Surbhi Sharma

Novel “3-D spacer” all fibre piezoelectric textiles for energy harvesting applications

The piezoelectric effect in poly(vinylidene fluoride), PVDF, was discovered over four decades ago and since then, significant work has been carried out aiming at the production of high β-phase fibres and their integration into fabric structures for energy harvesting. However, little work has been done in the area of production of “true piezoelectric fabric structures” based on flexible polymeric materials such as PVDF. In this work, we demonstrate “3D spacer” technology based all-fibre piezoelectric fabrics as power generators and energy harvesters. The knitted single-structure piezoelectric generator consists of high β-phase (∼80%) piezoelectric PVDF monofilaments as the spacer yarn interconnected between silver (Ag) coated polyamide multifilament yarn layers acting as the top and bottom electrodes. The novel and unique textile structure provides an output power density in the range of 1.10–5.10 μW cm−2 at applied impact pressures in the range of 0.02–0.10 MPa, thus providing significantly higher power outputs and efficiencies over the existing 2D woven and nonwoven piezoelectric structures. The high energy efficiency, mechanical durability and comfort of the soft, flexible and all-fibre based power generator are highly attractive for a variety of potential applications such as wearable electronic systems and energy harvesters charged from the ambient environment or by human movement.

Study of FePt deposited reduced graphene oxide's utility as a catalyst towards oxygen reduction and methanol oxidation reactions

Hydrogen and methanol fuelled polymer electrolyte fuel cells (PEFC) penetration in the commercial market is slowed by the use of expensive Pt and PtRu as electrocatalysts. Transition metal based Pt alloy catalysts have historically struggled for durability in acidic environments. Reduced graphene oxide (RGO) supported Pt alloy catalysts have gained significant interest recently due to improvements in catalyst–support interaction that lead to better durability and performance. In this report we investigate the performance and durability aspects of FePt supported on RGO towards oxygen reduction and methanol oxidation reactions. PXRD and TEM results show that the FePt nanoparticle size is in the range of 4–7 nm and TGA measurements show that the metal loading of the catalyst is ∼55%. Electrochemical measurements towards ORR reveal a significant improvement in activity and durability for FePtGO over commercial PtC and FePtC. The utilization of RGO as a support certainly increases the lifetime of transition metal–Pt alloys that are generally susceptible to durability issues under acidic environments in fuel cells.

Pt Diffusion Dynamics for the Formation Cr–Pt Core–Shell Nanoparticles

Layered core-shell bimetallic Cr-Pt nanoparticles were prepared by the formation and later reduction of an intermediate Pt-ion-containing supramolecular complex onto preformed Cr nanoparticles. The resultant nanoparticles were characterized by X-ray diffraction analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, and aberration-corrected scanning transmission electron microscopy. The results are consistent with the presence of Pt diffusion during or after bimetallic nanoparticle formation, which has resulted in a Pt/Cr-alloyed core and shell. We postulate that such Pt diffusion occurs by an electric-field-assisted process according to Cabrera-Mott theory and that it originates from the low work function of the preformed oxygen-defective Cr nanoparticles and the rather large electron affinity of Pt.

Pd nanoparticles supported on reduced graphene–E. coli hybrid with enhanced crystallinity in bacterial biomass

A novel method for simultaneous reduction of graphene oxide (GO) and palladium salt, Pd(II), using Escherichia coli (E. coli) in the separate presence of two different mild reducing agents (hydrogen and formate) is investigated to successfully produce reduced GO (rGO)-biomass/Pd hybrid material for potential use as an electrocatalyst. Transmission electron microscopy, X-ray diffraction, thermo-gravimetric analysis, X-ray photoelectron spectroscopy and Raman microscopy demonstrate the successful reduction of Pd(II), GO and the biomass, resulting in the formation of Pd nanoparticles (PdNPs) on an rGO–biomass hybrid. The distribution of the NPs was found to be dependent on the type of reducing agent. PdNPs formed on rGO sheets showed relatively uniform distribution and size control (2–5 nm), whereas PdNPs on the bacterial scaffold were larger (up to 10 nm in size). Raman spectroscopy studies suggest that the presence of Pd leads to oxygen reduction and increased crystallinity in the bacterial biomass. Previous studies have suggested the potential for a bacterially-supported Pd electrocatalyst in fuel cells and, independently, the suitability of rGO as a support for PdNPs. This study confirms the simultaneous bacterial reduction of Pd(II) and GO and the association between the bacterial cells and rGO. We suggest that the simultaneous presence of E. coli and mild reducing agent together with GO and Pd(II) creates an interactive and synergistic environment in a hybrid material to allow (a) better control of PdNP size and distribution both on the inside of the bacterial membrane and on the rGO sheets and (b) increased crystallinity of the bacterial biomass compared to systems with bacteria alone.

Carbon electrodes for energy storage: General discussion

Yury Gogotsi, Dirk Guldi, Richard McCreery, Chi-Chang Hu, Celine Merlet, Francois Beguin, Laurence Hardwick, Elzbieta Frackowiak, Julie Macpherson, Alexander Forse, George Zheng Chen, Katherine Holt, Robert Dryfe, Heisi Kurig, Surbhi Sharma, Patrick R. Unwin, Thomas Rabbow, Wanjing Yu, Fulian Qiu, Fernanda Juarez, Christopher Sole, Boris Dyatkin, Keith Stevenson, Yong Cao, Nico Cousens and Asa Noofeli

Nafion-stabilised bimetallic Pt–Cr nanoparticles as electrocatalysts for proton exchange membrane fuel cells (PEMFCs)

The current study investigated the unique combination of alloying (Pt with Cr) and Nafion stabilisation to reap the benefits of catalyst systems with enhanced catalytic activity and improved durability in PEMFCs.

Performance analysis of repairable system using GA and fuzzy Lambda-Tau methodology

Purpose – The purpose of this paper is to develop a new approach for computing various performance measures such as reliability, availability, MTBF, ENOF, etc. for any industrial system. Design/methodology/approach – Pulping system, the main functionary part of paper industry, is the subject of the study. The interactions among the working components are shown using Petri nets (PNs). Failure and repair rates are represented using triangular fuzzy numbers (TFNs), as they allow expert opinion, linguistic variables, operating conditions, uncertainty and imprecision in reliability information, to be incorporated into system model. The failure rates and repair times of all constituent components are obtained using genetic algorithms (GAs) and then various performance measures are computed using fuzzy Lambda-Tau methodology (FLTM). Findings – The proposed methodology provides a better understanding about the behavior of any repairable system through its graphical representation. Originality/value – A new approa...

Chemical Modification of Graphene Oxide by Nitrogenation: An X-ray Absorption and Emission Spectroscopy Study

Nitrogen-doped graphene oxides (GO:Nx) were synthesized by a partial reduction of graphene oxide (GO) using urea [CO(NH2)2]. Their electronic/bonding structures were investigated using X-ray absorption near-edge structure (XANES), valence-band photoemission spectroscopy (VB-PES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). During GO:Nx synthesis, different nitrogen-bonding species, such as pyrrolic/graphitic-nitrogen, were formed by replacing of oxygen-containing functional groups. At lower N-content (2.7 at%), pyrrolic-N, owing to surface and subsurface diffusion of C, N and NH is deduced from various X-ray spectroscopies. In contrast, at higher N-content (5.0 at%) graphitic nitrogen was formed in which each N-atom trigonally bonds to three distinct sp2-hybridized carbons with substitution of the N-atoms for C atoms in the graphite layer. Upon nitrogen substitution, the total density of state close to Fermi level is increased to raise the valence-band maximum, as revealed by VB-PES spectra, indicating an electron donation from nitrogen, molecular bonding C/N/O coordination or/and lattice structure reorganization in GO:Nx. The well-ordered chemical environments induced by nitrogen dopant are revealed by XANES and RIXS measurements.

Stochastic behaviour and performance analysis of an industrial system using GABLT technique

Stochastic behaviour of an industrial system will help to analyse the systems performance and to carry out design modifications to achieve the desired industrial goals. In the present study, genetic algorithms based Lambda-Tau, a hybridised technique is used to analyse the systems behaviour up to a desired degree of accuracy utilising imprecise data. Six reliability indices, namely, failure rate, repair time, mean time between failures, expected number of failures, availability and reliability of the system are used for systems behaviour analysis. A composite measure of these reliability indices as a performance index has been introduced in this paper to predict the systems performance at different preferences. The washing unit of a medium size paper mill has been considered to demonstrate the approach. The observed results show reduced uncertainty from traditional analysis and will be very helpful for plant personnel to improve the systems performance by adopting suitable maintenance strategies.

Role of surface contaminants, functionalities, defects and electronic structure: general discussion

Richard McCreery opened the discussion of the paper by Robert Dryfe: You stated that Ru(hexamine) shows a depression of the outer sphere ET rate, on graphene, possibly due to the proximity of its redox potential to the Dirac point. If so, then other redox systems with different Es should show an increasing kinetic trend as the potential moves from the Dirac point. Has anyone observed such a trend?