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Single-wall carbon nanotubes (SWNTs) were examined as catalysts for improving the hydrogen absorption and desorption properties of Ti/Zr-doped NaAlH4 hydride, proposed as a reversible hydrogen storage material. We studied the hydrogen charge and discharge characteristics and stability of sodium aluminium composites ball milled with carbon additives such as SWNTs, graphite or activated carbon (AX-21). The SWNT–NaAlH4 system was tested at 160 °C for up to 200 cycles, and the sorption kinetics were enhanced by a factor of four. Also, the catalyzed NaAlH4 hydride with graphite and activated carbon additives shows fast absorption and desorption kinetics. Our results indicate that by creating new hydrogen transition sites, the structure of carbon in the composites plays an important role in enhancing the hydrogen absorption and release rates.

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There is an opportunity to improve the efficiency of flat plate solar air collectors by replacing their conventional glass covers with lightweight polycarbonate panels filled with high performance aerogel insulation. The in situ performance of a 5.4m 2 solar air collector containing granular aerogel is simulated and tested. The collector is incorporated into the external insulation of a mechanically ventilated end terrace house, recently refurbished in London, UK. During the 7 day test period, peak outlet temperatures up to 45°C are observed. Resultant supply and internal air temperatures peak at 25 30°C and 21 22°C respectively. Peak efficiencies of 22 36% are calculated based on the proposed design across a range of cover types. Measured outlet temperatures are validated to within 5% of their predicted values. Estimated outputs range from 118 166 kWh/m 2 /year for collectors with different thickness granular aerogel covers, compared to 110 kWh/m 2 /year for a single glazed collector, 140 kWh/m 2 /year for a double glazed collector and 202 kWh/m 2 /year for a collector incorporating high performance monolithic aerogel. Payback periods of 9 16 years are calculated across all cover types. An efficiency up to 60% and a payback period as low as 4.5 years is possible with an optimised collector incorporating a 10mm thick granular aerogel cover.