Fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel-cell technology can gain a significant share of the electrical power market, important issues have to be addressed. These issues include optimal choice of fuel, and the development of alternative materials in the fuel-cell stack. Present fuel-cell prototypes often use materials selected more than 25 years ago. Commercialization aspects, including cost and durability, have revealed inadequacies in some of these materials. Here we summarize recent progress in the search and development of innovative alternative materials.

Materials for fuel-cell technologies

2.1. Solvents 4307 2.1.1. Propylene Carbonate (PC) 4308 2.1.2. Ethers 4308 2.1.3. Ethylene Carbonate (EC) 4309 2.1.4. Linear Dialkyl Carbonates 4310 2.2. Lithium Salts 4310 2.2.1. Lithium Perchlorate (LiClO4) 4311 2.2.2. Lithium Hexafluoroarsenate (LiAsF6) 4312 2.2.3. Lithium Tetrafluoroborate (LiBF4) 4312 2.2.4. Lithium Trifluoromethanesulfonate (LiTf) 4312 2.2.5. Lithium Bis(trifluoromethanesulfonyl)imide (LiIm) and Its Derivatives 4313

/pdf/nonaqueous-liquid-electrolytes-for-lithium-based-uxm5ffbi18.pdf

Nonaqueous liquid electrolytes for lithium-based rechargeable batteries.

Electrolytes and interphases in Li-ion batteries and beyond.

https://las493energy.files.wordpress.com/2014/11/2005_vetter_jpowsourc.pdf

Ageing mechanisms in lithium-ion batteries

Fuel cells directly and efficiently convert chemical energy to electrical energy. Of the various fuel cell types, solid-oxide fuel cells (SOFCs) combine the benefits of environmentally benign power generation with fuel flexibility. However, the necessity for high operating temperatures (800–1,000 °C) has resulted in high costs and materials compatibility challenges. As a consequence, significant effort has been devoted to the development of intermediate-temperature (500–700 °C) SOFCs. A key obstacle to reduced-temperature operation of SOFCs is the poor activity of traditional cathode materials for electrochemical reduction of oxygen in this temperature regime2. Here we present Ba_(0.5_Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-delta) (BSCF) as a new cathode material for reduced-temperature SOFC operation. BSCF, incorporated into a thin-film doped ceria fuel cell, exhibits high power densities (1,010 mW cm^(-2) and 402 mW cm^(-2) at 600 °C and 500 °C, respectively) when operated with humidified hydrogen as the fuel and air as the cathode gas. We further demonstrate that BSCF is ideally suited to 'single-chamber' fuel-cell operation, where anode and cathode reactions take place within the same physical chamber. The high power output of BSCF cathodes results from the high rate of oxygen diffusion through the material. By enabling operation at reduced temperatures, BSCF cathodes may result in widespread practical implementation of SOFCs.

A high-performance cathode for the next generation of solid-oxide fuel cells

The performance of a single-chamber solid oxide fuel cell was studied using a ceria-based solid electrolyte at temperatures below 773 kelvin. Electromotive forces of ∼900 millivolts were generated from the cell in a flowing mixture of ethane or propane and air, where the solid electrolyte functioned as a purely ionic conductor. The electrode-reaction resistance was negligibly small in the total internal resistances of the cell. The resulting peak power density reached 403 and 101 milliwatts per square centimeter at 773 and 623 kelvin, respectively.

https://science.sciencemag.org/content/sci/288/5473/2031.full.pdf

A low-operating-temperature solid oxide fuel cell in hydrocarbon-Air mixtures

Recent advances in single-chamber solid oxide fuel cells: A review

SnP 2 O 7 -based proton conductors were characterized by Fourier transform infrared spectroscopy (FTIR), temperature-programmed desorption (TPD), X-ray diffraction (XRD), and electrochemical techniques. Undoped SnP 2 O 7 showed overall conductivities greater than 10 -2 S cm -1 in the temperature range of 75-300°C. The proton transport numbers of this material at 250°C under various conditions were estimated, based on the ratio of the electromotive force of the galvanic cells to the theoretical values, to be 0.97-0.99 in humidified H 2 and 0.89-0.92 under fuel cell conditions. Partial substitution of In 3+ for Sn 4+ led to an increase in the proton conductivity (from 5.56 X 10 -2 to 1.95 X 10 -1 S cm -1 at 250°C, for example). FTIR and TPD measurements revealed that the effects of doping on the proton conductivity could be attributed to an increase in the proton concentration in the bulk Sn 1-x In x P 2 O 7 . The deficiency of P 2 O 2 ions in the Sn 1-x In x P 2 O 7 bulk decreased the proton conductivity by several orders of magnitude, which was explained as due to a decrease in the proton mobility rather than the proton concentration. The mechanism of proton incorporation and conduction is examined and discussed in detail.

Proton Conduction in In3 + -Doped SnP2O7 at Intermediate Temperatures

We report proton conduction in In 3+ -doped SnP 2 O 7 in the temperature range from 100 to 300°C, and the performance of a H 2 -air fuel cell using this material as the electrolyte. The proton conductivity of In 3+ -doped SnP 2 O 7 was more than 10 -1 S cm -1 between 125 and 300°C, and a conductivity value of 1.95 × 10 -1 S cm -1 was achieved at 250°C. The resulting fuel cell exhibited a reasonable power density of 264 mW cm -2 at 250°C (electrolyte thickness = 0.35 mm), together with perfect tolerance toward 10% CO and good thermal stability in unhumidified conditions.

A proton-conducting In3+-doped SnP2O7 electrolyte for intermediate-temperature fuel cells

The capacity fading of lithiated and delithiated graphite electrodes has been studied using lithium manganese oxide as a counter electrode. Higher storage temperatures and longer storage periods give larger capacity losses and larger amounts of manganese (Mn) deposition on the graphite. The capacity losses appear to be related to the amount of deposited Mn in storage experiments in dry electrolyte solutions containing various concentrations of Mn 2+ ions, but definite evidence has not been found that the Mn deposit is a simple and direct cause of the capacity fading. The capacity losses estimated from quantities of Mn deposition on the graphite, assuming a Mn 2+ -Li exchange process, appear negligible when compared with the experimental findings. Scanning electron microscope and transmission electron microscope observations show the presence of some amounts of fluoride compounds accompanying some Mn contents on the graphite. The capacities of the graphites are recovered to some extent during the cycles.

Mitsuru Sano

Papers

A low-operating-temperature solid oxide fuel cell in hydrocarbon-Air mixtures

Recent advances in single-chamber solid oxide fuel cells: A review

Proton Conduction in In3 + -Doped SnP2O7 at Intermediate Temperatures

A proton-conducting In3+-doped SnP2O7 electrolyte for intermediate-temperature fuel cells

Capacity Fading of Graphite Electrodes Due to the Deposition of Manganese Ions on Them in Li-Ion Batteries