Reversible conversion between bicarbonate and formate in solid state “storage ball” for chemical hydrogen storage

Abstract

During the renewable energy based “green hydrogen” utilization path, lack of efficient and safe hydrogen storage and transport solution is the predominant hindrance not allowing a wide use of “green hydrogen” to be possible. Here, we firstly reported a solid state “storage ball” assembling by mixing bicarbonate, Pd/C catalyst and water to form a gel-like mixture and then by coating a polypropylene (PP) thin film for hydrogen storage purpose. The single “storage ball” (∼7 mm diameter) containing potassium bicarbonate as the initial reactant yielded 87.3% conversion rate to potassium formate after being charged at 3.0 MPa hydrogen pressure at ambient temperature for 6 h. This process is associated with hydrogen uptake and the calculated hydrogen storage density by weight of the “storage ball” is ∼0.58 wt%, which is about 6 times higher than that of reported aqueous solution system. Impressively, the as-transformed potassium formate inside the “storage ball” can fully be converted back to potassium bicarbonate associated with H₂ release in 15 min at a moderate temperature below 80 °C. The charging/discharging cycling test result of the “storage ball” exhibited no obvious degradation in hydrogen release amount, indicating the high stability and reversibility of the “storage ball” during charging and discharging process. The aluminum cylinder loaded with 100 “storage balls” could continuously and steadily supply hydrogen to a 12 V/35 W fuel cell to drive a LED display. This work provides a new approach for developing cost competent and safe hydrogen storage system for large scale “green hydrogen” storage application.