Membrane electrode assemblies with low noble metal loadings for hydrogen production from solid polymer electrolyte water electrolysis

High performance membrane electrode assemblies (MEAs) with low noble metal loadings (NMLs) were developed for solid polymer electrolyte (SPE) water electrolysis. The electrochemical and physical characterization of the MEAs was performed by I–V curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Even though the total NML was lowered to 0.38 mg cm⁻², it still reached a high performance of 1.633 V at 2 A cm⁻² and 80 °C, with IrO₂ as anode catalyst. The influences of the ionomer content in the anode catalyst layer (CL) and the cell temperature were investigated with the purpose of optimizing the performance. SEM and EIS measurements revealed that the MEA with low NML has very thin porous cathode and anode CLs that get intimate contact with the electrolyte membrane, which makes a reduced mass transport limitation and lower ohmic resistance of the MEA. A short-term water electrolysis operation at 1 A cm⁻² showed that the MEA has good stability: the cell voltage maintained at ∼1.60 V without distinct degradation after 122 h operation at 80 °C and atmospheric pressure.     

Characterization of La0.995Ca0.005NbO4/Ni anode functional layer by electrophoretic deposition in a La0.995Ca0.005NbO4 electrolyte based PCFC

The Electrophoretic Deposition (EPD) technique has been applied to the preparation of a porous La_0.995Ca_0.005NbO₄/Ni composite anode layer, deposited on a porous pre-sintered La_0.995Ca_0.005NbO₄/Ni support. Powders of La_0.995Ca_0.005NbO₄ and NiO were suspended in a solution of acetylacetone, iodine and water. Selectivity in the composition of the deposited layer was analyzed as a function of the suspension compositions and deposition conditions. A quasi-symmetrical cell was produced by depositing La_0.995Ca_0.005NbO₄ electrolyte layer on the anode layer by EPD, and by applying a porous La_0.995Ca_0.005NbO₄/Ni counter electrode on the dense electrolyte layer by brushing. The performance of the electrodes was evaluated by electrochemical impedance spectroscopy in 3% wet H_2.     

Promising alloys for intermediate-temperature solid oxide fuel cell interconnect application

The formation of a low Cr-volatility and electrically conductive oxide outer layer atop an inner chromia layer via thermal oxidation is highly desirable for preventing chromium evaporation from solid oxide fuel cell (SOFC) metallic interconnects at the SOFC operation temperatures. In this paper, a number of ferritic Fe–22Cr alloys with different levels of Mn and Ti as well as a Ni-based alloy Haynes 242 were cyclically oxidized in air at 800 °C for twenty 100-h cycles. No oxide scale spallation was observed during thermal cycling for any of these alloys. A mixed Mn₂O₃/TiO₂ surface layer and/or a (Mn, Cr)₃O₄ spinel outer layer atop a Cr₂O₃ inner layer was formed for the Fe–22Cr series alloys, while an NiO outer layer with a Cr₂O₃ inner layer was developed for Haynes 242 after cyclic oxidation. For the Fe–22Cr series alloys, the effects of Mn and Ti contents as well as alloy purity on the oxidation resistance and scale area specific resistance were evaluated. The performance of the ferritic alloys was compared with that of Haynes 242. The mismatch in thermal expansion coefficient between the different layers in the oxide scale was identified as a potential concern for these otherwise promising alloys.     

Solid oxide fuel cell: Materials for anode,cathode and electrolyte

Solid oxide fuel cell technology is the technology which can be driving force to change the course of action of the modern era due to its optimal power generation features with maximum electrical efficiency for automobiles and household devices. Fuel cells can be best described as electrochemical devices that make use of fuel oxidation to convert chemical energy into electrical energy and also lower the amount of oxidant simultaneously.A typical SOFC consists of a cathode, anode and an electrolyte constituting a single cell. These single cells are stacked together for a bigger assembly to produce higher degree of power. The solid electrolyte fills the gap between the cathode and anode transporting O²⁻ ions only. This leaves out electrons as transporting medium, which then pass through the cell via external circuit. Out of the two electrodes, oxidation of fuel takes place at the anode and reduction of oxygen takes place at the cathode. The SOFCs operate at higher temperatures of 600–1200°C producing heat as a byproduct of high quality, actively encouraging quick electrocatalysis utilizing non-precious metals and allowing internal restructuration. The SOFC can also work with high purity hydrogen for proton transport other than O²⁻ ion transport. There are many ceramic materials which have been engineered to act as efficient electrolyte materials. Yttria-stabilized zirconia (YSZ) is the most widely used material as solid electrolyte in SOFC.The present review presents a detailed overview of the SOFC related materials and devices and is an effort to present various reported works in a concise manner.     

Performance analysis and temperature gradient of solid oxide fuel cell stacks operated with bio-oil sorption-enhanced steam reforming

A high temperature gradient within a solid oxide fuel cell (SOFC) stack is considered a major challenge in SOFC operations. This study investigates the effects of the key parameters on SOFC system efficiency and temperature gradient within a SOFC stack. A 40-cell SOFC stack integrated with a bio-oil sorption-enhanced steam reformer is simulated using MATLAB and DETCHEM. When the air-to-fuel ratio and steam-to-fuel ratio increase, the stack average temperature and temperature gradient decrease. However, a decrease in the stack temperature steadily reduces the system efficiency owing to the tradeoff between the stack performance and thermal balance between heat recovered and consumed by the system. With an increase in the bio-oil flow rate, the system efficiency decreases because of the lower resident time for the electrochemical reaction. This is not, however, beneficial to the maximum temperature gradient. To minimize the temperature gradient of the SOFC stack, a decrease in the bio-oil flow rate is the most effective way. The maximum temperature gradient can be reduced to 14.6 K cm⁻¹ with the stack and system efficiency of 76.58 and 65.18%, respectively, when the SOFC system is operated at an air-to-fuel ratio of 8, steam-to-fuel ratio of 6, and bio-oil flow rate of 0.0041 mol s⁻¹.     

The synthesis and characterization of the Sm0.5Sr0.5Co1−xCuxO3−δ cathode by the glycine-nitrate process

In this study, a new oxygen-deficient cathode material, Sm_0.5Sr_0.5Co_1−xCu_xO_3−δ (SSCCu) was developed. It is expected to enhance the efficiency of intermediate-temperature solid oxide fuel cells (IT-SOFCs). The structure, conductivity and electrochemical performance of SSCCu were examined as a function of copper content. The structure of Sm_0.5Sr_0.5Co_0.9Cu_0.1O_3−δ and Sm_0.5Sr_0.5Co_0.8Cu_0.2O_3−δ samples was a single orthorhombic perovskite phase. Second phase SrCoO_2.8, however, formed in the Sm_0.5Sr_0.5Co_0.7Cu_0.3O_3−δ and Sm_0.5Sr_0.5Co_0.6Cu_0.4O_3−δ samples. The conductivity of the Sm_0.5Sr_0.5Co_0.7Cu_0.3O_3−δ cathode was higher than that of other samples. However, the Sm_0.5Sr_0.5Co_0.8Cu_0.2O_3−δ electrode exhibited the lowest overpotential of 25 mV at 400 mA cm⁻² and the lowest area special resistance of 0.2 Ω cm² at 700 °C.     

Solid state synthesis of hydrous ruthenium oxide for supercapacitors

A novel solid state route has been successfully developed for the synthesis of nano-scale hydrous ruthenium oxide (denoted as RuO₂·xH₂O). The procedure involves directly mixing RuCl₂·xH₂O with alkali to form RuO₂·xH₂O in a mortar at room temperature. Transmission electron microscopy (TEM) and N₂ adsorption–desorption measurement indicate that the RuO₂·xH₂O particle is approximately 30–40 nm with mesoporous structure. The crystalline structure and the electrochemical properties of RuO₂·xH₂O have been systematically explored as a function of annealing temperature. At lower temperatures, the RuO₂·xH₂O powder was found in an amorphous phase and the maximum capacitance of 655 F g⁻¹ was obtained by annealing at 150 °C. Higher temperatures (exceeding 175 °C) presumably converted amorphous phase into crystalline one and the corresponding specific capacitance dropped rapidly from 547 F g⁻¹ at 175 °C to 87 F g⁻¹ at 400 °C. Also, the dependence of electrochemical performance on annealing conditions of RuO₂·xH₂O was investigated by electrical impedance spectroscopy (EIS) study.     

A maximum power point tracking for photovoltaic-SPE system using a maximum current controller

Processes to produce hydrogen from solar photovoltaic (PV)-powered water electrolysis using solid polymer electrolysis (SPE) are reported. An alternative control of maximum power point tracking (MPPT) in the PV-SPE system based on the maximum current searching methods has been designed and implemented.Based on the characteristics of voltage–current and theoretical analysis of SPE, it can be shown that the tracking of the maximum current output of DC–DC converter in SPE side will track the MPPT of photovoltaic panel simultaneously.This method uses a proportional integrator controller to control the duty factor of DC–DC converter with pulse-width modulator (PWM).The MPPT performance and hydrogen production performance of this method have been evaluated and discussed based on the results of the experiment.     

Nano-sized Fe2O3–SO4 solid superacid composite Nafion membranes for direct methanol fuel cells

In this paper, Fe₂O₃–SO₄²⁻/Nafion^® composite membranes were prepared by a solution casting method. The physico-chemical properties of composite membranes were characterized by X-ray diffraction (XRD), SEM–EDX and thermogravimetric analysis (TGA). The water uptake ability, proton conductivity, and methanol permeability of the composite membranes were evaluated and compared with the recast Nafion^® membrane. The results showed that the proton conductivity and the water uptake of the composite membranes were slightly higher than that of the recast Nafion^® membrane. The composite membrane containing 5 wt.% Fe₂O₃–SO₄^2- showed superior ability to suppress methanol crossover, and it further improved the direct methanol fuel cell (DMFC) performances with both 1 M and 5 M methanol feeding, compared with the recast Nafion^® membrane. The preliminary 30 h lifetime test of the DMFC with the composite membrane with 5% Fe₂O₃–SO₄²⁻ indicated that the composite membrane is stable working at the real DMFC operating conditions at least during the test. These results suggest the applicability of the composite membranes in DMFCs.