No abstract

No abstract

Nickel was electrodeposited on porous Ag/GDC (silver/Ce 0.9 Gd 0.1 O 2-x ) scaffolds and dense Ag/GDC composites for the fabrication of SOFC electrodes and catalytic membranes respectively. To control the distribution and amount of nickel deposition on the Ag/GDC surfaces; first, a systematic cyclic voltammetry study of nickel electrodeposition from a Watts bath on silver foils was carried out to understand the influence of operating conditions on the electrodeposition process. From the cyclic voltammetry study, it can be concluded that suitable operating conditions for nickel electrodeposition into porous Ag/GDC scaffolds and catalytic membranes are: 1.1 M Ni 2+ concentration in Watts bath; deposition potential between −0.65 to −1.0 V vs. Ag/AgCl; a temperature at 55 • C; sodium dodecyl sulfate (SDS) as the surfactant; pH 4.0 ± 0.2 and an agitation rate of 500 rpm. It was observed that the nickel surface microstructure changed with the deposition current densities due to the co-evolution of H 2 . Pulse and continuous electrodeposition modes allow nickel to be deposited throughout porous Ag/GDC scaffolds and onto catalytic membranes. The pulse electrodeposition mode is favored as this is shown to result in an even Ni distribution within the porous scaffolds at minimum H 2 pitting. Nickel is used as a catalyst and current collector in electrochemical energy conversion systems such as solid oxide fuel cells (SOFCs), electrolysers, and as a catalyst in catalytic membranes ( Figure 1). Conventionally, Ni is incorporated into SOFC anodes by mechanically mixing NiO and ionic conductive materials such as yttriastabilized zirconia (YSZ) and Ce 0.9 Gd 0.1 O 2-x (GDC), then sintering at high temperature. However, the use of relatively large volumes of Ni (∼30 vol%) needed to achieve adequate electronic conductivity in the electrodes will affect the stability of cell microstructure under redox cycling. Recent advances in the manufacture of SOFC anodes via infiltration of Ni nitrate solution into a porous backbone (scaffold) have made it possible to achieve an excellent performance with a significantly reduced amount of nickel.1,2 However, repeated infiltration involving heating and cooling cycles is a lengthy and energy consuming process, presenting challenges to its industrial application. An alternative is to use electroless and electrodeposition techniques, which offer the potential to accelerate the incorporation of Ni into porous scaffolds at room or near-room temperature. The electroless deposition of Ni is well known and it is a simple process used to coat any substrate, however the use of boron-or phosphorus-based reducing agents in this technique is unsuitable for fuel cells due to adverse catalytic effects of the residues.3 Alternatively, hydrazine has been used as the reducing agent in the past years 4-6 yet its high toxicity may not be suitable for large production.Catalytic membranes have shown their potential to reform methane to syngas (CO+H 2 ) by coupling oxygen separation from air and catalytic partial me...