Large-area (~cm 2 ) films of vertical heterostructures formed by alternating graphene and transition-metal dichalcogenide (TMD) alloys are obtained by wet chemical routes followed by a thermal treatment at low temperature. In particular, we synthesized stacked graphene and WxMo1-xS2 alloy phases that were used as hydrogen evolution catalysts. We observed a Tafel slope of 38.7 mV dec -1 and 96 mV onset potential (at current density of 10 mA cm -2 ) when the heterostructure alloy was annealed at 300 o C. These results indicate that heterostructures formed by graphene and W0.4Mo0.6S2 alloys are far more efficient than WS2 and MoS2 by at least a factor of two, and they are superior than other reported TMD systems. This strategy offers a cheap and low temperature synthesis alternative able to replace Pt in the hydrogen evolution reaction (HER). Furthermore, the catalytic activity of the alloy is stable over time,i.e. the catalytic activity does not experience a significant change even after 1000 cycles. Using density functional theory calculations, we found that this enhanced hydrogen evolution in the 4 WxMo1-xS2 alloys is mainly due to the lower energy barrier created by a favorable overlap of the d-orbitals from the transition metals and the s-orbitals of H2; with the lowest energy barrier occurring for the W0.4Mo0.6S2 alloy. Thus, it is now possible to further improve the performance of the "inert" TMD basal plane via metal alloying, in addition to the previously reported strategies such as creation of point defects, vacancies and edges. The synthesis of graphene/W0.4Mo0.6S2 produced at relatively low temperatures is scalable and could be used as an effective low cost Pt-free catalyst.5

In this study, we report a nonprecious metal catalyst for high-efficiency hydrogen evolution reaction (HER). A self-organized S-doped MoP nanoporous layer (S-MoP NPL) is achieved through a facile electrochemical anodic process and a two-step chemical vapor deposition treatment, which was directly used as a binder-free catalyst for HER in pH-universal electrolytes. S-MoP NPL exhibits HER behavior with a low overpotential of 86 mV at 10 mA cm–1 and low Tafel slope of 34 mV dec–1 in acidic solution. Moreover, S-MoP NPL also shows high HER activity in basic and neutral electrolytes. Density functional theory (DFT) computations were carried out to support our experiment. The calculations show that the H2 formation (via Volmer–Heyrovsky mechanism) from the reaction of a metal (Mo) absorbed hydride with a solvated proton is favored over S-MoP than MoS2. Both experimental and computational studies demonstrate that the extraordinary HER activity and stability performance displayed by a MoP catalyst can be enhanced by S-doping, opening up a promising paradigm for the conscious design of high-performance nonprecious metal catalyst for hydrogen generation.

has been widely regarded as one of the most promising energy conversion and storage technologies to meet the growing energy demands of largescale application for electric vehicles and other electricity-related devices. [1] The two prominent reactions involved in ZABs are oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), both of which determine the practical performance of ZABs. Thus, the use of highly efficient and stable electrocatalysts as air electrodes is of paramount significance for facilitating the sluggish ORR and OER, thereby attaining high power and long operating lifetime performance for ZABs. Typically, platinum group metals (PGM) are most favorable ORR and OER catalysts displaying the absolute superiority of catalytic activity. However, the high cost, poor stability/durability, and low poison resistance of PGM have been the primary barriers that hamper widespread commercialization of ZABs. [1b,2] With decades of intensive effort in developing the cost-effective catalysts that possess remarkable catalytic performance, a new generation of PGM-free electrocatalystsThe oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in zinc-air batteries (ZABs) require highly efficient, cost-effective, and stable electrocatalysts as alternatives to high cost and low poison resistant platinum group metals (PGM) catalysts. Although nitrogen-doped carbon nanotube (NCNT) arrays are now capable of catalyzing ORR efficiently, their hydrophobic surface and base-growth mode are found to limit the catalytic performance in the practical ZABs. Here, the concept of an apically dominant mechanism in improving the catalytic performance of NCNT by precisely encapsulating CoNi nanoparticles (NPs) within the apical domain of NCNT on the Ni foam (denoted as CoNi@NCNT/NF) is demonstrated. The CoNi@NCNT/NF exhibits a more excellent catalytic performance toward both ORR and OER than that of traditional NCNT derived from the base-growth method. The ZAB coin cell using CoNi@NCNT/NF as an air electrode shows a peak power density of 127 mW cm −2 with an energy density of 845 Wh kg Zn −1 and rechargeability over 90 h, which outperforms the performance of PGM catalysts. Density functional theory calculations reveal that the ORR catalytic performance of the CoNi@NCNT/NF is mainly attributed to the synergetic contributions from NCNT and the apical active sites on NCNT near to CoNi NPs.

Advancing beyond Li-ion batteries requires translating the beneficial characteristics of Li+ electrodes to attractive, yet incipient, candidates such as those based on K+ intercalation. Here, we use ultrathin few-layer graphene (FLG) electrodes as a model interface to show a dramatic enhancement of K+ intercalation performance through a simple conditioning of the solid-electrolyte interphase (SEI) in a Li+ containing electrolyte. Unlike the substantial plating occurring in K+ containing electrolytes, we found that a Li+ based SEI enabled efficient K+ intercalation with discrete staging-type phase transitions observed via cyclic voltammetry at scan rates up to 100 mVs–1 and confirmed as ion-intercalation processes through in situ Raman spectroscopy. The resulting interface yielded fast charge–discharge rates up to ∼360C (1C is fully discharge in 1 h) and remarkable long-term cycling stability at 10C for 1000 cycles. This SEI promoted the transport of K+ as verified via mass spectrometric depth profiling. This work introduces a convenient strategy for improving the performance of ion intercalation electrodes toward a practical K-ion battery and FLG electrodes as a powerful analytical platform for evaluating fundamental aspects of ion intercalation.

Covalent-organic frameworks (COFs) are intriguing platforms for designing functional molecular materials. Here, we present a computational study based on van der Waals dispersion-corrected hybrid density functional theory (DFT-D) to design boroxine-linked and triazine-linked COFs intercalated with Fe. Keeping the original P − 6m2 symmetry of the pristine COF (COF-Fe-0), we have computationally designed seven new COFs by intercalating Fe atoms between two organic layers. The equilibrium structures and electronic properties of both the pristine and Fe-intercalated COF materials are investigated here. We predict that the electronic properties of COFs can be fine tuned by adding Fe atoms between two organic layers in their structures. Our calculations show that these new intercalated-COFs are promising semiconductors. The effect of Fe atoms on the electronic band structures and density of states (DOSs) has also been investigated using the aforementioned DFT-D method. The contribution of the d-subshell electron density of the Fe atoms plays an important role in improving the semiconductor properties of these new materials. These intercalated-COFs provide a new strategy to create semi-conducting materials within a rigid porous network in a highly controlled and predictable manner.