Yee Seng Lim

In-situ electrochemically deposited polypyrrole nanoparticles incorporated reduced graphene oxide as an efficient counter electrode for platinum-free dye-sensitized solar cells

This paper reports a rapid and in-situ electrochemical polymerization method for the fabrication of polypyrrole nanoparticles incorporated reduced graphene oxide (rGO@PPy) nanocomposites on a ITO conducting glass and its application as a counter electrode for platinum-free dye-sensitized solar cell (DSSC). The scanning electron microscopic images show the uniform distribution of PPy nanoparticles with diameter ranges between 20 and 30 nm on the rGO sheets. The electrochemical studies reveal that the rGO@PPy has smaller charge transfer resistance and similar electrocatalytic activity as that of the standard Pt counter electrode for the I3−/I− redox reaction. The overall solar to electrical energy conversion efficiency of the DSSC with the rGO@PPy counter electrode is 2.21%, which is merely equal to the efficiency of DSSC with sputtered Pt counter electrode (2.19%). The excellent photovoltaic performance, rapid and simple fabrication method and low-cost of the rGO@PPy can be potentially exploited as a alternative counter electrode to the expensive Pt in DSSCs.

Preparation and characterization of polypyrrole/graphene nanocomposite films and their electrochemical performance

A one-step electrochemical process had been employed to synthesize nanocomposite films of polypyrrole/graphene (PPy/GR) by electrochemical polymerisation on indium tin oxide (ITO) from an aqueous solution containing pyrrole monomer, graphene oxide (GO) nanosheets and sodium p-toluenesulfonate (NapTS). The X-ray diffraction (XRD) patterns showed that the typical peak of GO at 9.9o was missing from the nanocomposite’s diffraction pattern, suggesting that the GO had been stripped off of its oxygenous groups after the reaction. We postulated that a nanocomposite film was produced through a layer-by-layer deposition based on field emission scanning electron microscope (FESEM) images. The Raman spectroscopy profiles exhibited that the D/G intensity ratio (ID/IG) of PPy was not altered by the inclusion of GO due to the low concentration of the material used. However, the concentration was sufficient to increase the specific capacitance of the nanocomposite by 20 times compared to that of pure PPy, reflecting a synergistic effect between PPy and GR, as analysed by a three-electrode electrochemical cell. The electrochemical performance of the nanocomposites was affected by varying the deposition parameters such as concentrations of pyrrole and GO, scan rate, deposition time and deposition potential.

Influence of particle size on performance of a nickel oxide nanoparticle-based supercapacitor

The influence of the particle size of an active material on its performance as a supercapacitor electrode was reported. Nickel oxide nanoparticles (NiO NPs) with a uniform particle size were synthesized via a facile sol–gel method, and various sizes of NiO NPs (8, 12, and 22 nm) were achieved by calcination at various temperatures (300, 400, and 500 °C). TEM observations and XRD analysis were used to determine the particle size of the NiO NPs. The field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images showed flake-like morphologies, which consisted of interconnected nanoparticles with a porous channel to facilitate the diffusion of the electrolyte. The NiO NPs with an average particle size of 8 nm gave the highest specific capacitance value of 549 F g−1 at a scan rate of 1 mV s−1 compared to the NiO NPs with average particle sizes of 12 and 22 nm. These results suggest that the particle size of the NiO nanostructure plays an important role because of the presence of a higher number of active sites for a faradaic reaction.

Graphene/polypyrrole-coated carbon nanofiber core–shell architecture electrode for electrochemical capacitors

Herein, we report a two-step electrospinning and potentiostatic electrodeposition method to fabricate electrodes with graphene/polypyrrole-coated carbon nanofiber core–shell architecture for supercapacitor applications. The electrospun carbon nanofiber core acts as an electrically conductive substrate that enables the incorporation of the graphene/polypyrrole shell. Constructing a porous and interconnected one-dimensional configuration with a carbon nanofiber core facilitates the maximum electrochemical utilization of the graphene/polypyrrole shell. The addition of graphene significantly decreases the charge transfer resistance of the electrode by reducing the distance for electron shuttling in the polypyrrole chains for rapid electrochemical redox reactions. As a consequence, the specific capacitance of the core–shell electrode was enhanced up to 386 F g−1 at 2 mV s−1. The enhanced conductivity and improved stability of the core–shell composite electrode is able to retain 84% of its initial capacitance value over 1000 charge/discharge cycles. The excellent electrochemical performance demonstrates that electrodes with a graphene/polypyrrole-coated carbon nanofiber core–shell architecture have great potential in electrochemical energy conversion and storage devices.

Electrodeposition of polypyrrole/reduced graphene oxide/iron oxide nanocomposite as supercapacitor electrode material

Polypyrrole (PPy) was reinforced with reduced graphene oxide (RGO) and iron oxide to achieve electrochemical stability and enhancement. The ternary nanocomposite film was prepared using a facile one-pot chronoamperometry approach, which is inexpensive and experimentally friendly. The field emission scanning electron microscopy (FESEM) image shows a layered morphology of the ternary nanocomposite film as opposed to the dendritic structure of PPy, suggesting hybridization of the three materials during electrodeposition. X-ray diffraction (XRD) profile shows the presence of Fe2O3 in the ternary nanocomposite. Cyclic voltammetry (CV) analysis illustrates enhanced current for the nanocomposite by twofold and fourfold compared to its binary (PPy/RGO) and individual (PPy) counterparts, respectively. The ternary nanocomposite film exhibited excellent specific capacitance retention even after 200 cycles of charge/discharge.

Catalyst-assisted electrochemical deposition of graphene decorated polypyrrole nanoparticles film for high-performance supercapacitor

A simple catalyst-assisted electrochemical deposition technique has been implemented to control the particle size of polypyrrole in the range of 5 to 10 nm embedded on graphene sheets, in which the nanocomposite will be used as a supercapacitor electrode material. The polypyrrole/graphene nanocomposite resulting from this approach maximizes the pseudocapacitive contribution of redox-active polypyrrole and electrical double layer capacitance (EDLC) contributed by individual graphene sheets. Specific capacitance, as high as 797.6 F g−1 is obtained when 1.0 mM of FeCl3 catalyst is added to the deposition solution, which is approximately four times higher than that of polypyrrole film and 2.6 times higher than that of polypyrrole/graphene nanocomposite in the absence of catalyst. This increase is attributed to the controlled particle size of polypyrrole growth on individual graphene sheets, which prevents the overlapping of graphene sheets. This gives rise to a highly open structure, which provides an easier access of electrolyte within the matrix of the nanocomposite film. A fabricated symmetric supercapacitor device yields a specific capacitance of 463.15 F g−1 and capacitance retention of 77.7% over 10 000 charge/discharge cycles at a current density of 1 A g−1. The nanocomposite serves as a promising electrode material for supercapacitors.

Hybrid silver nanoparticle/nanocluster-decorated polypyrrole for high-performance supercapacitors

In the present work, a composite electrode consisting of hybrid silver nanoparticle/nanocluster-decorated polypyrrole (PPy) demonstrates an enhanced specific capacitance of 414 F g−1 than that of the pure PPy electrode (273 F g−1). The enhanced specific capacitance was mainly attributed to the unique architecture and hybrid nanostructures of Ag. The Ag nanoparticles enhanced the electron hopping system of the PPy, effectively increasing the capacitance properties of the PPy. On the other hand, the Ag nanoclusters acted as spacers to prevent the restacking of PPy films, further extending the active sites for redox reactions, leading to improved specific capacitance. A symmetric supercapacitor device built from the hybrid Ag@PPy nanocomposite yielded a specific capacitance of 161 F g−1 per mass of one electrode and exhibited remarkable cycling stability of 98.9% capacitance retention over 1000 charge/discharge cycles. These excellent electrochemical performances show the promise of the hybrid Ag@PPy nanocomposite in energy storage devices.

Boosting the supercapacitive properties of polypyrrole with chitosan and hybrid silver nanoparticles/nanoclusters

We report a one-step route to hierarchical polypyrrole/chitosan decorated with hybrid Ag nanoparticles/nanoclusters (Ag@PPy/CS) via electrodeposition. The ternary nanocomposite electrode was applied as an electrode material for a supercapacitor. Experimental results showed that the ternary nanocomposite has a specific capacitance of 513 F g−1 at 0.2 A g−1, which was greatly improved from that of the PPy electrode (273 F g−1). The chitosan provided excellent hydrophilicity to the ternary nanocomposite, at the same time it controlled the growth of metallic Ag. The ultra-small Ag nanoparticles (1–2 nm) enhanced the electrical conductivity of the PPy while the Ag nanoclusters (30–80 nm) acted as spacers to prevent the restacking of the electrode films as well as contributing to the electrical conductivity. The as-assembled symmetric supercapacitor of the ternary nanocomposite delivered a specific capacitance of 183 F g−1 and outstanding cycling stability with 98.3% capacitance retention after 1000 charge/discharge cycles. Considering the facile preparation and moreover the exceptional electrochemical performance, the Ag@PPy/CS nanocomposite electrode could be well-suited for high-performance supercapacitors.