Xiaoning Tian

Amine-functionalized holey graphene as a highly active metal-free catalyst for the oxygen reduction reaction

Amine functionalized holey graphene (AFHG), synthesized by the hydrothermal reaction of GO and ammonia and the subsequent KOH etching, has been used as a metal-free catalyst for the oxygen reduction reaction (ORR). It shows that AFHG is highly active for the ORR and exhibits higher electrocatalytic activity than graphene, nitrogen-doped graphene (NG) and amine functionalized graphene (AFG), which could be demonstrated from its higher current density and more positive half-wave and onset potentials for the ORR. Although AFHG also exhibits a slightly higher overpotential towards ORR, it is indeed more kinetically facile than the commercial JM Pt/C 40 wt%. Its higher electrochemical performance could be attributed to the presence of the electron donating group (e.g. amine) and a large number of holes in its sheet plate and the porous structure in its randomly stacked solid, which provide AFHG with higher electrical conductivity, more active edge N atoms and easier accessibility to oxygen, respectively. The stability measurements show that AFHG is more stable than graphene, NG, AFG and the JM Pt/C 40 wt% and exhibits higher immunity towards methanol crossover and CO poisoning than the JM Pt/C 40 wt%. Over 10 h of the ORR, AFHG loses only <7% of its original activity in the absence of methanol or CO, and the introduction of methanol or CO has no effect on its oxygen reduction activity, which makes it highly desirable as a metal-free catalyst for the ORR.

Hydrothermal Synthesis of Boron and Nitrogen Codoped Hollow Graphene Microspheres with Enhanced Electrocatalytic Activity for Oxygen Reduction Reaction

Boron and nitrogen codoped hollow graphene microspheres (NBGHSs), synthesized from a simple template sacrificing method, have been employed as an electrocatalyst for the oxygen reduction reaction (ORR). Because of their specific hollow structure that consists of boron and nitrogen codoped graphene, the NBGHSs can exhibit even high electrocatalytic activity toward ORR than the commercial JM Pt/C 40 wt %. This, along with their higher stability, makes the NBGHSs particularly attractive as the electrocatalyst for the ORR with great potential to replace the commonly used noble-metal-based catalysts.

High performance of a free-standing sulfonic acid functionalized holey graphene oxide paper as a proton conducting polymer electrolyte for air-breathing direct methanol fuel cells

The membranes constructed from sodium dodecylbenzenesulfonate adsorbed holey graphene oxides (SDBS-HGO)s have been used as proton exchange membranes for air-breathing direct methanol fuel cell applications. Due to the specific holey structure of graphene oxide which provides additional transport pathways for protons across the graphene oxide nanosheet and the presence of strong proton exchange groups which provide them with high proton conductivity, the SDBS-HGO membranes exhibit comparable proton conductivity and lower methanol permeability in comparison to the commercial Nafion® 112. The electrochemical results show that the air-breathing direct methanol fuel cell with the SDBS-HGO membranes as the PEMs exhibit much higher performance and better stability than that with Nafion® 112, which clearly demonstrates the possibility of using such SDBS-HGO based papers for air-breathing direct methanol fuel cell applications.

Graphene oxide assisted template-free synthesis of nanoscale splode-like NiCo2O4 hollow microsphere with superior lithium storage properties

A facile template-free Ostwald ripening method is developed for the preparation of the reduced graphene oxide supported splode-like NiCo2O4 hollow microsphere (SNHM/rGO). The graphene oxide used in the reaction mixture is found to play a crucial role in the formation of the SNHM/rGO. It promotes the formation of the NiCo-glycerol microspheres suitable for the Ostwald ripening to form the reduced graphene oxide supported hollow NiCo-glycerol microspheres, which is important for the subsequent calcination to form the SNHM/rGO. The obtained SNHM/rGO shows a great promise as the anode for lithium-ion batteries and can deliver a stable reversible capacity of 1048.1 mA h g-1 at the current density of 100 mA g-1. The performance of the SNHM/rGO is much higher than that of most NiCo2O4-based materials reported previously, strongly suggesting that the SNHM/rGO could be used as the anode for practical applications. This is well supported by the higher performance of the LiCoO2//SNHM-rGO full cell. The excellent electrochemical performance can be attributed to the specific structure of the SNHM/rGO, which comprises the splode-like hollow NiCo2O4 microspheres with the reduced graphene oxide integrated.

Sulfonated Holey Graphene Oxide (SHGO) Filled Sulfonated Poly(ether ether ketone) Membrane: The Role of Holes in the SHGO in Improving Its Performance as Proton Exchange Membrane for Direct Methanol Fuel Cells

Sulfonated holey graphene oxides (SHGOs) have been synthesized by the etching of sulfonated graphene oxides with concentrated HNO3 under the assistance of ultrasonication. These SHGOs could be used as fillers for the sulfonated aromatic poly(ether ether ketone) (SPEEK) membrane. The obtained SHGO-incorporated SPEEK membrane has a uniform and dense structure, exhibiting higher performance as proton exchange membranes (PEMs), for instance, higher proton conductivity, lower activation energy for proton conduction, and comparable methanol permeability, as compared to Nafion 112. The sulfonated graphitic structure of the SHGOs is believed to be one of the crucial factors resulting in the higher performance of the SPEEK/SHGO membrane, since it could increase the local density of the -SO3H groups in the membrane and induce a strong interfacial interaction between SHGO and the SPEEK matrix, which improve the proton conductivity and lower the swelling ratio of the membrane, respectively. Additionally, the proton conductivity of the membrane could be further enhanced by the presence of the holes in the graphitic planes of the SHGOs, since it provides an additional channel for transport of the protons. When used, direct methanol fuel cell with the SPEEK/SHGO membrane is found to exhibit much higher performance than that with Nafion 112, suggesting potential use of the SPEEK/SHGO membrane as the PEMs.

Sulfonic acid-functionalized mesoporous carbon/silica as efficient catalyst for dehydration of fructose into 5-hydroxymethylfurfural

Mesoporous silica with desired pore structure (the appropriate channel length and pore size) was synthesized through a modified soft template method. Amorphous carbon layers were then introduced in mesoporous silica channels through infiltration of carbon precursor and carbonization processes. Finally, sulfonic acid groups (–SO3H) attached onto the amorphous carbons by sulfonation reaction to form sulfonic acid-functionalized mesoporous carbon/silica which was used as a sulfonic acid catalyst. The morphology, pore structure, surface functional groups, and compositions of the obtained sulfonic acid-functionalized mesoporous carbon/silica were investigated by field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption isotherm, X-ray photoelectron spectroscopy, thermogravimetric analysis and X-ray diffraction techniques. These materials are active for the catalytic dehydration of fructose into 5-hydroxymethylfurfural. The pore structure of hard template-mesoporous silica, and homogeneous coating of amorphous carbon layers are found to be critical to obtain sulfonic acid-functionalized mesoporous carbon/silica with enhanced catalytic activity. The sulfonic acid-functionalized mesoporous carbon/silica synthesized in the desired way could exhibit a high yield of 5-HMF and good recyclability, making them highly applicable in practical applications.

Core@shell structured Co–CoO@NC nanoparticles supported on nitrogen doped carbon with high catalytic activity for oxygen reduction reaction

A composite with a hierarchical structure consisting of nitrogen doped carbon nanosheets with the deposition of nitrogen doped carbon coated Co–CoO nanoparticles (Co–CoO@NC/NC) has been synthesized by a simple procedure involving the drying of the reaction mixture containing Co(NO3)2, glucose, and urea and its subsequent calcination. The drying step is found to be necessary to obtain a sample with small and uniformly sized Co–CoO nanoparticles. The calcination temperature has a great effect on the catalytic activity of the final product. Specifically, the sample prepared at the calcination temperature of 800 °C shows better catalytic activity of the oxygen reduction reaction (ORR). Urea in the reaction mixture is crucial to obtain the sample with the uniformly sized Co–CoO nanoparticles and also plays an important role in improving the catalytic activity of the Co–CoO@NC/NC. Additionally, there exists a strong electronic interaction between the Co–CoO nanoparticles and the NC. Most interestingly, the Co–CoO@NC/NC is highly efficient for the ORR and can deliver an ORR onset potential of 0.961 V vs. RHE and a half-wave potential of 0.868 V vs. RHE. Both the onset and half-wave potentials are higher than those of most catalysts reported previously and even close to those of the commercial Pt/C (the ORR onset and half-wave potential of the Pt/C are 0.962 and 0.861 V vs. RHE, respectively). This, together with its high stability, strongly suggests that the Co–CoO@NC/NC could be used as an efficient catalyst for the ORR.