Hydrogen storage capacity of selected activated carbon electrodes made from brown coal

Electrochemical storage of hydrogen in activated carbon (aC) electrodes as part of a reversible fuel cell offers a potentially attractive option for storing surplus electrical energy from inherently variable solar and wind energy resources. Such a system - which we have called a proton flow battery - promises to have a roundtrip energy efficiency comparable to lithium ion batteries, while having higher gravimetric and volumetric energy densities. Activated carbons with high internal surface area, high pore volume, light weight and easy availability have attracted considerable research interest as a solid-state hydrogen storage medium. This paper compares the physical characteristics and hydrogen storage capacities of four activated carbon (aC) electrodes made from brown coal. The fabrication methods for these samples are explained. Their proton conductivity was measured using electrochemical impedance spectroscopy and their hydrogen storage capacity by galvanostatic charging and discharging in a three-electrode electrolytic cell with 1 mol sulphuric acid as electrolyte at atmospheric pressure and room temperature. The highest hydrogen storage capacity obtained was 1.29 wt%, which compares favourably with metal hydrides used in commercially available solid-state hydrogen storages. Finally, the relation between the hydrogen storage capacity of the samples and their Dubinin-Radushkevich surface area (calculated by the CO2 adsorption method) was investigated. The results point the way towards selecting high-performing electrodes for proton flow batteries and signal the potential competitiveness of this energy storage technology.