A new concept is investigated for hydrogen storage in a supercapacitor based on large-surface-area carbon material (Black Pearls 2000). Protons and electrons of hydrogen are separated on a fuel cell-type electrode and then stored separately in the electrical double layer, the electrons on the carbon and the protons in the aqueous electrolyte of the supercapacitor electrode. The merit of this concept is that it works spontaneously and reversibly near ambient pressure and temperature. This is in pronounced contrast to what has been known as electrochemical hydrogen storage, which does not involve hydrogen gas and where electrical work has to be spent in the loading process. With the present hybrid device, a H(2) storage capacity of 0.13 wt% was obtained, one order of magnitude more than what can be stored by conventional physisorption on large-surface-area carbons at the same pressure and temperature. Raising the pressure from 1.5 to 3.5 bar increased the capacity by less than 20%, indicating saturation. A capacitance of 11 μF cm(-2), comparable with that of a commercial double layer supercapacitor, was found using H(2)SO(4) as electrolyte. The chemical energy of the stored H(2) is almost a factor of 3 larger than the electrical energy stored in the supercapacitor. Further developments of this concept relate to a hydrogen buffer integrated inside a proton exchange membrane fuel cell to be used in case of peak power demand. This serial setup takes advantage of the suggested novel concept of hydrogen storage. It is fundamentally different from previous ways of operating a conventional supercapacitor hooked up in parallel to a fuel cell.

Methanol is considered a promising liquid fuel in context with electrochemical energy conversion and storage for mobile applications. It is shown here that a direct methanol fuel cell can be used for spontaneous charging and discharging a supercapacitor for intermediate storage of chemical energy. Thereby, protons and electrons of the methanol-derived hydrogen are stored separately in the electrical double layer of the supercapacitor electrode. The charging and discharging of this fuel cell-supercapacitor hybride device is investigated in experiments of spontaneous conditions (closed circuit) and also under externally enforced constant voltage sweep rate (cyclic voltammetry) and under constant current conditions. Alternatively, gas phase hydrogen is generated from methanol in an electroreforming process. When more efficient anode electrocatalysts become available this may become the method of choice for on-board and on demand hydrogen production in mobile applications.