Switching on electrocatalytic activity in solid oxide cells

A new way of activating the electrodes in solid oxide cells involves applying an electrical potential to trigger the exsolution of metal catalysts to the electrode surface; the success of this technique raises the possibility of regenerating the electrodes during operation. Incorporating nanostructured electrodes into solid oxide fuel cells improves performance by increasing the active surface area and therefore increasing electrocatalytic activity. However, fabrication of such electrodes by physical or chemical deposition can be complex. Redox exsolution of nanoparticles from a parent perovskite was shown recently to be a viable means of producing electrodes with enhanced stability. Here, John Irvine and colleagues demonstrate that similar exsolution can be achieved by simply poling the cell for a few seconds, rather than the lengthy redox processes previously used. The resulting cells are highly stable in fuel and electrolysis modes, showing that high-performing electrodes can be fabricated quickly and easily in situ. 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 manufacture1. This has typically been achieved through lengthy and intricate ex situ procedures. These often require dedicated precursors and equipment1,2,3; moreover, although the degradation of such electrodes associated with their reversible operation can be mitigated4, they are susceptible to many other forms of degradation5. An alternative is to grow appropriate electrode nanoarchitectures under operationally relevant conditions, for example, via redox exsolution6,7,8,9,10. 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.