Fuel cells are highly efficient, environmental friendly power-generating systems that produce electrical energy by electrochemically combining a fuel and oxygen. Unlike internal combustion engine, they rely on electrochemical reaction rather than combustion and in this respect their efficiency is not limited by the Carnot cycle or by moving parts. Unlike battery, a fuel cell does not run down or require recharging but it operates as long as fuel is supplied . Solid Oxide Fuel Cells (SOFC), are expected to achieve, for electrical power generation in the 1 to 10 MW range, net electrical efficiencies up to 65% [1]. Gadolinia-doped ceria (GDC) is one of the most promising material for intermediate temperature SOFC [2]. Unfortunately, CeO2-based ceramics reach a suitable density at temperatures above 1300°C [3] involving high production costs and as a consequence of the reduction of CeIV to CeIII, poor mechanical stability [4, 5]. Nano-powders exhibit several size-dependent properties; among those, their high reactivity allows milder sintering conditions and consequently, higher efficiencies and lower production costs. Due to its versatility, precipitation in solution remains one of the best method to obtain nano-particles of controlled properties [6]. In particular, the “polyol route” allows the direct precipitation of oxides in a high-boiling alcohol [7]. The use of a nonaqueous environment hinders the formation of hydroxide as intermediate phase and at the same time the surface capping action of the alcohol prevents particle agglomeration. This is therefore a low cost and easily scalable method to produce nanometric powders in a single step. The polyol route has been successfully used to prepare a large variety of nanoscaled materials (oxides, sulfides, phosphates, elemental metals), but it has not yet been reported for gadolinia-doped ceria. Aim of this work was to find the better synthesis conditions to produce crystalline nanometric Ce0.8Gd0.2O2 powders by polyol method. For this purpose four parameters were considered: nature of solvent (ethylen-, diethylen-, propylen-glycol) and reagents (acetates, nitrates, chlorides), temperature (from 180 to 240°C) and hydrolysis ratio (OH- to metal molar ratio). The stoichiometric mixtures of reagents were dispersed in glycol and the solution was heated at the final temperature for 4h under vigorous stirring in solvent refluxing. The powders obtained were separated by centrifugation, washed in ethanol, dried and characterized by XRD, ICP, SEM.
E. Mercadelli, A. Di Santo, A. Sanson, S. Albonetti, A. Vaccari, E. Roncari (2008). Polyol mediated synthesis of Gadolinium-Doped Ceria nanopowders. s.l : s.n.
Polyol mediated synthesis of Gadolinium-Doped Ceria nanopowders
MERCADELLI, ELISA;ALBONETTI, STEFANIA;VACCARI, ANGELO;
2008
Abstract
Fuel cells are highly efficient, environmental friendly power-generating systems that produce electrical energy by electrochemically combining a fuel and oxygen. Unlike internal combustion engine, they rely on electrochemical reaction rather than combustion and in this respect their efficiency is not limited by the Carnot cycle or by moving parts. Unlike battery, a fuel cell does not run down or require recharging but it operates as long as fuel is supplied . Solid Oxide Fuel Cells (SOFC), are expected to achieve, for electrical power generation in the 1 to 10 MW range, net electrical efficiencies up to 65% [1]. Gadolinia-doped ceria (GDC) is one of the most promising material for intermediate temperature SOFC [2]. Unfortunately, CeO2-based ceramics reach a suitable density at temperatures above 1300°C [3] involving high production costs and as a consequence of the reduction of CeIV to CeIII, poor mechanical stability [4, 5]. Nano-powders exhibit several size-dependent properties; among those, their high reactivity allows milder sintering conditions and consequently, higher efficiencies and lower production costs. Due to its versatility, precipitation in solution remains one of the best method to obtain nano-particles of controlled properties [6]. In particular, the “polyol route” allows the direct precipitation of oxides in a high-boiling alcohol [7]. The use of a nonaqueous environment hinders the formation of hydroxide as intermediate phase and at the same time the surface capping action of the alcohol prevents particle agglomeration. This is therefore a low cost and easily scalable method to produce nanometric powders in a single step. The polyol route has been successfully used to prepare a large variety of nanoscaled materials (oxides, sulfides, phosphates, elemental metals), but it has not yet been reported for gadolinia-doped ceria. Aim of this work was to find the better synthesis conditions to produce crystalline nanometric Ce0.8Gd0.2O2 powders by polyol method. For this purpose four parameters were considered: nature of solvent (ethylen-, diethylen-, propylen-glycol) and reagents (acetates, nitrates, chlorides), temperature (from 180 to 240°C) and hydrolysis ratio (OH- to metal molar ratio). The stoichiometric mixtures of reagents were dispersed in glycol and the solution was heated at the final temperature for 4h under vigorous stirring in solvent refluxing. The powders obtained were separated by centrifugation, washed in ethanol, dried and characterized by XRD, ICP, SEM.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
