Fatemeh Razmjooei

A new class of electroactive Fe- and P-functionalized graphene for oxygen reduction

While metal and electronegative N-containing carbon has aroused great interest as an efficient catalyst towards the oxygen reduction reaction (ORR), no combination of metal with other heteroatom-containing carbon has received considerable attention. This has motivated us to explore the performance of carbon functionalized with metal and electropositive phosphorous. Herein, we present the first report on the synthesis of a new class of electroactive Fe- and P-functionalized graphene (GPFe) and its electrocatalytic properties in alkaline and acidic media. The introduction of Fe causes remarkable synergistic effects on P-doped reduced graphene oxide by increasing surface area, enhancing the P doping level due to the interaction between Fe and P and generating electrochemically active Fe–P species. N-oxides are known to be in-active for ORR in Fe–N systems, whereas in present Fe–P systems, oxides of Fe and P are found to be beneficial for ORR. Interestingly, after the introduction of Fe, mostly inactive P-doped carbon becomes active in acidic medium. We propose that this study will surely provide renewed insights into active sites for ORR in metal and heteroatom-doped carbon systems.

Nitrogen‐Doped Ordered Mesoporous Carbon with Different Morphologies for the Oxygen Reduction Reaction: Effect of Iron Species and Synergy of Textural Properties

Nitrogen‐doped ordered mesoporous carbons (N‐OMCs) with different morphologies are prepared as oxygen reduction reaction (ORR) catalysts through pyrolysis of iron phthalocyanine‐infiltrated SBA‐15 silica with different mesochannel lengths. Excellent ORR activity with a nearly four‐electron transfer process is observed in both alkaline and acidic media. In particular, the difference in half‐wave potential for ORR relative to commercial Pt/C catalyst is only 50u2005mV negative in acidic medium, whereas it is 50u2005mV more positive in alkaline medium. Interestingly, it is found that although the use of iron is necessary for the preparation of highly active nitrogen‐doped ORR carbon catalysts, its presence is not necessary for N‐OMC to be active in the ORR in either alkaline or acidic media. In addition, the ORR activity increases gradually with decreasing mesopore channel length, with maximum activity in N‐OMC with short channels, demonstrating the high synergistic influence of structural morphology on ORR in heteroatom‐doped carbon.

Active sites and factors influencing them for efficient oxygen reduction reaction in metal-N coordinated pyrolyzed and non-pyrolyzed catalysts: a review

With increasing demand for clean energy and approaching commercialization of polymer electrolyte membrane fuel cells (PEMFCs), replacing expensive Pt-based cathode catalysts with much cheaper non-precious metal (NPM) catalysts has become absolutely essential. This review highlights the parameters that have been considered vital to improving the overall performance of the NPM-based catalysts for oxygen reduction reaction (ORR). In the present review, we focus on well-known catalytic systems in three categories of NPM catalysts, i.e. biomimetic heme–copper oxidase enzymes, non-pyrolyzed/polymeric systems, and pyrolyzed NPM–nitrogen-doped carbon (M–N/C) (M = Fe, Ni, Co, etc.) catalysts. The ORR mechanism on the reported active sites and the effect of varying their local environments are considered and discussed in detail. Among all the catalysts, only pyrolyzed M–N/C catalysts have shown activity and stability much closer to that of the state-of-the-art commercial carbon-supported platinum (Pt/C) catalyst. Although great heights have been climbed in pyrolyzed M–N/C-based catalysts, still general consensuses need to be established regarding the active sites in the NMP-based M–N/C catalysts to help enhance the activity and stability of the catalytic system. By comparing the ORR mechanisms of the three studied systems, various similarities between the active sites are identified and reported comprehensively. On the basis of the information amassed, some future directions for improving the activity, selectivity, and durability of the NPM-based catalysts are also discussed.

Effect of pristine graphene incorporation on charge storage mechanism of three-dimensional graphene oxide: superior energy and power density retention

In the race of gaining higher energy density, carbon’s capacity to retain power density is generally lost due to defect incorporation and resistance increment in carbon electrode. Herein, a relationship between charge carrier density/charge movement and supercapacitance performance is established. For this purpose we have incorporated the most defect-free pristine graphene into defective/sacrificial graphene oxide. A unique co-solvent-based technique is applied to get a homogeneous suspension of single to bi-layer graphene and graphene oxide. This suspension is then transformed into a 3D composite structure of pristine graphene sheets (GSs) and defective N-doped reduced graphene oxide (N-RGO), which is the first stable and homogenous 3D composite between GS and RGO to the best of our knowledge. It is found that incorporation of pristine graphene can drastically decrease defect density and thus decrease relaxation time due to improved associations between electrons in GS and ions in electrolyte. Furthermore, N doping is implemented selectively only on RGO and such doping is shown to improve the charge carrier density of the composite, which eventually improves the energy density. After all, the novel 3D composite structure of N-RGO and GS greatly improves energy and power density even at high current density (20u2009A/g).

Urine to highly porous heteroatom-doped carbons for supercapacitor: A value added journey for human waste

Obtaining functionalized carbonaceous materials, with well-developed pores and doped heteroatoms, from waste precursors using environmentally friendly processes has always been of great interest. Herein, a simple template-free approach is devised to obtain porous and heteroatom-doped carbon, by using the most abundant human waste, “urine”. Removal of inherent mineral salts from the urine carbon (URC) makes it to possess large quantity of pores. Synergetic effect of the heteroatom doping and surface properties of the URC is exploited by carrying out energy storage application for the first time. Suitable heteroatom content and porous structure can enhance the pseudo-capacitance and electric double layer capacitance, eventually generating superior capacitance from the URC. The optimal carbon electrode obtained particularly at 900u2009°C (URC-900) possesses high BET surface area (1040.5u2009m2g−1), good conductivity, and efficient heteroatom doping of N, S, and P, illustrating high specific capacitance of 166 Fg−1 at 0.5u2009Ag−1 for three-electrode system in inorganic electrolyte. Moreover, the URC-900 delivers outstanding cycling stability with only 1.7% capacitance decay over 5,000 cycles at 5u2009Ag−1. Present work suggests an economical approach based on easily available raw waste material, which can be utilized for large-scale production of new age multi-functional carbon nanomaterials for various energy applications.

Silicon core-mesoporous shell carbon spheres as high stability lithium-ion battery anode

An innovative and simple synthesis strategy of silicon nanoparticle (Si NP) core covered by mesoporous shell carbon (MSC) structure is demonstrated. The Si core@MSC (SCMSC) composite is developed for addressing the issues for Si anode material in lithium ion batteries (LIBs) such as high volume expansion and low electrical conductivity. Significant improvement in the electrochemical performance for the SCMSC anode is observed compared with bare Si anode. The SCMSC composite delivers an initial specific capacity of 2450u202fmAhu202fg-1 at 0.166u202fAu202fg-1u2009with Coulombic efficiency of 99.2% for 100 cycles. Compared to bare Si anode, the SCMSC anode exhibits much higher Li storage capacity, superior cyclability, and good rate capability, highlighting the advantages of hierarchical MSC in the SCMSC structure.