提升二维材料的电催化析氢和光催化析氢性能的策略

世界能源危机问题和环境问题日益突出,寻找低廉、易得且能够替代化石的清洁能源是目前研究的热点.氢气具有可再生性、安全、高能量密度、环境友好型等优点,因而成为替代化石燃料的首选.在众多途径中,电催化产氢和光催化产氢是目前应用较广且比较成熟的方法,其工艺过程简单、无污染,但由于效率较低或生产成本较高等因素,其大规模应用受到一定的限制.因此,开发高效的析氢催化剂意义重大.迄今为止,贵金属铂是公认的最好的析氢催化剂,但其稀有性和价格高阻碍了大规模的商业应用.因此,寻找高效、稳定、价格合理的析氢催化剂迫在眉睫.近年来,已研究和设计了很多析氢催化材料,其中,二维材料以其独特的物理化学性质(如电子在二维空间内快速移动、超薄结构、较大的比表面积等)引起了科学家的兴趣.但实际研究的二维材料的析氢性能与理论值相比还有很大的差距.因此,提高二维材料的导电性、增加活性位点、提高光电催化剂的循环稳定性是提升其性能的关键.本文综述了四种二维材料(二硫化钼、石墨烯、过渡金属碳氮化物、黑磷)在析氢方面的最新研究进展,包括(1)二维材料的合成方法,(2)二维材料析氢性能,(3)析氢催化机理.并从三个方面总结了提升二维材料析氢性能的策略:(1)缺陷位工程,(2)异质结策略,(3)金属及非金属杂原子掺杂.在提高二维材料的策略方面,本文着重讨论了d带理论、状态密度和费米能级,为更多二维析氢催化材料的制备提供了有效的指导.最后,本文分析了二维催化剂领域目前面临的问题和挑战,展望了未来的发展趋势.

Three-dimensional graphitic carbon sphere foams as sorbents for cleaning oil spills

Frequent offshore oil spill accidents, industrial oily sewage, and the indiscriminate disposal of urban oily sewage have caused seri- ous impacts on the human living environment and health. The traditional oil-water separation methods not only cause easily environmental secondary pollution but also a waste of limited resources. Therefore, in this work, three-dimensional (3D) graphitic carbon sphere (GCS) foams (collectively referred hereafter as 3D foams) with a 3D porous structure, pore size distribution of 25-200 μm, and high porosity of 62vol% were prepared for oil adsorption via gel casting using GCS as the starting materials. The results indicate that the water contact angle (WCA) of the as-prepared 3D foams is 130°. The contents of GCS greatly influenced the hydrophobicity, WCA, and microstructure of the as-prepared samples. The adsorption capacities of the as-prepared 3D foams for paraffin oil, vegetable oil, and vacuum pump oil were approximately 12-15 g/g, which were 10 times that of GCS powder. The as-prepared foams are desirable characteristics of a good sorbent and could be widely used in oil spill accidents.

Methylammonium-and bromide-free perovskites enable efficient and stable photovoltaics

Hybrid perovskite solar cell(PSC)has attracted extensive research interest due to its rapid increase in efficiency,regarding as one of the most promising candidates for the next-generation photovoltaic technology.The certified power conversion efficiency of the devices based on formamidinium lead iodide(FAPbI_(3))perovskite has reached 25.5%,approaching the record of monocrystalline silicon solar cells.Unfortunately,the blackα-phase FAPbI_(3)materials can spontaneously transform to non-optically activeδ-phase at room temperature,which greatly hinder their photovoltaic application.In order to overcome this problem,various strategies,especially introducing methylammonium(MA^(+)),caesium(Cs^(+))and bromide(Br^(-))ions into the materials,have been widely adopted.However,MA^(+)can largely reduce the thermal stability of the materials.Furthermore,the introduction of Br^(-)can enlarge the materials'bandgap,resulting in a reduced theoretical efficiency.Keeping these in mind,developing the strategies which without using MA^(+)and Br^(-)is the inevitable trend.Here,we focus on the recent progresses of stabilizingαFAPbI_(3)without employing MA^(+)and Br^(-),and discuss the advantages of inorganic ions doping and dimensionality engineering to stabilizedαFAPbI_(3).Meanwhile,in order to deeply understand the relationship between the semiconducting properties and device performance of the corresponding materials,we then summarize several significant strategies to suppress the non-radiation recombination,such as interface modification and trap passivation.Finally,we propose to develop more effective'A-site'alternatives to stabilizeαFAPbI_(3),which is expected to achieve high-efficient PSCs with long-term stability,facilitating its commercialization process.

Synergetic effect of lattice distortion and oxygen vacancies on high-rate lithium-ion storage in high-entropy perovskite oxides

High-entropy oxides(HEOs)have gained great attention as an emerging kind of highperformance anode materials for lithium-ion batteries(LIBs)due to the entropy stabilization and multi-principal synergistic effect.Herein,the porous perovskite-type RE(Co_(0.2)Cr_(0.2)Fe_(0.2)Mn_(0.2)Ni_(0.2))O_(3)(RE(=La,Sm,and Gd)is the abbreviation of rare earth)HEOs were successfully synthesized by a solution combustion synthesis(SCS)method.Owing to the synergistic effect of lattice distortion and oxygen vacancies(Ov),the Gd(Co_(0.2)Cr_(0.2)Fe_(0.2)Mn_(0.2)Ni_(0.2))O_(3) electrode exhibits superior high-rate lithium-ion storage performance and excellent cycling stability.A reversible capacity of 403 mAh·g^(-1) at a current rate of 0.2 A·g^(-1) after 500 cycles and a superior high-rate capacity of 394 mAh·g^(-1)even at 1.0 A·g^(-1)after 500 cycles are achieved.Meanwhile,the Gd(Co_(0.2)Cr_(0.2)Fe_(0.2)Mn_(0.2)Ni_(0.2))O_(3) electrode also exhibits a pronounced pseudo-capacitive behavior,contributing to an additional capacity.By adjusting and balancing the lattice distortion and oxygen vacancies of the electrode materials,the lithium-ion storage performance can be further regulated.

Employ ionic liquid to stabilize black-phase formamidinium perovskites

The certified power conversion efficiency(PCE)of per-ovskite solar cells which have emerged as the most promising candidates for next-generation thin-film photovoltaics has exceeded 25%.Among all available compositions,formamidinium lead iodide perovskite(FAPbI_(3))has a theoretically higher efficiency than the other perovskite analogues due to its narrower bandgap[1,2]and hence has attracted widespread attention.

Influence of lignin content on enzymatic saccharification of poplar wood chips by different pretreatment methods

Bioconversion of lignocellulose to fermentable sugars is a promising approach to produce potential bio-based energy and chemicals.Pretreatment is the key step to remove or delocalize lignin in lignocellulose,thus improving enzymatic saccharification efficiency.In this study,three kinds of pretreatment methods(ethanol,bisulfite and sulfate)were employed to produce substrates with various lignin contents which were subsequently subjected to biological saccharification processes.Results showed that a lower lignin content led to a higher fermentable sugar yield based on reducing sugar release for all samples.Additionally,the sulfate pretreatment improved the enzymatic saccharification efficiency in a greater extent than the others.Fourier transform infrared(FTIR)spectroscopy confirmed the structure changes during pretreatment.

超亲水疏油材料的制备及其油水分离性能

含油污水的随意排放对海洋、沿海周边环境以及人类健康造成了严重的影响。传统的油水分离方法易造成环境二次污染,同时也是对有限资源的一种损耗。因此,如何高效环保地解决含油污水问题具有重要意义。物理过滤/吸附法被认为是一种高效环保的分离方法,基于仿生学原理,许多可用于物理选择性分离的超亲油疏水和超亲水疏油材料被制备出来。超亲油疏水材料易被油污染,重复利用率低;相比之下,超亲水疏油材料具有自清洁性且重复利用率高,在油水分离方面具有广阔的应用前景。根据基底材料的选择不同,本文综述了金属基以及高分子基超亲水疏油材料的研究现状,总结了其优缺点,并对今后超亲水疏油材料的研究方向和重点进行了展望。

Advances and challenges in two-dimensional materials for oxygen evolution

Oxygen evolution reaction(OER)plays an important role in many energy conversions and storage technologies,such as water splitting,rechargeable metal air batteries,renewable fuel cells,and electrocatalytic carbon dioxide reduction and nitrogen reduction,but its slow kinetics and high overpotential seriously affect the energy efficiency.Fabrication of high-performance and well-stocked OER catalysts is the key to the large-scale implementation of these energy-related technologies.Two-dimensional(2D)materials get a lot of attention as OER catalysts due to their large specific surface area,abundant active sites,and adjustable structures and compositions.Here,an overview is presented for the latest achievements in design and synthesis of 2D materials(including layered double hydroxides,metal-organic frameworks and their derivatives,covalent-organic frameworks,graphene,and black phosphorus)for the OER,emphasizing novel strategies(including metal/nonmetal doping,defect engineering,interface engineering,lattice strain,and fabrication of heterojunction)for achieving high electrocatalytic activity.Peculiarly,the structure–function relationship is analyzed in detail to gain deeper insight into the reaction mechanism,which is crucial to rational design of more high-performance 2D materials for the OER.Finally,the remaining challenges to improve the OER performance of 2D electrocatalysts are put forward to indicate possible future development of 2D materials.