Electrochemical pneumatic actuators utilising carbon nanotube electrodes

Electrochemical gas generation and consumption at carbon nanotube (CNT) electrodes was investigated as a means of powering pneumatic actuators. Two different types of carbon nanotubes were evaluated in a variety of aqueous electrolytes. Chlorine gas generation from aqueous sodium chloride electrolyte was found to be the most suitable system investigated, based on the ability to electrochemically reduce the gas generated. Carbon nanotubes produced by different techniques exhibit different chlorine oxidation and reduction capabilities with HiPCO nanotubes showing a higher electrochemical activity than nanotubes made by the laser ablation method. In a closed electrochemical cell fitted with a pressure transducer, the oxidation of Cl− ions to Cl2 gas was ∼40% efficient based on the charge passed. In contrast, the reduction of Cl2 gas pressure was almost 100% efficient, although the exact mechanisms of gas reduction were complicated by side reactions and kinetic processes. A carbon nanotube electrode of 2.4 mm3 was capable of producing 0.5 cm3 of gas at atmospheric pressure, or an increase of up to 50 kPa in a closed cell depending upon the headspace volume. The work capacity based on the size of the electrode was 5000 kJ/m3, which is nearly two orders of magnitude larger than other low voltage electrochemical actuators.