Abstract:Transition metal nitrides have been widely studied due to their high electrical conductivity and excellent chemical stability. However, their preparation traditionally requires harsh conditions because of the ultrahigh activation energy barrier they need to cross in nucleation. Herein, we report three-dimensional porous VN, MoN, WN, and TiN with high surface area and porosity that are prepared by a general and mild molten-salt route. Trace water is found to be a key factor for the formation of these porous tra… Show more
“…Inspired by this idea, we consider molten salt (MS) synthesis, a classical method for preparing functional materials owing to its simplicity, speed, large-scale compatibility, and low cost. [24][25][26][27][28] The MS melts can exhibit homogeneous heat and mass transfer to carry out chemical transformation even at low temperature. [24,29] MS methods have been widely used in industrial production.…”
efficiency of laboratory-scale all-inorganic solar cells has been improved to 20.37%, [5] approaching ~70% of the efficiency limit based on the Shockley-Queisser (S-Q) theory. [9][10][11] Among all the high-performance all-inorganic perovskite devices, the photocurrent and fill factor have exceeded 95% and 90% of their theoretical S-Q limits, respectively, while the open-circuit voltage (V oc ) falls at ≈80% of the limit. Therefore, there is relatively larger room for improvement in the V oc for yielding higher power conversion efficiency (PCE). [5,[12][13][14][15] The V oc depends on the dynamics of charge carrier recombination, which is connected to the non-radiative recombination processes. [16][17][18][19] Defects usually scatter the carriers as non-radiative recombination reaction centers. [20][21][22][23] Therefore, preparing high-quality perovskite films with low-defect density is a prerequisite for high-performance photovoltaic devices. The quality of the perovskite active layer can be manipulated by the crystallization processes, thus dynamic control of crystallization appears to be very important. In a common solvent crystallization process, the perovskite grain growth is mainly completed in the initial solvent evaporation process because: 1) solvent evaporation leads to the super-saturation of the solute, producing a mass of seed crystals; 2) solvent evaporation drives the migration of the perovskite precursor colloids, which is beneficial to the grain growth. Subsequent extended annealing has faint effect on the grain growth. We assumed that if the "reactive solvent medium" can remain for a longer time, the colloids will react completely and the grains can merge better. Inspired by this idea, we consider molten salt (MS) synthesis, a classical method for preparing functional materials owing to its simplicity, speed, large-scale compatibility, and low cost. [24][25][26][27][28] The MS melts can exhibit homogeneous heat and mass transfer to carry out chemical transformation even at low temperature. [24,29] MS methods have been widely used in industrial production. For example, they are regarded as ideal reactors for the closed Th-U cycle due to their lower fissile inventory [30] and are applied in lignite pyrolysis to affect the products. [31] The MS processes have been applied not only in chemical reactions but also in material morphology manipulation. [32][33][34] So far, MS can be classified into two types: solid high-temperature MS, [27,34,35] and low-temperature MS (ionic liquids [ILs]) [32,36,37] depending on their states within a certain temperature range. The solid MSs show high ionic conductivity only in the liquid state, and thereby should be used at high temperatures above their melting points. ILs are considered Dynamic manipulation of crystallization is pivotal to the quality of polycrystalline films. A molten-salt-assisted crystallization (MSAC) strategy is presented to improve grain growth of the all-inorganic perovskite films. Compared with the traditional solvent annealing, MSAC enables...
“…Inspired by this idea, we consider molten salt (MS) synthesis, a classical method for preparing functional materials owing to its simplicity, speed, large-scale compatibility, and low cost. [24][25][26][27][28] The MS melts can exhibit homogeneous heat and mass transfer to carry out chemical transformation even at low temperature. [24,29] MS methods have been widely used in industrial production.…”
efficiency of laboratory-scale all-inorganic solar cells has been improved to 20.37%, [5] approaching ~70% of the efficiency limit based on the Shockley-Queisser (S-Q) theory. [9][10][11] Among all the high-performance all-inorganic perovskite devices, the photocurrent and fill factor have exceeded 95% and 90% of their theoretical S-Q limits, respectively, while the open-circuit voltage (V oc ) falls at ≈80% of the limit. Therefore, there is relatively larger room for improvement in the V oc for yielding higher power conversion efficiency (PCE). [5,[12][13][14][15] The V oc depends on the dynamics of charge carrier recombination, which is connected to the non-radiative recombination processes. [16][17][18][19] Defects usually scatter the carriers as non-radiative recombination reaction centers. [20][21][22][23] Therefore, preparing high-quality perovskite films with low-defect density is a prerequisite for high-performance photovoltaic devices. The quality of the perovskite active layer can be manipulated by the crystallization processes, thus dynamic control of crystallization appears to be very important. In a common solvent crystallization process, the perovskite grain growth is mainly completed in the initial solvent evaporation process because: 1) solvent evaporation leads to the super-saturation of the solute, producing a mass of seed crystals; 2) solvent evaporation drives the migration of the perovskite precursor colloids, which is beneficial to the grain growth. Subsequent extended annealing has faint effect on the grain growth. We assumed that if the "reactive solvent medium" can remain for a longer time, the colloids will react completely and the grains can merge better. Inspired by this idea, we consider molten salt (MS) synthesis, a classical method for preparing functional materials owing to its simplicity, speed, large-scale compatibility, and low cost. [24][25][26][27][28] The MS melts can exhibit homogeneous heat and mass transfer to carry out chemical transformation even at low temperature. [24,29] MS methods have been widely used in industrial production. For example, they are regarded as ideal reactors for the closed Th-U cycle due to their lower fissile inventory [30] and are applied in lignite pyrolysis to affect the products. [31] The MS processes have been applied not only in chemical reactions but also in material morphology manipulation. [32][33][34] So far, MS can be classified into two types: solid high-temperature MS, [27,34,35] and low-temperature MS (ionic liquids [ILs]) [32,36,37] depending on their states within a certain temperature range. The solid MSs show high ionic conductivity only in the liquid state, and thereby should be used at high temperatures above their melting points. ILs are considered Dynamic manipulation of crystallization is pivotal to the quality of polycrystalline films. A molten-salt-assisted crystallization (MSAC) strategy is presented to improve grain growth of the all-inorganic perovskite films. Compared with the traditional solvent annealing, MSAC enables...
“… Figure 8. A) Synthesis scheme of crystalline mesoporous titanium oxynitride (Reproduced with permission from [ 178 ]) b) synthesis scheme of porous single MNs of vanadium, molybdenum, titanium, and tungsten via molten salt route, and c) their formation mechanism (Reproduced with permission from [ 180 ]). …”
Section: Synthesis Of Porous Mnsmentioning
confidence: 99%
“…The molten salt route can be extended to synthesize porous MN as well. For example, vanadium, molybdenum, tungsten, and titanium nitrides with a reasonable high surface area can be synthesized from their respective chloride salts by activation with zinc chloride [ 180 ]. A mixture of individual metal chlorides, lithium nitride (Li 3 N), and zinc chloride in both hydrated and anhydrous forms was grounded into a solid mass and subjected to heating at a relatively low temperature of 290°C to obtain porous MNs ( Figure 8b ).…”
The over-dependence on fossil fuels is one of the critical issues to be addressed for combating greenhouse gas emissions. Hydrogen, one of the promising alternatives to fossil fuels, is renewable, carbon-free, and non-polluting gas. The complete utilization of hydrogen in every sector ranging from small to large scale could hugely benefit in mitigating climate change. One of the key aspects of the hydrogen sector is its production via cost-effective and safe ways. Electrolysis and photocatalysis are well-known processes for hydrogen production and their efficiency relies on electrocatalysts, which are generally noble metals. The usage of noble metals as catalysts makes these processes costly and their scarcity is also a limiting factor. Metal nitrides and their porous counterparts have drawn considerable attention from researchers due to their good promise for hydrogen production. Their properties such as active metal centres, nitrogen functionalities, and porous features such as surface area, pore-volume, and tunable pore size could play an important role in electrochemical and photocatalytic hydrogen production. This review focuses on the recent developments in metal nitrides from their synthesis methods point of view. Much attention is given to the emergence of new synthesis techniques, methods, and processes of synthesizing the metal nitride nanostructures. The applications of electrochemical and photocatalytic hydrogen production are summarized. Overall, this review will provide useful information to researchers working in the field of metal nitrides and their application for hydrogen production.
“…With the advantages of excellent conductivity, high hardness, and superior stability, transition-metal nitrides (TMNs) are widely applied in catalysis, energy storage, and medicine [42][43][44][45]. In recent years, TMNs have also been reported to be the SERS substrates [46][47][48][49][50]. For instance, Guan et al reported that ultrathin δ-MoN nanosheets were synthesized via a solution route at 270 o C and 12 atm, and the Raman EF of these nanosheets is determined to 8.16 × 10 6 [46].…”
Section: Introductionmentioning
confidence: 99%
“…George et al demonstrated that few-layered Ti2N MXenes exhibited ultrasensitive detection of explosives at micromolar level [47]. Xi et al developed a molten-salt method for preparing plasmonic vanadium nitride porous materials, which could be used as sensitive and stable SERS substrates [48]. Nevertheless, to the best of our knowledge, the current study is almost limited to titanium nitride, molybdenum nitride and vanadium nitride, the systematic preparation and research of other TMNs have not been reported, besides the Raman enhancement mechanism is still unclear.…”
Noble-metal-free surface-enhanced Raman scattering (SERS) substrates have attracted great attention for their abundant sources, good signal uniformity, superior biocompatibility, and high chemical stability. However, the lack of controllable synthesis and fabrication of noble-metal-free substrates with high SERS activity impedes their practical applications. Herein, we propose a general strategy to fabricate a series of planar transition-metal nitride (TMN) SERS chips via an ambient temperature sputtering deposition route. These planar TMN (tungsten nitride, tantalum nitride, and molybdenum nitride) chips show remarkable Raman enhancement factors (EFs) with ~10 5 owing to efficient photoinduced charge transfer process between TMN chips and probe molecules. Further, structural engineering of 2 these TMN chips is used to improve their SERS activity. Benefiting from the synergistic effect of charge transfer process and electric field enhancement by constructing nanocavity structure, the Raman EF of WN nanocavity chips could be greatly improved to ∼1.29 × 10 7 , which is an order of magnitude higher than that of planar chips. Moreover, we also design the WN/monolayer MoS2 heterostructure chips. With the increase of surface electron density on the upper WN and more exciton resonance transitions in the heterostructure, a ∼1.94 × 10 7 level EF and a 5 × 10 -10 M level detention limit could be achieved. Our results provide important guidance for the structural design of ultrasensitive noble-metal-free SERS chips.
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