Potassium-doped PC71BM for hydrogen storage: Photoelectron spectroscopy and first-principles studies

Abstract We consider the fullerene C70 derivative PC71BM as a potential onboard hydrogen storage material. As the cases of many sorbents, metal-decoration is needed to increase the adsorption energy of H2. We study the metal-decoration by intercalating K atoms into a PC71BM film and performing photoelectron spectroscopy measurements. The results reveal that the maximum stoichiometry is K9–10PC71BM. Then we study the hydrogen storage property of an isolated K9PC71BM molecule with density functional theory calculations. A K9PC71BM molecule can compactly adsorb 45H2 (6.22 wt%); the compact adsorption structure does not require large interstitial space in solid phase and thus should be able to be realized in experiments. Considering the poor crystallinity of solid PC71BM (with many large interstitial spaces), a gravimetric capacity >7 wt% can be anticipated. The adsorption energy meets the DOE target of onboard operating temperatures, and van der Waals interaction contributes more than 40% of the adsorption energy.