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Abstract Nanoflowers are highly beneficial structural features for improving catalysis on transitional metal-based materials with regarded to the electrocatalytic activity, cost effectiveness and durability. In this study, the manganese dioxide nanoflowers onto sulfonated graphene sheets (denoted as δ-MnO 2 /SGS) is synthesized by a simple hydrothermal method for bifunctional electrocatalytic application in oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). The formation of δ-MnO 2 nanoflowers onto SGS plays a crucial role in intrinsic catalytic activity, resulting in an impressive enhancement in both ORR and HER in alkaline electrolyte. The morphological features and X-ray analysis are shown the successful sulfonation and the Mn presents in oxide form with δ-type crystallographic structure. The growth reaction mechanism of δ-MnO 2 nanoflowers is proposed in alkaline media. The robust electrocatalysis is inherited from the cave among crystalline lego-block-like petals at microscale level and the large interlayer spacing at nanoscale level of δ-MnO 2 nanoflowers with significant electrical conductivity. The δ-MnO 2 /SGS catalyst exhibits nearly same ORR and HER activity in terms of current density with electron transfer and final current density with Tafel slope, respectively, compare to the benchmark Pt/C. [ABSTRACT FROM AUTHOR]

Still it's a main challenge to design of highly efficient electrocatalysts to reduce the high overpotential of the oxygen reduction reaction (ORR). The 1 dimensional (1D) palladium nanonetworks (Pd-Net) can be a promising alternative to platinum (Pt)-based electrocatalyst for ORR. In this study, the Pd-Net electrocatalysts have been synthesized via a simple wet-chemical method with the assistance of cetyltrimethylammonium bromide (CTAB) and zinc precursor. Further investigation indicates that the thickness of Pd-Net can be regulated by simply changing the molar ratio of CTAB and the 5 ± 0.1 nm is proven as an efficient ORR electrocatalyst without any support material. The freestanding 1D Pd-Net has shown 2.2 and 3.6-fold higher electrochemical surface area than that of commercially available Pt/C and homemade Pd nanoparticles (PdNPs) catalysts, respectively. As a result, it provides a higher density of ORR active sites and facilitated the electron transport. The Pd-Net catalyst shows 2.1 and 4.1 times higher mass activity and 1.3 and 3.1 higher specific activity at 0.85 V (vs. RHE) with better ORR kinetics than that of Pt/C and PdNPs, respectively. Additionally, the Pd-Net catalyst has been demonstrated a significant tolerance to the anodic fuels (i.e. methanol) and enhanced durability than the Pt/C and PdNPs catalysts for ORR. [ABSTRACT FROM AUTHOR]

1,5-diaminonaphthalene and ultrasmall palladium nanoparticles (PdNPs) embedded electrochemically reduced graphene oxide (denoted as ERGO-DAN-Pd) was successfully synthesized and employed as a cathode catalyst for enhanced oxygen reduction reaction (ORR) in direct alkaline fuel cells (DAFCs). The physical properties of ERGO-DAN-Pd were investigated using several instrumental methods. The morphological characterizations demonstrate that the ultrasmall PdNPs were homogeneously dispersed on the ERGO-DAN film. X-ray analysis confirmed the successful covalent functionalization of graphene sheets with DAN. The electrocatalytic activity of ERGO-DAN-Pd towards ORR was excellent compared to other electrodes in 0.1 M KOH electrolyte. Particularly, it showed 1.8 and 2.7 magnitude higher mass activity with large specific activity compared to 20 wt.% Pt/C and nonfunctionalized ERGO/Pd, respectively. Moreover, the reaction kinetic parameters confirmed that the ORR at ERGO-DAN-Pd catalyst was followed by a 4e − process with faster electron transfer rate per O 2 with better stability and fuel selectivity than state-of-the-are Pt/C for DAFCs application. [ABSTRACT FROM AUTHOR]

A porous graphene catalyst was prepared with 1,4-diaminobutane (DAB) through amide functionalization and was used as a metal-free electrocatalyst for oxygen reduction reaction (ORR) in alkaline fuel cells. DAB was used as a junction among functionalized graphene layers to impart electrocatalytic activity for the ORR resultant from the interlayer charge transfer. The successful amidation and subsequent reduction in the process of catalyst preparation were confirmed using X-ray photoelectron spectroscopy. A hierarchical porous structure was also confirmed through the surface morphological analysis. The Brunauer–Emmett–Teller specific surface area and thermal stability increased by 2.6- and 1.5-fold, respectively, after successful amide functionalization. The as-prepared catalyst was proved an efficient metal-free electrocatalyst with better electrocatalytic activity, stability, and tolerance to the crossover effect than commercially available Pt/C for ORR by a direct four-electron involved pathway. These results indicate that the amide-functionalized graphene metal-free catalyst reported in this study is a promising alternative to traditional noble metal-based ORR catalysts. [ABSTRACT FROM AUTHOR]

Various carbon chain linkages were introduced during the process of synthesizing silver-nanoparticles (AgNPs)-decorated graphene nanocomposites [referred to as GO- C x -Ag where, HS-(CH 2 ) x -SH = C x and x = 0, 2, or 4] to evaluate antibacterial properties. The nano-structures of GO- C x -Ag were characterized using TEM and XPS, revealing that GO- C 2 -Ag comprises well-dispersed and smaller AgNPs anchored onto the surface of graphene sheets than the GO- C 0 -Ag and GO- C 4 -Ag. The antibacterial activities of those nanocomposites were assessed using paper-disk diffusion and minimal inhibitory concentration (MIC) methods against Gram-negative and Gram-positive bacteria. The results showed that carbon chain linkers enhanced the antibacterial activity against Gram-negative Salmonella typhimurium and Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus . In particular, GO- C 2 -Ag showed higher antibacterial activity than GO- C 0 -Ag and GO- C 4 -Ag due to nearly eight times higher reactive oxygen species (ROS) formation which determined by fluorescence-based ROS detection experiment. Also, LC-inductively coupled plasma mass spectrometer (LC-ICP-MS) demonstrated that the Ag release from GO- C x -Ag was insignificant (0.03%). However, the higher ROS formation from GO- C 2 -Ag was facilitated by higher dispersion, smaller size, and well attachment of AgNPs with AgO species onto graphene sheets. These results suggest that the medium length carbon chain linkers in between Ag and GO can be utilized to improve antibacterial activity. [ABSTRACT FROM AUTHOR]

In this study, an electrochemical sensor for hydrazine oxidation was synthesized using graphene functionalized by benzylamine molecules (both para and meta) and subsequently palladium (denoted as rGO-P x DA-Pd and rGO-M x DA-Pd, respectively). The synthesized materials were characterized using X-ray photon spectroscopy (XPS) and transmission electron microscopy (TEM). The TEM study suggested that the PdNPs was well dispersed on the surface of the rGO-P x DA-Pd rather than on the rGO-M x DA-Pd. The XPS confirm the benzylamine functionalization and Pd attachment. These materials were investigated using several electrochemical techniques including cyclic voltammetry, differential pulse voltammetry and chronoamperometry in 0.05 M phosphate buffer solution at pH 7.4. From these results, it is confirm that the rGO-P x DA-Pd is better catalyst than rGO-M x DA-Pd due to resonance, steric and aggregation effects. The superior hydrazine sensor, rGO-P x DA-Pd, appeared to exhibit a good linear range of 1 × 10 −6 M–7.4 × 10 −3 M and a detection limit of ( S/N = 3) 1.7 × 10 −7 M with a fast response time of 3 s. The selectivity of the rGO-P x DA-Pd for hydrazine was studied for a number of ions such as, Na + , Cl − , Ca +2 , Mg +2 , and SO 4 −2 and biomolecules such as glucose and ascorbic acid. [ABSTRACT FROM AUTHOR]

Abstract: Oligothiophene (nTP, n =1,2,3) has been used as the reductant for the first time in the preparation of graphene by the reduction of graphene oxide (GO). A simple single-step chemical approach has been developed to reduce and/or functionalize GO with nTP. The reaction takes place at room temperature under stirring of a suspension of GO and nTP in MeCN. The nTP has been grafted onto the surface of GO by reacting epoxy groups together with the reduced graphene oxide (rGO). It was observed that increasing the thiophene ring (hereafter, thiophene is referred to as TP; 2,2′ bithiophene as 2TP; and 2,2′:5′,2″ terthiophene as 3TP) can enhance the reduction reaction. All instrumental experiments have confirmed that nTP not only covalently bonded to the GO but also partly restored the conjugate structure of GO, as a reducing agent. The resultant rGO with 3TP (rGO3TP) has been demonstrated to show remarkable electrocatalytic activity toward oxygen reduction reaction (ORR) compared to typical rGO. The observed ORR electrocatalytic activity induced by the intermolecular charge-transfer provides a general approach to various carbon-based metal-free ORR catalysts. [Copyright &y& Elsevier]

Abstract: A carbon nanostructure has fabricated from covalently grafted platinum (Pt) to multi walled carbon nanotube (MWCNT) with the assistance of sulfur atom on the MWCNT''s sidewall, MWCNT–S–Pt. The MWCNT–S–Pt displays an excellent electrocatalytic performance for oxygen reduction reaction (ORR) than that of an unbonded Pt to MWCNT, MWCNT/Pt. Here we describe a comparative study of the ORR on two MWCNT-supported Pt-based catalysts in aqueous acidic electrolyte. Both MWCNT–S–Pt and MWCNT/Pt catalysts have the compositions of 1.03 and 2.18at% Pt, respectively. For the characterization, the bonding features have confirmed by the X-ray photoelectron spectroscopic (XPS) and electron microscopy have used to determine the size and shape as well as the distribution of the particle on both catalysts. Electrochemical measurements have performed using the cyclic voltammetry and hydrodynamic voltammetry methods in 0.1moll−1 HClO4 solution. Kinetic analysis in comparison to unbonded MWCNT/Pt a significant enhancement for the covalently bonded MWCNT–S–Pt has been found. The MWCNT/Pt is unstable at electrode potentials for long term use than that of MWCNT–S–Pt. Ring-current collection measurements for peroxide indicate MWCNT–S–Pt catalyst has a less peroxide yield. [Copyright &y& Elsevier]

Abstract: Cathodic dioxygen (O2) reduction was performed at a modified glassy carbon electrode (GCE) by single-walled carbon nanotubes (SWCNT)/Nafion® (NF) film with cobalt (II) tetra (2-amino-phenyl) porphyrin (CoTAPP) and palladium (Pd) nanoparticles incorporated and employed as doping agents. Both the electrochemical behavior of SWCNT with a P(CoTAPP)–Pd nanoparticle matrix and the electrocatalytic reduction of O2 were investigated using transmission electron microscopy (TEM), cyclic voltammetry (CV) and rotating ring-disk electrode (RRDE) techniques in 0.1moll−1 H2SO4 aqueous solutions. The electrocatalytic reduction of O2 at the SWCNT/NF/P(CoTAPP)–Pd composite film established a pathway of four-electron transfer reductions into H2O. Hydrodynamic voltammetry revealed that the modified electrode was catalyzed effectively by the four-electron transferred reduction of dioxygen into H2O with minimal generation of H2O2. The SWCNT/NF/P(CoTAPP)–Pd composite film showed a highly efficient electrocatalytic performance. P(CoTAPP)–Pd was an effective mediator for the reduction of dioxygen and was responsible for the enhanced catalytic activity. [Copyright &y& Elsevier]

Schematic of preparation of all the catalysts. • Novel fabrication method for superior ORR electrocatalysis is developed by surface functionalization of graphene. • AGO was used to increase the amidation reaction sites where AT attaches via covalent attachment. • ArGO-AT-120 catalyst showed enhanced electrocatalytic activity for ORR compared to Pt/C catalysts. • Higher degree of amidation is important factor for improving ORR performance and stability of ArGO-AT-120 catalyst. Introducing nitrogen atoms is an effective approach to generate graphene-based electrode materials for energy conversion-electrochemical devices. Herein we propose a novel strategy to covalently functionalize the surface of graphene using 4-amino-4H-1,2,4-triazole (AT) and acidified graphene oxide (AGO) to convert the epoxy group to a carboxyl group in the latter to increase the number of amidation sites via a wet chemical method. It has been proven that, compared to graphene oxide (GO), AGO can be covalently functionalized with AT more efficiently due to the selective amidation between the carboxyl and amine groups. Covalent functionalization incorporates nitrogen and creates pores, which increase the number of oxygen reduction reaction (ORR) sites and prevents π-π stacking of graphene sheets. The prepared catalyst exhibits superior ORR activity, in terms of current density, electron transfer and stability compared to Pt/C. It has found that the superior ORR performance of the prepared catalyst is due to the higher degree of amidation that leads to the creation of abundant ORR active N-sites at nanoscale level and a porous structure at microscale level, which enhances O 2 mass transportation to the active sites and improve tolerance against methanol during ORR. [ABSTRACT FROM AUTHOR]

• Ni nanoflakes on 4-Amino-4H-1,2,4-triazole functionalized graphene through amidation. • HER performance on prepared catalyst in both alkaline and acidic media. • To gain current density at η j 10 it requires 48 and 58 mV overpotential, respectively. The development of highly active and stable non-noble-metal-based electrocatalysts for the sustainable hydrogen production by hydrogen evolution reaction (HER) in water-splitting cells is now vitally needed. Herein, we design a facile strategy to fabricate the nickel nanoflakes onto 4-Amino-4H-1,2,4-triazole (ATz) functionalized graphene surface through the amidation reaction (Ni/ATz-G) via wet-chemical method. For the development of nickel nanoflakes, nitrogen atoms of ATz which grafted onto graphene sheets are coordinated to nickel atoms initially, and then the formation of nickel nanoflakes is proceeded via epitaxial film growth. Several instrumental characterizations confirm that the nickel nanoflakes are in the Ni(OH) 2 form. The as prepared catalyst exhibits remarkable electrocatalytic activity towards the HER while it requires only 48 and 58 mV overpotential to gain current density at 10 mA cm−2 in alkaline and acidic media, respectively. Also it shows improved kinetics and higher stability in both media which makes it a promising catalyst for practical application. The coordination in between nitrogen and nickel nanoflakes and the amidation between ATz and graphene (Ni-N-C system) play a key role in not only intrinsic catalytic activity for HER but also high stability through better grafting of nickel nanoflakes active sites onto the graphene. [ABSTRACT FROM AUTHOR]

The Fe–N–C active site containing non-precious metal catalysts (NPMCs) as the substitute to platinum-based catalysts are highly desired for oxygen reduction reaction (ORR) but it's a huge challenge to achieve such a high-performance and long term stabile one. In this study, the iron nanoparticles-implanted polyaniline ( Fe N P s @PANI) metal–organic–frameworks (MOFs) on reduced graphene oxide (rGO) has been synthesized through metal-ligand strategy via a simple chemical process. Strong interaction has been observed between Fe N P s and nitrogen in PANI suggesting abundant Fe–N–C active sites in the Fe N P s @PANI/rGO catalyst. Owing to the Fe–N–C active sites with less amount of oxygenated carbon in the molecular scale and mesoporous channels with the synergy of PANI and graphene in microscale, the Fe N P s @PANI/rGO catalyst exhibits excellent catalytic activity and stability than the benchmark Pt/C catalyst towards ORR in respect to the onset potential and half-wave potential. Very importantly, the Fe–N–C active sites in Fe N P s @PANI are comparatively better active against SCN− and methanol poisoning than bare Fe N P s /rGO during ORR. Image 1 • Fe NPs @PANI MOFs on rGO was prepared through metal-ligand strategy. • Abundant Fe–N–C active sites with strong interaction in between Fe N P s and N. • Superior ORR catalytic activity and stability than the Pt/C catalyst E onset and E 1/2. • Fe–N–C is better active against SCN− and methanol poisoning due to surface coating. [ABSTRACT FROM AUTHOR]

Orange II, an azo dye, is sometimes illegally used as a red dye in food products despite its adverse health effects if consumed. Therefore, the determination of low concentrations of Orange II is an important target. An Orange II sensor was prepared using electrochemically reduced graphene oxide grafted with 5-amino-1,3,4-thiadiazole-2-thiol-Pt nanoparticles (denoted as ERGO-ATDT-Pt) onto a glassy carbon electrode (GCE) and investigated for Orange II detection in 0.1 M acetate buffer solution (ABS at pH 4.5) with prominent reversible redox peaks. A wide linear range of 1 × 10 − 8 –6 × 10 − 7 M with a low detection limit of 3.4 × 10 − 10 M ( s/n = 3) was found for Orange II detection. This developed ERGO-ATDT-Pt/GCE sensor showed good selectivity, excellent stability and better response to the real sample analysis with excellent recovery. [ABSTRACT FROM AUTHOR]

Reported herein are the synthesis of graphene-derivative and its application for the electrochemical detection of dopamine (DA). Graphene oxide–ferulic acid (GO–FA) was formed from the condensation reaction of GO and FA. The GO–FA was characterized via Fourier transform infrared spectroscopy (FT-IR), ultraviolet–visible spectroscopy (UV–vis spectroscopy) and scanning electron microscopy (SEM). The electrochemical reduction of GO–FA (ERGO–FA) can be employed for the electrochemical detection of DA. The electrochemical detection of dopamine was verified through the cyclic voltammetry (CV), differential pulse voltammetry (DPV) in the presence of AA at a high concentration and amperometric techniques, in a 0.1 M citrate buffer solution (pH 6.0). The influence on the pH (3.99–9.02) of the 0.1 M citrate buffer solution of ERGO–FA/GCE on the oxidation of DA was determined, and interference experiments using interfering substances such as serotonin (5-HT), glucose, ascorbic acid (AA), H 2 O 2 and uric acid (UA) were conducted. The detection limit of DA was found to be 0.19 μM (where s/n = 3), and the linear ranges were 0.6–1000 μM at the ERGO–FA modified glassy carbon electrode (GCE). [ABSTRACT FROM AUTHOR]