Comments on abstract, title, references Hydrogen is an essential component in many industrial processes. However, the most important problem in hydrogen use is the transportation. The traditional gas cyclinders have limits in efficiency (low volumetric/gravimetric hydrogen densities) and safety (high pressure and low temperature). How to dissolve this problem? The use of metals to storage hydrogen has attracted great attention. Herein, according to the abstract, authors have reported that the metal-organic framework (MOF) HKUST-1 covered Pd nanocrystals have remarkably enhanced capacity and speed of hydrogen storage. It provides a new view for researchers who now are working in this area. The title is novel and clear, while the references are appropriate. Therefore, it is quite appropriate for publishing in Nat. Mater.

Comments on introduction/background As a clean and efficient energy carrier, hydrogen is of great importance for a sustainable future. Herenin, authors given a brief induction of the recent progress in the hydrogen use. They also pointed out that the hydrogen storage of Pd have typically involved the creation of Pd alloys. However, a creative strategy is required. Therefore, authors proposed a new strategy to enhance the hydrogen stoarage properties of Pd crystals by using MOFs. The introduction in this paper is quite clear and professional.

Comments on methodology Up to now, attempts to improve the hydrogen storage properties of Pd have typically involved the creation of Pd alloys. Herein, authors reported on the remarkably enhanced capacity and speed of hydrogen storage in Pd crystals as a result of coating with the MOF. The Pd crystals was coated with HKUST-1 by using a facile reactive seeding method, where the Pd nanocrystals acted as seed sites for MOF growth. The method is very creative. Several advanced instruments, including hydrogen pressure-composition (PC) isotherms, in situ power X-ray diffraction (XRD), transmission electron microscopy (TEM) and solid-state deuterium nuclear magnetic resonance (2H NMR), were used to characterize the phases, microstructures, and properties. It is so much amazing! This paper provides a new standard for hydrogen storage research.

Comments on data and results According to XRD and TEM, we can clearly observe that Pd crystals were covered by HKUST-1. According to PC isotherms, we can clearly observe that Pd crystals which covered by HKUST-1 can have an enhanced hydrogen storage properties. Specially, the NMR confirms that more hydrogen can enter into the lattice of Pd crystals by covering with MOFs. All factors were investigated and the data and results were sufficient for the title and conclusions.

Comments on discussion and conclusions On the basis of above advanced technologies and results, authors given us the reason of the enhancement of hydrogen storage properties of Pd crystals. The discussion and conclusion part are very strong. The paper is quite appropriate for publisihing in Nature Materials.