钨掺杂镍铁水滑石高效电催化析氧反应

电解水对制备可持续和清洁的氢气能源至关重要。电解水的阳极析氧反应设计复杂的4-电子转移过程,所需能耗较高,是电解水的速控步骤。催化剂对于析氧反应的进行具有重要作用。镍铁水滑石是最具潜力的碱性非贵金属析氧反应(OER)催化剂,但是由于水滑石导电性差、活性位点暴露不充分、对反应中间体吸附较弱等问题,催化活性还需要进一步提高。如何提升催化活性已经被科学家们广泛关注,比如:制造缺陷、掺杂、将水滑石剥离为单层结构和组装为阵列结构等。在本论文中,通过简单的“一锅法”醇解合成了一系列不同量W掺杂NiFe-LDH的样品。XRD结果表明合成的NiFeW-LDH的衍射峰与完美NiFe-LDH标准卡片相同,没有其他的衍射峰,表明W没有单独成相,被成功掺杂进入NiFe-LDH。扫描电镜表明NiFeW-LDH为纳米片(尺寸约为~500 nm)组成的3d立体花状结构,且材料中Ni、Fe和W均匀分布。XPS表明材料中W的价态为6+,与未掺杂的NiFe-LDH相比,Fe向高价态移动,表面吸附的OH增多。在密度泛函理论(DFT)计算中,结果同样表明W6+掺杂有利于H2O和O*中间体的吸附,提高了Fe位点的活性。在1 mol∙L^(−1) KOH中,NiFeW-LDH达到10 mA·cm^(−2)所需过电位是199和237 mV,这比大多数的NiFe基粉末催化剂的性能好。综上,实验和计算表明W掺杂调控催化剂中Fe位点电子结构,优化对反应中间体的吸附,使催化剂具有更高活性。

Layered double hydroxides with atomic-scale defects for superior electrocatalysis

Atomic composition tuning and defect engineering are effective strategies to enhance the catalytic performance of multicomponent catalysts by improving the synergetic effect; however, it remains challenging to dramatically tune the active sites on mulficomponent materials through simultaneous defect engineering at the atomic scale because of the similarities of the local environment. Herein, using the oxygen evolution reaction （OER） as a probe reaction, we deliberately introduced base-soluble Zn（II） or AI（III） sites into NiFe layered double hydroxides （LDHs）, which are one of the best OER catalysts. Then, the Zn（II） or AI（III） sites were selectively etched to create atomic M（I0/M（IIo defects, which dramatically enhanced the OER activity. At a current density of 20 mA.cm-2, only 200 mV overpotential was required to generate M（II） defect-rich NiFe LDHs, which is the best NiFe-based OER catalyst reported to date. Density functional theory （DFT） calculations revealed that the creation of dangling Ni-Fe sites （i.e., unsaturated coordinated Ni-Fe sites） by defect engineering of a Ni-O-Fe site at the atomic scale efficiently lowers the Gibbs free energy of the oxygen evolution process. This defect engineering strategy provides new insights into catalysts at the atomic scale and should be beneficial for the design of a variety of catalysts.

Enhancing oxygen evolution reaction by cationic surfactants

Oxygen evolution reaction is critical for water splitting or metal-air batteries,but previous research mainly focuses on electrode material or structure optimization.Herein,we demonstrate that surfactant modification of a NiFe layered double hydroxide (LDH) array electrode,one of the best catalysts for oxygen evolution reaction (OER),could achieve superaerophobic surface with balanced surface charges,affording fast mass transfer,quick gas release,and boosted OER performance.The assembled surfactants on the electrode surface are responsible for lowering the bubble adhesive force (~ 1.03 μN) and corresponding fast release of small bubbles generated during OER.In addition,the bipolar nature of the hexadecyl trimethyl ammonium bromide (CTAB) molecule lead to bilayer assembly of the surfactants with the polar ends facing the electrode surface and the electrolyte,resulting in neutralized charges on the electrode surface.As a result,OH-transfer was facilitated and OER performance was enhanced.With the modified superaerophobic surface and balanced surface charge,NiFe LDHs-CTAB nanostructured electrode showed ultrahigh current density increase (9.39 mA(mV·cm^2)),2.3 times higher than that for conventional NiFe LDH nanoarray electrode),dramatically fast gas release,and excellent durability.The introduction of surfactants to construct under-water superaerophobic electrode with in-time repelling ability to the as-formed gas bubbles may open up a new pathway for designing efficient electrodes for gas evolution systems with potentially practical application in the near future.

基于富缺陷镍铁水滑石材料的高效析氧电极(英文)

探索低成本高效率的析氧电极对于工业电解水技术的发展至关重要.尽管镍铁水滑石已被公认为是一种高效析氧的非贵金属催化剂,但其本征活性还有待进一步提高.本研究通过将氧空位缺陷引入镍铁水滑石,设计出一种低成本高效率的析氧电极.通过精确电子结构调控,暴露更多活性位点,提高电极导电性,富缺陷镍铁水滑石电极展现出1.40 V(vs.RHE)的低起峰电位.同时,它仅需200 m V过电势就能达到10 m A cm^(-2)的电流密度,这相比未经处理的镍铁水滑石降低了48 m V.我们进一步通过密度泛函理论计算发现,氧空位缺陷的引入使Fe的价态降低,带隙减小,使得催化过程中电子更容易被激发到导带中,从而降低反应过电势并使析氧活性增强.

ZnNC的循环合成及其在氧还原法制备过氧化氢中的应用

电催化制备过氧化氢并用于消毒、灭菌和废物处理,是一种具有可移动性且适用于家庭规模的过氧化氢制备方法.但催化剂制备过程中对于原材料的原子利用率低,制备过程涉及到大量废气、废液的排放.本文基于单原子催化剂可高效电催化制备过氧化氢的特点,提出利用甲酰胺和金属单质作为前驱物循环制备单原子锌-氮-碳催化剂的方法.该催化剂在制备过程中产生废物少,在氧还原反应中催化产生过氧化氢的选择性超过80%,连续工作超过10,000秒无明显活性衰减.本文提出的单原子材料的绿色合成策略对于其他类型单原子材料的制备具有启发性和普适性,将大力推动单原子催化剂的制备及未来应用.

3D printed hierarchical spinel monolithic catalysts for highly efficient semi-hydrogenation of acetylene

Porous monolithic catalysts with high specific surface areas,which can not only facilitate heat/mass transfer,but also help to expose active sites,are highly desired in strongly exothermic or endothermic gas–solid phase reactions.In this work,hierarchical spinel monolithic catalysts with a porous woodpile architecture were fabricated via extrusion-based three-dimensional(3D)printing(direct ink writing,DIW in brief)of aluminate-intercalated layered double hydroxide(AI-LDH)followed by low temperature calcination.The intercalation of aluminate in LDH is found crucial to tailor the M^(2+)/Al^(3+)ratio,integrate LDH nanosheets into monolithic catalyst,and enable the conversion of LDH to spinel at the temperature as low as 500℃ with high specific surface areas(>350 m^(2)/g).The rapid mass/heat transfer resulted from the versatile 3D network at macroscale and the highly dispersed and fully exposed active sites benefited from the porous structure at microscale endow the 3D-printed Pd loaded spinel MgAlmixed metal oxide(3D-AI-Pd/MMO)catalyst with excellent catalytic performance in semi-hydrogenation of acetylene,achieving 100%conversion at 60℃ with more than 84%ethylene selectivity.

Highly efficient and stable solar-powered desalination by tungsten carbide nanoarray film with sandwich wettability

Solar-powered desalination is a promising way to resolve the worldwide water crisis for its low con- sumption and simple facility. Considering the fragility and aggregations of traditional materials, which may decrease efficiency, we herein introduce a robust tungsten carbide (WC) nanoarray film as a stable and efficient photothermal material, whose absorption is over 97.5% throughout almost the whole solar spectrum range (220–2200 nm) due to nanoarray structure and thus enhanced localized surface plasmon resonance. Besides, for the first time, we modified the film with sandwich wettability. It accelerates evap- oration by reducing water’s reflection of light, enlarging hydrophobic-hydrophilic boundaries, and depressing heat dissipation. Combining high absorption with unique wettability, the WC nanoarray film offers high solar-to-vapor efficiency of 90.8% and produces drinking water at the rate of (1.06 ± 0.10) kg m^(-2)h^(-1)from man-made seawater and (0.98 ± 0.18) kg m^(-2)h^(-1)from heavy metal sewage under one sun (AM 1.5) while 98% performance remains after 1 h×100 times’ reutilization.

Effects of redox-active interlayer anions on the oxygen evolution reactivity of NiFe-layered double hydroxide nanosheets

Nickel-iron layered double hydroxide （NiFe-LDH） nanosheets have shown optimal oxygen evolution reaction （OER） performance; however, the role of the intercalated ions in the OER activity remains unclear. In this work, we show that the activity of the NiFe-LDHs can be tailored by the intercalated anions with different redox potentials. The intercalation of anions with low redox potential （high reducing ability）, such as hypophosphites, leads to NiFe-LDHs with low OER overpotential of 240 mV and a small Tafel slope of 36.9 mV/dec, whereas NiFe-LDHs intercalated with anions of high redox potential （low reducing ability）, such as fluorion, show a high overpotential of 370 mV and a Tafel slope of 80.8 mV/dec. The OER activity shows a surprising linear correlation with the standard redox potential. Density functional theory calculations and X-ray photoelectron spectroscopy analysis indicate that the intercalated anions alter the electronic structure of metal atoms which exposed at the surface. Anions with low standard redox potential and strong reducing ability transfer more electrons to the hydroxide layers. This increases the electron density of the surface metal sites and stabilizes their high-valence states, whose formation is known as the critical step prior to the OER process.

Kinetic study of electrochemically produced hydrogen bubbles on Pt electrodes with tailored geometries

Understanding bubbles evolution kinetics on electrodes with varied geometries is of fundamental importance for advanced electrodes design in gas evolution reaction.In this work,the evolution kinetics of electro-generated hydrogen bubbles are recorded in situ on three(i.e.smooth,nanoporous,and nanoarray)Pt electrodes to identify the geometry dependence.The bubble radius shows a time-dependent growth kinetic,which is tightly-connected to the electrode geometry.Among the three electrodes,the smooth one shows a typical time coefficient of 0.5,in consistence with reported values;the nanoporous one shows a time coefficient of 0.47,less than the classic one(0.5);while the nanoarray one exhibits fastest bubble growth kinetics with a time coefficient higher than 0.5(0.54).Moreover,the nanoarray electrode has the smallest bubble detachment size and the largest growth coefficient(23.3)of all three electrodes.Based on the experimental results,a growth model combined direct bottom-injection with micro-convection is proposed to illustrate the surface geometry dependent coefficients,i.e.,the relationship between geometry and bubble evolution kinetics.The direct injection of generated gas molecules from the bottom of bubbles at the three phase boundaries are believed the key to tailor the bubble wetting states and thus determine the bubble evolution kinetics.