Graphene-covering is a promising approach for achieving an acid-stable, non-noble-metal-catalysed hydrogen evolution reaction (HER). Optimization of the number of graphene-covering layers and the ...density of defects generated by chemical doping is crucial for achieving a balance between corrosion resistance and catalytic activity. Here, we investigate the influence of charge transfer and proton penetration through the graphene layers on the HER mechanisms of the non-noble metals Ni and Cu in an acidic electrolyte. We find that increasing the number of graphene-covering layers significantly alters the HER performances of Ni and Cu. The proton penetration explored through electrochemical experiments and simulations reveals that the HER activity of the graphene-covered catalysts is governed by the degree of proton penetration, as determined by the number of graphene-covering layers.
Developing bifunctional electrocatalysts with high activities and long durability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial toward the practical ...implementation of rechargeable metal–air batteries. Here, a 3D nanoporous graphene (np‐graphene) doped with both N and Ni single atoms/clusters is reported. The predoping of N by chemical vapor deposition (CVD) dramatically increases the Ni doping amount and stability. The resulting N and Ni codoped np‐graphene has excellent electrocatalytic activities for both the ORR and the OER in alkaline aqueous solutions. The synergetic effects of N and Ni dopants are revealed by density functional theory calculations. The free‐standing Ni,N codoped 3D np‐graphene shows great potential as an economical catalyst/electrode for metal–air batteries.
The presence of N facilitates the loading of a high density of isolated Ni single atoms on graphene. The Ni and N codopod 3D nanoporous graphene exhibits greatly enhanced bifunctional oxygen catalytic activities due to the synergetic effect between Ni and N. Due to the superior catalytic performance and structure advantage, a nanoporous graphene‐based all‐solid‐state Zn–air battery exhibits superior performance.
Heavy chemical doping and high electrical conductivity are two key factors for metal‐free graphene electrocatalysts to realize superior catalytic performance toward hydrogen evolution. However, heavy ...chemical doping usually leads to the reduction of electrical conductivity because the catalytically active dopants give rise to additional electron scattering and hence increased electrical resistance. A hierarchical nanoporous graphene, which is comprised of heavily chemical doped domains and a highly conductive pure graphene substrate, is reported. The hierarchical nanoporous graphene can host a remarkably high concentration of N and S dopants up to 9.0 at % without sacrificing the excellent electrical conductivity of graphene. The combination of heavy chemical doping and high conductivity results in high catalytic activity toward electrochemical hydrogen production. This study has an important implication in developing multi‐functional electrocatalysts by 3D nanoarchitecture design.
Hierarchical nanoporous graphene containing heavily doped catalytic domains and highly conductive substrates was fabricated by a two‐step chemical vapor deposition (CVD) method. The hierarchical nanoarchitecture effectively avoids the trade‐off between catalysis and conductivity in chemically doped graphene and paves a new way to design high‐performance multi‐functional graphene catalysts.
Establishing an effective real-time monitoring and early warning system for glacier lake outburst floods (GLOFs) requires a full understanding of their occurrence mechanism. However, the harsh ...conditions and hard-to-reach locations of these glacial lakes limit detailed fieldwork, making satellite imagery a critical tool for monitoring. Lake Mercbacher, an ice-dammed lake in the central Tian Shan mountain range, poses a significant threat downstream due to its relatively high frequency of outbursts. In this study, we first monitored the daily changes in the lake area before the 2022 Lake Mercbacher outburst. Additionally, based on historical satellite images from 2014 to 2021, we calculated the maximum lake area (MLA) and its changes before the outburst. Furthermore, we extracted the proportion of floating ice and water area during the period. The results show that the lake area of Lake Mercbacher would first increase at a relatively low speed (0.01 km2/day) for about one month, followed by a relatively high-speed increase (0.04 km2/day) until reaching the maximum, which would last for about twenty days. Then, the lake area would decrease slowly until the outburst, which would last five days and is significant for early warning. Moreover, the floating ice and water proportion provides more information about the outburst signals. In 2022, we found that the floating ice area increased rapidly during the early warning stage, especially one day before the outburst, accounting for about 50% of the total lake area. Historical evidence indicates that the MLA shows a decreasing trend, and combining it with the outburst date and climate data, we found that the outburst date shows an obvious advance trend (6 days per decade) since 1902, caused by climate warming. Earlier melting results in an earlier outburst. This study provides essential references for monitoring Lake Mercbacher GLOFs and building an effective early warning system.
Catalyzing oxygen reduction reaction (ORR) and accelerating oxygen diffusion are two key challenges for the requirements of the cathode catalysts in the metal‐air batteries. A promising strategy for ...improving both ORR performance and mass diffusion simultaneously is to build carbon‐based catalysts with ORR‐active chemical dopants and 3D interconnected porosity. Herein, a 3D nanoporous N‐doped carbon with bicontinuous porosity and interconnected open‐pore channels is reported, which is prepared by a polyaniline‐assisted template method. The polyaniline can efficiently inhibit the surface diffusion‐caused template coarsening, achieving a small pore size of 35 nm. The small porous morphology gives rise to a high N‐dopant concentration up to 7.20 at.%, which in turn exhibits a commercial Pt/C‐comparable ORR performance together with satisfied durability in alkaline media. Using these nanoporous carbon catalysts as air electrodes, an all‐solid‐state flexible Al‐air battery is assembled with the measured maximum power density reaching 130.5 mW cm−2, as compared to 106.2 mW cm−2 when the commercial Pt/C standard is used. This study provides an efficient method to synthesize 3D N‐doped carbon with bicontinuous nano‐sized pore channels for wide‐ranging applications in portable and flexible devices.
A polyaniline‐assisted template method is developed to synthesize the nanoporous bicontinuous N‐doped carbon particles, achieving a small pore size of 35 nm. The polyaniline plays a key role in the suppression of surface diffusion and pore enlargement of the Mn2O3 template at the high pyrolysis temperature. The product exhibits excellent electrocatalytic activity in all‐solid‐state Al‐air batteries.
We report on a spatial mapping of the electronic and vibrational structure of three-dimensional (3D) nanoporous graphene architectures, which have a hierarchical pore structure. We demonstrate that ...the topology, curvature, and pores lead to local changes in the electronic and vibrational structure and in the hybridization states of the carbon atoms (sp2 vs. sp3-like). Nitrogen substitutions in pyrrolic bonding configurations also contribute to local distortions of the planar geometry of graphene. The distortions influence the electronic density of states at the Fermi level by shifting the Dirac cone apex, opening potential avenues for applications of two-dimensional graphene in 3D devices.
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Abstract
The diffusion of light by random materials is a general phenomenon that appears in many different systems, spanning from colloidal suspension in liquid crystals to disordered metal sponges ...and paper composed of random fibers. Random scattering is also a key element behind mimicry of several animals, such as white beetles and chameleons. Here, random scattering is related to micro and nanosized spatial structures affecting a broad electromagnetic region. In this work, we have investigated how random scattering modulates the optical properties, from terahertz to ultraviolet light, of a novel functional material, i.e., a three-dimensional graphene (3D Graphene) network based on interconnected high-quality two-dimensional graphene layers. Here, random scattering generates a high-frequency pass-filter behavior. The optical properties of these graphene structures bridge the nanoworld into the macroscopic world, paving the way for their use in novel optoelectronic devices.
Carbon‐based metal‐free catalysts for the hydrogen evolution reaction (HER) are essential for the development of a sustainable hydrogen society. Identification of the active sites in heterogeneous ...catalysis is key for the rational design of low‐cost and efficient catalysts. Here, by fabricating holey graphene with chemically dopants, the atomic‐level mechanism for accelerating HER by chemical dopants is unveiled, through elemental mapping with atomistic characterizations, scanning electrochemical cell microscopy (SECCM), and density functional theory (DFT) calculations. It is found that the synergetic effects of two important factors—edge structure of graphene and nitrogen/phosphorous codoping—enhance HER activity. SECCM evidences that graphene edges with chemical dopants are electrochemically very active. Indeed, DFT calculation suggests that the pyridinic nitrogen atom could be the catalytically active sites. The HER activity is enhanced due to phosphorus dopants, because phosphorus dopants promote the charge accumulations on the catalytically active nitrogen atoms. These findings pave a path for engineering the edge structure of graphene in graphene‐based catalysts.
Edge engendering of holey graphene with the edge containing abundant chemical dopants can provide designable carbon‐based electrocatalysts for water splitting. The edge‐enhanced catalytically active sites facilitate hydrogen evolution reactions, directly confirmed by in situ electrochemical measurements with scanning electrochemical cell microscopy. The origin of the catalytic ability is also investigated by density functional theory.
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