Hierarchical Nanostructured Carbons with Meso–Macroporosity: Design, Characterization, and Applications

Abstract

Nanostructured porous carbon materials have diverse applications including sorbents, catalyst supports for fuel cells, electrode materials for capacitors, and hydrogen storage systems. When these materials have hierarchical porosity, interconnected pores of different dimensions, their potential application is increased. Hierarchical nanostructured carbons (HNCs) that contain 3D-interconnected macroporous/mesoporous and mesoporous/microporous structures have enhanced properties compared with single-sized porous carbon materials, because they have improved mass transport through the macropores/mesopores and enhanced selectivity and increased specific surface area on the level of fine pore systems through mesopores/micropores. The HNCs with macro/mesoporosity are of particular interest because chemists can tailor specific applications through controllable synthesis of HNCs with designed nanostructures. An efficient and commonly used technique for creating HNCs is "nanocasting", a technique that first involves the creation of a sacrificial silica template with hierarchical porous nanostructure and then the impregnation of the silica template with an appropriate carbon source. This is followed by carbonization of the filled carbon precursor, and subsequent removal of the silica template. The resulting HNC is an inverse replica of its parent hierarchical nanostructured silica (HNS). Through such nanocasting, scientists can create different HNC frameworks with tailored pore structures and narrow pore size distribution. Generally, HNSs with specific structure and 3D-interconnected porosity are needed to fabricate HNCs using the nanocasting strategy. However, how can we fabricate a HNS framework with tailored structure and hierarchical porosity of meso-macropores? This Account reports on our recent work in the development of novel HNCs and their interesting applications. We have explored a series of strategies to address the challenges in synthesis of HNSs and HNCs. Through careful control of experimental parameters, we found we could readily create new HNSs and HNCs with tailored structure and hierarchical porosity. In this Account, we describe the applications of the HNCs in low-temperature fuel cells, in Li ion batteries, in quantum-dot-sensitized solar cells (QDSSCs) and as hydrogen storage materials. Fuel cell and QDSSC polarization performance data reveal that both the ordered HNC and spherical HNC with uniform macro- and mesoporosity demonstrate superior catalyst support effect and considerably enhanced photovoltaic performance due to their incredible structural characteristics. For hydrogen and lithium storage applications, primary experimental results show that spherical HNCs with uniform macroporous core/mesoporous shell and ordered HNC are highly beneficial in terms of a high hydrogen (or Li) uptake, good rate capability and excellent cycling retainability. These data suggest that the innovative HNCs with tailored nanostructure may find promising applications in the rapid and efficient storage of hydrogen (or Li).

Nanoarchitectured materials composed of fullerene-like spheroids and disordered graphene layers with tunable mechanical properties

“…Significant progress has been made in recent years in producing hierarchical nanostructured carbon forms at various length scales 39 . The atomistic mechanism of deformation in type-II GC, along with the understandings from mechanical metamaterials, suggest that it is feasible to tailor mechanical properties of carbon-based nanoarchitectured materials by controlling the size, concentration and connectivity of the FLS, [60][61][62][63] , metals [64][65][66][67] , glasses (for example, high-density glass for nuclear pacific X-ray plate, Pyrex glass) 64 , plastics (for example, polyamide nylon, polyethylene, polyvinyl chloride and polycarbonate) 64 , rubbers (for example, silastic, neoprene and Goodrich D-402) 64,68 , wood (for example, pine and birch) 64 , porous carbon and polymer foams 64 .…”

High‐Performance Electrocatalysts for Oxygen Reduction Based on Nitrogen‐Doped Porous Carbon from Hydrothermal Treatment of Glucose and Dicyandiamide

“…[7][8][9] Among the various carbon materials, nitrogen-doped carbon is of particular interest because it exhibits excellent electrocatalytic activity in the oxygen reduction reaction (ORR), [10][11][12][13][14][15] which is a key reaction at fuel-cell cathodes. For instance, Gong et al [16] reported that N-doped carbon nanotube arrays acted as efficient metal-free electrocatalysts for oxygen reduction in alkaline media with a performance even better than that of commercial platinum catalysts.…”

Non-Precious Electrocatalysts for Oxygen Reduction Reaction in Alkaline Media: Latest Achievements on Novel Carbon Materials

“…In addition, the offered large active area of mesopore structure that can provide more active sites, in combination with microporous structure that reduces the electrolyte diffusion distances to the interior surfaces and serves as an electrolyte buffering reservoir, significantly enhances the ORR activity [24,25]. The addition of nitrogen at this advantageous carbon structure further facilitates ORR.…”