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water splitting is usually obstructed by the large overpotential of kinetically sluggish oxygen evolution reaction (OER). [2] Therefore, highly active and stable catalysts are urgently required to boost OER efficiency by minimizing the overpotential. [3] Although the noble metal oxides of IrO 2 and RuO 2 are the benchmark OER catalysts, their scarcity and high cost hinder the wide applications. [4] Thus, non-precious materials, such as transition metal complexes (e.g., Ni, Co, Mn, and Fe), [5] oxides/hydroxides, [2,6] doped nanocarbons (e.g., N, O, S, and P), [7] organic species, [8] have been intensively researched as valuable electrocatalysts for OER. Despite their low overpotential, the active sites of these OER catalysts are normally existed in nanoparticle form, tend to be sparsely distributed at the primarily exposed facet or edge sites. [9] As a result, the interior active sites of the catalysts cannot be fully utilized, eventually resulting in the waste of catalysts and partial loss of the entire electrocatalytic activity. [10] Recently, single-atom catalysts (SACs) incorporated into 2D substrates [11] are becoming highly attractive for various reactions and systems, e.g., oxygen reduction reaction, [12] hydrogen Single-atom catalysts (SACs) are efficient for maximizing electrocatalytic activity, but have unsatisfactory activity for the oxygen evolution reaction (OER). Herein, the NaCl template synthesis of individual nickel (Ni) SACs is reported, bonded to oxygen sites on graphene-like carbon (denoted as Ni-O-G SACs) with superior activity and stability for OER. A variety of characterizations unveil that theNi-O-G SACs present 3D porous framework constructed by ultrathin graphene sheets, single Ni atoms, coordinating nickel atoms to oxygen. Consequently, the catalysts are active and robust for OER with extremely low overpotential of 224 mV at current density of 10 mA cm −2 , 42 mV dec −1 Tafel slope, oxygen production turn over frequency of 1.44 S −1 at 300 mV, and long-term durability without significant degradation for 50 h at exceptionally high current of 115 mA cm −1 , outperforming the state-of-the-art OER SACs. A theoretical simulation further reveals that the bonding between single nickel and oxygen sites results in the extraordinary boosting of OER performance of Ni-O-G SACs. Therefore, this work opens numerous opportunities for creating unconventional SACs via metal-oxygen bonding.

Graphene and graphene oxide (GO), as wonder materials, have penetrated nearly every field of research. One of their most attractive features is the functionality and assembly of graphene or GO, in which they can be considered to be chemically functionalized building blocks for creating unconventional porous graphene materials (PGMs) that not only combine the merits of both porous materials and graphene, but also have major advantages over other porous carbons for specific applications. The chemistry and approaches for functionalizing graphene and GO are first introduced, and typical procedures for pore creation (e.g., in-plane pores, 2D laminar pores, and 3D interconnected pore assemblies), self-assembly, and tailoring mechanisms for PGMs to highlight the significance of precise control over the pore morphology and pore size are summarized. Because of their unique pore structures, with different morphologies and intriguing properties, PGMs serve as key components in a variety of applications such as energy storage, electrocatalysis, and molecular separation. Finally, the challenges relating to PGMs from the understanding of chemical self-assembly to specific applications are discussed, and promising solutions on how to tackle them are presented. This provides an insightful outlook for the future development of the chemistry and applications of PGMs.

Li-metal anode is widely acknowledged as the ideal anode for high-energy-density batteries, but seriously hindered by the uncontrollable dendrite growth and infinitely volume change. To this goal, seeking suitable stable scaffolds for dendrite-free Li anodes with large current density (> mA cm -2 ) and high Li loading (> 90%) are highly in demand. Herein, a conductive and lithiophilic three-dimensional (3D) MXene/graphene (MG) framework is demonstrated for dendrite-free Limetal anode. Benefiting from its high surface area (259 m 2 g -1 ) and lightweight nature with uniformly dispersed lithiophilic MXene nanosheets as Li nucleation sites, the as-formed 3D MG scaffold showcases an ultrahigh Li content (~92% of the theoretical capacity), as well as strong capabilities in suppressing the Li-dendrites formation and accommodating the volume changes.Consequently, the MG based electrode exhibits high Coulombic efficiencies (~99%) with a record lifespan up to 2700 h, and is stable for 230 cycles at an ultrahigh current density of 20 mA cm -2 .When coupled with Li4Ti5O12 or sulfur, the MG-Li/Li4Ti5O12 full-cell offers an enhanced capacity of 142 mAh g -1 after 450 cycles while the MG-Li/sulfur cell delivers improved rate performance, implying the great potential of this 3D MG framework for building long lifetime, high-energydensity batteries.

Alkali metals are ideal anodes for high-energydensity rechargeable batteries, while seriously hampered by limited cycle life and low areal capacities. To this end, rationally designed frameworks for dendrite-free and volume-changeless alkali-metal deposition at both high current densities and capacities are urgently required. Herein, a general 3D conductive Ti 3 C 2 T X MXene-melamine foam (MXene-MF) is demonstrated as an elastic scaffold for dendrite-free, high-areal-capacity alkali anodes (Li, Na, K). Owing to the lithiophilic nature of F-terminated MXene, conductive macroporous network, and excellent mechanical toughness, the constructed MXene-MF synchronously achieves a high current density of 50 mA cm −2 for Li plating, high areal capacity (50 mAh cm −2 ) with high Coulombic efficiency (99%), and long lifetime (3800 h), surpassing the Li anodes reported recently. Meanwhile, MXene-MF shows flat voltage profiles for 720 h at 10 mA cm −2 for the Na anode and 800 h at 5 mA cm −2 for the K anode, indicative of the wide applicability. Notably, the high current density of 20 mA cm −2 for 20 mAh cm −2 for the Na anode, accompanying good recyclability was rarely achieved before. When coupled with sulfur or Na 3 V 2 (PO 4 ) 3 cathodes, the assembled MXene-MF alkali (Li, Na)-based full batteries showcase enhanced rate capability and cycling stability, demonstrating the potential of MXene-MF for advanced alkali-metal batteries.

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Guiding the lithium ion (Li-ion) transport for homogeneous,d ispersive distribution is crucial for dendritefree Li anodes with high current density and long-term cyclability,b ut remains challenging for the unavailable welldesigned nanostructures.H erein, we propose at wo-dimensional (2D) heterostructure composed of defective graphene oxide (GO) clipped on mesoporous polypyrrole (mPPy) as ad ual-functional Li-ion redistributor to regulate the stepwise Li-ion distribution and Li deposition for extremely stable, dendrite-free Li anodes.Owing to the synergy between the Liion transport nanochannels of mPPy and the Li-ion nanosieves of defective GO,t he 2D mPPy-GO heterostructure achieves ultralong cycling stability (1000 cycles), even tests at 0 and 50 8 8C, and an ultralowo verpotential of 70 mV at ah igh current density of 10.0 mA cm À2 ,outperforming most reported Li anodes.F urthermore,m PPy-GO-Li/LiCoO 2 full batteries demonstrate remarkably enhanced performance with acapacity retention of > 90 %a fter 450 cycles.T herefore,t his work opens many opportunities for creating 2D heterostructures for high-energy-density Li metal batteries.

Contact engineering is a possible solution to decrease the pervasive Schottky barrier in a two dimensional (2D) material transistor with bulk metal electrodes. In this paper, two kinds of typical van der Waals (vdW)-type electrical contacts (a 2D metal contact and a 2D material/bulk metal hybrid contact) in monolayer (ML) black phosphorus (BP) transistors are investigated by ab initio energy band calculations and quantum transport simulations. Compared with the traditional bulk metal Ni contact, the gate electrostatic control is significantly improved by using both 2D graphene and borophene electrodes featuring a decrease of 30-50% in the subthreshold swing and an increase by a factor of 4-7 in the on-state current due to the depressed metal induced gap states and reduced screening of the 2D metal electrodes to the gate. In contrast, graphene insertion between the Ni electrode and ML BP shows only a slight improvement in the gate electrostatic control ability and BN insertion shows almost no improvement. The higher efficiency using the 2D metal contact than the 2D material/bulk metal hybrid contact in improving the ML BP FET device performance also provides helpful guidance in the selection of vdW-type electrical contacts of other 2D transistors.