Fuel cells - Page 3

A team of researchers at Northwestern University has created a new fuel cell with a perovskite-based cathode, that offers both exceptional power densities and long-term stability at optimal temperatures.

"For years, industry has told us that the holy grail is getting fuel cells to work at 500-degrees Celsius and with high power density, which means a longer life and less expensive components," said the team. "With this research, we can now envision a path to making cost-effective fuel cells and transforming the energy landscape."

Fuel cells are a hoped to be a key future energy technology for achieving renewable energy sources that are eco-friendly and low-cost. In particular, solid oxide fuel cells composed of ceramic materials are gaining increasing amounts of attention for their ability to directly convert various forms of fuel such as biomass, LNG, and LPG to electric energy. Researchers at KAIST have relied on pervoskite materials to develop a new technique to improve the chemical stability of electrode materials that can extend their lifespan by employing minimal amounts of metals.

The core factor that determines the performance of solid oxide fuel cells is the cathode at which the reduction reaction of oxygen takes place. Conventionally, perovskite structure oxides (ABO3) are used in cathodes. However, despite the high performance of perovskite oxides at initial operation, performance degrades with time, limiting their long-term use. In particular, the condition of a high-temperature oxidation state required for cathode operation leads to a surface segregation phenomenon in which second phases such as strontium oxide (SrOx) accumulate on the surface of oxides, resulting in a decrease in electrode performance. The detailed mechanism of this phenomenon and a way to effectively inhibit it has not been suggested.

A team of researchers from the U.S-based Georgia Institute of Technology have designed ultrafine perovskite nanofibers as highly efficient and stable catalysts for OER - oxygen evolution reaction, a component reaction of the electrochemical splitting of water into hydrogen and oxygen. Water splitting is a key step in a number of sustainable energy technologies including hydrogen production, fuel cells, and rechargeable metal-air batteries.

The OER takes place at the anode of an electrolyzer, while the hydrogen evolution reaction takes place at the cathode. The energy required for the reaction is supplied by an electronic current. Currently, a large overpotential is required to accelerate the OER. For this reason, water splitting technologies for hydrogen production are not very competitive as the increased energy required results in more expensive hydrogen compared with production from natural gas. Therefore, much research is focused on the search for cost-effective, efficient and stable catalysts for the OER that can reduce the required overpotential. The new research highlights the potential of doped double perovskite nanofibers as the next generation of OER catalysts.

The Australian Nuclear Science and Technology Organisation (ANSTO) has collaborated with researchers at the University of Queensland in Australia, and Shandong University and Nanjing Tech Universities in China on research investigating the possible synergistic effects of a new perovskite cathode material for a low-temperature solid-oxide fuel cell (LT-SOFC) that demonstrates impressive and stable electrochemical performance below 500 °C.

Solid-oxide fuel cells (SOFC) convert the chemical energy in fuel into electricity directly by the oxidation of the fuel. These cells are considered to be highly efficient, exhibit long-term stability, produce low emissions, and are relatively low cost.

Researchers at MIT tackled the known problem of degradation suffered when perovskite oxides, promising candidates for electrodes in energy conversion devices like fuel cells, are exposed to water or gases such as oxygen or carbon dioxide at elevated temperatures.

The scientists explain that this degradation occurs as the surfaces of these perovskites get covered up by a strontium oxide'related layer, and this layer is insulating against oxygen reduction and oxygen evolution reactions, which are critical for the performance of fuel cells, electrolyzers and thermochemical fuel production. This layer on the electrode surface is detrimental to the efficiency and durability of the device, causing the surface reactions to slow down by more than an order of magnitude.

Researchers at Purdue University have found that nickel-based perovskites have exceptional properties for use as solid electrolytes in fuel cells. Unlike conventional electrolytes, these nickel-based perovskites are chemically stable in the fuel cell's environment, which could lead to higher performing and longer lasting fuel cells.

Schematic of the perovskite samarium nickelate (SNO)-electrolyte solid-oxide fuel cell.

Solid-oxide fuel cells are considered as one of the most efficient types of fuel cells. They typically use polymers or ceramics as an electrolyte, but finding an effective solid electrolyte'one that conducts protons but blocks electrons'at low operating temperatures of 300'500°C has been a challenge. Most materials, when exposed to low pressure, start to lose oxygen and become electron conductors; The electrolyte separator becomes leaky so it can short circuit the fuel cell or it can start to crack and allow fuel to mix with oxygen.