Facile synthesis of bimodal porous silica and multimodal porous carbon as an anode catalyst support in proton exchange membrane fuel cell

Ready-to-use binder-free Co(OH)2 plates@porous rGO layers/Ni foam electrode for high-performance supercapacitors

In this work, an outstanding nano-structured composite electrode is fabricated through the co-deposition of Co(OH)2 nanoplates and porous reduced GO (p-rGO) nanosheets onto Ni foam (NF). Through field emission scanning electron microscopy and transmission electron microscopy observations, it was confirmed that porous reduced graphene oxide sheets are completely wrapped by uniform hexagonal Co(OH)2 plates. Due to the unique architecture of both components of the prepared composite, a high surface area of 234.7 m2 g-1 and mean pore size of 3.65 nm were observed for the Co(OH)2@p-rGO composite. The constructed Co(OH)2@p-rGO/NF composite electrode shows higher energy storage capability compared to that of Co(OH)2/NF and p-rGO/NF electrodes. The Co(OH)2/NF electrode shows specific capacitances of 902 and 311 F g-1 at 5 and 30 A g-1, while the Co(OH)2@p-rGO/NF electrode delivers 1688 and 1355 F g-1 under the same current loads, respectively. Furthermore, when the current load was increased from 1 to 30 A g-1, 74.5% capacitance retention was observed for the Co(OH)2@p-rGO/NF electrode, indicating its outstanding high-power capability, while the Co(OH)2/NF electrode retained only 38.5% of its initial capacitance. The fabricated Co(OH)2@p-rGO/NF//rGO/NF ASC device shows an areal capacitance of 3.29 F cm-2, cycling retention of 91.2% after 4500 cycles at 5 A g-1 and energy density of 68.7 W h kg-1 at a power density of 895 W kg-1. The results of electrochemical tests prove that Co(OH)2@p-rGO/NF exhibits good performance as a positive electrode for use in an asymmetric supercapacitor device. The prepared porous composite electrode is thus a promising candidate for use in supercapacitor applications.

Dense Pt Nanowire Electrocatalyst for Improved Fuel Cell Performance Using a Graphitic Carbon Nitride-Decorated Hierarchical Nanocarbon Support

An innovative strategy is presented to engineer supported-Pt nanowire (NW) electrocatalysts with a high Pt content for the cathode of hydrogen fuel cells. This involves deposition of graphitic carbon nitride (g-CN) onto 3D multimodal porous carbon (MPC) (denoted as g-CN@MPC) and using the g-CN@MPC as an electrocatalyst support. The protective coating of g-CN on the MPC provides good stability for the electrocatalyst support against electrochemical oxidation, and also enhances oxygen adsorption and provides additional active sites for the oxygen reduction reaction. Compared with commercial carbon black Vulcan XC-72R (denoted as VC) support material, the larger hydrophobic surface area of the g-CN@MPC enables the supported high-content Pt NWs to disperse uniformly on the support. In addition, the unique 3D interconnected pore networks facilitate improved mass transport within the g-CN@MPC support material. As a result, the g-CN@MPC-supported high-content Pt catalysts show improved performance with respect to their counterparts, namely, MPC, VC, and g-CN@VC-supported Pt NW catalysts and the conventional Pt nanoparticle (NP) catalyst (i.e., Pt(20 wt%)NPs/VC (Johnson Matthey)) used as the benchmark. More importantly, the g-CN-tailored high-content Pt NW (≈60 wt%) electrocatalyst demonstrates high PEM fuel cell power/performance at a very low cathode catalyst loading (≈0.1 mg_Pt  cm^-2 ).

Ordered SnO2@C Flake Array as Catalyst Support for Improved Electrocatalytic Activity and Cathode Durability in PEMFCs

Pt-SnO2@C-ordered flake array was developed on carbon paper (CP) as an integrated cathode for proton exchange membrane fuel cell through a facile hydrothermal method. In the integrated cathode, Pt nanoparticles were deposited uniformly with a small particle size on the SnO2@C/CP support. Electrochemical impedance spectroscopy analysis revealed lower impedance in a potential range of 0.3-0.5 V for the ordered electrode structure. An electrochemically active surface area and oxygen reduction peak potential determined by cyclic voltammetry measurement verified the synergistic effect between Pt and SnO2, which enhanced the electrochemical catalytic activity. Besides, compared with the commercial carbon-supported Pt catalyst, the as-developed SnO2@C/CP-supported Pt catalyst demonstrated better stability, most likely due to the positive interaction between SnO2 and the carbon coating layer.

The lightest solid meets the lightest gas: an overview of carbon aerogels and their composites for hydrogen related applications

Hydrogen, a renewable and recyclable energy, has been regarded as the best solution for global energy supply in the 21^st century. Hydrogen production, hydrogen storage and hydrogen sensing are three most important aspects for hydrogen economy. Interestingly, the lightest solid, carbon aerogels (CAs), has found wide applications in these aspects due to its unique characteristics including large specific surface area, hierarchical porous structure, high electrical conductivity, superb chemical stability, and low fabrication cost. Herein, various fabrication strategies of CAs are presented, and their applications in the three most important aspects are comprehensively reviewed. In addition, the challenges and prospects are also discussed. In the light of the recent progress in CAs for hydrogen-related applications, this review provides a comprehensive assessment on materials selection, synthesis, hydrogen adsorption characteristics of CAs and catalytic activity of CA-supported nanocatalysts, offering a strategic guide to build a close connection between CAs and hydrogen economy.

Hierarchical meso/macro-porous carbon fabricated from dual MgO templates for direct electron transfer enzymatic electrodes

We designed a three-dimensional (3D) hierarchical pore structure to improve the current production efficiency and stability of direct electron transfer-type biocathodes. The 3D hierarchical electrode structure was fabricated using a MgO-templated porous carbon framework produced from two MgO templates with sizes of 40 and 150 nm. The results revealed that the optimal pore composition for a bilirubin oxidase-catalysed oxygen reduction cathode was a mixture of 33% macropores and 67% mesopores (MgOC33). The macropores improve mass transfer inside the carbon material, and the mesopores improve the electron transfer efficiency of the enzyme by surrounding the enzyme with carbon.

A highly efficient PtCo/C electrocatalyst for the oxygen reduction reaction

A novel strategy was developed to fabricate leached PtCo/C electrocatalyst which demonstrates considerably enhanced ORR activity than commercial Pt/C (TKK).

Effect of different solvent ratio (ethylene glycol/water) on the preparation of Pt/C catalyst and its activity toward oxygen reduction reaction

Particle size and distribution of 50 wt% Pt/C can be determined by the volume ratio of EG/H₂O in the synthesis.

Hierarchical nanostructured carbons with meso-macroporosity: design, characterization, and applications

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).