In Situ Grown Monolayer N‐Doped Graphene on CdS Hollow Spheres with Seamless Contact for Photocatalytic CO2 Reduction

Photocatalytic CO₂ reduction is an effective way to simultaneously mitigate the greenhouse effect and the energy crisis. Herein, CdS hollow spheres, on which monolayer nitrogen‐doped graphene is in situ grown by chemical vapor deposition, are applied for realizing effective photocatalytic CO₂ reduction. The constructed photocatalyst possesses a hollow interior for strengthening light absorption, a thin shell for shortening the electron migration distance, tight adhesion for facilitating separation and transfer of carriers, and a monolayer nitrogen‐doped graphene surface for adsorbing and activating CO₂ molecules. Achieving seamless contact between a photocatalyst and a cocatalyst, which provides a pollution‐free and large‐area transport interface for carriers, is an effective strategy for improving the photocatalytic CO₂ reduction performance. Therefore, the yield of CO and CH₄, as dominating products, can be increased by four and five times than that of pristine CdS hollow spheres, respectively. This work emphasizes the importance of contact interface regulation between the photocatalyst and the cocatalyst and provides new ideas for the seamless and large‐area contact of heterojunctions.     

Strong Coupling of MoS2 Nanosheets and Nitrogen‐Doped Graphene for High‐Performance Pseudocapacitance Lithium Storage

Layered material MoS₂ is widely applied as a promising anode for lithium‐ion batteries (LIBs). Herein, a scalable and facile dopamine‐assisted hydrothermal technique for the preparation of strongly coupled MoS₂ nanosheets and nitrogen‐doped graphene (MoS₂/N‐G) composite is developed. In this composite, the interconnected MoS₂ nanosheets are well wrapped onto the surface of graphene, forming a unique veil‐like architecture. Experimental results indicate that dopamine plays multiple roles in the synthesis: a binding agent to anchor and uniformly disperse MoS₂ nanosheets, a morphology promoter, and the precursor for in situ nitrogen doping during the self‐polymerization process. Density functional theory calculations further reveal that a strong interaction exists at the interface of MoS₂ nanosheets and nitrogen‐doped graphene, which facilitates the charge transfer in the hybrid system. When used as the anode for LIBs, the resulting MoS₂/N‐G composite electrode exhibits much higher and more stable Li‐ion storage capacity (e.g., 1102 mAh g^?1 at 100 mA g^?1) than that of MoS₂/G electrode without employing the dopamine linker. Significantly, it is also identified that the thin MoS₂ nanosheets display outstanding high‐rate capability due to surface‐dominated pseudocapacitance contribution.     

Well‐Combined Magnetically Separable Hybrid Cobalt Ferrite/Nitrogen‐Doped Graphene as Efficient Catalyst with Superior Performance for Oxygen Reduction Reaction

Catalysts with low‐cost, high activity and stability toward oxygen reduction reaction (ORR) are extremely desirable, but its development still remains a great challenge. Here, a novel magnetically separable hybrid of multimetal oxide, cobalt ferrite (CoFe₂O₄), anchored on nitrogen‐doped reduced graphene oxide (CoFe₂O₄/NG) is prepared via a facile solvothermal method followed by calcination at 500 °C. The structure of CoFe₂O₄/NG and the interaction of both components are analyzed by several techniques. The possible formation of Co/Fe N interaction in the CoFe₂O₄/NG catalyst is found. As a result, the well‐combination of CoFe₂O₄ nanoparticles with NG and its improved crystallinity lead to a synergistic and efficient catalyst with high performance to ORR through a four‐electron‐transfer process in alkaline medium. The CoFe₂O₄/NG exhibits particularly comparable catalytic activity as commercial Pt/C catalyst, and superior stability against methanol oxidation and CO poisoning. Meanwhile, it has been proved that both nitrogen doping and the spinel structure of CoFe₂O₄ can have a significant contribution to the catalytic activity by contrast experiments. Multimetal oxide hybrid demonstrates better catalysis to ORR than a single metal oxide hybrid. All results make the low‐cost and magnetically separable CoFe₂O₄/NG a promising alternative for costly platinum‐based ORR catalyst in fuel cells and metal‐air batteries.     

Low‐Temperature Carbide‐Mediated Growth of Bicontinuous Nitrogen‐Doped Mesoporous Graphene as an Efficient Oxygen Reduction Electrocatalyst

Nitrogen‐doped graphene exhibits high electrocatalytic activity toward the oxygen reduction reaction (ORR), which is essential for many renewable energy technologies. To maximize the catalytic efficiency, it is desirable to have both a high concentration of robust nitrogen dopants and a large accessible surface of the graphene electrodes for rapid access of oxygen to the active sites. Here, 3D bicontinuous nitrogen‐doped mesoporous graphene synthesized by a low‐temperature carbide‐mediated graphene‐growth method is reported. The mesoporous graphene has a mesoscale pore size of ≈25 nm and large specific surface area of 1015 m² g^?1, which can effectively host and stabilize a high concentration of nitrogen dopants. Accordingly, it shows an excellent electrocatalytic activity toward the ORR with an efficient four‐electron‐dominated pathway and high durability in alkaline media. The synthesis route developed herein provides a new economic approach to synthesize bicontinuous porous graphene materials with tunable characteristic length, porosity, and chemical doping as high efficiency electrocatalysts for a wide range of electrochemical reactions.     

Tuning Surface Wettability and Adhesivity of a Nitrogen‐Doped Graphene Foam after Water Vapor Treatment for Efficient Oil Removal

An environment‐friendly water vapor treatment for realizing a highly hydrophobic (contact angle ≈147.5°) and oleophilic N‐doped graphene foam (NGF) for efficiently removing oil from oil/water emulsions is presented. 3D porous networks of NGF with high N content are prepared by subjecting a mixture of graphene oxide and 5 vol% pyrrole to a hydrothermal process; the mixture is then freeze‐dried and annealed under a N₂ atmosphere. The surface wettability and adhesivity are tuned through water vapor treatment by forming a low‐surface‐energy hydrocarbon layer, with no chemical modification. The effectiveness of the hydrophobic/oleophilic NGF in removing oil from an oil/water emulsion is demonstrated.     

Impact of Interfacial Electron Transfer on Electrochemical CO2 Reduction on Graphitic Carbon Nitride/Doped Graphene

Effective electrocatalysts are required for the CO₂ reduction reaction (CRR), while the factors that can impact their catalytic activity are yet to be discovered. In this article, graphitic carbon nitride (g‐C₃N₄) is used to investigate the feasibility of regulating its CRR catalytic performance by interfacial electron transfer. A series of g‐C₃N₄/graphene with and without heteroatom doping (C₃N₄/XG, XG = BG, NG, OG, PG, G) is comprehensively evaluated for CRR through computational methods. Variable adsorption energetics and electronic structures are observed among different doping cases, demonstrating that a higher catalytic activity originates from more interfacial electron transfer. An activity trend is obtained to show the best catalytic performance of CRR to methane on C₃N₄/XG with an overpotential of 0.45 V (i.e., ?0.28 V vs reverse hydrogen electrode [RHE]). Such a low overpotential has never been achieved on any previously reported metallic CRR electrocatalysts, therefore indicating the availability of C₃N₄/XG for CO₂ reduction and the applicability of electron transfer modulation to improve CRR catalytic performance.     

Controllable Design of MoS2 Nanosheets Anchored on Nitrogen‐Doped Graphene: Toward Fast Sodium Storage by Tunable Pseudocapacitance

Transition‐metal disulfide with its layered structure is regarded as a kind of promising host material for sodium insertion, and intensely investigated for sodium‐ion batteries. In this work, a simple solvothermal method to synthesize a series of MoS₂ nanosheets@nitrogen‐doped graphene composites is developed. This newly designed recipe of raw materials and solvents leads the success of tuning size, number of layers, and interplanar spacing of the as‐prepared MoS₂ nanosheets. Under cut‐off voltage and based on an intercalation mechanism, the ultrasmall MoS₂ nanosheets@nitrogen‐doped graphene composite exhibits more preferable cycling and rate performance compared to few‐/dozens‐layered MoS₂ nanosheets@nitrogen‐doped graphene, as well as many other reported insertion‐type anode materials. Last, detailed kinetics analysis and density functional theory calculation are also employed to explain the Na⁺‐ storage behavior, thus proving the significance in surface‐controlled pseudocapacitance contribution at the high rate. Furthermore, this work offers some meaningful preparation and investigation experiences for designing electrode materials for commercial sodium‐ion batteries with favorable performance.     

Pd Single‐Atom Catalysts on Nitrogen‐Doped Graphene for the Highly Selective Photothermal Hydrogenation of Acetylene to Ethylene

The selective hydrogenation of acetylene to ethylene in an ethylene‐rich gas stream is an important process in the chemical industry. Pd‐based catalysts are widely used in this reaction due to their excellent hydrogenation activity, though their selectivity for acetylene hydrogenation and durability need improvement. Herein, the successful synthesis of atomically dispersed Pd single‐atom catalysts on nitrogen‐doped graphene (Pd₁/N‐graphene) by a freeze‐drying‐assisted method is reported. The Pd₁/N‐graphene catalyst exhibits outstanding activity and selectivity for the hydrogenation of C₂H₂ with H₂ in the presence of excess C₂H₄ under photothermal heating (UV and visible‐light irradiation from a Xe lamp), achieving 99% conversion of acetylene and 93.5% selectivity to ethylene at 125 °C. This remarkable catalytic performance is attributed to the high concentration of Pd active sites on the catalyst surface and the weak adsorption energy of ethylene on isolated Pd atoms, which prevents C₂H₄ hydrogenation. Importantly, the Pd₁/N‐graphene catalyst exhibits excellent durability at the optimal reaction temperature of 125 °C, which is explained by the strong local coordination of Pd atoms by nitrogen atoms, which suppresses the Pd aggregation. The results presented here encourage the wider pursuit of solar‐driven photothermal catalyst systems based on single‐atom active sites for selective hydrogenation reactions.     

Nitrogen‐Doped Graphene‐Encapsulated Nickel–Copper Alloy Nanoflower for Highly Efficient Electrochemical Hydrogen Evolution Reaction

Development of high‐performance and low‐cost nonprecious metal electrocatalysts is critical for eco‐friendly hydrogen production through electrolysis. Herein, a novel nanoflower‐like electrocatalyst comprising few‐layer nitrogen‐doped graphene‐encapsulated nickel–copper alloy directly on a porous nitrogen‐doped graphic carbon framework (denoted as Ni_x Cu_y @ NG‐NC) is successfully synthesized using a facile and scalable method through calcinating the carbon, copper, and nickel hydroxy carbonate composite under inert atmosphere. The introduction of Cu can effectively modulate the morphologies and hydrogen evolution reaction (HER) performance. Moreover, the calcination temperature is an important factor to tune the thickness of graphene layers of the Ni_x Cu_y @ NG‐NC composites and the associated electrocatalytic performance. Due to the collective effects including unique porous flowered architecture and the synergetic effect between the bimetallic alloy core and graphene shell, the Ni₃Cu₁@ NG‐NC electrocatalyst obtained under optimized conditions exhibits highly efficient and ultrastable activity toward HER in harsh environments, i.e., a low overpotential of 122 mV to achieve a current density of 10 mA cm^?2 with a low Tafel slope of 84.2 mV dec^?1 in alkaline media, and a low overpotential of 95 mV to achieve a current density of 10 mA cm^?2 with a low Tafel slope of 77.1 mV dec^?1 in acidic electrolyte.     

Lithiophilic 3D Nanoporous Nitrogen‐Doped Graphene for Dendrite‐Free and Ultrahigh‐Rate Lithium‐Metal Anodes

The key bottlenecks hindering the practical implementations of lithium‐metal anodes in high‐energy‐density rechargeable batteries are the uncontrolled dendrite growth and infinite volume changes during charging and discharging, which lead to short lifespan and catastrophic safety hazards. In principle, these problems can be mitigated or even solved by loading lithium into a high‐surface‐area, conductive, and lithiophilic porous scaffold. However, a suitable material that can synchronously host a large loading amount of lithium and endure a large current density has not been achieved. Here, a lithiophilic 3D nanoporous nitrogen‐doped graphene as the sought‐after scaffold material for lithium anodes is reported. The high surface area, large porosity, and high conductivity of the nanoporous graphene concede not only dendrite‐free stripping/plating but also abundant open space accommodating volume fluctuations of lithium. This ingenious scaffold endows the lithium composite anode with a long‐term cycling stability and ultrahigh rate capability, significantly improving the charge storage performance of high‐energy‐density rechargeable lithium batteries.     

Active Sites and Mechanism of Oxygen Reduction Reaction Electrocatalysis on Nitrogen‐Doped Carbon Materials

The oxygen reduction reaction (ORR) is a core reaction for electrochemical energy technologies such as fuel cells and metal–air batteries. ORR catalysts have been limited to platinum, which meets the requirements of high activity and durability. Over the last few decades, a variety of materials have been tested as non‐Pt catalysts, from metal–organic complex molecules to metal‐free catalysts. In particular, nitrogen‐doped graphitic carbon materials, including N‐doped graphene and N‐doped carbon nanotubes, have been extensively studied. However, due to the lack of understanding of the reaction mechanism and conflicting knowledge of the catalytic active sites, carbon‐based catalysts are still under the development stage of achieving a performance similar to Pt‐based catalysts. In addition to the catalytic viewpoint, designing mass transport pathways is required for O₂. Recently, the importance of pyridinic N for the creation of active sites for ORR and the requirement of hydrophobicity near the active sites have been reported. Based on the increased knowledge in controlling ORR performances, bottom‐up preparation of N‐doped carbon catalysts, using N‐containing conjugative molecules as the assemblies of the catalysts, is promising. Here, the recent understanding of the active sites and the mechanism of ORRs on N‐doped carbon catalysts are reviewed.