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1. Recent advances in graphene‐based materials for fuel cell applications

   https://doi.org/10.1002/ese3.833  

   Su, Hanrui; Hu, Yun_Hang (October 2020, Energy Science & Engineering)

   Abstract The unique chemical and physical properties of graphene and its derivatives (graphene oxide, heteroatom‐doped graphene, and functionalized graphene) have stimulated tremendous efforts and made significant progress in fuel cell applications. This review focuses on the latest advances in the use of graphene‐based materials in electrodes, electrolytes, and bipolar plates for fuel cells. The understanding of structure‐activity relationships of metal‐free heteroatom‐doped graphene and graphene‐supported catalysts was highlighted. The performances and advantages of graphene‐based materials in membranes and bipolar plates were summarized. We also outlined the challenges and perspectives in using graphene‐based materials for fuel cell applications. 

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2. Precursor-mediated in situ growth of hierarchical N-doped graphene nanofibers confining nickel single atoms for CO ₂ electroreduction

   https://doi.org/10.1073/pnas.2219043120  

   Wang, Huan; Li, Youzeng; Wang, Maoyu; Chen, Shan; Yao, Meng; Chen, Jialei; Liao, Xuelong; Zhang, Yiwen; Lu, Xuan; Matios, Edward; et al (April 2023, Proceedings of the National Academy of Sciences)

   Despite the various strategies for achieving metal–nitrogen–carbon (M–N–C) single-atom catalysts (SACs) with different microenvironments for electrochemical carbon dioxide reduction reaction (CO 2 RR), the synthesis–structure–performance correlation remains elusive due to the lack of well-controlled synthetic approaches. Here, we employed Ni nanoparticles as starting materials for the direct synthesis of nickel (Ni) SACs in one spot through harvesting the interaction between metallic Ni and N atoms in the precursor during the chemical vapor deposition growth of hierarchical N-doped graphene fibers. By combining with first-principle calculations, we found that the Ni-N configuration is closely correlated to the N contents in the precursor, in which the acetonitrile with a high N/C ratio favors the formation of Ni-N 3 , while the pyridine with a low N/C ratio is more likely to promote the evolution of Ni-N 2 . Moreover, we revealed that the presence of N favors the formation of H-terminated edge of sp 2 carbon and consequently leads to the formation of graphene fibers consisting of vertically stacked graphene flakes, instead of the traditional growth of carbon nanotubes on Ni nanoparticles. With a high capability in balancing the *COOH formation and *CO desorption, the as-prepared hierarchical N-doped graphene nanofibers with Ni-N 3 sites exhibit a superior CO 2 RR performance compared to that with Ni-N 2 and Ni-N 4 ones. 

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3. Lateral Graphene p–n Junctions Realized by Nanoscale Bipolar Doping Using Surface Electric Dipoles and Self‐Organized Molecular Anions

   https://doi.org/10.1002/admi.201801380  

   Zhang, Yong; Hu, Guangliang; Gong, Maogang; Alamri, Mohammed; Ma, Chunrui; Liu, Ming; Wu, Judy_Z (November 2018, Advanced Materials Interfaces)

   Abstract Lateral p–n junctions take the unique advantages of 2D materials, such as graphene, to enable single‐atomic layer microelectronics. A major challenge in fabrication of the lateral p–n junctions is in the control of electronic properties on a 2D atomic sheet with nanometer precision. Herein, a facile approach that employs decoration of molecular anions of bis‐(trifluoromethylsulfonyl)‐imide (TFSI) to generate p‐doping on the otherwise n‐doped graphene by positively polarized surface electric dipoles (pointing toward the surface) formed on the surface oxygen‐deficient layer “intrinsic” to an oxide ferroelectric back gate is reported. The characteristic double conductance minimaV_Dirac−andV_Dirac+illustrated in the obtained lateral graphene p–n junctions can be tuned in the range of −1 to 0 V and 0 to +1 V, respectively, by controlling the TFSI anions and surface dipoles quantitatively. The unique advantage of this approach is in adoption of polarity‐controlled molecular ion attachment on graphene, which could be further developed for various lateral electronics on 2D materials. 

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4. Leveraging electrochemistry to uncover the role of nitrogen in the biological reactivity of nitrogen-doped graphene

   https://doi.org/10.1039/C9EN00802K  

   Wang, Yan; Aquino de Carvalho, Nathalia; Tan, Susheng; Gilbertson, Leanne M. (December 2019, Environmental Science: Nano)

   While nitrogen doping greatly broadens graphene applications, relatively little is known about the influence of this heteroatom on the biological activity of graphene. A set of systematically modified nitrogen-doped graphene (NG) materials was synthesized using the hydrothermal method in which the degree of N-doping and N-bonding type is manipulated using two nitrogen precursors (urea and uric acid) and different thermal annealing temperatures. The bioactivity of the NG samples was evaluated using the oxidation of the intracellular antioxidant glutathione (GSH) and bacterial viability (of Escherichia coli K12), and oxidative stress was identified as the predominant antibacterial mechanism. Two key energy-relevant electrochemical reactions, oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), were used to characterize the influence of different N-types on the electronic properties of the NG materials. Electron-donating graphitic-N and electron-withdrawing pyridinic-N were identified as effective promoters for ORR and OER, respectively. The similar mechanisms between the GSH oxidation (indicative of oxidative stress) and ORR mechanisms reveal the role of graphitic-N as the active site in oxidative stress related bioactivity, independent of other consequential properties ( e.g. , defect density, surface area). This work advances a growing rational design paradigm for graphene family materials using chemical composition and further provides valuable insight into the performance-hazard tradeoffs of NG applications in related fields. 

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5. Cation–π Interaction Assisted Molecule Attachment and Photocarrier Transfer in Rhodamine/Graphene Heterostructures

   https://doi.org/10.1002/admi.202000796  

   Liu, Bo; López‐González, Luis_E; Alamri, Mohammed; Velázquez‐Contrera, Enrique_F; Santacruz‐Ortega, Hisila; Wu, Judy_Z (June 2020, Advanced Materials Interfaces)

   Abstract Cation–π interactions between molecules and graphene are known to have a profound effect on the properties of the molecule/graphene nanohybrids and motivate this study to quantify the attachment of the rhodamine 6G (R6G) dye molecules on graphene and the photocarrier transfer channel formed across the R6G/graphene interface. By increasing the R6G areal density of the R6G on graphene field‐effect transistor (GFET) from 0 up to ≈3.6 × 10¹³cm⁻², a linear shift of the Dirac point of the graphene from originally 1.2 V (p‐doped) to −1 V (n‐doped) is revealed with increasing number of R6G molecules. This indicates that the attachment of the R6G molecules on graphene is determined by the cation–π interaction between the NH+ in R6G and π electrons in graphene. Furthermore, a linear dependence of the photoresponse on the R6G molecule concentration to 550 nm illumination is observed on the R6G/graphene nanohybrid, suggesting that the cation–π interaction controls the R6G attachment configuration to graphene to allow formation of identical photocarrier transfer channels. On R6G/graphene nanohybrid with 7.2 × 10⁷R6G molecules, high responsivity up to 5.15 × 10²A W⁻¹is obtained, suggesting molecule/graphene nanohybrids are promising for high‐performance optoelectronics. 

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