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Here, we have synthesized reduced graphene oxide (rGO) aerogels using a nanocellulose-assisted low temperature (less than 500 °C) thermal treatment route where nanocelluloses promote the gelation of graphene oxide (GO) solution that benefits the fabrication of GO aerogels from low concentration dispersion (2.85 mg mL−1), and after their thermal decomposition the residual nanofibers act as spacer both prevent the re-stacking of graphene sheets and integrate with rGO sheets to give a particular kind of carbon-based aerogel along with numerous defects (holes). Thermal decomposition of nanocellulose appears to be complete beyond 350 °C thus its presence in form of amorphous carbon nanofibers in rGO sheets. The rGO aerogels synthesized at 350 °C provide the best balance in terms of wide interlayer spacing, high content of CO-type functional groups, and high defects content. This translates into a high discharge capacitance of 270 F g−1 at a current rate of 1 A g−1 for compressed rGO aerogels without any binder or conductive additive. Detailed electrochemical tests using 6 M KOH electrolyte establish the fact that pseudocapacitance component has substantial contribution towards the overall capacitance; closely approaching the contribution of the double layer capacitance that is the most dominant capacitance component.

The development of high performance perovskite cathode for solid oxide fuel cells (SOFCs) relies upon the knowledge and understanding of the interplay between the metal oxide components, structure, redox properties and conductivity. In this work, we partially substituted Fe on SrFeO3-delta with Nb. In particular, 3 Nb-doped compositions were prepared, e.g. SrNb0.5Fe0.95O3-delta (SNF0.05), SrNb0.1Fe0.9O3-delta (SNF0.1) and SrNb0.2Fe0.8O3-delta (SNF0.2). Mossbauer spectroscopy revealed decreasing ratio of Fe4+ to Fe3+ at the higher Nb doping content which translates to the gradual decrease of the average Fe oxidation state from 3.403 (for SNF0.05) to 3.375 (for SNF0.1) and to 3.291 (for SNF0.2). Likewise, the oxygen desorption process and the thermal expansion coefficients decreased with increasing Nb content, therefore providing evidence on their correlation with the thermal reduction of Fe4+. The temperature-dependent oxygen nonstoichiometry displayed two different regimes separated by a transition temperature of 625 degrees C, below which SNF0.2 showed the highest nonstoichiometry and above which SNF0.05 provided the highest nonstoichiometry. The analogous shifting in trends was reproduced for oxygen reduction reaction (ORR) performance which signifies oxygen nonstoichiometry as the main variable affecting ORR performance. (C) 2015 Elsevier B.V. All rights reserved.

Constructing catalysts with a low overpotential for the oxygen evolution reaction (OER) is critical for the increased application of rechargeable Zn-air batteries. Herein, an in-situ cobalt extraction and simultaneous coordination growth strategy is adopted to develop an active and robust interface between nanostructural Co-metal-organic framework (Co-MOF) pillars and perovskite LaCoO3-δ (LC). Moreover, the multi-active cobalt sites, including Co3+ in the LC and coordinatively unsaturated cobalt sites in the Co-MOF, could promote the deprotonation of oxygen adsorption intermediates and act as catalytic active centres. Therefore, the optimal sample exhibits excellent OER activity with a low overpotential of 330 mV. Notably, the Zn-air battery with Co-MOF/LC-0.5 as the OER catalyst exhibits a low charge potential of 2.03 V and excellent cycling stability. This work illustrates efficient electrochemical catalysts based on perovskites with low overpotentials that are prepared by an in-situ growth strategy, and have great potential in rechargeable Zn-air batteries.

Dual-ion (oxygen ion and proton) conducting electrolyte BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) is one of the most commonly used electrolyte materials for proton conducting fuel cells (PCFCs). Here, we improve conducting property and performance of BZCYYb electrolyte through simply introducing B-site cation deficiency. Dual-ion conductivities for Ba(Zr0.1Ce0.7Y0.1Yb0.1)0.95O3-δ (BZCYYb-0.95) electrolyte are improved to a large extent as 2.5 times protonic conductivity (4.6 × 10−2 S cm−1 at 700 °C) and 6.3 times oxygen ionic conductivity (1.2 × 10−2 S cm−1 at 900 °C) compared to BZCYYb electrolyte. Low-temperature (1350 °C) sinterability of BZCYYb-0.95 is achieved for the higher concentration of defect compared to the original material (BZCYYb, 1500 °C). Meanwhile, a cell with the BZCYYb-0.95 electrolyte illustrates prominent power density of 794 mW cm−2 at 650 °C, superior to the cell with BZCYYb (643 mW cm−2) at the same condition. The collaborative diffusions of dual-ion via two different conducting mechanisms enhance the cell performance with BZCYYb-0.95 electrolyte. The cell voltage and power density actually have no observable performance degradation during the course of the 300-h test. Therefore, it indicates the dual-ion diffusions of BZCYYb-0.95 electrolyte as the promising future for practical application.

Improving the activity of a cathode material towards the oxygen reduction reaction (ORR) and its tolerance against CO2 impurities is of prime importance to realizing the application of solid oxide fuel cells that operate under intermediate temperatures (IT-SOFCs). Here, by adopting an A- and B-site co-doping strategy, we report a new perovskite-type oxide, Nd0.2Sr0.8Nb0.1Co0.9O3-δ (N0.2SNC), as an active and CO2-tolerant cathode material for IT-SOFCs. Compared with single-site doped Nd0.2Sr0.8CoO3-δ (N0.2SC, A-site doping) and SrNb0.1Co0.9O3-δ (SNC, B-site doping) and the parent oxide SrCoO3-δ (SC), N0.2SNC shows improved electrocatalytic activity for the ORR and superior resistance towards CO2 poisoning, achieving a low area specific resistance (ASR) of 0.037 Ω cm2 at 650 °C. In addition, the ASR value of the N0.2SNC electrode only increases from 0.08 to 0.20 Ω cm2 after operating for 300 min under an air atmosphere with 5% CO2. A- and B-site cation synergy is obtained through co-doping, leading to the improved performance. A peak power density of 1563 mW cm−2 is achieved at 650 °C. This A- and B-site cation synergy may offer a new avenue for developing high-performance and CO2-stable cathode materials for IT-SOFCs.

Although intensive efforts have been made during the past decades, development of an anode material with high specific capacity and stable cycling performance for lithium-ion batteries (LIBs) using a cost-effective preparation method still remains challenging. Herein, we report a polyaniline (PANI)-coated mechanochemically synthesized SnO2/graphene (SG) nanocomposite via in situ polymerization. PANI-coated nanocomposites are successfully prepared with different raw material mass ratios (aniline:SG, 0.15:1, 0.2:1, 0.25:1). The nanocomposite with initial aniline:SG mass ratio of 0.2:1 (20%PANI-SG) contains an optimal structure housing genuine PANI nanofibers as conductive bridges and a relatively high surface area of 158.5 m2 g−1; furthermore, it exhibits a stable cycling performance over 100 cycles at high current density (1000 mA g−1) with a specific capacity of more than twice that of the starting SG electrode at the 100th cycle. Additionally, this material achieved an outstanding cycling rate with current densities changing stepwise from 100 to 3000 mA g−1 and back, and exhibited a specific capacity of 467 mA h g−1 even at 2000 mA g−1. In terms of the electrochemical stability, rate capability and cost-effective preparation process, the PANI-SG nanocomposite is a viable anode material for next-generation high-power and high-energy LIBs.

Al2O3 and SnO2 additives are introduced into the Ni–YSZ cermet anode of solid oxide fuel cells (SOFCs) for operation on simulated biogas. The effects of incorporating Al2O3/SnO2 on the electrical conductivity, morphology, coking resistance and catalytic activity for biogas reforming of the cermet anode are systematically studied. The electrochemical performance of the internal reforming SOFC is enhanced by introducing an appropriate amount of Al2O3 into the anode, but it becomes worse with excess alumina addition. For SnO2, a negative effect on the electrochemical performance is demonstrated, although the coking resistance of the anode is improved. For fuel cells operating on biogas, stable operation under a polarization current for 130 h at 750 °C is achieved for a cell with an Al2O3-modified anode, while cells with unmodified or SnO2-modified Ni–YSZ anodes show much poorer stability under the same conditions. The improved performance of the cell with the Al2O3-modified anode mainly results from the suppressed coking and sintering of the anode and from the formation of NiAl2O4 in the unreduced anode. In sum, modifying the anode with Al2O3 may be a useful and facile way to improve the coking resistance and electrochemical performance of the nickel-based cermet anodes for SOFCs.

In this study, pyridine was used to suppress the coke formation in solid oxide fuel cells (SOFCs) operating on liquid fuels. Pyridine can selectively occupy acidic sites of the Ni/Al 2 O 3 catalyst layer and solves the problem of dehydration of ethanol in principle, resulting in a significant reduction in the coke formation rate for operating on ethanol fuel. At 600 °C, by adding 12.5 vol.% pyridine into the ethanol fuel, the coke formation rate over the Ni/Al 2 O 3 catalyst is reduced by 64% while a cell power output comparable to that operating on hydrogen is still achieved based on total potential hydrogen available from ethanol. The effective reduction of carbon deposition on the catalyst layer thus protects the anode layer from carbon deposition by strongly suppressing coke formation, especially near the anode-electrolyte interface. Pyridine is adsorbed onto the acidic sites of the Ni/Al 2 O 3 catalyst and the adsorbed pyridine may reduce the amount of carbonium ions formed, thereby reducing coke formation. This study suggested that the addition of pyridine could suppress the coke formation in SOFCs with Ni/Al 2 O 3 catalyst layer operated on ethanol or some other similar liquid fuels.

Practical applications of single-chamber solid oxide fuel cells (SC-SOFCs) are partially limited by the difficulties and complications associated with the initialization process, which mainly involves the reduction of NiO to Ni in the anode. Here we propose a facile approach to the in situ activation (initialization) of SC-SOFCs with a state-of-the-art sintered nickel-based anode using a methane–oxygen gas mixture, combined with the introduction of nanocatalysts into the anode. RuO 2 , CeO 2 or Co 3 O 4 with the high activity for methane oxidation are investigated for above purpose. XRD results demonstrate that the nanocatalysts are successfully introduced into the anode via a simple solution impregnation technique. Using FESEM, different nanoparticle morphologies are observed for the three catalysts. The time dependence of the cell voltage operating on the methane–oxygen gas mixture demonstrates successful activation following nanocatalyst introduction. Single cells with different nanocatalyst-modified anodes, initialized by in situ reduction, deliver high open circuit voltages of approximately 1.0 V and significant peak power outputs of approximately 1000 mW cm −2 at a furnace temperature of 650 °C. XRD and FESEM analysis indicates that only the CeO 2 retains a same structure and morphology after the test. It suggests that the CeO 2 nanocatalyst is the most promising for practical applications.

Proton-conducting perovskite oxides are excellent electrolyte materials for SOFCs that may improve power density at reduced temperatures and increase fuel efficiency, thus encouraging the widespread implementation of this attractive technology. The main challenges in the application of these oxides in SOFCs are difficult sintering and insufficient conductivity in real cells. In this study, we propose a novel method to significantly enhance the performance of a yttrium-doped barium cerate proton conductor as an electrolyte for SOFCs through a Pd ingress–egress approach to the development of BaCe0.8Y0.1Pd0.1O3−δ (BCYP10). The capability of the Pd egress from the BCYP10 perovskite lattice is demonstrated by H2-TPR, XRD, EDX mapping of STEM and XPS. Significant improvement in the sinterability is observed after the introduction of Pd due to the increased ionic conductivity and the sintering aid effect of egressed Pd. The formation of a B-site cation defect structure after Pd egress and the consequent modification of perovskite grain boundaries with Pd nanoparticles leads to a proton conductivity of BCYP10 that is approximately 3 times higher than that of BCY under a reducing atmosphere. A single cell with a thin film BCYP10 electrolyte reaches a peak power density as high as 645 mA cm−2 at 700 °C.

Mesoporous three-dimensional (3D) TiO2/carbon nanotube conductive hybrid nanostructures can be successfully developed using polyethylene oxide (PEO) to modify the surfaces of carbon nanotubes (CNTs). During the synthesis process, PEO acts as not only “bridges” to connect the TiO2 nanoparticles to the CNT surfaces but also as “hosts” to accommodate and stabilize the in situ generated TiO2 particles. As the electrodes for lithium-ion batteries, such mesoporous 3D TiO2/CNT hybrids, demonstrate high Li storage capacity, superior rate performance and excellent long-term cycling stability. They exhibit a reversible specific capacity of 203 mA h g−1 at 100 mA g−1 and a stable capacity retention of 91 mA h g−1 at 8000 mA g−1 (47.6 C) over 100 cycles; they also retain approximately 90% (71 mA h g−1) of their initial discharge capacity after 900 cycles at an extremely high rate of 15,000 mA g−1 (89 C). This facile synthetic strategy to construct mesoporous 3D TiO2/CNT conductive hybrids provides a convenient route that efficiently assembles various inorganic oxide components on the CNTs' surfaces and enables the formation of heterogeneous nanostructures with novel functionalities. In particular, utilizing a conductive 3D CNT network can serve as a promising strategy for developing high-performance electrodes for Li secondary batteries and supercapacitors.