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Ion-selective membranes with high efficiency and long-term cycling stability at high current densities are critical for the widespread application of vanadium redox flow batteries (VRFBs). In order...

Novel nitrogen-functionalized multimodal porous graphite felt (GF) electrodes for all-vanadium redox flow batteries (VRFB) have been developed using a simple binder-free fabrication method. We synergistically combined a polymer of intrinsic microporosity (PIM), as a carbon and nitrogen precursor, with vapor-induced phase separation. The GF with a carbonized PIM skin layer showed a high surface area and multimodal pore architecture featuring interconnected micro-, meso-, and macropores. The enhanced electrochemical reactivity and wettability , and excellent electronic conductivity of the prepared electrodes successfully improved the overall kinetics of the redox reactions of the vanadium ion species by providing highly active catalytic sites and efficient ion and electron transport pathways. This resulted in the outstanding performance of VRFB single cells using this material as electrodes.

We develop a novel approach to improve the robustness of the interface between the hydrocarbon (HC) membrane and the perfluorosulfonic acid (PFSA) ionomer-based catalyst layer (CL) in membrane electrode assemblies (MEAs). This approach involves the creation of a gradient-composition interfacial bonding layer, in which the HC and PFSA contents are gradually varied along the thickness direction. The layer is fabricated using a simple spray-coating method, in which HC and PFSA ionomer mixtures with different compositions are sprayed stepwise onto both sides of the HC membrane surface. The interfacial structure developed in this process minimizes the chemical incompatibility between the HC and PFSA polymers. Owing to the tightly bound sublayers resulting from the intertwined HC and PFSA microdomains, the gradient-composition bonding layer provides a significantly improved interfacial adhesion strength (14 times higher than that of the pristine membrane without bonding layer) between the HC membrane and the PFSA-based CL. Finally, the fabricated MEA exhibits a >433% higher durability in humidity cycling tests compared with the pristine MEA without interfacial bonding layer, together with a better retention of its initial performance.

Novel nitrogen-doped CNT-containing graphite felt (N-CNT/GF) hybrid electrodes with high electrocatalytic activity were developed for all-vanadium redox flow batteries (VRFBs). A simple, effective preparation method for N-CNT/GFs using metal (Fe, Co, and Ni) phthalocyanines as the carbon and nitrogen precursor is presented. We found that different metal precursors generated different densities of N-CNTs on the surface of the GFs due to the various interactions of the metals (Fe, Co, Ni) with the carbon precursor during carbonization. Higher density and longer N-CNTs were obtained for N-CNT/GF (Fe), which gave rise to a higher N-doping concentration, enhanced wettability and conductivity, and improved electrochemical reactivity. When used as an electrode in a VRFB single cell, this material showed outstanding performance with an increase in energy efficiency of more than 20% compared to pure GF at a high current density (150 mA/cm2).

Anodic water splitting is driven by hydroxide (OH–) adsorption on the catalyst surface and consequent O2 desorption. In this work, various heteroatoms (S/N/B/P) with different electronegativities and oxophilicities are introduced to alter the catalytic activity of reduced graphene oxide (RGO) as a catalyst for the oxygen evolution reaction (OER). It is found that, surprisingly, S-doped RGO outperforms the other RGOs doped with more electropositive or electronegative and more oxophilic heteroatoms, and this effect becomes more prominent after Fe treatment of the respective catalysts. Herein, we evaluate the OER activity of a series of Fe-treated mono-heteroatom (S/N/B/P)-doped RGO (Fe-X-G) catalysts, among which interestingly S-doped RGO catalyst treated with Fe (Fe-S-G) is found to show better OER activity than the well-known active Fe-N-C catalyst, demonstrating the best activity among all of the prepared catalysts, close to that of the state of the art IrO2/C catalyst, along with pronounced long-term st...

Poly(p-phenylene)-based ionomers with remarkable durability and rate capability for use in vanadium redox flow batteries (VRFBs) are reported. The family of synthesized ionomers, sPBPSP-z, exhibited not only well-developed phase separation between hydrophilic domains and hydrophobic domains but also well-connected hydrophilic channels, resulting in enhanced proton conductivities and excellent dimensional stabilities. sPBPSP-8, which has an ion exchange capacity of 1.83 meq g−1, showed high discharge capacity retention and superior efficiencies over 100 cycles at a current density of 50 mA cm−2. In addition, the sPBPSP-8 ionomer exhibited stable performance at various current densities (50–180 mA cm−2) and retained high efficiencies at high current densities. Furthermore, this material exhibited superior chemical stability under oxidizing conditions, excellent capacity retention, and high efficiencies during long-term VRFB operation (1000 cycles). These results indicate that the sPBPSP-8 membrane is a superb material for VRFB applications.

Bio-inspired non-precious-metal catalysts based on iron and cobalt porphyrins are promising alternatives to replace costly platinum-based catalysts for oxygen reduction reaction (ORR) in fuel cells. However, the exact nature of the active sites is still not clearly understood, and further optimization design is needed for practical applications. Here, we report a rational catalyst design process by combining density functional theory (DFT) calculations and experimental validations. Two sets of square-planar (MNxC4−x) and square-pyramid (MNxC5−x) active centers (M=Mn, Fe, Co, Ni) incorporated in graphene were examined using DFT. Fe-N5 and Co-N4 sites were identified theoretically to have the best performance in fuel cells, while Ni-NxC4−x sites catalyze the most H2O2 byproduct. Graphene samples with well-dispersed incorporations of metals were synthesized, and the following electrochemical measurements show an excellent agreement with the theoretical predictions, indicating that a successful design framework and systematic understanding toward the catalytic nature of these materials are established.

There are many studies portraying iron (Fe) and nitrogen (N)-functionalzed carbon as an electrocatalyst along with possible elucidation of catalytically active sites. Despite continuous controversial debate on the active sites/species, the presence of N is believed to be undeniably needed for the efficient catalysis, whereas the necessity and role of Fe are still debated. To clearly understand the role of Fe in Fe and N-functionalized electrocatalyst, N-doped hollow mesoporous shell carbon (N-HMSC) is prepared as a uniform model electrocatalyst by a simple template nanocasting using Fe phthalocyanine (FePc) as a single precursor for carbon, N, and Fe. It is found that the presence of Fe in N-HMSC leads to the efficient graphitization of N-HMSC structure, which can be beneficial for electrocatalytic oxygen evolution reaction (OER). Interestingly, it is observed that Fe is a must for the preparation of high efficient catalyst, but may not be necessary for OER.

A new facile template-free method is presented to synthesize Fe-treated N-doped carbon (Fe/N–C) catalysts for oxygen reduction reaction (ORR) by employing a synthesis protocol of pyrolysis–leaching–stabilization (PLS) sequence of polypyrrole in the presence of ferric source, which serves dual purposes of an oxidant for pyrrole polymerization and an iron source. Each step in the PLS sequence is assessed in detail in terms of the related structural properties of the resulting carbon catalysts, and their effects on ORR activities are elaborated to confirm the validity of the current synthesis protocol. It is found that the as-prepared carbon catalyst exhibits outstanding high catalytic activity in both alkaline and acidic conditions. The carbon catalyst prepared at a pyrolysis temperature of 900 °C (FePPyC-900) shows remarkably high ORR activity with onset potential of 0.96 V (vs. RHE), which is similar to that of Pt/C, whereas the half-wave potential (E1/2) of FePPyC-900 is 0.877 V, more positive than that of Pt/C at the same catalyst loading amount under alkaline conditions. Furthermore, the FePPyC-900 catalyst also illustrates exceptionally high activity under acidic conditions with onset and half-wave potentials of 0.814 and 0.740 V, respectively, which are almost comparable to those (0.817 and 0.709 V) of the state-of-the-art Pt/C catalyst, which is rarely observed for non-Pt-based carbon catalysts. In addition, the FePPyC-900 catalyst displays much better stability and methanol tolerance than the Pt/C and exhibits a four electron transfer pathway under both alkaline and acidic conditions. Such extraordinary high ORR activity and stability of the FePPyC-samples can be attributed to the implementation of extra stabilization step in addition to conventional sample preparation steps of pyrolysis and subsequent leaching in current PLS synthesis protocol as well as to the use of highly conducting PPy as a single precursor of carbon and nitrogen in the presence of Fe.

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 50 mV negative in acidic medium, whereas it is 50 mV 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.

It has been considered that the presence of Fe-N in the carbon network helps to enhance oxygen reduction reaction (ORR) activity of the carbon. In this study, N-doped platelet ordered mesoporous carbon is prepared using Fe-phthalocyanine as a single precursor for nitrogen, iron and carbon sources. We show that the physical presence of Fe is not necessary to enhance the ORR activity of N-doped carbon, although Fe is required to create more active sites and to increase the electrical conductivity in the carbon framework.

A simple binder-free synthesis approach of just rubbing nitrogen-doped reduced graphene oxide (N-RGO) powder on a mechanically grinded Cu-foil substrate with a rough surface is proposed for a lithium ion battery (LIB). The nitrogen content of N-RGO is found to be 2.1 wt%. The binder-free N-RGO electrode shows excellent reversible capacity of 551 mA h g−1 as compared to 433 mA h g−1 of the binder-added N-RGO electrode at a current density of 50 mA g−1 after 100 cycles. The process is not only highly reproducible and successful, but also results in high LIB performance, proposing easy scaling-up of such an electrode for commercial application.

In this study, novel nitrogen (N)-doped hollow core-mesoporous shell carbon (N-HCMSC) capsules with high surface area are synthesized by simple three-step processes and explored as metal-free counter electrode (CE) in comparison with undoped HCMSC in dye-sensitized solar cells (DSSCs). It is shown that N-HCMSC significantly improves the catalytic activity toward the reduction of both Co(bpy)33+ and I3– due to much lower charge-transfer resistance (RCT) at the CE/electrolyte interface. This is attributed not only to excellent surface properties including three-dimensionally interconnected hierarchical marco/mesoporosity with high surface area but also to N doping in N-HCMSC framework. Among various N species in the N-HCMSC framework, pyridinic and quaternary N species are considered to contribute significantly to the catalytic activity. In addition, N-HCMSC CE exhibits much better electrochemical stability than Pt CE toward both Co(bpy)32+/3+ and I–/I3– redox reactions. The N-HCMSC enhances the cell effici...

Platinum-free electrocatalysts especially, various heteroatom-doped carbon nanostructures have attracted particular attraction as plausible solution for commercializing fuel cell technology. In this direction, novel phosphorus-doped platelet ordered mesoporous carbon (P-pOMC) is developed for the first time as metal-free electrocatalyst for alkaline oxygen reduction reaction. The P-pOMC is synthesized by nanocasting method using platelet ordered mesoporous silica as template. Various characterizations reveal that the P-pOMC materials have covalently bound P atoms with carbon framework for facilitation of oxygen reduction reaction (ORR) and also have very high surface area with uniform distribution of short mesoporous channels for unhindered mass transfer. Combination of P doping and excellent surface properties empowers the newly-developed P-pOMC catalyst to show high ORR activity nearly equal to that of state of the art Pt catalyst along with superior long-term stability and excellent methanol tolerance.

A simple, efficient and scalable approach is developed for synthesis of Vulcan XC-72(carbon)-supported Pt nanoparticles (NPs) that combines homogeneous deposition (HD) of Pt complex species through reaction with OH - ions generated by in situ hydrolysis of urea and subsequent reduction by reducing species generated from radiolysis of water by γ-rays. This method not only avoids addition of any commonly used reducing agent, but also offers more uniform homogeneous dispersion of Pt NPs with much smaller particle size. Thus, when used as a cathode catalyst for proton exchange membrane fuel cell, the synthesized carbon-supported Pt NPs demonstrate excellent oxygen reduction electro–catalytic activity, higher Pt utilization efficiency, and considerably improved fuel cell polarization performance compared to those of Pt catalysts prepared with other synthesis strategies such as conventional NaBH 4 reduction and HD-ethylene glycol method as well as commercial Pt catalyst. The combined HD-γ-irradiation strategy is found to be simple, reproducible and efficient with mild synthesis condition and in particular, holds great promises for large scale production of highly efficient Pt-based catalysts for fuel cells.

Rod-shaped ordered mesoporous carbons (OMCs) with different lengths, prepared by replication method using the corresponding size-tunable SBA-15 silicas with the same rodlike morphology as templates, are explored as anode material for Li-ion battery. All of the as-synthesized OMCs exhibit much higher Li storage capacity and better cyclability along with comparable rate capability as compared with commercial graphite. Particularly, the OMC-3 with the shortest length demonstrates the highest reversible discharge capacity of 1012 mAh g(-1) at 100 mA g(-1) and better cyclability with 86.6% retention of initial capacity after 100 cycles. Although the Coulombic efficiencies of all the OMCs are relatively low at the beginning, they improve promptly and after 10 cycles reach the level comparable to commercial graphite. Based on their specific capacity, cycle efficiency, and rate capability, the OMC-3 outperforms considerably its carbon peers, OMC-1 and OMC-2 with longer length. This behavior is mainly attributed to higher specific surface area, which provides more active sites for Li adsorption and storage along with the larger mesopore volume and shorter mesopore channels, which facilitate fast Li ion diffusion and electrolyte transport. The enhancement in reversible Li storage performance with decrease in the channel length is also supported by low solid electrolyte interphase resistance, contact resistance, and Warburg impedance in electrochemical impedance spectroscopy.

Platinum counter electrodes in DSSC are generally prepared by thermal reduction method. Poor control over Pt particle size, agglomeration and bad adhesion to the transparent conducting substrate, are some of the shortcomings affecting overall efficiency of the cell. In order to achieve better dispersion and control over the particle size, we explored direct deposition of metal nanoparticles (NPs) from their precursor solution onto the FTO glass substrate by using a simple and effective urea-assisted homogenous deposition (HD) method. This method works at substantially lower temperature for hydrolysis of urea and uses mild reducing agent, ethylene glycol (EG), giving better control over particle size along with better adhesion and negligible agglomeration compared to the thermal reduction method. DSSC prepared from such Pt counter electrode exhibited much enhanced photovoltaic performance compared to ones prepared by thermal and EG reduction alone, with better light-to-electricity conversion efficiency of 9.34% under one sun illumination. This excellent conversion efficiency is attributed to the uniform dispersion and smaller size of the Pt NPs prepared by the novel, combined urea-assisted HD–EG synthesis method.

Phosphorus-doped ordered mesoporous carbons (POMCs) with different lengths were synthesized using a metal-free nanocasting method of SBA-15 mesoporous silica with different sizes as template and triphenylphosphine and phenol as phosphorus and carbon sources, respectively. The resultant POMC with a small amount of P doping is demonstrated as a metal-free electrode with excellent electrocatalytic activity for oxygen reduction reaction (ORR), coupled with much enhanced stability and alcohol tolerance compared to those of platinum via four-electron pathway in alkaline medium. Interestingly, the POMC with short channel length is found to have superior electrochemical performances compared to those with longer sizes.

A simple and efficient approach has been developed for the synthesis of carbon-supported binary PtFe (50:50) electrocatalyst with high metal loading that combines homogeneous deposition (HD) of PtFe hydroxide complex species through generation of OH− ions realized by in situ hydrolysis of urea and subsequent uniform reduction of the complex by ethylene glycol (EG) in a polyol process, providing control over the size and dispersion of PtFe nanoparticles (NPs). Compared to PtFe catalysts prepared with other common synthesis methods using NaBH4 and EG and commercial PtFe catalyst, the supported PtFe catalyst prepared by the HD-EG method reveals more uniform homogenous dispersion of PtFe NPs with much smaller particle size, thus demonstrating excellent electrocatalytic ability and fuel cell performance. The structural properties and catalytic activities of Pt–Fe catalysts prepared in various synthesis methods were evaluated on the basis of the analysis of HR-TEM, HR-SEM, XRD, electrochemical surface area and fuel cell polarization performance.

Pt–M@FP-MWNT catalysts (M = Ru, Ni, Co, Sn, and Au) were prepared by one-step γ-ray irradiation. Two different types of functional polymers (FP), such as poly(vinylphenyl boronic acid) (PVPBAc) and poly(vinylpyrorridone) (PVP), were used as anchoring agents, when Pt–M nanoparticles were deposited on the multi-walled carbon nanotube (MWNT) using γ-ray irradiation in aqueous solution at room temperature. The obtained Pt–M@FP-MWNT catalysts were then characterized by XRD, TEM, and elemental analysis. The catalytic efficiency of the Pt–M@FP-MWNT catalysts was examined for CO stripping and MeOH oxidation for use in a direct methanol fuel cell (DMFC). The catalytic efficiency of the Pt–M@FP-MWNT catalyst for MeOH oxidation follows this order: Pt–Sn@FP-MWNT > Pt–Co@FP-MWNT > Pt–Ru@FP-MWNT > Pt–Au@FP-MWNT > Pt–Ni@FP-MWNT catalysts. The CO adsorption capacity of the Pt–M@FP-MWNT catalyst for CO stripping is as follows: Pt–Ru@FP-MWNT > Pt–Sn@FP-MWNT > Pt–Au@FP-MWNT > Pt–Co@FP-MWNT > Pt–Ni@FP-MWNT catalyst.

This paper describes the functionalization of multi-walled carbon nanotubes (MWNTs) by radiation-induced graft polymerization (RIGP) of vinyl monomers with functional groups and the application of these MWNTs in enzyme-free biosensors. The vinyl monomers used were acrylic acid (AAc), methacrylic acid (MAc), glycidyl methacrylate (GMA), maleic anhydride (MAn), and 4-vinylphenylboronic acid (VPBAc). Tubular-type MWNTs were obtained via RIGP of various vinyl monomers. The poly(VPBAc)-grafted MWNTs (PVBAc- g -MWNTs) were used as sensing sites in enzyme-free glucose sensors for the detection of glucose without enzymes. The PVBAc- g -MWNTs electrode displayed an excellent linear response to glucose concentration in the range 1.0–10 mM. The functionalized MWNTs prepared by RIGP can be used as biosensor materials.

A COOH-F-MWCNT-Nafion-Ru(bpy) 32+ -Au-ADH electrogenerated chemi-luminescence (ECL) electrode using COOH-functionalized MWCNT (COOH-F-MWCNT) and Au nanoparticles synthesized by the radiation method was fabricated for ethanol sensing. A higher sensing efficiency for ethanol for the ECL biosensor prepared by PAAc- g -MWCNT was measured compared to that of the ECL biosensor prepared by PMAc- g -MWCNT, and purified MWCNT. Experimental parameters affecting ethanol detection were also examined in terms of pH and the content of PAAc- g -MWCNT in Nafion. Little interference of other compounds was observed for the assay of ethanol. Results suggest this ECL biosensor could be applied for ethanol detection in real samples. Keywords: Ru(bpy) 32+ , Electrogenerated chemiluminescence, COOH-functionalized MWCNT, Au nanoparticle, ethanol, biosensor, real sample 1. Introduction The detection and quantification of alcohol with high sensitivity, selectivity, and accuracy are required in many different fields from the food industry and clinic analysis, to investigation of

Nitrogen-doped carbon nanostructures are considered as a possible alternative to platinum-based catalysts for fuel cells. The surface density of catalytic sites, electrical conductivity, and nitrogen content play important roles in designing electrode materials for fuel cells. Herein, N-doped carbon fibers are prepared by electrospinning the poly(acrylonitrile) (PAN) solution followed by carbonization. Some of the key issues of the oxygen reduction reaction (ORR) are addressed in terms of nitrogen content, porosity, and electrical conductivity in the N-containing carbon nanofibrous system. Nitrogen content and the amount of the graphitic phase are varied by changing the carbonization temperature. In addition, N-doped carbon fibers with high porosity are prepared by electrospinning the solution mixture of poly(ethylene oxide) (PEO)/PAN followed by carbonization, and the porosity is tuned by varying the ratio of PEO to PAN. The effect of porosity or the surface density of catalytic sites on the ORR is studied. A medium porous sample prepared from the PEO/PAN mixture in a 1:1 ratio by carbonization at 1000 °C is found to be favorable for improved ORR performance for such a system. The observations made herein are explained in terms of trade-offs between electrical conductivity, nitrogen content, and surface density of active sites.

We report the template-free pyrolysis of easily available natural seaweed, Undaria pinnatifida, as a single precursor, which results in "seaweed carbon" (SCup). Interestingly, thus-obtained SCup not only contains heteroatoms such as nitrogen and sulfur in its framework, but it also possesses a well-developed porous structure with high surface area. The heteroatoms in SCup originate from the nitrogen- and sulfur-containing ingredients in seaweed, whereas the porosity is created by removal of salts inherently present in the seaweed. These essential and fundamental properties make seaweed a prime choice as a precursor for heteroatom-containing highly porous carbon as a metal-free efficient electrocatalyst. As-synthesized SCup showed excellent electrocatalytic activity in the oxygen reduction reaction (ORR) in alkaline medium, which can be addressed in terms of the presence of the nitrogen and sulfur heteroatoms, the well-developed porosity, and the electrical conductivity in the carbon framework. The pyrolysis temperature was a key controlling parameter that determined the trade-off between heteroatom doping, surface properties, and electrical conductivity. In particular, SCup prepared at 1000 °C showed the best ORR performance. Additionally, SCup exhibited enhanced durability and methanol tolerance relative to the state of the art commercial Pt catalyst, which demonstrates that SCup is a promising alternative to costly Pt-based catalysts for the ORR.

Pt-Ru catalysts based on functional polymer-grafted MWNT (Pt-Ru@FP-MWNT) were prepared by radiolytic deposition of Pt-Ru nanoparticles on functional polymer-grafted multiwalled carbon nanotube (FP-MWNT). Three different types of functional polymers, poly(acrylic acid) (PAAc), poly(methacrylic acid) (PMAc), and poly(vinylphenyl boronic acid) (PVPBAc), were grafted on the MWNT surface by radiation-induced graft polymerization (RIGP). Then, Pt-Ru nanoparticles were deposited onto the FP-MWNT supports by the reduction of metal ions usingγ-irradiation to obtain Pt-Ru@FP-MWNT catalysts. The Pt-Ru@FP-MWNT catalysts were then characterized by XRD, XPS, TEM ,and elemental analysis. The catalytic efficiency of Pt-Ru@FP-MWNT catalyst was examined for CO stripping and MeOH oxidation for use in a direct methanol fuel cell (DMFC). The Pt-Ru@PVPBAc-MWNT catalyst shows enhanced activity for electro-oxidation of CO and MeOH oxidation over that of the commercial E-TEK catalyst.

Hollow core–mesoporous shell carbon (HCMSC) with hierarchical nanoarchitecture was prepared and explored as an anode with ultra-high Li storage capacity in Li ion batteries. Compared with commercial graphite and ordered mesoporous carbon (CMK-3), the HCMSC not only demonstrates higher Li storage capacity, but also better cycling performance and rate capability. HCMSC possesses unique structural characteristics such as large surface area and mesopore volume. Particularly the hierarchical macro-scaled hollow core/mesoporous shell nanostructure along with 3D large interconnected interstitial volume guarantees fast mass transport in HCMSC, resulting in ultra-high Li storage capacity and excellent cycling performance and rate capability. Furthermore, the hollow macro-scaled core encapsulated in a well-developed 3D interconnected mesoporous shell serves as an efficient Li storage and buffer reservoir to reduce volume change during the charge–discharge cycling especially at high rates, which contributes greatly to the enhanced cycling performance and rate capability.

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