Wenfang Deng

Synthesis and oxygen reduction properties of three-dimensional sulfur-doped graphene networks.

Novel three-dimensional sulfur-doped graphene networks were synthesized using an ion-exchange/activation combination method using a 732-type sulfonic acid ion exchange resin as the carbon precursor, which showed high electrocatalytic activity, good stability and excellent methanol tolerance for four-electron oxygen reduction in alkaline solution.

Immobilization of enzymes at high load/activity by aqueous electrodeposition of enzyme-tethered chitosan for highly sensitive amperometric biosensing.

Electrodeposition has been so widely used to immobilize biomacromolecules, and it is always an important topic to increase the load and activity of the immobilized biomacromolecules. We report here on a new, simple and rather universal method for the highly efficient immobilization of enzymes by aqueous electrodeposition of enzyme-tethered chitosan (CS) for sensitive amperometric biosensing. Glucose oxidase (GOx) is chosen here to examine the proposed protocol in detail. GOx was crosslinked to CS with low-concentration glutaraldehyde (GA, 0.080 wt%), and the electroreduction of added H(2)O(2) increased the electrode-surface pH and triggered the electrodeposition of a GOx-GA-CS composite film. The GOx-GA-CS electrodeposition was monitored by an electrochemical quartz crystal microbalance and is theoretically discussed based on an electrogenerated base-to-acid titration model. The prepared first-generation enzyme electrode (CS-GA-GOx/Pt(nano)/Au) exhibits a current sensitivity as high as 102 microA mM(-1) cm(-2) at 0.70 V vs SCE, being 13 times that of the CS-GOx/Pt(nano)/Au prepared similarly but without the GOx-CS precrosslinking. UV-vis spectrophotometric determination of the GOx remains in the supernatant liquids after pH-induced CS precipitation suggested a high enzyme load in the GOx-GA-CS film, and amperometric measurements suggested a negligible decrease in the enzymatic activity of GOx after its reaction with the low-concentration GA. Also, the proposed protocol works well for the precrosslinking manner of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide/N-hydroxysulfosuccinimide activation, the water-electroreduction-triggered CS electrodeposition, the second-generation biosensing mode, a 5.0-microm-radius Pt ultramicroelectrode, and immobilization of alkaline phosphatase for phenyl phosphate biosensing. The proposed protocol of pretethering the target biomacromolecules to the electrodeposition precusor for immobilization of the biomacromolecule at high load/activity is recommended for wide applications.

Three-Dimensional Graphene Networks as a New Substrate for Immobilization of Laccase and Dopamine and Its Application in Glucose/O2 Biofuel Cell

We report here three-dimensional graphene networks (3D-GNs) as a novel substrate for the immobilization of laccase (Lac) and dopamine (DA) and its application in glucose/O2 biofuel cell. 3D-GNs were synthesized with an Ni(2+)-exchange/KOH activation combination method using a 732-type sulfonic acid ion-exchange resin as the carbon precursor. The 3D-GNs exhibited an interconnected network structure and a high specific surface area. DA was noncovalently functionalized on the surface of 3D-GNs with 3,4,9,10-perylene tetracarboxylic acid (PTCA) as a bridge and used as a novel immobilized mediating system for Lac-based bioelectrocatalytic reduction of oxygen. The 3D-GNs-PTCA-DA nanocomposite modified glassy carbon electrode (GCE) showed stable and well-defined redox current peaks for the catechol/o-quinone redox couple. Due to the mediated electron transfer by the 3D-GNs-PTCA-DA nanocomposite, the Nafion/Lac/3D-GNs-PTCA-DA/GCE exhibited high catalytic activity for oxygen reduction. The 3D-GNs are proven to be a better substrate for Lac and its mediator immobilization than 2D graphene nanosheets (2D-GNs) due to the interconnected network structure and high specific surface area of 3D-GNs. A glucose/O2 fuel cell using Nafion/Lac/3D-GNs-PTCA-DA/GCE as the cathode and Nafion/glucose oxidase/ferrocence/3D-GNs/GCE as the anode can output a maximum power density of 112 μW cm(-2) and a short-circuit current density of 0.96 mA cm(-2). This work may be helpful for exploiting the popular 3D-GNs as an efficient electrode material for many other biotechnology applications.

Facile fabrication of network film electrodes with ultrathin Au nanowires for nonenzymatic glucose sensing and glucose/O2 fuel cell.

We report here on the facile fabrication of network film electrodes with ultrathin Au nanowires (AuNWs) and their electrochemical applications for high-performance nonenzymatic glucose sensing and glucose/O2 fuel cell under physiological conditions (pH 7.4, containing 0.15M Cl(-)). AuNWs with an average diameter of ~7 or 2 nm were prepared and can self-assemble into robust network films on common electrodes. The network film electrode fabricated with 2-nm AuNWs exhibits high sensitivity (56.0 μA cm(-2)mM(-1)), low detection limit (20 μM), short response time (within 10s), excellent selectivity, and good storage stability for nonenzymatic glucose sensing. Glucose/O2 fuel cells were constructed using network film electrodes as the anode and commercial Pt/C catalyst modified glassy carbon electrode as cathode. The glucose/O2 fuel cell using 2-nm AuNWs as anode catalyst output a maximum power density of is 126 μW cm(-2), an open-circuit cell voltage of 0.425 V, and a short-circuit current density of 1.34 mA cm(-2), respectively. Due to the higher specific electroactive surface area of 2-nm AuNWs, the network film electrode fabricated with 2-nm AuNWs exhibited higher electrocatalytic activity toward glucose oxidation than the network film electrode fabricated with 7-nm AuNWs. The network film electrode exhibits high electrocatalytic activity toward glucose oxidation under physiological conditions, which is helpful for constructing implantable electronic devices.

Sulfur-doped porous carbon nanosheets as an advanced electrode material for supercapacitors

Direct carbonization and simultaneous chemical activation of a cobalt ion-impregnated sulfonic acid ion exchange resin is found to be an efficient approach to the large-scale synthesis of sulfur-doped porous carbon nanosheets (S-PCNS) for supercapacitors with high specific energy and excellent rate capability. The as-prepared S-PCNS showed a three-dimensional interconnected structure, high graphitization degree, high C/O atomic ratio (22.9 : 1), high-level sulfur doping (9.6 wt%), high specific surface area (2005 m2 g−1), and good porosity. The S-PCNS serving as an electrode material for supercapacitors exhibited a specific capacitance as high as 312 F g−1 at 0.5 A g−1, excellent rate capability (78% of capacitance retention at 50 A g−1), high energy density (11.0 W h kg−1 at 0.5 A g−1), and outstanding cycling stability (∼97% of its initial capacitance after 10 000 cycles at 2 A g−1) in 6.0 M aqueous KOH electrolyte. Due to the unique structure of S-PCNS, the specific capacitance of S-PCNS is higher than that of sulfur-doped activated carbon. The excellent capacitance performance coupled with the facile synthesis of S-PCNS indicates a potential electrode material for supercapacitors.

Highly Sensitive Glucose Biosensor Based on One-Pot Biochemical Preoxidation and Electropolymerization of 2,5-Dimercapto-1,3,4-thiadiazole in Glucose Oxidase-Containing Aqueous Suspension

A novel and high-performance biosensing platform was prepared on the basis of one-pot biochemical preoxidation and electropolymerization of monomer (BPEM) for high-load and high-activity immobilization of enzymes. As representative materials here, 2,5-dimercapto-1,3,4-thiadiazole (DMcT) was used as the monomer, glucose oxidase (GOx) was used as the model enzyme, and enzymatically generated H2O2 (EG-H2O2) in the presence of glucose was used as the preoxidant. In the BPEM protocol, glucose was added to a pH 7.0 phosphate buffer suspension containing ultrasonically dispersed DMcT and GOx, in order to enzymatically generate H2O2, which preoxidized DMcT to DMcT oligomers/polymer (DMcTO) and thus led to the formation of DMcTO-GOx composites with a great deal of GOx entrapped; the composites were then co-electrodeposited with poly(DMcT) on a Au electrode. For comparison, the enzyme immobilization was also conducted by a preoxidation-free conventional electropolymerization protocol (CEP), as well as a chemical preoxidation and electropolymerization of monomer (CPEM) protocol with externally added H2O2 (EA-H2O2) as the preoxidant. The glucose biosensors constructed by the BPEM and CPEM protocols exhibited detection sensitivities enhanced by 119 and 88 times, respectively, compared to that constructed by the CEP protocol, as well as limits of detection lowered by ca. 2 orders of magnitude. The higher sensitivity of the enzyme electrode prepared by the BPEM protocol compared to that prepared by the CPEM protocol is probably due to the improved proximity of biochemical preoxidation around the enzyme molecules and thus a larger enzyme load. The electrochemical quartz crystal microbalance technique was used to investigate various electrode modification processes, which also revealed that poly(DMcT) could be cathodically detached from the electrode surface, favorably enabling the electrochemical regeneration of the electrode substrate. The proposed BPEM strategy is recommended for wide biosensing and biocatalysis applications based on many other polymers/enzymes.

Co-, N-, and S-Tridoped Carbon Derived from Nitrogen- and Sulfur-Enriched Polymer and Cobalt Salt for Hydrogen Evolution Reaction

A series of cobalt and heteroatom (N and/or S) doped carbon materials were prepared and explored as electrocatalysts for hydrogen evolution reaction (HER). The most active catalyst is a Co-, N-, and S-tridoped carbon (CoNS-C), which was prepared through heat treatment of nitrogen- and sulfur-enriched poly(m-aminobenzenesulfonic acid) and cobalt(II) nitrate, followed by acid leaching. The presence of cobalt-heteroatom complexes in CoNS-C is confirmed and identified as highly active molecule catalytic centers for HER. The overpotential of CoNS-C is 180 mV at 10 mA cm(-2) in 0.5 M aqueous H2SO4. Besides the high HER activity, the CoNS-C also shows excellent durability and can be produced readily in large quantities. This work may have provided a new and simple route in the design and batch-synthesis of highly active and durable carbonaceous electrocatalysts for HER.

Facile Fabrication of Graphene‐Containing Foam as a High‐Performance Anode for Microbial Fuel Cells

Facile fabrication of novel three-dimensional anode materials to increase the bacterial loading capacity and improve substrate transport in microbial fuel cells (MFCs) is of great interest and importance. Herein, a novel graphene-containing foam (GCF) was fabricated easily by freeze-drying and pyrolysis of a graphene oxide-agarose gel. Owing to the involvement of graphene and stainless-steel mesh in the GCF, the GCF shows high electrical conductivity, enabling the GCF to be a conductive electrode for MFC applications. With the aid of agarose, the GCF electrode possesses a supermacroporous structure with pore sizes ranging from 100-200 μm and a high surface area, which greatly increase the bacterial loading capacity. Cell viability measurements indicate that the GCF possesses excellent biocompatibility. The MFC, equipped with a 0.4 mm-thick GCF anode, shows a maximum area power density of 786 mW m(-2) , which is 4.1 times that of a MFC equipped with a commercial carbon cloth anode. The simple fabrication route in combination with the outstanding electrochemical performance of the GCF indicates a promising anode for MFC applications.

A compartment-less nonenzymatic glucose–air fuel cell with nitrogen-doped mesoporous carbons and Au nanowires as catalysts

A compartment-less glucose–air fuel cell with nitrogen-doped mesoporous carbons and Au nanowires as cathodic and anodic catalysts, respectively, can output high and stable power density in physiological solution, indicating a promising candidate for potentially implantable electronic devices.

Three-dimensional graphene-like carbon frameworks as a new electrode material for electrochemical determination of small biomolecules.

Three-dimensional (3D) graphene-like carbon frameworks (3DGLCFs) were facilely prepared via copyrolysis of polyaniline and nickel nitrate powder, followed by acid etching. The as-prepared 3DGLCFs possess graphene-like network structure, high specific surface area, and high content nitrogen dopant. Because these features enable large electrochemically active surface area, rapid electron transfer, and fast transport of analytes to electrode surface, the 3DGLCFs modified glassy carbon electrode (GCE) shows current response much higher than commercial graphene (CG) modified GCE towards the oxidation of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The anodic peak separations at 3DGLCFs/GCE are 0.23V between AA and DA, 0.13V between DA and UA, and 0.36V between AA and UA. For the simultaneous electrochemical determination of AA, DA and UA using differential pulse voltammetry, the 3DGLCFs/GCE shows linear response ranges of 1.25×10(-5)-4×10(-4)M for AA, 5×10(-8)-1.0×10(-5)M for DA, and 5×10(-8)-1.5×10(-5)M for UA, with low detection limits of 2×10(-6)M for AA, 1×10(-8)M for DA, and 1×10(-8)M for UA. The 3DGLCFs/GCE was also applied for the measurement of human serum, exhibiting satisfactory recoveries.