Magnesiothermic reduction of various types of silica/carbon (SiO 2 /C) composites has been frequently used to synthesize silicon/carbon (Si/C) composites and silicon carbide (SiC) materials, which are of great interest in the research areas of lithium-ion batteries (LIBs) and nonmetal oxide ceramics, respectively. Up to now, however, it has not been comprehensively understood how totally different crystal phases of Si or SiC can result from the compositionally identical parent materials (SiO 2 /C) via magnesiothermic reduction. In this article, we propose a formation mechanism of Si and SiC by magnesiothermic reduction of SiO 2 /C; SiC is formed at the interface between SiO 2 and carbon when silicon intermediates, mainly in situ-formed Mg 2 Si, encounter carbon through diffusion. Otherwise, Si is formed, which is supported by an ex situ reaction between Mg 2 Si and carbon nanosphere that results in SiC. In addition, the resultant crystalline phase ratio between Si and SiC can be controlled by manipulating the synthesis parameters such as the contact areas between silica and carbon of parent materials, reaction temperatures, heating rates, and amount of the reactant mixtures used. The reasons for the dependence on these synthesis parameters could be attributed to the modulated chance of an encounter between silicon intermediates and carbon, which determines the destination of silicon intermediates, namely, either thermodynamically preferred SiC or kinetic product of Si as a final product. Such a finding was applied to design and synthesize the hollow mesoporous shell (ca. 3−4 nm pore) SiC, which is particularly of interest as a catalyst support under harsh environments.

Highly enhanced CO2 and H2 adsorption properties were achieved with a series of phenolic resin-based carbon spheres (resorcinol–formaldehyde carbon (RFC) and phenol–formaldehyde carbon (PFC)) by carbonization of RF and PF polymer (RFP and PFP) spheres synthesized via a sol–gel reaction and subsequent activation with hot CO2 or NH3 treatment. Monodisperse and size-tunable (100–600 nm) RFC and PFC spheres had intrinsic nitrogen contents (ca. 1.5 wt %), which are attributed to the synthesis conditions that utilized NH3 as a basic catalyst as well as nitrogen precursor. A series of CO2-activated and N-doped RFC and PFC spheres showed almost perfect correlation (R 2 = 0.99) between CO2 adsorption capacities and accumulated pore volumes of fine micropores (ultramicropore <1 nm) obtained using the nonlocal density functional theory (NLDFT) model. Interestingly, NH3 activation served not only as an effective method for heteroatom doping (i.e., nitrogen) into the carbon framework but also as an excellent activation process to fine-tune the surface area and pore size distribution (PSD). Increased nitrogen doping levels up to ca. 2.8 wt % for NH3-activated RFC spheres showed superior CO2 adsorption capacities of 4.54 (1 bar) and 7.14 mmol g–1 (1 bar) at 298 and 273 K, respectively. Compared to CO2-activated RFC spheres with similar ultramicropore volume presenting CO2 uptakes of 4.41 (1 bar) and 6.86 mmol g–1 (1 bar) at 298 and 273 K, respectively, NH3-activated nitrogen-enriched RFC was found to have elevated chemisorption ability. Moreover, prolonged activation of RFC and PFC spheres provided ultrahigh surface areas, one of which reached 4079 m2g–1 with an unprecedented superb H2 uptake capacity of 3.26 wt % at 77 K (1 bar), representing one of the best H2 storage media among carbonaceous materials and metal–organic frameworks (MOFs).

We investigated the carbon support microporosity effect on active site formation for the oxygen reduction reaction in Fe–N–C catalysts.

No abstract

Highly N-doped nanoporous carbons have been of great interest as a high uptake CO2 adsorbent and as an efficient metal-free oxygen reduction reaction (ORR) catalyst. Therefore, it is essential to produce porosity-tunable and highly N-doped carbons through cost-effective means. Herein, we introduce the bioinspired synthesis of a monodisperse and N-enriched melaninlike polymer (MP) resembling the sepia biopolymer (SP) from oceanic cuttlefish. These polymers were subsequently utilized for highly N-doped synthetic carbon (MC) and biomass carbon (SC) spheres. An adequate CO2 activation process fine-tunes the ultramicroporosity (<1 nm) of N-doped MC and SC spheres, those with maximum ultramicroporosities of which show remarkable CO2 adsorption capacities. In addition, N-doped MC and SC with ultrahigh surface areas of 2677 and 2506 m2/g, respectively, showed excellent ORR activities with a favored four electron reduction pathway, long-term durability, and better methanol tolerance, comparable to a commercial Pt-based catalyst.