Electrochemical conversion of CO2 into valued products is one of the most important issues but remains a great challenge in chemistry. Herein, we report a novel synthetic approach involving prolonged thermal pyrolysis of hemin and melamine molecules on graphene for the fabrication of a robust and efficient single‐iron‐atom electrocatalyst for electrochemical CO2 reduction. The single‐atom catalyst exhibits high Faradaic efficiency (ca. 97.0 %) for CO production at a low overpotential of 0.35 V, outperforming all Fe‐N‐C‐based catalysts. The remarkable performance for CO2‐to‐CO conversion can be attributed to the presence of highly efficient singly dispersed FeN5 active sites supported on N‐doped graphene with an additional axial ligand coordinated to FeN4. DFT calculations revealed that the axial pyrrolic nitrogen ligand of the FeN5 site further depletes the electron density of Fe 3d orbitals and thus reduces the Fe–CO π back‐donation, thus enabling the rapid desorption of CO and high selectivity for CO production.

A high-rate graphene-based supercapacitor is very attractive for the practical application of graphene. Here, we first synthesized the films of the hybrids of biomass cellulose and large literal sheet sizes and weakly defective graphene flakes reaching high thermal conductivity and then converted them into hierarchical porous graphene carbon materials reaching superior supercapacity. The interconnected porous carbon framework, with macroporous walls sandwiched by micro/mesoporous activated carbon covering graphene flakes, was synthesized by template-free low-temperature activation of the cellulose/graphene hybrids at 650°C. The graphene flakes could probably assist both the decrease in the temperature of the chemical activation of cellulose and the formation of the hierarchical carbon pores without destroying their sp 2 bonds. The porous graphene carbon-based supercapacitors exhibit a reversible specific capacitance of ∼300 F/g and ultrahigh energy storage performance of 67 Wh/kg, 54 Wh/L, and 60 kW/kg over a 45 s discharge time. ■ INTRODUCTIONHigh-energy density storage and fast response supercapacitors are needed to serve the people to keep up with the high pace of modern life. 1−6 A hierarchical porous carbon framework with micro-, meso-, and macropores can be made into desirable electrodes for high-performance supercapacitors. 7−10 The macropores can work as a fast buffering reservoir for electrolytes, minimizing the diffusion distance of the ions and electrolytes from each pore, while the meso-and micropores provide a large accessible surface area for ion transport and charge accommodation. 11,12 Recently, porous graphene-based composites have received intense attention because the flat open atomic structure of graphene allows ions and electrolytes fast access to its surface with the result being a fast charging or discharging rate for energy storage. 13−17 On the other hand, although the theoretical specific surface area of a single graphene sheet is 2630 m 2 /g, experimentally accessible surface areas of graphene materials are far below this value because of the strong self-aggregation/stacking tendency of graphene flakes (GFs). To prevent the aggregation, many scientists and engineers are trying to design a three-dimensional (3D) framework, including converting flat flexible two-dimensional (2D) into 3D structure or making activated carbon and graphene hybrids. 18−22 Recently, Zhu and his co-workers 23 reported that reduced graphene oxide activated KOH at 800°C to yield a special 3D activated carbon analogue with a large surface area of >3000 m 2 /g as the electrode in a two-electrode symmetrical supercapacitor with excellent electrochemical performance. More recently, graphene oxide and polymer were also activated to produce 3D porous carbon with a large surface area and high specific capacity. 24,25 However, in most cases, (reduced) graphene oxides were used as a starting material, which remains costly and is not competitive with commercial activated carbon. In addition, (reduced) graphene oxides were c...

Low-cost preparation of durable electrocatalysts is vital for energy storage and conversion. Here, we integrated two methods of synthesizing isolated iron atoms into a special carbon matrix as an advanced electrocatalyst. Atomic Fe isolation and graphene nanomeshes or curved carbon nanoshells were almost synthesized simultaneously. The hierarchical atomic Fe/carbon material with 0.53 atom % Fe exhibited superior oxygen reduction reaction (ORR) performance to Pt–C (20 wt % Pt) with 40 mV more positive onset potential, larger current density, and stronger methanol-tolerant capability. We demonstrated that the catalytic active sites were Fe isolation and coordinated with nitrogen in the porous curved carbon-graphene matrix. This strategy could be developed into a general approach to prepare atomic metal/carbon electrocatalysts.

It is challenging to realize a dual-ion mode of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for detecting small molecules. Herein, graphene coated by porous amorphous carbon with P−O surface group and codoped by phosphorus and nitrogen (O−P,N-C/G) was synthesized from an aerogel formed by phytic acid, polyaniline, and electrochemically exfoliated graphene. The carbon material synthesized has the feature of large surface area (583 m 2 /g), good electrical conductivity, strong UV absorption, heteroatom doping, and surface functional groups suitable for laser-induced desorption/ionization. It was employed as a novel matrix suitable for both positive-ion and negative-ion modes in MALDI-TOF MS for the analysis of various small molecules including amino acids, small peptides, saccharides, drugs, and environmental pollutants, significantly outperforming control materials and a traditional CHCA (α-cyano-4hydroxycinnamic acid) or 2,5-dihydroxybenzoic (DHB) matrix. Remarkably, the detection limit of the anticancer drugs (5fluorouracil and ellagic acid) reaches 50 pmol. In addition, nice MALDI-TOF MS images can be mapped to detect mixed amino acids corresponding to homogeneous distribution of ion intensity. The monosaccharides and disaccharides can be distinguished by using the new matrix. Last but not least, it can be used to quantitatively detect glucose in human serum and soft drinks (glucose/fructose, 203.1 mM) without adding standards.

Carbon dots modified with polydopamine (CDs/PDA), a low‐cost and environmentally friendly photothermal material, is prepared in this work. The results show that the polymerization of dopamine is significantly accelerated due to the interaction between CDs and dopamine. Importantly, the interaction also greatly promotes nonradiative recombination of photoexcited charge carriers, thereby enhancing the photothermal conversion performance of CDs/PDA. The obtained CDs/PDA composite shows superior photothermal evaporation efficiency in comparison with CDs and PDA owing to the enhanced light absorption, porous structure, and appropriate interaction. In addition, CDs/PDA exhibits excellent stability. These merits enable CDs/PDA show great promise in solar‐energy‐related applications.

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Synthesized atomic Fe/bamboo-CNTs/graphene exhibits ∼95% faradaic efficiency in the electroreduction of CO2 into CO at 0.55 V overpotential over 12 h.