PdCo supported on multiwalled carbon nanotubes as an anode catalyst in a microfluidic formic acid fuel cell

This work reports the synthesis of Pd-based alloys of Co and their evaluation as anode materials in a microfluidic formic acid fuel cell (μFAFC). The catalysts were prepared using the impregnation method followed by thermal treatment. The synthesized catalysts contain 22 wt.% Pd on multiwalled carbon nanotubes (Pd/MWCNT) and its alloys with two Co atomic percent in the sample with 4 at.% Co (PdCo1/MWCNT) and 10 at.% Co (PdCo2/MWCNT). The role of the alloying element was determined by XRD and XPS techniques. Both catalysts were evaluated as anode materials in a μFAFC operating with different concentrations of HCOOH (0.1 and 0.5 M), and the results were compared to those obtained with Pd/MWCNT. A better performance was obtained for the cell using PdCo1/MWCNT (1.75 mW cm⁻²) compared to Pd/MWCNT (0.85 mW cm⁻²) in the presence of 0.5 M HCOOH. By means of external electrode measurements, it was also possible to observe shifts in the formic acid oxidation potential due to a fuel concentration increment (ca. 0.05 V for both PdCo1/MWCNT and PdCo2/MWCNT catalysts and 0.23 V for Pd/MWCNT) that was attributed to deactivation of the catalyst material. The maximum current densities obtained were 8 mA cm⁻² and 5.2 mA cm⁻² for PdCo2/MWCNT and Pd/MWCNT, respectively. In this way, the addition of Co to the Pd catalyst was shown to improve the tolerance of intermediates produced during formic acid oxidation that tend to poison Pd, thus improving the catalytic activity and stability of the cell.     

Graphene supported platinum nanoparticles as anode electrocatalyst for direct borohydride fuel cell

The graphene supported Pt nanoparticles are prepared by ethylene glycol reduction method. The obtained Pt/graphene (Pt/G) nanocomposites are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). TEM images show that the spherical Pt nanoparticles with sizes of 3.1 nm disperse uniformly on the surface of the graphene, which is consistent with the XRD date of 2.97 nm. The Pt/G nanocomposites show electrochemically active surface area (ECSA) of 62.7 m²/g. It has been found by electrochemical measurements (i.e., cyclic voltammetry, chronoamperometry) that the Pt/G nanocomposites exhibit good electrocatalytic activity and stability toward borohydride oxidation. Besides, the Pt/G nanocomposites are used as anode electrocatalyst in a direct borohydride fuel cell at 298 K, and the maximum power density is 42 mW/cm², which is apparently higher than Vulcan XC-72R supported Pt (Pt/C) nanoparticles (34 mW/cm²).     

Cobalt nickel boride nanocomposite as high-performance anode catalyst for direct borohydride fuel cell

Similar to MXene, MAB is a group of 2D ceramic/metallic boride materials which exhibits unique properties for various applications. However, these 2D sheets tend to stack and therefore lose their active surface area and functions. Herein, an amorphous cobalt nickel boride (Co–Ni–B) nanocomposite is prepared with a combination of 2D sheets and nanoparticles in the center to avoid agglomeration. This unique structure holds the 2D nano-sheets with massive surface area which contains numerous catalytic active sites. This nanocomposite is prepared as an electrocatalyst for borohydride electrooxidation reaction (BOR). It shows outstanding catalytic activity through improving the kinetic parameters of BH₄^? oxidation, owing to abundant ultrathin 2D structure on the surface, which provide free interspace and electroactive sites for charge/mass transport. The anode catalyst led to a 209 mW/cm² maximum power density with high open circuit potential of 1.06 V at room temperature in a miniature direct borohydride fuel cell (DBFC). It also showed a great longevity of up to 45 h at an output power density of 64 mW/cm², which is higher than the Co–B, Ni–B and PtRu/C. The cost reduction and prospective scale-up production of the Co–Ni–B catalyst are also addressed.     

Investigation of amorphous CoB alloy as the anode catalyst for a direct borohydride fuel cell

Co-B amorphous alloy powders have been synthesized by chemical reduction of cobalt chloride with potassium borohydride in an aqueous solution. We find that this alloy can be used as an anode catalyst for a direct borohydride fuel cell (DBFC). This catalyst exhibits excellent electrocatalytic activity. An essential power output of 220 mW cm⁻² has been achieved at 15 °C, and a life test last for 160 h with no attenuation has been observed. The amorphous structure of the CoB alloy is still stable after the life test.     

Study of CoO as an anode catalyst for a membraneless direct borohydride fuel cell

In this paper, cobalt(II) oxide (CoO) has been used as an anode catalyst in a direct borohydride fuel cell (DBFC). The microstructure of CoO has been characterised by X-ray diffraction. The cell performance and short-term performance stability of the DBFC using the CoO as anode catalyst have been investigated. At the optimum conditions, the maximum power density of 80 mW cm⁻² has been achieved at 30 °C for this cell without using any precious metals and ion exchange membranes. Results from XRD, TEM, and XPS analysis confirm that the good performance of the fuel cell is attributed to the co-operation of CoO and CoB which formed from CoO during the operation.     

A novel anode modified by 1,5‐dihydroxyanthraquinone/multiwalled carbon nanotubes composite in marine sediment microbial fuel cell and its electrochemical performance

A novel anode modified by 1,5‐dihydroxyanthraquinone/multiwalled carbon nanotubes (DAQ/MWCNTs) composite was fabricated in order to improve its electrochemical performance in marine sediment microbial fuel cell (MSMFC). The number of microbes on the DAQ/MWCNTs modified anode is 18.02 times of blank anode, and it has the best electrochemical performance compared with other anodes. Its exchange current density and biofilm capacitance are 1472.15 times and 18.66 times higher than that of blank anode, respectively. The maximum power density of composite modified MSMFC (890.12 mW·m^?2) is 3.01‐fold of blank cell (296.11 mW·m^?2). The mechanism analysis of DAQ/MWCNTs shows that DAQ, as an electron‐transfer mediator, can accelerate electron transfer to benefit the electrochemical performance of anode. This provides a new anode modification method for the development of high power MSMFC as long‐term power source to drive monitoring instruments.     

A solid oxide carbon fuel cell operating on pomelo peel char with high power output

The pomelo peel char (PC) was prepared and used as fuel for solid oxide electrolyte direct carbon fuel cells with nickel‐yttrium stabilized zirconia anode, thin‐film YSZ electrolyte, and La_0.8Sr_0.2MnO₃ cathode. The power densities of fuel cells operating on PC and catalyst‐loaded PC (PCC) fuels achieved 309 and 518 mW cm^?2 at 850°C, respectively, which are among the highest power densities reported in the literature on DCFCs. The PC exhibited superior gasification reactivity than coal char due to its unique reticulated foam carbon structure with a homogeneously distributed inherent catalyst. The stability tests at a current density of 50 mA cm^?2 and 825°C indicate that the cell using PC fuel operated in a more stable manner than that using PCC, and the fuel availabilities for PC and PCC were 47.25% and 34.71%, respectively. The results suggest that PC is a promising solid carbonaceous fuel for solid oxide electrolyte direct carbon fuel cells based on its adequate gasification reactivity and high compatibility with the fuel cells.     

Amorphous NiB alloy decorated by Cu as the anode catalyst for a direct borohydride fuel cell

In this study, amorphous NiB alloy decorated by Cu is prepared by chemical reduction. Moreover, the effect of Cu addition for the electrocatalytic activity of borohydride (BH₄⁻) oxidation is studied. The physical characteristics of NiB or NiBCu_x nanoparticles are confirmed by transmission X-ray diffraction (XRD) and scanning electron microscopy (SEM). The physical characterization results demonstrate that the NiB or NiBCu_x nanoparticles have an amorphous structure and NiBCu_x nanoparticles have improved dispersity. The borohydride oxidation activity of the as-prepared catalysts is investigated by cyclic voltammetry (CV), linear scan voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Results indicate that the NiBCu_x/C nanoparticles have higher electrocatalytic activity for borohydride oxidation than NiB/C, and the borohydride oxidation current of NiBCu_x/C nanoparticles initially increases and then decreases with the increase in Cu content. The optimum molar content of copper in the six prepared catalysts is 2.2%. It is proposed that the addition of Cu is conducive to sodium borohydride adsorption, thereby improving the electro-oxidation activity for borohydride. Hence, amorphous NiB alloy decorated by Cu can enhance the electro-oxidation performance for borohydride.     

Preparation and characterization of nanoporous carbon-supported platinum as anode electrocatalyst for direct borohydride fuel cell

The nanoporous carbon (NPC) is synthesized by carbonization of metal–organic framework-5 (MOF-5, [Zn₄O(bdc)₃], bdc = 1,4-benzenedicarboxylate) with furfuryl alcohol (FA) as carbon source and used as the carrier of the anode catalyst for the direct borohydride–hydrogen peroxide fuel cell (DBHFC). Then the NPC-supported Pt anode catalyst (Pt/NPC) is firstly prepared by a modified NaBH₄ reduction method. The obtained Pt/NPC catalyst is characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), cyclic voltammetry, chronopotentiometry, chronoamperometry and fuel cell test. The results show that the Pt/NPC is made up of the spherical Pt nanoparticles which disperse uniformly on the surface of the NPC with average size 2.38 nm, and exhibits 36.38% higher current density for directly borohydride oxidation than the Vulcan XC-72 carbon supported Pt (Pt/XC-72). Besides, the DBHFC using the Pt/NPC as anode electrocatalyst shows the maximum power density as high as 54.34 mW cm⁻² at 25 °C.     

SnO2 nanocrystals deposited on multiwalled carbon nanotubes with superior stability as anode material for Li-ion batteries

We report a novel ethylene glycol-mediated solvothermal-polyol route for synthesis of SnO₂-CNT nanocomposites, which consist of highly dispersed 3-5 nm SnO₂ nanocrystals on the surface of multiwalled carbon nanotubes (CNTs). As anode materials for Li-ion batteries, the nanocomposites showed high rate capability and superior cycling stability with specific capacity of 500 mAh g⁻¹ for up to 300 cycles. The CNTs served as electron conductors and volume buffers in the nanocomposites. This strategy could be extended to synthesize other metal oxides composites with other carbon materials.     

Improving the direct borohydride fuel cell performance with thiourea as the additive in the sodium borohydride solution

In this study, the effects of the additive thiourea (TU) have been investigated under steady state/steady-flow and uniform state/uniform-flow systems with the aim of minimizing the anodic hydrogen evolution on Pd in order to increase the performance of a direct borohydride fuel cell. The fuel cell has consisted of Pd/C anode, Pt/C cathode and Na⁺ form Nafion membrane as the electrolyte. There has been a small improvement in peak power density and fuel utilization ratio by addition of TU (1.6 × 10⁻³ M) into the sodium borohydride solution; the peak power densities of 14.4 and 15.1 mW cm⁻², and fuel utilization ratios of 21.6% and 23.2% have been obtained without and with TU, respectively.     

Welding assembly of 3D interconnected carbon nanotubes on carbon fiber as the high-performance anode of microbial fuel cells

The development of large surface-area and high conductivity electrode is a prerequisite for the construction of high-performance microbial fuel cells. Herein, we report an innovative approach to the fabrication of such high-performance electrodes via the welding assembly of 3D interconnected carbon nanotubes (CNTs) on a carbon-fiber (CF) paper electrode. The minimized interfacial ohmic loss between CNTs and the CF scaffold endowed the microbial fuel cells with the welding-assembled CNT-CF electrodes excellent electrochemical properties with the maximum power density of 2015.6 mW m⁻², 10.0 times higher than that obtained with the untreated CP/CNT (499.8 mW m⁻²) carbon paper anode. As compared to the conventional chemical vapor deposition (CVD) growth technique for fabricating CNT- CF electrodes, this welding assembly approach is more versatile and much easier for up-scaling; on this basis, our work may pave a new avenue to the large-scale production of high-performance microbial fuel cells.     

Microbial fuel cell performance of multiwall carbon nanotubes on carbon cloth as electrodes

Microbial fuel cell (MFC), which can produce electricity during treatment of wastewater, has become one of the emerging technologies in the field of environmental protection and energy recovery. Of all parts of MFC, the electrode materials play a crucial role in the electricity generation. In this study, we investigate the performance of carbon nanotube (CNT) modified carbon cloth electrodes in single-chamber MFC. The MFC is first inoculated with bacteria in wastewater and then its capability of using acetate sodium as fuel is examined. The results show that the MFC with CNT coated onto carbon cloth electrode improves the power density. In this study, the obtained maximum power density is 65 mW m⁻², the highest chemical oxygen demand (COD) removal efficiency is 95%, and the maximum Coulombic efficiency is 67%. Compared with other reported studies, the CNT/carbon cloth composite electrode has demonstrated high potential for the use of MFC.     

Investigation of carbon supported Au-Ni bimetallic nanoparticles as electrocatalyst for direct borohydride fuel cell

The carbon supported Au₈₀Ni₂₀, Au₅₈Ni₄₂ and Au₄₁Ni₅₉ nanoparticles for the application of direct borohydride-hydrogen peroxide fuel cell (DBHFC) are synthesized in a sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelle system. The physical and electrochemical properties are investigated by transmission electron microscopy (TEM), cyclic voltammetry, chronoamperometry, chronopotentiometry and fuel cell test. The TEM results reveal that the Au-Ni bimetallic particles are uniformly dispersed on carbon with narrow size distribution and regular spherical shape. The average size of the particles is about 3 nm. The electrochemical measurements show that Au-Ni bimetallic particles can apparently promote the electrode kinetics of BH₄⁻ oxidation. The DBHFCs using carbon supported Au-Ni bimetallic particles as anode electrocatalysts are fabricated. The results show that the performance of DBHFC using Au₅₈Ni₄₂/C as anode electrocatalyst excels markedly to the others, and the maximum power density of 45.74 mW cm⁻² is obtained at 20 °C.     

The use of polypyrrole modified carbon-supported cobalt hydroxide as cathode and anode catalysts for the direct borohydride fuel cell

A polypyrrole modified carbon-supported cobalt hydroxide (Co(OH)₂-PPY-C) has been prepared by the impregnation-chemical method and used as the electrode catalyst in a direct borohydride fuel cell (DBFC). The microstructure of Co(OH)₂-PPY-C has been characterized by X-ray diffraction and transmission electron microscopy. The cell performance and short-term performance stability of the DBFC using the Co(OH)₂-PPY-C as catalysts have been investigated. A maximum power density of 83 mW cm^?2 has been achieved at 0.6 V under ambient conditions. The Co(OH)₂-PPY-C catalyst demonstrates a smaller value of polarization than the carbon-supported Co(OH)₂ catalyst. Results from electrochemical impedance spectrum analysis confirm that the polypyrrole addition to the cathode effectively decreases its resistance. During operation of the DBFC using Co(OH)₂-PPY-C as catalyst, the Co(OH)₂ tends to be converted into CoHO₂.     

A combined physicochemical and electrocatalytic study of microwave synthesized tungsten mono-carbide nanoparticles on multiwalled carbon nanotubes as a co-catalyst for a proton-exchange membrane fuel cell

Tungsten mono-carbide (WC) nanoparticles supported on multiwalled carbon nanotube (MWCNT) was synthesized by a microwave-assisted solid-state carburization. The prepared samples were used as a co-catalyst to prepare Pt-WC/MWCNT catalyst for a proton-exchange membrane fuel cell. MWCNTs with and without oxidative pretreatments were characterized as the starting precursors. The influence of the carbide formation conditions on the physicochemical characteristics of the final product were extensively investigated. According to the results, surface pretreatment of the MWCNTs can improve the yield of carbide formation. Furthermore, carburization process can improve the catalyst utilization due to increasing the number of surface defects of the MWCNT supporting materials which can be interpreted as structural effect of the carburization process. It is believed that the superior performance of electrodes modified with tungsten carbide is mostly due to the structural effect of the carburization process and synergistic effect between the electrocatalytic activity of WC and Pt.     

The studies of performance of the Au electrode modified by Zn as the anode electrocatalyst of direct borohydride fuel cell

The carbon supported Au-base electrocatalysts (Au_(1−x)Zn_x/C, 0 ≤ x < 1) modified by Zn were synthesized by reverse microemulsion method and employed as anode electrocatalysts of direct borohydride fuel cell (DBFC). The physical and electrochemical properties were investigated by energy dispersive X-ray (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV), chronopotentiometry and fuel cell test. The results showed that the morphologies of Au_(1−x)Zn_x nanoparticles all were uniformly spherical no matter what Zn content changed, and the average particle size of Au_(1−x)Zn_x bimetallics varied from 3 to 6 nm. The electrochemical measurements revealed that the Au_(1−x)Zn_x/C electrocatalysts showed no activity toward the NaBH₄ hydrolysis reaction and obviously improved the catalytic activity of borohydride oxidation. Compared with Au/C anode electrocatalyst, the stability of DBFC using the Au_0.65Zn_0.35/C as anode electrocatalyst was apparently improved, and the maximum power density of 39.5 mW cm⁻² was obtained at 20 °C.     

Solid oxide fuel cell bi-layer anode with gadolinia-doped ceria for utilization of solid carbon fuel

Pyrolytic carbon was used as fuel in a solid oxide fuel cell (SOFC) with a yttria-stabilized zirconia (YSZ) electrolyte and a bi-layer anode composed of nickel oxide gadolinia-doped ceria (NiO-GDC) and NiO-YSZ. The common problems of bulk shrinkage and emergent porosity in the YSZ layer adjacent to the GDC/YSZ interface were avoided by using an interlayer of porous NiO-YSZ as a buffer anode layer between the electrolyte and the NiO-GDC primary anode. Cells were fabricated from commercially available component powders so that unconventional production methods suggested in the literature were avoided, that is, the necessity of glycine-nitrate combustion synthesis, specialty multicomponent oxide powders, sputtering, or chemical vapor deposition. The easily-fabricated cell was successfully utilized with hydrogen and propane fuels as well as carbon deposited on the anode during the cyclic operation with the propane. A cell of similar construction could be used in the exhaust stream of a diesel engine to capture and utilize soot for secondary power generation and decreased particulate pollution without the need for filter regeneration.     

Improving proton exchange membrane fuel cell performance with carbon nanotubes as the material of cathode microporous layer

The cathode microporous layer (MPL) is fabricated by various multiwall carbon nanotubes (CNTs), and its influence on the performance of a proton exchange membrane fuel cell (PEMFC) is evaluated. Three types of CNT with different dimensions are employed in the experiments, and the conventional MPL made by acetylene black (AB) is also considered for the purpose of comparison. The results show that the employment of CNT as MPL composition indeed may improve fuel cell performance significantly in comparison with the case of AB. The type of CNT with the largest tube diameter and straight cylinder in shape exhibits the highest cell performance. The corresponding optimal CNT loading and polytetrafluoroethylene (PTFE) content in the MPL are also evaluated. Results show that the case of cathode MPL composed of 1.5 mg cm^?2 CNT and 20 wt% PTFE exhibits the best performance in all the experimental cases. The present data reveal that the application of CNT for MPL fabrication is beneficial to promote PEMFC performance. Copyright © 2015 John Wiley & Sons, Ltd.     

Modeling the performance of molten carbonate based direct carbon fuel cell anode

A mathematical model is developed to study the performance of a molten carbonate based direct carbon fuel cell anode. The direct carbon fuel cell(DCFC) is a fuel cell which uses solid carbon as fuel and molten carbonate as electrolyte. The model assumes that the 4 electron carbon oxidation reaction is the primary reaction driving the DCFC. However, the 2 electron CO oxidation reaction and the reverse Boudouard reaction is also considered in this model. The model studies the effect of performance parameters on the performance of the DCFC. The effect of the bulk conductivity in the solid phase, the bulk conductivity in the liquid phase, carbon loading and the thickness of the anode layer on the potential and current distribution in the cell is modeled. Model results are compared with experimental data and found to compare well.