hydrogen uptake, has been demonstrated in 6 M KOH for the HN-HCMSC with a core size of 180 nm and a shell thickness of 40 nm at a discharge rate of 25 mA/g. Furthermore, the HN-HCMSC also possesses excellent cycling capacity retainability and rate capability.