In Operando Generation and Storage of Hydrogen by Coupling Monolithically Integrated Photoelectrochemical Cell with Clathrate Hydrates Molecular Storage

Abstract

Hydrogen production from water has been considered as one of the potential clean and futuristic alternates to fossil fuel. However, the development of a complete efficient system for hydrogen fuel coming from water lacks not only efficient, stable, and cost-effective generation but also off-line efficient storage. Herein, first, we present a newly designed monolithically integrated photoelectrochemical (PEC) device for hydrogen generation with a semitransparent MoOx/MoS2/FTO heterostructure as a photoanode and black 2D-MoS2/Si as a photocathode. This integrated cell eliminates the use of expensive metal (like Pt) as a counter electrode and enhances the overall stable H2 and O2 evolution, with a stable measured rate of 61 μmol/h and 28 μmol/h, respectively. The applied bias photon-to-current efficiency (ABPE) was measured to be ∼3.5% at −0.3 V vs reversible hydrogen electrode (RHE). Second, we demonstrate the storage of molecular H2 as solid hydrates, where the release of hydrogen from the hydrate requires no additional energy as it is not chemically bound to water. Operating at a moderate pressure of 10 MPa, we achieved hydrates of hydrogen with a maximum storage capacity of 1.3 wt %, which could be enhanced to 3 wt % with further fine-tuning of the process. The theoretical capacity of hydrogen storage in clathrate hydrates are ∼5 wt %. This concept of monolithic generation and molecular storage of hydrogen provides a complete long-demanding efficient and stable solution for large-scale commercial applications.