ORIGINAL PAPER Characterization in MCFC conditions of high-temperature, potentiostatically deposited Co-based thin films on NiO cathode V. Lair & A. Ringuedé & V. Albin & M. Cassir Received: 15 November 2007 / Revised: 21 February 2008 / Accepted: 22 February 2008 / Published online: 2 April 2008 # Springer-Verlag 2008 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 chronoamper- ometry 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 chronopotenti- ometry at I =0 (open-circuit potential) or impedance spec- troscopy 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. Keywords Cathode . MCFC . Electrodeposition . Cobalt . Impedance spectroscopy . Electrochemical characterizations . Thin films . Cathodes . Fuel cells Introduction In the near future, new power generation devices are needed to replace the fossil energies, with respect to the environment. Among different systems, fuel cells have a significant role to play. Molten carbonate fuel cell (MCFC), in particular, is considered as a promising power generation system because it can lead to high energy conversion efficiency (up to 60% under atmosphere pressure) without pollution. Thus, the high working temperature (650 °C) allows the production of both electrical and heat energy by using a large variety of fuels (H 2 , coal gas, etc.). The classical MCFC single cell is made of Ni- based anode (generally NiAl or NiCr alloys), NiO cathode, stainless steel bipolar plates, and molten carbonates electro- lyte (Li–K, Li–Na, or Li–Na–K) maintained in an alumina matrix. The standard anodic atmosphere is composed of H 2 – CO 2 –H 2 O whereas the cathodic atmosphere is a CO 2 –air mixture. Nevertheless, its commercialization is still limited because of a relatively short lifetime (less than 40,000 h) even if numerous prototypes have shown good results up to 30,000 h. This is mostly due to the state-of-the-art NiO cathode dissolution in the acidic molten carbonate melt, according to the following reaction: NiO þ CO 2 ¼ Ni 2þ þ CO 2À 3 Then, the dissolved nickel ions can diffuse to the anode where the precipitation of Ni occurs in the reductive anodic conditions. The electrical efficiency of the cell is, then, reduced either by the loss of active cathode material or the possibility to short-circuit between anode and cathode via Ni formation [1]. Ionics (2008) 14:555–561 DOI 10.1007/s11581-008-0219-y V. Lair (*) : A. Ringuedé : V. Albin : M. Cassir CNRS UMR 7575, ENSCP, rue Paris 6, Paris, France e-mail: virginie-lair@enscp.fr