Baizeng Fang

Carbon-supported Pt-based alloy electrocatalysts for the oxygen reduction reaction in polymer electrolyte membrane fuel cells: particle size, shape, and composition manipulation and their impact to activity.

Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells: Particle Size, Shape, and Composition Manipulation and Their Impact to Activity Yan-Jie Wang,†,‡ Nana Zhao,‡ Baizeng Fang,† Hui Li,* Xiaotao T. Bi,*,† and Haijiang Wang* †Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, BC Canada V6T 1Z3 ‡Vancouver International Clean-Tech Research Institute Inc., 4475 Wayburne Drive, Burnaby, Canada V5G 4X4 Electrochemical Materials, Energy, Mining and Environment, National Research Council Canada, 4250 Wesbrook Mall, Vancouver, BC, Canada V6T 1W5

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.

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.

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%.

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.

Facile synthesis of open mesoporous carbon nanofibers with tailored nanostructure as a highly efficient counter electrode in CdSe quantum-dot-sensitized solar cells

A simple but very efficient reproducible approach was developed to fabricate novel mesoporous carbon nanofibers (MCNFs) with tailored nanostructure by using porous anodic aluminium oxide (AAO) membrane and colloidal silica as hard templates and phenolic resin as a carbon source. The as-prepared MCNFs with a channel diameter of ca. 200 nm reveal uniform one-dimensional (1D) nanofiber structure, created by the replication of the AAO template, and open interconnected spherical mesopores of ca. 30 nm in diameter embedded in the CNFs, mainly controlled by the particle size of the silica template. Due to their large mesopore size and volume, high specific surface area and unique nanostructure constituted by the 1D macro-scaled porous CNF and 3D interconnected mesopore structure, the MCNFs not only possess a large electrochemically active surface area, but also an open highway network favoring rapid electron transfer and fast mass transport. As a counter electrode in a CdSe quantum-dot-sensitized solar cell, the MCNF has demonstrated higher catalytic activity towards the reduction of polysulfide electrolyte and superior photovoltaic performance to its peers such as activated carbon (AC), hollow core/mesoporous shell carbon and ordered multimodal porous carbon, and the commonly used Pt electrode, revealing a fill factor of 0.60 and a power conversion efficiency of up to 4.81%. Excellent photovoltaic performance demonstrated by the MCNF suggests synergetic effects from the combination of 1D and 3D nanostructures.

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.

Fabrication of hollow core carbon spheres with hierarchical nanoarchitecture for ultrahigh electrical charge storage

A simple and reproducible sol–gel synthesis strategy was developed to fabricate hollow core carbon spheres (HCCSs) with hierarchical nanoarchitecture through the hydrolysis, self-assembly and co-condensation of bis-[3-(triethoxysilyl)propyl]disulfide (TESPDS) and octadecyltrimethoxysilane (C18TMS). This synthesis route allows one to fabricate thioether-bridged organosilica (TBOS) with tailored spherical structure and particle size which can be further converted to HCCS upon calcination under N2 flow. It is assumed that hydrophobic octadecyl chains of hydrolyzed C18TMS first form a micelle-like self-assembly structure with hydrophilic trihydroxysilyl groups as heads, and a reactive core is then expanded by the base-catalyzed co-condensation of TESPDS and/or C18TMS over the C18TMS self-assembly structure. The organic moieties of TESPDS and C18TMS not only serve as a porogen during the formation of TBOS but also as a carbon precursor for transformation of TBOS into HCCS during the carbonization. Due to its unique hierarchical nanostructure composed of hollow macroporous core and meso/microporous shell, which facilitates fast mass transport, along with large surface area for electrical charge storage, the HCCS for the first time exhibits ultrahigh specific capacitance and energy, good cycling performance and rate capability.

Hierarchical nanostructured hollow spherical carbon with mesoporous shell as a unique cathode catalyst support in proton exchange membrane fuel cell

Hierarchical nanostructured spherical carbon with hollow macroporous core in combination with mesoporous shell has been explored to support Pt cathode catalyst with high metal loading in proton exchange membrane fuel cell (PEMFC). The hollow core-mesoporous shell carbon (HCMSC) has unique structural characteristics such as large specific surface area and mesoporous volume, ensuring uniform dispersion of the supported high loading (60 wt%) Pt nanoparticles with small particle size, and well-developed three-dimensionally interconnected hierarchical porosity network, facilitating fast mass transport. The HCMSC-supported Pt(60 wt%) cathode catalyst has demonstrated markedly enhanced catalytic activity toward oxygen reduction and greatly improved PEMFC polarization performance compared with carbon black Vulcan XC-72 (VC)-supported ones. Furthermore, the HCMSC-supported Pt(40 wt%) or Pt(60 wt%) outperforms the HCMSC-supported Pt(20 wt%) even at a low catalyst loading of 0.2 mg Pt cm(-2) in the cathode, which is completely different from the VC-supported Pt catalysts. The capability of supporting high loading Pt is supposed to accelerate the commercialization of PEMFC due to the anticipated significant reduction in the amount of catalyst support required, diffusion layer thickness and fabricating cost of the supported Pt catalyst electrode.