等浓度的氯化铵和硫酸铵溶液哪个pH高

有中学化学参考资料题:0.10 mol/L的NH4Cl和(NH4)2SO4溶液哪个pH值高?这似乎是个中学生可做的简单题目,仔细考虑不是如此.如果简单地认为盐酸和硫酸都是强酸,而硫酸是二元酸,硫酸铵溶液中铵盐浓度为0.20 mol/L,那么NH4Cl溶液pH高,那是不妥的.硫酸是二元酸,第一个氢离子能完全电离,第二个氢离子部分电离,如此考虑情况怎么样呢?是不是答案发生变化?这要通过计算来说明.     

Enhanced efficiency and stability in Sn-based perovskite solar cells with secondary crystallization growth

The conversion efficiencies reported for Tin(Sn)halide-based perovskite solar cells(PSCs)fall a large gap behind those of lead halide-based PSCs,mainly because of poor film quality of the former.Here we report an efficient strategy based on a simple secondary crystallization growth(SCG)technique to improve film quality for tin halide-based PSCs by applying a series of functional amine chlorides on the perovskite surface.They were discovered to enhance the film crystallinity and suppress the oxidation of Sn²⁺remarkably,hence reduce trap state density and non-irradiative recombination in the absorber films.Furthermore,the SCG film holds the band levels matching better with carrier transport layers and herein favoring charge extraction at the device interfaces.Consequently,a champion device efficiency of 8.07% was achieved alo ng with significant enhancements in VOC and JSC,in contrast to 5.35% of the control device value.Moreover,the SCG film-based devices also exhibit superior stability comparing with the control one.This work explicitly paves a novel and general strategy for developing high performance lead-free PSCs.     

Energy level engineering of charge selective contact and halide perovskite by modulating band offset:Mechanistic insights

Mixed cation and anion based perovskites solar cells exhibited enhanced stability under outdoor conditions,however,it yielded limited power conversion efficiency when TiO₂ and Spiro-OMeTAD were employed as electron and hole transport layer(ETL/HTL)respectively.The inevitable interfacial recombination of charge carriers at ETL/perovskite and perovskite/HTL interface diminished the efficiency in planar(n-i-p)perovskite solar cells.By employing computational approach for uni-dimensional device simulator,the effect of band offset on charge recombination at both interfaces was investigated.We noted that it acquired cliff structure when the conduction band minimum of the ETL was lower than that of the perovskite,and thus maximized interfacial recombination.However,if the conduction band minimum of ETL is higher than perovskite,a spike structure is formed,which improve the performance of solar cell.An optimum value of conduction band offset allows to reach performance of 25.21%,with an open circuit voltage(VOC)of 1231 mV,a current density JSC of 24.57 mA/cm² and a fill factor of 83.28%.Additionally,we found that beyond the optimum offset value,large spike structure could decrease the performance.With an optimized energy level of Spiro-OMeTAD and the thickness of mixed-perovskite layer performance of 26.56% can be attained.Our results demonstrate a detailed understanding about the energy level tuning between the charge selective layers and perovskite and how the improvement in PV performance can be achieved by adjusting the energy level offset.     

Recent Advances of Pure Organic Room Temperature Phosphorescence Materials for Bioimaging Applications

Bioimaging,as a powerful and helpful tool,which allows people to investigate deeply within living organisms,has contributed a lot for both clinical theranostics and scientific research.Pure organic room temperature phosphorescence(RTP)materials with the unique features of ultralong luminescence lifetime and large Stokes shift,can efficiently avoid biological autofluorescence and scattered light through a time-resolved imaging modality,and thus are attracting increasing attention.This review classifies pure organic RTP materials into three categories,including small molecule RTP materials,polymer RTP materials and supramolecular RTP materials,and summarizes the recent advances of pure organic RTP materials for bioimaging applications.     

A new strategy to access Co/N co-doped carbon nanotubes as oxygen reduction reaction catalysts

Carbon nanotubes(CNTs),as one-dimensional nanomaterials,show great potential in energy conversion and storage due to their efficient electrical conductivity and mass transfer.However,the security risks,time-consuming and high cost of the preparation process hinder its further application.Here,we develop that a negative pressure rather than a following gas environment can promote the generation of cobalt and nitrogen co-doped CNTs(Co/N-CNTs) by using cobalt zeolitic imidazolate framework(ZIF-67) as a precursor,in which the negative pressure plays a key role in adjusting the size of cobalt nanoparticles and stimulating the rearragement of carbon atoms for forming CNTs.Importantly,the obtained Co/N-CNTs,with high content of pyridinic nitrogen and abundant graphitized structure,exhibit superior catalytic activity for oxygen reduction reaction(ORR) with half-wave potential(E_1/2) of 0.85 V and durability in terms of the minimum current loss(2%) after the 30,000 s test.Our development provides a new pathway for large-scale and cost-effective preparation of metal-doped CNTs for various applications.     

Stabilizing High-voltage Cathode Materials for Next-generation Li-ion Batteries

The pressing demand for high-energy/power lithium-ion batteries requires the deployment of cathode materials with higher capacity and output voltage.Despite more than ten years of research,high-voltage cathode mate-rials,such as high-voltage layered oxides,spinel LiNi0.5Mn1.5O4,and high-voltage polyanionic compounds still cannot be commercially viable due to the instabilities of standard electrolytes,cathode materials,and cathode electrolyte interphases under high-voltage operation.This paper summarizes the recent advances in addressing the surface and interface issues haunting the application of high-voltage cathode materials.The understanding of the limitations and advantages of different modification protocols will direct the future endeavours on advancing high-energy/power lithium-ion batteries.     

Suppressing trap states and energy loss by optimizing vertical phase distribution through ternary strategy in organic solar cells

Suppressing the trap-state density and the energy loss via ternary strategy was demonstrated.Favorable vertical phase distribution with donors(acceptors)accumulated(depleted)at the interface of active layer and charge extraction layer can be obtained by introducing appropriate amount of polymer acceptor N2200 into the systems of PBDB-T:IT-M and PBDB-TF:Y6.In addition,N2200 is gradiently distributed in the vertical direction in the ternary blend film.Various measurements were carried out to study the effects of N2200 on the binary systems.It was found that the optimized morphology especially in vertical direction can significantly decrease the trap state density of the binary blend films,which is beneficial for the charge transport and collection.All these features enable an obvious decrease in charge recombination in both PBDB-T:IT-M and PBDB-TF:Y6 based organic solar cells(OSCs),and power conversion efficiencies(PCEs)of 12.5%and 16.42%were obtained for the ternary OSCs,respectively.This work indicates that it is an effective method to suppress the trap state density and thus improve the device performance through ternary strategy.     

Conformational Properties of Comb-shaped Polyelectrolytes with Negatively Charged Backbone and Neutral Side Chains Studied by a Generic Coarse-grained Bead-and-Spring Model

A generic coarse-grained bead-and-spring model,mapped onto comb-shaped polycarboxylate-based(PCE)superplasticizers,is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit counterions.The agreement on the radius of gyration of the PCEs with experiments shows that our model can be useful in studying the equilibrium sizes of PCEs in solution.The effects of ionic strength,side-chain number,and side-chain length on the conformational behavior of PCEs in solution are explored.Single-chain equilibrium properties,including the radius of gyration,end-to-end distance and persistenee length of the polymer backbone,shape-asphericity parameter,and the mean span dimension,are determined.It is found that with the increase of ionic strength,the equilibrium sizes of the polymers decrease only slightly,and a linear dependenew of the persistence length of backbone on the Debye screening length is found,in good agreement with the theory developed by Dobrynin.Increasing side-chain numbers and/or side-chain lengths increases not only the equilibrium sizes(radius of gyration and mean span)of the polymer as a whole,but also the persistence length of the backbone due to excluded volume interactions.     

Three-dimensionalization via control of laser-structuring parameters for high energy and high power lithium-ion battery under various operating conditions

Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery(LIB)electrodes.In this work,the effects of laser structuring parameters(groove pitch and depth)on the fundamental characteristics of LIB electrode,such as interfacial area,internal resistances,material loss and electrochemical performance,are investigated,LiNi_0.5Co_0.2Mn_0.3O₂ cathodes were structured by a femtosecond laser by varying groove depth and pitch,which resulted in a material loss of 5%-14%and an increase of 140%-260%in the in terfacial area between electrode surface and electrolyte.It is shown that the importance of groove depth and pitch on the electrochemical performance(specific capacity and areal discharge capacity)of laser-structured electrode varies with current rates.Groove pitch is more im porta nt at low current rate but groove depth is at high curre nt rate.From the mapping of lithium concentration within the electrodes of varying groove depth and pitch by laser-induced breakdown spectroscopy,it is verified that the groove functions as a diffusion path for lithium ions.The ionic,electronic,and charge transfer resistances measured with symmetric and half cells showed that these internal resistances are differently affected by laser structuring parameters and the changes in porosity,ionic diffusion and electronic pathways.It is demonstrated that the laser structuring parameters for maximum electrode performance and minimum capacity loss should be determined in consideration of the main operating conditions of LIBs.     

Mesh-like vertical structures enable both high areal capacity and excellent rate capability

In order to balance electrochemical kinetics with loading level for achieving efficient energy storage with high areal capacity and good rate capability simultaneously for wearable electronics,herein,2 D meshlike vertical structures(NiCo_2 S_4@Ni(OH)_2) with a high mass loading of 2.17 mg cm^-2 and combined merits of both 1 D nanowires and 2 D nanosheets are designed for fabricating flexible hybrid supercapacitors.Particularly,the seamlessly interconnected NiCo_2 S_4 core not only provides high capacity of 287.5 μAh cm^-2 but also functions as conductive skeleton for fast electron transport;Ni(OH)_2 sheath occupying the voids in NiCo_2 S_4 meshes contributes extra capacity of 248.4 μAh cm^-2;the holey features guarantee rapid ion diffusion along and across NiCO_2 S_4@Ni(OH)_2 meshes.The resultant flexible electrode exhibits a high areal capacity of 535.9 μAh cm^-2(246.9 mAh g^-1) at 3 mA cm^-2 and outstanding rate performance with 84.7% retention at 30 mA cm^-2,suggesting efficient utilization of both NiCo_2 S_4 and Ni(OH)_2 with specific capacities approaching to their theoretical values.The flexible solid-state hybrid device based on NiCo_2 S_4@Ni(OH)_2 cathode and Fe_2 O_3 anode delivers a high energy density of 315 μWh cm^-2 at the power density of 2.14 mW cm^-2 with excellent electrochemical cycling stability.     

铜基串联催化剂电催化CO2还原的研究进展

化石燃料的燃烧和其他人类活动排放了大量的CO₂气体,引发了诸多环境问题。电催化CO₂还原反应(CO₂RR)可以储存间歇可再生能源,实现人为闭合碳循环,被认为是获得高附加值化学品和燃料的有效途径。电催化CO₂RR涉及多个电子-质子转移步骤,其中^*CO通常被认为是关键中间体。铜由于对^*CO具有合适的吸附能,已被广泛证明是唯一能够有效地将CO₂还原为碳氢化合物和含氧化合物的金属催化剂。然而,纯Cu稳定性差、产品选择性低、过电位高,阻碍了工业级多碳产品的生产。构筑Cu基串联催化剂是提高CO₂RR性能的一种有前途的策略。本文首先介绍电催化CO₂RR的反应路线和串联机理。然后,系统地总结铜基串联催化剂对电催化CO₂RR的最新研究进展。最后,提出合理设计和可控合成新型电催化CO₂RR串联催化剂面临的挑战和机遇。     

富氧空位的非晶氧化铜高选择性电催化还原CO2制乙烯（英文）

过量化石能源的消耗导致大气中的二氧化碳含量不断上升,由此引发包括温室效应在内的环境问题。对此,常温常压下的电催化二氧化碳还原手段为制备高附加值的化工原料和实现碳循环提供了一种很有前景的技术储备。在众多的二氧化碳还原产物中,碳氢化合物尤其是乙烯,它作为塑料和其他化工产品的重要原料受到广泛的关注。电催化二氧化碳还原制乙烯工艺不仅可适配于现有的生产设备也可作为取代目前工业化的裂解方法。近年来,研究者们为了开发高效的电催化二氧化碳还原制乙烯催化剂开展了大量的研究。不过值得注意的是,大部分研究集中于铜基材料。尽管目前研究者取得了很多成果,但仍缺少可高选择性产乙烯的二氧化碳还原催化剂。如何设计出可活化二氧化碳分子,同时对*CO和*COH中间物有强吸附能力的催化剂是研究难点。针对此问题,本文中通过真空蒸镀的方法制备出一种富氧空位的非晶氧化铜纳米薄膜催化剂。受益于纳米薄膜的构建和氧空位的引入,该催化剂可快速进行电荷和物质的交换,并利于二氧化碳分子的吸附及优化还原中间产物的亲和力,进而表现出优异的电催化二氧化碳制乙烯的性能。结果表明,在加有0.1 mol·L^-1碳酸氢钾溶液的H型电...     

调控单位点M-N-C电催化剂的电子结构提升二氧化碳还原性能

全球的动力来源主要依靠化石能源,然而无节制地开采引起了一系列的能源危机和环境问题,例如,能源枯竭、气温逐年升高、气候恶化和海洋酸化等,这已经威胁了人类的可持续发展,因此寻找可再生能源和减缓二氧化碳的排放成为目前的关键问题,反应条件相对温和的电催化二氧化碳还原反应(CO₂RR)可将CO₂转化为具有工业价值的产品,例如C1、C2和C2+,这是解决“碳中和”的一种有效措施。电催化CO₂RR是一个复杂的多个电子/质子转移过程,反应机理相对复杂,涉及很多反应中间体,影响产物的选择性,CO₂RR的大规模应用需要开发低成本和高效的电催化剂。具有大比表面积、100%的原子利用率、不饱和配位、相对均匀的活性位点的原子分散的金属和氮共掺杂碳(M-N-C)材料是一种很有前途的催化剂。M-N-C材料具有可调变性,通过调节中心金属离子或中心金属离子的配位环境,中心金属离子的电子性质和原子结构将会发生变化,这为设计具有高效催化CO₂性能的催化剂提供了新的途径。因此,探讨在原子水平上调控M-N-C材料的电子...     

二氧化碳电催化还原中的电解质效应（英文）

二氧化碳(CO₂)电催化还原反应利用可再生能源将CO₂转化为高值燃料和化学品,是一种新型的碳中和技术。CO₂电催化还原反应在电极/电解质界面上进行,因此除催化剂以外,电解质对提高CO₂电催化还原反应性能同样至关重要。本文深度剖析了CO₂电催化还原反应中的电解质效应,结合近几年的最新研究进展,详细讨论了局部p H、阳离子、阴离子和离子交换膜等电解质组成和性质对电催化活性和产物选择性的影响,阐述了电解质效应的催化作用机制。本文特别强调了电化学原位红外/拉曼等振动光谱在电解质效应机理研究方面的优势以及面向实际应用的膜电极CO₂电解器中阴离子、阳离子、水、液体产物等物质传输对活性、选择性、能量效率及CO₂利用效率等关键催化性能指标的影响。本文最后提出了当前电解质效应研究中存在的挑战,并展望了未来的研究机遇和发展趋势。     

CO2和N2电还原中缺陷及界面工程的最新进展

实现碳氮循环是人类社会发展的迫切要求,也是催化领域的热门研究课题。在可再生能源的推动下,电催化技术引起了人们的广泛关注,且可以通过改变反应电压获得不同的目标产品。基于此,电催化技术被认为是缓解当前能源危机和环境问题的有效策略,对实现碳中和具有重要意义。其中,电催化CO₂还原反应(CO₂RR)和N₂还原反应(N₂RR)是一种有前途的小分子转化策略。然而,CO₂和N₂均为线性分子,其中C＝O和N≡N键的高解离能导致了它们高的化学惰性。此外,最高占据分子轨道(HOMO)和最低未占分子轨道(LUMO)之间的巨大能量间隙使它们具有高的化学稳定性;且CO₂和N₂的低质子亲和力使它们难以被直接质子化。另一方面,由于CO₂RR和N₂RR与析氢反应(HER)具有相近的氧化还原电位,造成其与HER之间存在竞争性关系,这也是致使催化剂在CO₂RR和N₂RR转化效率低的重要影响因素。因此,CO₂RR和N₂RR仍然面临着过电位高及法拉第效率低等问题。为了克服这些瓶颈,人们为提升CO₂RR和N₂RR电催化剂性能做出了很多努力。众所周知,电催化过程发生在催化剂表面,主要涉及质量传递和电子转移等过程。由此可见,催化剂的性能与其质量和电子传输能力密切相关,而调控催化剂表面结构可以优化活性点的质量和电子转移行为。电催化剂的缺陷和界面工程可通过表面原子工程来实现电子结构调控,对于提高气体吸附能力、抑制HER、富集气体及稳定中间产物等具有重要意义。到目前为止,所报道的各种缺陷和复合电催化剂在提高CO₂RR和N₂RR催化性能等方面均表现出巨大的潜力。在此,我们综述了CO₂RR和N₂RR中催化剂缺陷工程及界面工程的最新进展;首先讨论了四种不同的缺陷(空位、高指数晶面、晶格应变和晶格无序)对CO₂RR和N₂RR性能的影响;然后,总结了界面工程在聚合物-无机复合材料催化剂中的重要作用,并给出了典型实例;最后,展望了原子级电催化剂工程的发展前景,提出了开发和设计高效CO₂RR和N₂RR电催化剂的未来发展方向。     

一体化电极电催化二氧化碳还原研究进展

电催化二氧化碳还原反应(E-CO₂RR)可在温和条件下将CO₂转化成高附加值燃料或化学品,近年来受到广泛关注,其在实际反应中涉及到气体扩散和多电子转移等复杂过程,构筑高效、稳定的催化电极是其发展的核心之一。然而,传统涂敷电极制备时,需要将催化剂与粘结剂混合涂覆于集流体表面,此过程会造成活性位点包埋和传质过程受限,致使催化剂活性位利用率下降,同时在反应过程中电极表面容易粉化,造成稳定性下降,难以重复利用。因此,如何调控电极反应界面,提升催化剂活性位的利用率仍面临挑战。将催化剂原位生长于集流体上得到的一体化电极可直接应用于电催化反应,不仅有利于提升活性位利用率以及电荷传输能力,还能有效调控三相界面处的微观反应环境(如pH、反应物及反应中间体的浓度等),从而实现电催化性能强化。本文综述了一体化电极用于E-CO₂RR的最新进展,分析了结构和表界面调控对E-CO₂RR性能的影响规律,并对该领域仍然存在的挑战和未来一体化E-CO₂RR电极的发展进行了评述与展望。     

Polymeric Carbon Nitride-based Single Atom Photocatalysts for CO2 Reduction to C1 Products

Photocatalytic CO₂ reduction to C₁ fuels is considered to be an important way for alleviating increasingly serious energy crisis and environmental pollution. Due to the environment-friendly, simple preparation, easy formation of highly-stable metal-nitrogen(M-N_x) coordination bonds, and suitable band structure, polymeric carbon nitride-based single-atom catalysts(C₃N₄-based SACs) are expected to become a potential for CO₂ reduction under visible-light irradiation. In this review, we summarize the recent advancement on C₃N₄-based SACs for photocatalytic CO₂ reduction to C₁ products, including the reaction mechanism for photocatalytic CO₂ reduction to C₁ products, the structure and synthesis methods of C₃N₄-based SACs and their applications toward photocatalytic CO₂ reduction reaction(CO₂RR) for C₁ production. The current challenges and future opportunities of C₃N₄-based SACs for photoreduction of CO₂ are also discussed.     

电催化动力学简介（英文）

电催化过程是实现社会向可再生能源与化学品转型的主要驱动力之一。电催化动力学分析是探索反应机理和建立电催化剂构效关系行之有效的方法。本文将通过三个广泛研究的电催化反应：电化学CO₂、CO还原反应和氧还原反应,探讨Tafel分析的普遍过程、隐含假设以及需要注意的问题。此外,本文将介绍电化学反应活化参数的基本概念和关键热力学、动力学变量之间的关系。     

高催化活性M-BHT(M=Co， Cu)电催化还原CO2为CH4的密度泛函理论研究

具有独特电子结构和丰富催化位点的二维金属有机框架材料是具有高活性的CO₂还原反应的电催化剂. 本文基于密度泛函理论(DFT)计算, 发现单层Co-BHT(BHT=benzenehexathiol, 苯六硫醇)将CO₂还原为CH₄时具有很高的催化活性. 吉布斯自由能变化计算结果表明, 在Co-BHT上将CO₂还原成CH₄的最佳反应路径为CO₂→^*COOH→^*CO→^*CHO→^*CHOH→^*CH→^*CH₂→^*CH₃→CH₄; 整个反应的速度控制步骤为^*CO→^*CHO; 速度控制步骤的吉布斯自由能变化(ΔG_L)为0.66 eV, 比在二维Cu-C₃N₄(ΔG_L=0.75 eV)和传统的Cu(211) 表面(ΔG_L=0.74 eV) 将CO₂还原为CH₄的吉布斯自由能变化都小. 而在单层Cu-BHT表面的反应路径和速度控制步骤 (CO₂→^*COOH)与Co-BHT均不同, 且ΔG_L为0.76 eV. 与Cu-BHT相比, Co-BHT将CO₂还原为CH₄的ΔG_L更低, 这可能归因于Co-BHT的d能带中心高于Cu-BHT, 导致Co-BHT与中间体的相互作用更强.     

电解液调控CO2电催化还原性能微观机制的研究进展

二氧化碳(CO₂)排放导致了严重的温室效应, 但作为重要的碳资源, CO₂电催化还原合成化学品因反应条件温和、 反应产物可调及可有效利用分布式电能等优势而备受关注. 在该反应体系中, 电解液作为反应介质, 可提供质子和反应微环境, 影响分子/离子传输. 因此, 构建新型电解液体系对于提高CO₂电催化还原产物的选择性和电流密度起到重要作用. 本文综合评述了CO₂电催化还原过程中电解液的作用和研究现状, 重点总结了水系电解液中阴阳离子(碱金属阳离子、 卤素离子等)和离子液体电解液对CO₂溶解度、 界面双电层结构(pH值、 电场效应)和中间体稳定性等的影响机制, 揭示了其调控对反应产物的选择性、 电流密度等的影响规律. 最后, 对电解液调控CO₂电催化还原性能的研究进行了展望.