Characterization in MCFC conditions of high-temperature, potentiostatically deposited Co-based thin films on NiO cathode

Abstract

Molten carbonate fuel cell (MCFC) is one of the most advanced high-temperature devices to convert chemical energy into electrical energy without pollution. It can be used in cogeneration as electrical and thermal generator because of its high working temperature (650°C). Nevertheless, its commercialization is still limited. In fact, its lifetime is mostly reduced by the dissolution of the cathode into the corrosive molten carbonate electrolyte. One of the ways to overcome this problem is to modify or protect the state-of-the-art cathode. In the last case, the deposit must present conductivity as good as the classical NiO porous cathode one but a lower solubility in the electrolyte. For this reason, thin films of cobalt(III) were electrodeposited. A classical three-electrode cell was used to deposit Co-based thin films by chronoamperometry in aqueous solution, at relatively high temperature (80°C). The deposition conditions lead to homogeneous, covering, and crystallized films. The microstructure and the crystallinity of the deposits were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements. Then, their electrochemical properties were studied in the molten carbonate electrolyte under a mixture of CO 2 and air. In situ measurements such as chronopotentiometry at I=0 (open-circuit potential) or impedance spectroscopy were carried out during 48 h. Moreover, ex situ measurements such as inductively coupled plasma atomic emission spectroscopy to evaluate the solubility, or SEM and XRD measurements were performed to characterize the thin Co-based films in such molten carbonate fuel cell working cathodic conditions.

Electrochemical devices for energy: fuel cells and electrolytic cells

“…Alternative electrode materials should be more stable in the carbonate medium and allow obtaining electrical performance as well as Li x Ni 1− x O. In order to solve this problem, different materials can be possible substitutes: (a) Single oxides: LiFeO 2 , Li 2 MnO 3 , La 0.8 Sr 0.2 CoO 3 and LiCoO 2 (Carewsca et al , 1997 ;Fukui et al , 1998 ;Janowitz et al , 1999 ;Belhomme et al , 2001 ;Mohamedi et al , 2001 ); (b) NiO-based materials containing other oxides less soluble and with performance close to that of Li x Ni 1-x O, such as alloys Ni-M (M = Nb, Al, Ti, Co) (Wijayasinghe et al , 2004 ;Ringued é et al , 2006 ) and mixed oxides LiFeO 2 -LiCoO 2 -NiO (Daza et al , 2000 ;Fukui et al , 2000 ), NiO-LiCoO 2 (Kuk et al , 2001 ) or NiO-CeO 2 (Durairajan et al , 2002 ); (c) Ni state-of-the-art cathode by thin coatings of oxides, mostly LiCoO 2 or cobalt-based oxides, more corrosion-resistant and presenting interesting electrocatalytic properties (Yuh et al , 1995 ;Mendoza et al , 2003 ;Mendoza et al , 2004 ;Pauport é et al , 2005 ;Escudero et al , 2006 ;Lair et al , 2008 ;Paoletti et al , 2009 ;Kim et al ., 2011 ).…”