A review of thin film electrolytes fabricated by physical vapor deposition for solid oxide fuel cells

The ohmic resistance in solid oxide fuel cells (SOFCs) mainly comes from the electrolyte, which can be reduced by developing novel electrolyte materials with higher ionic conductivity and/or fabricating thin-film electrolytes. Among various kinds of thin-film fabrication technology, the physical vapor deposition (PVD) method can reduce the electrolyte thickness to a few micrometers and mitigate the issues associated with high-temperature sintering, which is necessary for wet ceramic methods. This review summarizes recent development progress in thin-film electrolytes fabricated by the PVD method, especially pulsed laser deposition (PLD) and magnetron sputtering. At first, the importance of the substrate surface morphology for the quality of the film is emphasized. After that, the fabrication of thin-film doped-zirconia and doped-ceria electrolytes is presented, then we provide a brief summary of the works on other types of electrolytes prepared by PVD. Finally, we have come to the summary and made perspectives.     

Study on power generation and Congo red decolorization of 3D conductive PPy-CNT hydrogel in bioelectrochemical system

In this paper, a polypyrrole-carbon nanotube hydrogel (PPy-CNT) with 3D macroporous structure was prepared by secondary growth method. This self-supporting material with good conductivity and biocompatibility can be directly used as anode in a microbial fuel cell (MFC). The prepared material had a uniform structure with rich 3D porosity and showed good water retention performance. The effect of the mass ratio of PPy and CNT in the hydrogel were also investigated to evaluate the electrical performance of MFC. The MFC with 10:1 PPy-CNT hydrogel anode could reached the maximum power density of 3660.25 mW/m3 and the minimal electrochemical reaction impedance of anode was 5.06 Ω. The effects of Congo red concentration, external resistance and suspended activated sludge on decolorazation and electricity generation were also investigated in the MFC with the best performance hydrogel. When the Congo red concentration was 50 mg/L and the external resistance was 200 Ω, the dye decolorization rate and chemical oxygen demand (COD) removal rate could reach 94.35% and 42.31% at 48h while the output voltage of MFC was 480 mV. When activated sludge was present, the decolorization rate and COD removal rate could be increased to 99.55% and 48.08% at 48 h. The above results showed that the porous hydrogel anode had broad application prospects in synchronous wastewater treatment and electricity production of MFC.     

β-FeOOH modified carbon monolith anode derived from wax gourd for microbial fuel cells

The preparation of high-performance anode materials is of significance for enhanced power generation in microbial fuel cells (MFCs). Herein, porous carbon monolith was prepared by simple freeze drying of wax gourd and subsequent pyrolysis (WGC). β-FeOOH was coated on WGC to further improve the performance of the anode (β-FeOOH/WGC). The maximum power density of the MFCs with WGC and β-FeOOH/WGC anode was 913.9 and 1355.1 mW/m² respectively, which was much higher than that of the control (558.2 mW/m²). WGC possessed three-dimensional pore structure, nitrogen and oxygen-containing functional groups, which endowed it with satisfactory bacterial loading. Improved MFC performance after β-FeOOH modification could be ascribed to two aspects: β-FeOOH enhanced the electrochemical activity and decrease the transfer resistance; β-FeOOH was conducive to exoelectrogens formation. This study demonstrated that the synthesis of β-FeOOH modified carbon monolith anode offered an efficient route to enhance the power generation of MFCs.     

A novel design for humidifying an open-cathode proton exchange membrane fuel cell using anode purge

The low performance of open-cathode proton-exchange-membrane fuel cells (OCPEMFCs) is attributed to the low-humidity ambient air supplied to the cathode using electric fans. To improve the OCPEMFC performance, this paper proposes a novel humidification method by collecting water purged from the anode and supplying it to the open cathode. The OCPEMFC performance is evaluated at various humidifier distances from the cathode inlet, and it is compared with that where no humidifier is used when the OCPEMFC operates under three different current levels of 1, 5, and 8 A. The results show that the novel design improves the stack power, and optimal performance is achieved at a humidifier distance of 2 cm. The energy efficiency achieves an improvement between 1.4% and 1.8% when a humidifier is used.     

Sea urchin-like LiAlO2@NiCoO2 hybrid composites with core-shell structure as high-performance Li storage materials

Sea urchin-like LiAlO₂@NiCoO₂ hybrid composites with core-shell structure assembled with nanoneedles have been successfully fabricated through a facile hydrothermal route followed by a calcination procedure in N₂ for the first time. The sea urchin-like architecture with large accessible surface can offer numerous active sites for redox reaction. The synergy of two advantages has dramatically improved the electrochemical behavior in terms of specific capacity, cycle performance and rate capability, especially at high current densities. The LiAlO₂(5.0 wt%)@NiCoO₂ displays charge capacities are 1309.0 and 933.6 mAh g^?1 at 0.5 and 1A g^?1, respectively, after 400 cycles. However, the charge capacities of bare NiCoO₂ are only 562.9 and 476.7 mAh g^?1 at corresponding rates. Especially, LiAlO₂(5.0 wt%)@NiCoO₂ preserves 358.1 mAh g^?1 after 500 cycles at 2A g^?1 with a capacity retention of 74%. The superior electrochemical property is related to the sea urchin-like nature and the ingenious composition design. In addition, the DFT calculation result shows that the formed stable, well-coordinated, and metallic interface between LiAlO₂ and NiCoO₂ are very helpful for reducing the interfacial impedance and beneficial for the improved rate capability of the materials. Therefore, such LiAlO₂@NiCoO₂ composites with unique morphology demonstrate a huge potential as electrode materials for Li-ion batteries.     

Transition metal nanoparticles doped carbon paper as a cost-effective anode in a microbial fuel cell powered by pure and mixed biocatalyst cultures

The poor wettability and high cost of the carbonaceous electrodes materials prohibited the practical applications of microbial fuel cells (MFCs) on large scale. Here, a novel nanoparticles of metal sheathed with metal oxide is electrodeposited on carbon paper (CP) to introduce as high-performance anodes of microbial fuel cell (MFC). This thin layer of metal/metal oxide significantly enhance the microbial adhesion, the wettability of the anode surface and decrease the electron transfer resistance. The investigation of the modified CP anodes in an air-cathode MFCs fed by various biocatalyst cultures shows a significant improving in the MFC performance. Where, the generated power and current density was 140% and 210% higher as compared to the pristine CP. Mixed culture of exoelectrogenic microorganism in wastewater exhibited good performance and generated higher power and current density compared to yeast as pure culture. The excellent capacitance with a distinctive nanostructure morphology of the modified-CP open an avenues for practical applications of MFCs.     

Core/shell Fe3O4@Fe encapsulated in N-doped three-dimensional carbon architecture as anode material for lithium-ion batteries

Core-shell Fe₃O₄@Fe nanoparticles embedded into porous N-doped carbon nanosheets was prepared by a facile method with NaCl as hard-template. The three-dimensional carbon architecture built by carbon nanosheets enhance the conductivity of the encapsulated Fe₃O₄@Fe nanoparticles and strengthen the structure stability suffering from volume expansion during extraction and insertion of lithium ions. Rich Pores enhance the surface between electrode and electrolyte, which short the transmission path of ions and electrons. The core-shell structure with Fe as core further improves charge transferring inside particles thus lead to high capacity. The as-prepared Fe₃O₄@Fe/NC composite displays an irreversible discharge capacity of 839 mAh g^?1 at 1 A g^?1, long cycling life (722.2 mAh g^?1 after 500th cycle at 2 A g^?1) and excellent rate performance (1164.2 and 649.2 mAh g^?1 at 1 and 20 A g^?1, respectively). The outstanding electrochemical performance of the Fe₃O₄@Fe/NC composite indicates its application potential as anode material for LIBs.     

In situ characterization of LiY(WO4)2 nanotubes for electrochemical energy storage

Here, LiY(WO₄)₂ nanotubes are prepared via a feasible electrospinning technique. This new anode material shows excellent electrochemical properties. The capacity loss of LiY(WO₄)₂ nanotubes is as low as 6.9% after 156 cycles, while bulk LiY(WO₄)₂ presents the capacity loss higher than 55.0%. Even after 600 long-life cycles, the capacity loss of the nanotubes is only 9%. It can be seen that the hollow structure with a rough surface and a porous morphology contributes to the improvement of electrochemical performance. Furthermore, online X-ray diffraction (XRD) method is firstly applied to understand the lithium ions insertion/extraction mechanism of LiY(WO₄)₂ nanotubes. It can be concluded that it is an asymmetrical two-phase reaction. A phase transformation from LiY(WO₄)₂ to Li₃Y(WO₄)₂ can be obviously seen from the in situ XRD during discharge process. While Li₂Y(WO₄)₂ appears as an intermediate phase with a reverse charge reaction. In addition, in situ XRD also demonstrates that LiY(WO₄)₂ nanotubes have surprised electrochemical reversibility. All the above results indicate that LiY(WO₄)₂ nanotubes can be expected to be anode candidate for rechargeable lithium ion batteries (LIBs).     

Bimetallic PtPd nanoparticles relying on CoNiO2 and reduced graphene oxide as a most operative electrocatalyst toward ethanol fuel oxidation

Of late, fuel cells have drawn great attentions owing to high-energy demands, fossil fuel depletion and worldwide environmental pollution. Direct ethanol fuel cell (DEFC) constituted as one of the most promising sources of green energy, howbeit the ethanol oxidation reaction (EOR) sluggish kinetic is one of the essential challenges toward the commercialization of DEFCs. Herein, we introduce bimetallic catalyst on CoNiO₂ modified reduced graphene oxide (rGO) to completely exploit the advantages of nano-surface structures as well as the reduction of Pt and Pd loading in fuel cells. With the combined advantages of PtPd, CoNiO₂ and rGO, a significant enhancement in electrocatalytic behavior, stability and CO poisoning tolerance of PtPd have been observed. Regarding the implications, PtPd/CoNiO₂/rGO is greatly preferable than Pt/CoNiO₂/rGO and Pd/CoNiO₂/rGO in terms of high electroactive surface area (ECSA), electro-catalytic activity, and lower onset potential (E_ons) towards the EtOH oxidation in alkaline media. Furthermore, the chronoamperometry curve (CA) illustrated 77% after 3600 s which is dramatically soared compared with the other electrodes (≤40%), demonstrating the high stability of the PtPd bimetallic nanoparticle electrocatalyst. Ultimately, PtPd/CoNiO₂/rGO nanocomposite is found to be an excellent anode electrocatalyst for application in DEFCs.     

Exploration of amorphous hollow FeOOH@C nanosphere on energy storage for sodium ion batteries

Sodium ion batteries (SIBs) have enjoyed a high profile in recent years and gradually been commercialized to supplement the lithium-ion batteries system. However, the large volume expansion of anode materials within discharging and low electrical conductivity hinder the application of SIBs. In this work, a FeOOH@C composite was synthesized with the use of hydrothermal method and pyrolyzing of polydopamine. The amorphous FeOOH exhibits a hollow spherical structure to offer free space for buffering the volumetric variation. Furthermore, the outer carbon served as a protective shell could maintain the sphere integrity and enhance the electrical conductivity. Hence, benefiting from the achieved synergy of the hollow architecture, amorphous structure and carbon shell, the composite presented a long cycle life (316 mA h g^?1 after 500 cycles at a current density of 100 mA g^?1 and 234.5 mA h g^?1 after 400 cycles at 2 A g^?1) and high-rate performance (180 mA h g^?1 at 5 A g^?1), revealing a potential to be a promising candidate for electrode material of SIBs.