Enhancement of hydrogen storage by electrophoresis deposition of CNTs into nanoscale pores of silver foams

Hydrogen storage capacity of Ag-CNTs foamed electrodes was studied by chronopotentiometry method. The CNTs (carbon nanotubes) were deposited inside pores of the nanoscale silver foam by electrophoresis deposition (EPD) method and it was believed that the interconnections between the CNTs and the Ag frames were increased and were more stable; therefore, charge transfer process through the electrode became facilitated. XRD, TGA and SEM techniques were employed to examine the purity of the CNTs and the quality of the Ag foam surface.Hydrogen storage was done by using the Ag-CNTs electrodes as the working electrodes in the electrochemical cell. A set of regulated currents were applied to the cell to produce charge and discharge (C&D) cycles. It was found that the storage capacity strongly depended on the applied current value and it became optimum corresponding to 4 mA current. In this manner the storage capacity inside the CNTs of the working electrodes approached 5.2%wt, which was quite noticeable in comparison with the other reports (storage capacity of pure silver is negligible). This optimization of the hydrogen storage capacity can be explained as a result of being in harmony with the applied current value and charge transferring ability of the local silver-nanotube junctions. However, re-alignment of the CNTs (inside the pores of the foam) during subsequent C&D cycles caused approaching the optimized capacity to occur after a few initial cycles. Whereas, oxidation of the silver part of the electrode after 30–40 subsequent C&D cycles caused functional instability of the electrode. Finally the effects of heat treatments on the storage capacity were studied, as well. After annealing of the electrode, the capacity increased substantially but with rising the ambient temperature it was reduced.

► Using EPD method to increase and stabilize interconnections between the CNTs and the Silver foam. ► Hydrogen storage capacity of the Ag-CNTs sample has been optimized at 4 mA cyclic regulated current (about 5.2%). ► Reversibility of the charge and discharge cycles has been checked up to 30 cycles. ► Enhancement of hydrogen storage after annealing of the prepared Ag-CNTs sample.