Jae-ha Myung

Switching on electrocatalytic activity in solid oxide cells

Solid oxide cells (SOCs) can operate with high efficiency in two ways—as fuel cells, oxidizing a fuel to produce electricity, and as electrolysis cells, electrolysing water to produce hydrogen and oxygen gases. Ideally, SOCs should perform well, be durable and be inexpensive, but there are often competitive tensions, meaning that, for example, performance is achieved at the expense of durability. SOCs consist of porous electrodes—the fuel and air electrodes—separated by a dense electrolyte. In terms of the electrodes, the greatest challenge is to deliver high, long-lasting electrocatalytic activity while ensuring cost- and time-efficient manufacture. This has typically been achieved through lengthy and intricate ex situ procedures. These often require dedicated precursors and equipment; moreover, although the degradation of such electrodes associated with their reversible operation can be mitigated, they are susceptible to many other forms of degradation. An alternative is to grow appropriate electrode nanoarchitectures under operationally relevant conditions, for example, via redox exsolution. Here we describe the growth of a finely dispersed array of anchored metal nanoparticles on an oxide electrode through electrochemical poling of a SOC at 2 volts for a few seconds. These electrode structures perform well as both fuel cells and electrolysis cells (for example, at 900 °C they deliver 2 watts per square centimetre of power in humidified hydrogen gas, and a current of 2.75 amps per square centimetre at 1.3 volts in 50% water/nitrogen gas). The nanostructures and corresponding electrochemical activity do not degrade in 150 hours of testing. These results not only prove that in operando methods can yield emergent nanomaterials, which in turn deliver exceptional performance, but also offer proof of concept that electrolysis and fuel cells can be unified in a single, high-performance, versatile and easily manufactured device. This opens up the possibility of simple, almost instantaneous production of highly active nanostructures for reinvigorating SOCs during operation.

Nano-composite structural Ni-Sn alloy anodes for high performance and durability of direct methane-fueled SOFCs

Ni-based cermets have commonly been used as anode materials with good catalytic properties for hydrocarbon fuels. However, carbon deposition can occur due to the non-ideal electrochemical reaction of hydrocarbon fuel and the structural limitation resulting from the unsymmetrical Ni-based anode-supported single cells. This critical problem leads to loss of cell performance and poor long-term stability of solid oxide fuel cells (SOFCs). Our designed anode material with an extremely small amount (0.5 wt%) of Sn catalyst incorporated into the Ni and nano-composite structure was employed not only to prevent carbon deposition in oxygen deficient areas found for unsymmetrical cells, but also to increase the cell performance due to its excellent microstructure. The nano-composite Sn doped Ni-GDC cells showed a power density of 0.93 W cm−2 with stable operation in dry methane at 650 °C.