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Single-atomic metal catalysts are attractive for green chemistry in terms of their outstanding catalytic performance and savings in precious metal usage owing to maximized metal utilization, including anode catalysts in polymer electrolyte fuel cells (PEFCs). Heteroatom-doped porous carbons are extensively used as supports, where the heteroatoms contribute to the immobilization of single-atomic metals. However, high-content doping of heteroatoms, especially sulphur (S), into carbon supports is still challenging because S species can be readily desorbed during heat treatment. Herein, we present a bottom-up fabrication approach for S-rich porous carbons from molecular precursors via a thermal polymerization process. A simple carbonization of molecules with thermally stable S-containing building blocks and polymerizable ethynyl moieties at 900 °C yields microporous carbon materials with record-high S content (over 15 wt%). The abundant S species function as an effective anchoring site for single-atomic platinum (Pt) species. Toward anode catalysts in PEFCs, the prepared single-atomic Pt catalysts efficiently promote the electrochemical hydrogen oxidation reaction, whose activity is comparable to that of commercial Pt/C, despite the significantly low Pt loading amount. [ABSTRACT FROM AUTHOR]

Template-assisted chemical vapor deposition (CVD) is a promising approach for fabricating nanoporous materials based on graphene walls. Among conventional metal oxide templates, CaO, produced through the thermal decomposition of CaCO3, offers improved environmental sustainability and lower production costs, thereby potentially making it a viable candidate for green template materials. Nevertheless, the underlying reaction mechanisms of the interaction on the CaO surface during the CVD process remain indeterminate, giving rise to challenges in regulating graphene formation and obtaining high-quality materials. In this work, a comprehensive experimental–theoretical investigation has unveiled the CVD mechanism on CaO. CaO exhibits efficient catalytic activity in the dissociation of CH4, thereby facilitating a thermodynamically favorable conversion of CH4 to graphene. These findings highlight the potential of using CaO as a substrate for graphene growth, combining both sustainability and cost-effectiveness. When the shell-like graphene layer deposited on CaO particles is released through the dissolution of CaO with HCl, the resulting nanoporous graphene-based materials can be readily compacted by the capillary force of the liquid upon drying. The folded surfaces, however, can become available for electric double-layer capacitance via electrochemical exfoliation under a low applied potential (<1.2 V vs. Ag/AgClO4). [ABSTRACT FROM AUTHOR]

Ordered carbonaceous frameworks (OCFs) are a new class of carbon materials with a three-dimensional ordered structure synthesized by simple carbonization of metalloporphyrin crystals with polymerizable moieties. Carbonization via solid-state polymerization results in the formation of graphene-based ordered frameworks in which regularly aligned single-atomic metals are embedded. These unique structural features afford molecular-level designability like organic-based frameworks together with high electrical conductivity, thermal/chemical stability, and mechanical flexibility, towards a variety of applications including electrocatalysis and force-driven phase transition. This feature article summarizes the synthetic strategies and characteristics of OCFs in comparison with conventional organic-based frameworks and porous carbons, to discuss the potential applications and further development of the OCF family. [ABSTRACT FROM AUTHOR]

Graphene mesosponge (GMS) is a new class of mesoporous carbon consisting mainly of single-layer graphene walls. GMS has traditionally been synthesized via chemical vapour deposition (CVD) of methane onto a template of alumina (Al2O3) nanoparticles, which catalyses methane conversion. However, the Al2O3 template needs to be removed using costly and environmentally concerning processes such as hydrofluoric acid or concentrated base. In this work, we examine methane conversion catalysed by magnesium oxide (MgO) and utilized MgO as an alternative catalytic template. In contrast to Al2O3, a solid acid catalyst, MgO is a solid base catalyst that is also active for methane conversion into graphene sheets but dissolves easily in hydrochloric acid. We have investigated the reaction mechanism using in situ weight measurements and gas-emission analysis during CVD complemented by density functional theory calculations. We found that the pure MgO surface is activated via O-elimination with methane above 778 °C. On the activated MgO surface, methane is converted into a graphene sheet with a relatively low activation energy of 134 kJ mol−1. Once the first graphene layer is formed, the methane-to-graphene conversion rate decreases and the activation energy increases to 234 kJ mol−1, which is comparable to that reported in thermal methane-CVD on carbon. As a result of the faster growth rate of the first layer with respect to additional layers, it is easier to obtain single-graphene layers using MgO. The MgO-derived GMS has a unique combination of properties including a high surface area, developed mesopores, high oxidation resistance, significant softness and elasticity, very low bulk modulus (0.05 GPa), and force-driven reversible liquid–gas phase transition. Thus, we expect the MgO-derived GMS can be employed in a variety of applications including high-voltage supercapacitors and as a new type of heat pump based on the force-driven phase transition. [ABSTRACT FROM AUTHOR]

Force-responsive ordered carbonaceous frameworks (OCFs) are synthesized for the first time. Carbonization of Ni porphyrin monomers having eight polymerizable ethynyl groups yields OCFs with atomically dispersed divalent Ni species and developed micropores. The highest specific surface area (673 m2 g−1) among the OCFs has been achieved. The OCFs thus synthesized comprise non-stacked graphene sheets, affording a unique mechanical flexibility that enables force-driven reversible phase transition. [ABSTRACT FROM AUTHOR]

Realizing accurate control of catalytically active centers on solid surfaces is one of the most essential goals in the development of functionalized heterogeneous catalysts. Controlled synthesis of carbon-supported Co catalysts from single-site to nanoparticles can be successfully achieved by the structural transformation of the deposited Co(salen) complex precursor under heat treatment. The obtained structures were characterized using techniques such as XRD, in situ XAFS, and TEM. The first decomposition of the Co(salen) complex is initiated by the dissociation of Co–O–C bonds at around 250 °C, which produces isolated single-atom Co species while retaining the Co–N–C bonds even up to 400 °C. When the heat treatment temperature exceeds 450 °C, the second decomposition of the Co–N–C bonds occurs to form Co oxide nanoclusters followed by the growth of Co NPs upon further increase of the heat treatment temperature. The single-site catalyst is highly dispersed and electronically deficient owing to the interaction with the carbon support, and shows activity and selectivity for the oxidation of ethylbenzene, as compared to the inherent Co(salen) complex and nanoparticle catalysts. [ABSTRACT FROM AUTHOR]