Iron phthalocyanine as a cathode catalyst for a direct borohydride fuel cell

A direct borohydride fuel cell (DBFC) is constructed using a cathode based on iron phthalocyanine (FePc) catalyst supported on active carbon (AC), and a AB₅-type hydrogen storage alloy (MmNi_3.55Co_0.75Mn_0.4Al_0.3) was used as the anode catalyst. The electrochemical properties are investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), etc. methods. The electrochemical experiments show that FePc-catalyzed cathode not only exhibits considerable electrocatalytic activity for oxygen reduction in the BH₄⁻ solutions, but also the existence of BH₄⁻ ions has almost no negative influences on the discharge performances of the air-breathing cathode. At the optimum conditions of 6 M KOH + 0.8 M KBH₄ and room temperature, the maximal power density of 92 mW cm⁻² is obtained for this cell with a discharge current density of 175 mA cm⁻² at a cell voltage of 0.53 V. The new type alkaline fuel cell overcomes the problem of the conventional fuel cell in which both noble metal catalysts and expensive ion exchange membrane were used.     

Carbon monoxide-fueled solid oxide fuel cell

This study explored CO as a primary fuel in anode-supported solid oxide fuel cells (SOFCs) of both tubular and planar geometries. Tubular single cells with active areas of 24 cm² generated power up to 16 W. Open circuit voltages for various CO/CO₂ mixture compositions agreed well with the expected values. In flowing dry CO, power densities up to 0.67 W cm⁻² were achieved at 1 A cm⁻² and 850 °C. This performance compared well with 0.74 W cm⁻² measured for pure H₂ in the same cell and under the same operating conditions. Performance stability of tubular cells was investigated by long-term testing in flowing CO during which no carbon deposition was observed. At a constant current of 9.96 A (or, 0.414 A cm⁻²) power output remained unchanged over 375 h of continuous operation at 850 °C. In addition, a 50-cell planar SOFC stack was operated at 800 °C on 95% CO (balance CO₂), which generated 1176 W of total power at a power density of 224 mW cm⁻². The results demonstrate that CO is a viable primary fuel for SOFCs.     

Solid-oxide fuel cell operated on in situ catalytic decomposition products of liquid hydrazine

Hydrazine was examined as a fuel for a solid-oxide fuel cell (SOFC) that employed a typical nickel-based anode. An in situ catalytic decomposition of hydrazine at liquid state under room temperature and ambient pressure before introducing to the fuel cell was developed by applying a Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) oxide catalyst. Catalytic testing demonstrated that liquid N₂H₄ can be decomposed to gaseous NH₃ and H₂ at a favorable rate and at a temperature as low as 20 °C and H₂ selectivity reaching values as high as 10% at 60 °C. Comparable fuel cell performance was observed using either the in situ decomposition products of hydrazine or pure hydrogen as fuel. A peak power density of ∼850 mW cm⁻² at 900 °C was obtained with a typical fuel cell composed of scandia-stabilized zirconia and La_0.8Sr_0.2MnO₃ cathode. The high energy and power density, easy storage and simplicity in fuel delivery make it highly attractive for portable applications.     

Studies of electrochemical performance of carbon supported Pt-Cu nanoparticles as anode catalysts for direct borohydride-hydrogen peroxide fuel cell

Carbon supported Pt-Cu bimetallic nanoparticles are prepared by a modified NaBH₄ reduction method in aqueous solution and used as the anode electrocatalyst of direct borohydride-hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties of the as-prepared electrocatalysts are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry (CV), chronoamperometry (CA), chronopotentiometry (CP) and fuel cell test. The results show that the carbon supported Pt-Cu bimetallic catalysts have much higher catalytic activity for the direct oxidation of BH₄⁻ than the carbon supported pure nanosized Pt catalyst, especially the Pt₅₀Cu₅₀/C catalyst presents the highest catalytic activity among all as-prepared catalysts, and the DBHFC using Pt₅₀Cu₅₀/C as anode electrocatalyst and Pt/C as cathode electrocatalyst shows as high as 71.6 mW cm⁻² power density at a discharge current density of 54.7 mA cm⁻² at 25 °C.     

Direct borohydride fuel cell using Ni-based composite anodes

In this study, nickel-based composite anode catalysts consisting of Ni with either Pd on carbon or Pt on carbon (the ratio of Ni:Pd or Ni:Pt being 25:1) were prepared for use in direct borohydride fuel cells (DBFCs). Cathode catalysts used were 1 mg cm⁻² Pt/C or Pd electrodeposited on activated carbon cloth. The oxidants were oxygen, oxygen in air, or acidified hydrogen peroxide. Alkaline solution of sodium borohydride was used as fuel in the cell. High power performance has been achieved by DBFC using non-precious metal, Ni-based composite anodes with relatively low anodic loading (e.g., 270 mW cm⁻² for NaBH₄/O₂ fuel cell at 60 °C, 665 mW cm⁻² for NaBH₄/H₂O₂ fuel cell at 60 °C). Effects of temperature, oxidant, and anode catalyst loading on the DBFC performance were investigated. The cell was operated for about 100 h and its performance stability was recorded.     

A direct borohydride fuel cell employing Prussian Blue as mediated electron-transfer hydrogen peroxide reduction catalyst

A direct borohydride-hydrogen peroxide fuel cell employing carbon-supported Prussian Blue (PB) as mediated electron-transfer cathode catalyst is reported. While operating at 30 °C, the direct borohydride-hydrogen peroxide fuel cell employing carbon-supported PB cathode catalyst shows superior performance with the maximum output power density of 68 mW cm⁻² at an operating voltage of 1.1 V compared to direct borohydride-hydrogen peroxide fuel cell employing the conventional gold-based cathode with the maximum output power density of 47 mW cm⁻² at an operating voltage of 0.7 V. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Analysis (EDAX) suggest that anchoring of Cetyl-Trimethyl Ammonium Bromide (CTAB) as a surfactant moiety on carbon-supported PB affects the catalyst morphology. Polarization studies on direct borohydride-hydrogen peroxide fuel cell with carbon-supported CTAB-anchored PB cathode exhibit better performance with the maximum output power density of 50 mW cm⁻² at an operating voltage of 1 V than the direct borohydride-hydrogen peroxide fuel cell with carbon-supported Prussian Blue without CTAB with the maximum output power density of 29 mW cm⁻² at an operating voltage of 1 V.     

Monolithic micro-direct methanol fuel cell in polydimethylsiloxane with microfluidic channel-integrated Nafion strip

We demonstrate a monolithic polymer electrolyte membrane fuel cell by integrating a narrow (200 μm) Nafion strip in a molded polydimethylsiloxane (PDMS) structure. We propose two designs, based on two 200 μm-wide and two 80 μm-wide parallel microfluidic channels, sandwiching the Nafion strip, respectively. Clamping the PDMS/Nafion assembly with a glass chip that has catalyst-covered Au electrodes, results in a leak-tight fuel cell with stable electrical output. Using 1 M CH₃OH in 0.5 M H₂SO₄ solution as fuel in the anodic channel, we compare the performance of (I) O₂-saturated 0.5 M H₂SO₄ and (II) 0.01 M H₂O₂ in 0.5 M H₂SO₄ oxidant solutions in the cathodic channel. For the 200 μm channel width, the fuel cell has a maximum power density of 0.5 mW cm⁻² and 1.5 mW cm⁻² at room temperature, for oxidants I and II, respectively, with fuel and oxidant flow rates in the 50-160 μL min⁻¹ range. A maximum power density of 3.0 mW cm⁻² is obtained, using oxidant II for the chip with 80 μm-wide channel, due to an improved design that reduces oxidant and fuel depletion effects near the electrodes.     

Proton-conducting fuel cells operating on hydrogen,ammonia and hydrazine at intermediate temperatures

Anode-supported proton-conducting fuel cell with BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) electrolyte and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) cathode was fabricated. Peak power densities of ∼420 and 135 mW/cm² were achieved, respectively, at 700 and 450 °C for a cell with 35 μm thick electrolyte operating on hydrogen fuel. The endothermic nature of the ammonia decomposition reaction, however, resulted in cell temperature 30–65 °C lower than the furnace when operating on ammonia. Accounting the cooling effect, comparable power density was achieved for the cell operating on ammonia and hydrogen at high temperature. At reduced temperature, the cell demonstrated worse performance when operating on ammonia than on hydrogen due to the poor activity of the anode towards NH₃ catalytic decomposition. By applying on-line catalytic decomposition products of N₂H₄ as the fuel, similar cell performance to that with NH₃ fuel was also observed.     

LaNi0.8Co0.2O3 as a cathode catalyst for a direct borohydride fuel cell

A perovskite-type oxide LaNi_0.8Co_0.2O₃ is prepared as a direct borohydride fuel cell (DBFC) cathode catalyst. Its electrochemical properties are studied by cyclic voltammetry. The results demonstrate that LaNi_0.8Co_0.2O₃ exhibits excellent electrochemical activity with respect to the oxygen reduction reaction (ORR) and good tolerance of BH₄⁻ ions. Maximum power densities of 114.5 mW cm⁻² at 30 °C and 151.3 mW cm⁻² at 62 °C are obtained, and good stability (300-h stable performance at 20 mA cm⁻²) is also exhibited, which shows that such perovskite-type oxides as LaNi_0.8Co_0.2O₃ can be excellent catalysts for DBFCs.     

GdBaCo2O5+x layered perovskite as an intermediate temperature solid oxide fuel cell cathode

GdBaCo₂O_5+x (GBCO) was evaluated as a cathode for intermediate-temperature solid oxide fuel cells. A porous layer of GBCO was deposited on an anode-supported fuel cell consisting of a 15 μm thick electrolyte of yttria-stabilized zirconia (YSZ) prepared by dense screen-printing and a Ni–YSZ cermet as an anode (Ni–YSZ/YSZ/GBCO). Values of power density of 150 mW cm⁻² at 700 °C and ca. 250 mW cm⁻² at 800 °C are reported for this standard configuration using 5% of H₂ in nitrogen as fuel. An intermediate porous layer of YSZ was introduced between the electrolyte and the cathode improving the performance of the cell. Values for power density of 300 mW cm⁻² at 700 °C and ca. 500 mW cm⁻² at 800 °C in this configuration were achieved.     

The study of Au/MoS2 anode catalyst for solid oxide fuel cell (SOFC) using H2S-containing syngas fuel

Au/MoS₂ is a promising anode catalyst for conversion of all components of H₂S-containing syngas in solid oxide fuel cell (SOFC). MoS₂-supported nano-Au particles have catalytic activity for conversion of CO when syngas is used as fuel in SOFC systems, thus preventing poisoning of MoS₂ active sites by CO. In contrast to use of MoS₂ as anode catalyst, performance of Au/MoS₂ anode catalyst improves when CO is present in the feed. Current density over 600 mA cm⁻² and maximum power density over 70 mW cm⁻² were obtained at 900 °C, showing that Au/MoS₂ could be potentially used as sulfur-tolerant catalyst in fuel cell applications.     

Concentration ratio of [OH]/[BH4]: A controlling factor for the fuel efficiency of borohydride electro-oxidation

The fuel efficiency of borohydride electro-oxidation on carbon-supported Au and Ag electrodes was found to be highly dependent on the concentration ratio of [OH⁻]/[BH₄⁻] in the solution. Near-8e reactions occurred when [OH⁻]/[BH₄⁻] ≥ 5. However when [OH⁻]/[BH₄⁻] was smaller than 5, hydrogen gas was evolved and the fuel efficiency was reduced. Only 3e reaction stoichiometry was obtained at [OH⁻]/[BH₄⁻] = 1. Detailed cyclic voltammetry (CV) studies revealed that both the Au/C and Ag/C showed different anodic waves in varied NaOH–NaBH₄ solutions. The CV analysis results suggest that BH₃OH⁻, an intermediate possibly produced by homogeneous hydrolysis, is responsible for the electrochemical reaction at [OH⁻]/[BH₄⁻] = 1. Comparison of CV voltammograms in borohydride solutions with that in the H₂-bubbled NaOH solution suggests that borohydride electro-oxidation on Au or Ag electrode is through direct BH₄⁻ oxidation rather than through a hydrogen ionization mechanism. It is concluded that there exists an inherent competition between two oxidizing species of OH⁻ and H₂O during borohydride electro-oxidation, that is, if accessible OH⁻ ions are not sufficient for each BH₄⁻ to accomplish the 8e electro-oxidation, part of BH₄⁻ will react simultaneously with H₂O to generate hydrogen.     

Protonic membrane for fuel cell for co-generation of power and ethylene

Yttrium-doped barium cerate, BaCe_0.85Y_0.15O_3−α (BCY15), membranes are proton-conducting electrolytes for intermediate-temperature protonic ceramic fuel cells (IT-PCFC), useful for, among other processes, co-production of power and ethylene by dehydrogenation of ethane. BCY15 membranes showed good conductivity at intermediate temperatures, 15 and 20 mS cm⁻¹ at 700 and 750 °C, respectively. Maximum power density was 174 mW cm⁻² at 700 °C, with a corresponding current density of 320 mA cm⁻², using a C₂H₆,Pt/BCY15/Pt,O₂ fuel cell, with a ca. 0.5 mm thick membrane, producing 34% ethane conversion with 96% ethylene selectivity Comparison of performances using vertical and horizontal set-ups showed that horizontal set-ups are subject to torsional strain, causing reduced cell performance resulting from even minor leakage at the glass seal.     

Catalytic dehydrogenation of ammonia borane in non-aqueous medium

Dehydrogenation of Ammonia Borane (NH₃BH₃, AB) catalyzed by transition metal heterogeneous catalysts was carried out in non-aqueous solution at temperatures below the standard polymer electrolyte membrane (PEM) fuel cell operating conditions. The introduction of a catalytic amount (∼2 mol%) of platinum to a solution of AB in 2-methoxyethyl ether (0.02–0.33 M) resulted in a rapid evolution of H₂ gas at room temperature. At 70 °C, the rate of platinum catalyzed hydrogen release from AB was the dehydrogenation rate which was 0.04 g s⁻¹ H₂ kW⁻¹.     

Study of fuel efficiency in a direct borohydride fuel cell

In this study, direct borohydride fuel cells (DBFCs) potentialities are evaluated. These emerging systems make it possible to reach maximum powers of about 200 mW cm⁻² at room temperature and ambient air (natural convection) with high concentrated borohydride solutions. On the other hand, a part of borohydride hydrolyses during cell operating which leads to hydrogen formation and fuel loss: the practical capacity represents about only 18% of the theoretical one. In order to improve fuel efficiency, thiourea is tested as an inhibitor of the catalytic hydrolysis associated with BH₄⁻ electro-oxidation on Pt. The practical capacity is drastically improved: it represents about 64% of the theoretical one. Against, electrochemical performances (I–E curves) are affected by the presence of thiourea.     

Effects of NaOH addition on performance of the direct hydrazine fuel cell

In this work, we suggested a figuration of the direct hydrazine fuel cell (DHFC) using non-precious metals as the anode catalyst, ion exchange membranes as the electrolyte and alkaline hydrazine solutions as the fuel. NaOH addition in the anolyte effectively improved the open circuit voltage and the performance of the DHFC. A power density of 84 mW cm⁻² has been achieved when operating the cell at room temperature. It was found that the cell performance was mainly influenced by anode polarization when using alkaline N₂H₄ solutions with low NaOH concentrations. However, when using alkaline N₂H₄ solutions with high NaOH concentrations as the fuel, the cell performance was mainly influenced by cathode polarization.     

Characteristics of a fluidized bed electrode for a direct carbon fuel cell anode

The characteristics of a fluidized bed electrode applied as a direct carbon fuel cell anode, which has an inner diameter of 35 mm and height of 520 mm and employed bamboo-based activated carbon (BB-AC) as a feedstock, are vigorously studied under various experimental conditions. The optimal performance of the fluidized bed electrode direct carbon fuel cell (FEBDCFC) anode with the BB-AC as a fuel is obtained under the following conditions with a limiting current density of 95.9 mA cm⁻²: reaction temperature, 923 K; N₂ flow rate, 385 ml min⁻¹; O₂/CO₂ flow rate, 10/20 ml min⁻¹; nickel particle content, 30 g; and a cylindrically curved nickel plate as a current collector. Under the same optimal conditions, the limiting current density of the FEBDCFC anode with oak wood-based activated carbon and activated carbon fiber as the fuel is determined to be 94.5 and 88.4 mA cm⁻², which is lower than that determined for BB-AC as the fuel. Comparatively, the limiting current density for graphite, which is utilized as the carbon fuel for this fuel cell system, could not be unequivocally determined because no plateau of the limiting current density against the overpotential is observed.     

Sr2Fe4/3Mo2/3O6 as anodes for solid oxide fuel cells

Sr₂Fe_4/3Mo_2/3O₆ has been synthesized by a combustion method in air. It shows a single cubic perovskite structure after being reduced in wet H₂ at 800 °C and demonstrates a metallic conducting behavior in reducing atmospheres at mediate temperatures. Its conductivity value at 800 °C in wet H₂ (3% H₂O) is about 16 S cm⁻¹. This material exhibits remarkable electrochemical activity and stability in H₂. Without a ceria interlayer, maximum power density (P_max) of 547 mW cm⁻² is achieved at 800 °C with wet H₂ (3% H₂O) as fuel and ambient air as oxidant in the single cell with the configuration of Sr₂Fe_4/3Mo_2/3O₆|La_0.8Sr_0.2Ga_0.83Mg_0.17O₃ (LSGM)| La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF). The P_max even increases to 595 mW cm⁻² when the cell is operated at a constant current load at 800 °C for additional 15 h. This anode material also shows carbon resistance and sulfur tolerance. The P_max is about 130 mW cm⁻² in wet CH₄ (3% H₂O) and 472 mW cm⁻² in H₂ with 100 ppm H₂S. The cell performance can be effectively recovered after changing the fuel gas back to H₂.     

Characterization of bubble formation in microfluidic fuel cells employing hydrogen peroxide

In order to examine bubble evolution and discuss the effects of bubbles effect on the performance of microfluidic fuel cells, two 1.2-mm-depth microfluidic fuel cells employing 0.1-M H₂O₂ dissolved in 0.1-M NaOH solution and 0.05-M H₂SO₄ solution as fuel and oxidant, respectively, with transparent lids having width of 1.0 mm and 0.5 mm, are fabricated in the present study for both cell performance measurement and flow visualization. The results show that the present cells operating at either a higher volumetric flow or a smaller microchannel width yield both better performance and more violent bubble growth. The bubble growth rate, Q_g, in a given microfluidic fuel cell is almost the same at different regions of that cell at a given volumetric flow rate, i.e. 10⁻⁵ cm³ s⁻¹ and 5 × 10⁻⁵ cm³ s⁻¹, respectively, for cells having widths of 0.5 mm and 1.0 mm at Q_l = 0.05 mL min⁻¹, and slightly increases at higher volumetric flow rates. Furthermore, the present study reports approximately constant values of Q_g/C_dA at various volumetric flow rates, which are 2 × 10⁻² and 5 × 10⁻² cm³ s⁻¹ A⁻¹, respectively, for cells having channel widths of 0.5 mm and 1.0 mm. In addition, the 0.5-mm-wide cell has higher cell output and performs more tortuous polarization curve.     

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.