Switching on electrocatalytic activity in solid oxide cells

Abstract

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.

Highly efficient electrochemical reforming of CH 4 /CO 2 in a solid oxide electrolyser

“…The growth of metal nanoparticles drastically improves the current density to 1.2 A cm −2 at 1.5 V when optimum alloy compositions are obtained. These values are comparable to the performances of nickel-decorated (La,Sr)(Ti,Mn)O 3+δ cathodes and La 0.43 Ca 0.37 Ni 0.06 Ti 0.94 O 3+δ prepared with an electrochemical switching method ( 14 , 23 ). The in situ impedance spectra in fig.…”

Green synthesis of carbon quantum dots embedded onto titanium dioxide nanowires for enhancing photocurrent

“…The Ti 2p spectra were deconvoluted and resolved into four spin orbit components at 2p3/2 binding energies 457.6, 458.14 eV and their corresponding 2p1/2 components (463.21, 464.0 eV) which are assigned as Ti 3+ (TiOOH/coordinatively unsaturated) and Ti 4+ (TiO 2 ), respectively [42,43]. The large ratio of Ti 3+ is suggested owing to the increased electron content of the lattice surface of TiO 2 within the voltage-driven reduction process [44]. The peaks at 284.24, 285.44 and 287.99 eV for C 1 s spectrum are ascribed to the C–C bond with sp 2 orbital, C–O and C=O bonds, respectively.…”

Recent Advances in Novel Nanostructuring Methods of Perovskite Electrocatalysts for Energy‐Related Applications

“…In a broad sense, exsolution refers to the process of releasing compositional elements from the perovskite lattice to form nanoparticles anchored on the surface, with the driving force being the oxygen partial pressure gradient between the oxide lattice and external environment. This process can occur through “electrochemical switching” (a term recently initiated by Irvine and co‐workers) or through reduction by hydrogen . For example, Zhou et al reported an intercalation/de‐intercalation mechanism of A‐site silver‐doped (La 0.8 Sr 0.2 ) 0.95 Ag 0.05 MnO 3− δ perovskite under polarization conditions ( Figure a), where Ag can be stripped from the lattice under cathodic polarization, forming Ag nanoparticle–modified A‐site‐deficient (La 0.8 Sr 0.2 ) 0.95 MnO 3− δ , and then restored into the perovskite lattice under anodic polarization.…”

“…For example, Zhou et al reported an intercalation/de‐intercalation mechanism of A‐site silver‐doped (La 0.8 Sr 0.2 ) 0.95 Ag 0.05 MnO 3− δ perovskite under polarization conditions ( Figure a), where Ag can be stripped from the lattice under cathodic polarization, forming Ag nanoparticle–modified A‐site‐deficient (La 0.8 Sr 0.2 ) 0.95 MnO 3− δ , and then restored into the perovskite lattice under anodic polarization. More recently, Irvine and co‐workers observed the exsolution of Ni nanoparticles on the surface of La 0.43 Ca 0.37 Ni 0.06 Ti 0.94 O 3− γ perovskite upon the application of a 2 V potential at 900 °C . Compared with conventional reduction by hydrogen, such electrochemical switching happens faster (almost instantly), causes a higher extent of exsolution, and produces a greater particle population at a smaller average particle size.…”

“…b) A schematic of exsolution through hydrogen reduction. Reproduced with permission . Copyright 2016, Springer Nature.…”