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Nano-Particles for Fuel Cells

Final Activity Report Summary - NAFCELL (Nano-Particles for Fuel Cells)

Fuel cells are promising clean energy generators for the future; however their high cost and low durability make them non-competitive in commercial applications at present. As the key component in the system, the catalyst is the place where reactions occur and electricity is generated, playing a primary role in the performance and economics of the fuel cells system. Nevertheless, catalyst structure and performance were inadequate until now. To solve this problem, a combination of the chemistry of making catalysts and the engineering of fuel cells in applications was needed. Thus, the overall aim of the project was to develop new high performance and economic nanoparticle catalysts for fuel cells, taking advantage of the latest techniques that were built up for preparing nanoparticles. In addition, new nanoparticle characterisation and testing techniques were implemented.

A series of platinum (Pt), palladium (Pd), ruthenium (Ru), nickel (Ni) and copper Cu nanoparticles in aqueous solution was prepared and characterised. Then carbon substrates were introduced into the reaction to deposit nanoparticle catalysts for fuel cells. This work included an impregnation method which was commonly used for making nanoparticle catalysts on carbon support in proton exchange membrane fuel cells (PEMFCs) at present, but suffered from the low catalytic performance due to the large particle size and low maximum loading amount achieved. To overcome these limitations, a facile one-step deposition method was developed for in-situ, growing single crystal Pt nanowire catalysts on carbon substrates, with which integrated gas diffusion electrodes (GDEs) in PEMFCs were prepared at room temperature.

The testing results showed a 25 % higher maximum power density than the commercial GDE, i.e. ELAT 120EW, even with a lower catalyst loading. This approach was much simpler than the current method for preparing GDEs because there was no catalyst ink preparation and printing steps, thus decreasing the cost and improving the performance. Furthermore, we made integrated membrane electrode assemblies (MEAs) with Pt nanowires grown on electrolyte membrane by this one-step deposition technique, giving a low preparation cost and an enhanced performance because of the improved contact between the catalyst and membrane.

In this project, for the first time, Pt nanoparticle and nanowire hybrid catalysts were prepared. This novel nanostructure improved the electrochemical reaction interface of catalysts in PEMFCs and an enhanced performance was demonstrated. In addition, Pt and Ru hybrid nanowire catalysts were synthesised, in which the Ru nanoparticle could be tailored from the spherical to nanowire shape, and this hybrid nanostructure was shown to possess a high catalytic performance and good carbon monoxide (CO) tolerance.

The work also included a simple modification process for the anode supported micro-tubular solid oxide fuel cell (SOFC). By a simple one-step impregnation of Ni-YSZ supported YSZ micro tube with Y-GDC sol before cathode painting, micro-tubular SOFC was prepared with a composite anode and an interlayer between the cathode and electrolyte. The very good conductivity of Y-GDC along with its excellent performance for preventing coke formation was shown to improve the microtubular output.

Finally, a new method for measuring the atomic attractions between nanoparticles based on the observation of aggregates was studied. With a novel nanoparticle tracking device (NanoSight, UK) the ratio of the doublet aggregates to singlets was determined and used to calculate the attractive energy and range of interaction between nanoparticles. In this way, polystyrene nanospheres with different sizes and concentrations were observed and a very small adhesive energy was measured, which was much lower than ever previously detected with scanning tunnelling microscopy (STM) and atomic force microscopy (AFM). Moreover, this approach was successfully applied to measure number concentrations of nanoparticles. Viral particles of adenoviruses were calibrated too, in collaboration with Dr S. Morris in the University of Warwick and Dr C. Sweet in the University of Birmingham. This new method was shown to be superior to the commonly used spectrophotometry technique for calibrating adenoviruses.