The component-activity interrelationship of cobalt-based bifunctional electrocatalysts for overall water splitting:Strategies and performance

Cobalt-based electrocatalysts take advantage of potentially harmonizable microstructure and flexible coupling effects compared to commercial noble metal-based catalytic materials.However,conventional water electrolysis systems based on cobalt-based monofunctional hydrogen evolution reaction(HER)or oxygen evolution reaction(OER)catalysts have certain shortcomings in terms of resource utilization and universality.In contrast,cobalt-based bifunctional catalysts(CBCs)have attracted much attention in recent years for overall water splitting systems because of their practicality and reduced preparation cost of electrolyzer.This review aims to address the latest development in CBCs for total hydrolysis.The main modification strategies of CBCs are systematically classified in water electrolysis to provide an overview of how to regulate their morphology and electronic configuration.Then,the catalytic performance of CBCs in total-hydrolysis is summarized according to the types of cobalt-based phosphides,sulfides and oxides,and the mechanism of strengthened electrocatalytic ability is emphasized through combining experiments and theoretical calculations.Future efforts are finally suggested to focus on exploring the dynamic conversion of reaction intermediates and building near-industrial CBCs,designing advanced CBC materials through micro-modulation,and addressing commercial applications.

A Facile and Template-Free One-Pot Synthesis of Mn_3O_4 Nanostructures as Electrochemical Supercapacitors

In this paper, we report an effective, simple, and cost-effective strategy of electrochemical deposition to prepare hausmannite Mn_3O_4 thin films for the applications of supercapacitors. Various precursor concentrations and deposition durations were manipulated to tailor the surface morphologies of Mn_3O_4 nanostructures and to optimize their electrochemical performances. The Mn_3O_4 samples prepared at 0.05 M Mn(NO3)2solution for 30 min delivered a large gravimetric specific capacitance of 210 F g-1at a current density of 0.5 A g-1, and a good rate capability over other samples. This superior electrochemical performance may be attributed to the improved electrode conductivity with increased accessible area for electrolytes ions. Furthermore, a nanocomposite film based on Mn_3O_4/carbon foam was fabricated by utilizing the developed optimized conditions. The Mn_3O_4/carbon foam films exhibit an excellent specific capacitance with negligible degradation in retaining specific capacitance values up to 4000 cycles. These findings could further broaden the applications of hausmannite Mn_3O_4 in electrochemical energy storage electrodes.

Carbon-based bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions:Optimization strategies and mechanistic analysis

Electrocatalysts are one of the essential components for the devices of high-efficiency green energy storage and conversion,such as metal-air cells,fuel cells,and water electrolysis systems.While catalysts made from noble metals possess high catalytic performance in both oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),their scarcity and expensiveness significantly limit large-scale applications.In this regard,metal-free/non-noble metal carbon-based catalysts have become competitive alternatives to replace catalysts made of noble metals.Nevertheless,low catalytic ORR/OER performance is the challenge of carbon-based catalysts for the commercial applications of metal-air batteries.To solve the problem of poor catalytic performance,two strategies have been proposed:(1)controlling the microstructure of the catalysts to expose more active sites as the channels of rapid mass and electron transfer;and(2)reducing the reaction energy barrier by optimizing the electronic structures of the catalysts via surface engineering.Here,we review different types of bifunctional ORR/OER electrocatalysts with the activated surface sites.We focus on how the challenge can be overcome with different methods of material synthesis,structural and surface characterization,performance validation/optimization,to outline the principles of surface modifications behind catalyst designs.In particular,we provide critical analysis in the challenges that we are facing in structural design and surface engineering of bifunctional ORR/OER catalysts and indicate the possible solution for these problems,providing the society with clearer ideas on the practical prospects of noble-metal-free electrocatalysts for their future applications.

Molybdenum disulfide(MoS2)-based electrocatalysts for hydrogen evolution reaction:From mechanism to manipulation

Molybdenum disulfide(MoS_(2))-based materials as the non-noble metal catalysts have displayed the potential capability to drive electrocatalytic hydrogen evolution reaction(HER)for green hydrogen production along with their intrinsic activity,tunable electronic properties,low cost,and abundance reserves,which have attracted intensive attention as alternatives to the low-abundance and high-cost platinum-based catalysts.However,their insufficient catalytic HER activities and stability are the major challenges for them to become practically applicable.Hereby,the MoS_(2)-based electrocatalysts for HER are comprehensively reviewed to explain the fundamental science behind the manipulations of the crystal structure,microstructure,surface,and interface of MoS_(2) in order to enhance its catalytic performance through changing the electrical conductivity,the number of active sites,surface wettability,and the Gibbs free energy for hydrogen adsorption(ΔGH).Recent studies in surface/interface engineering,such as phase engineering,defect engineering,morphology design,and heterostructure construction,are analyzed to reveal the state-of-the-art strategies for designing and preparing the cost-effective and highperformance MoS_(2)-based catalysts through optimizing the charge transfer,surface-active sites,ΔGH,and surface hydrophilicity.Lastly,the perspectives,challenges,and future research directions of HER electrocatalysis are also given to facilitate the further research and development of HER catalysts.

Growth and Electrical Properties of Doped ZnO by Electrochemical Deposition

In this work, pure and different metal ions doped ZnO thin films were obtained by a facile electrochemical deposition process. Different morphologies of ZnO, such as nanoplates, nanoparticles, as well as dense film can be obtained by doping Cu2+, In3+, and Al3+, respectively. Besides, the electrical properties of ZnO were also dependent on the doping ions. In this work, only pure ZnO shows resistive switching characteristics, indicating that the defects in ZnO is a key role in inducing resistive switching behaviour.

简约柔雅

经过与屋主夫妇商讨后，设计师决定以浅色清简作设计主题，并于室内设置大量的储物空间，供存放杂物。至于客厅的设计，设计师在靠窗位置，依单位的弧形玻璃间隔，于天花设置弧形灯糟，选衬泰国的丝质窗帘，营造优雅的气氛。在电视机与窗台间，设有一L型光柱，光柱旁是一个以白色手扫漆饰面的大型CD柜，柜内最多可存放达300百张CD。

理想家居

拥有十多年楼龄的鲤景湾因拥有广阔的临海景致和高达85％的空间实用率而广受欢迎。本单位的一对年轻夫妇也不例外，购入合心意的单位后，便找来专业的设计师为他们打造理想家居。

清简主义

两个人的世界．简单已是最好。

这里阳光充沛

这是一所住着一家三口的温馨房子——父母及女儿。各有各空间．同时也有共同空间。

Energizing the future:Empowering sustainability with Electron

The advent of industrial civilization has brought about enormous materials advancements;yet it has also caused a rapid depletion of natural resources,leading to global energy crisis and environmental pollution.Facing human civilization,one fundamental issue stands at its core:how can we achieve a harmonious coexistence between humanity and nature?This question has become the key challenge of our time,demanding our utmost attention and concerted efforts.

High-entropy catalysts for electrochemical water-electrolysis of hydrogen evolution and oxygen evolution reactions

High entropy materials (HEMs) have developed rapidly in the field of electrocatalytic water-electrolysis for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) due to their unique properties. In particular, HEM catalysts are composed of many elements. Therefore, they have rich active sites and enhanced entropy stability relative to single atoms. In this paper, the preparation strategies and applications of HEM catalysts in electrochemical water-electrolysis are reviewed to explore the stabilization of HEMs and their catalytic mechanisms as well as their application in support green hydrogen production. First, the concept and four characteristics of HEMs are introduced based on entropy and composition. Then, synthetic strategies of HEM catalysts are systematically reviewed in terms of the categories of bottom-up and top-down. The application of HEMs as catalysts for electrochemical water-electrolysis in recent years is emphatically discussed, and the mechanisms of improving the performance of electrocatalysis is expounded by combining theoretical calculation technology and ex-situ/in situ characterization experiments. Finally, the application prospect of HEMs is proposed to conquer the challenges in HEM catalyst fabrications and applications.

Advanced Strategies for Stabilizing Single‑Atom Catalysts for Energy Storage and Conversion

Well-defined atomically dispersed metal catalysts(or single-atom catalysts)have been widely studied to fundamentally under-stand their catalytic mechanisms,improve the catalytic efficiency,increase the abundance of active components,enhance the catalyst utilization,and develop cost-effective catalysts to effectively reduce the usage of noble metals.Such single-atom cata-lysts have relatively higher selectivity and catalytic activity with maximum atom utilization due to their unique characteristics of high metal dispersion and a low-coordination environment.However,freestanding single atoms are thermodynamically unstable,such that during synthesis and catalytic reactions,they inevitably tend to agglomerate to reduce the system energy associated with their large surface areas.Therefore,developing innovative strategies to stabilize single-atom catalysts,including mass-separated soft landing,one-pot pyrolysis,co-precipitation,impregnation,atomic layer deposition,and organometallic complexation,is critically needed.Many types of supporting materials,including polymers,have been commonly used to stabilize single atoms in these fabrication techniques.Herein,we review the stabilization strategies of single-atom catalyst,including different synthesis methods,specific metals and carriers,specific catalytic reactions,and their advantages and disadvantages.In particular,this review focuses on the application of polymers in the synthesis and stabilization of single-atom catalysts,including their functions as carriers for metal single atoms,synthetic templates,encapsulation agents,and protection agents during the fabrication process.The technical challenges that are currently faced by single-atom catalysts are summarized,and perspectives related to future research directions including catalytic mechanisms,enhancement of the catalyst loading content,and large-scale implementation are proposed to realize their practical applications.

Molten salt assisted self-activated carbon with controllable architecture for aqueous supercapacitor

Activated carbons have been widely employed as electrode materials of aqueous supercapacitors but the use of hazardous and corrosive activating agents challenges conventional activation procedures.Here,using a unique molten salt assisted self-activation technique,we have devised an eco-friendly and simple method to synthesize oxygen-rich hierarchical porous carbon with controllable architecture.Mixture of sodium carboxymethylcellulose and NaCl was pyrolyzed in one step,creating in-situ produced Na_(2)CO_(3)-NaCl molten salt that carried out the activation work.Na2 CO3 acts as the activating agent in the reaction media of NaCl during the self-activation process.The obtained carbon exhibited a remarkable specific capacitance of 278 F g^(−1) at 0.5 A g^(−1) and retained 76%capacitance at 50 A g^(−1) in a three-electrode cell.The fabricated aqueous coin cell achieved 81%capacitance retention at 50 A g^(−1) and the highest specific energy density of 12.8 Wh kg^(−1) at 214.6 W kg^(−1),which are superior compared to the commercial activated carbon(64%at 50 A g^(−1) and 8.4 Wh kg^(−1) at 194.8 W kg^(−1)).Moreover,capacitance fading was not observed after 10000 cycles at 5 A g^(−1).Considering the species diversity and low cost of self-salt polymers on the market,this strategy will expect to become a scalable approach for synthesizing high-performance capacitive carbons.

Controlled fabrication of Pr(OH)_3 nanowires for enhanced photocatalytic activities

In this report, praseodymium hydroxide Pr(OH)_3 nanowires with different aspect ratios (length to diameter ratios) were synthesized by a facile hydrothermal approach. The variations in alkali concentration during synthesis are found to form different aspect ratios of nanowires. The X-ray diffraction and Raman spectroscopy analysis demonstrate the absence of any impurity phases in as-prepared materials.Subsequently, photocatalytic activities of as-prepared nano wires were evaluated by the degradation of methyl orange (MO). Our findings reveal that the nanowires with larger aspect ratios have higher photocatalytic efficiency than the smaller aspect ratio samples. X-ray photospectroscopy investigations reveal that the samples with higher aspect ratio are found to exhibit more oxygen vacancies as compared to lower aspect ratio samples. The enhanced photocatalytic activities can be attributed to the presence of higher percentage of active crystal facet (100), higher concentration of defects densities and narrower band gap. Thus, Pr(OH)_3 nanowires can be considered as a potential candidate for the application of wastewater treatment and related technologies.

Thermoelectric performance enhancement by manipulation of Sr/Ti doping in two sublayers of Ca_(3)Co_(4)O_(9)

Thermoelectric(TE)performance of Ca_(3)Co_(4)O_(9)(CCO)has been investigated extensively via a doping strategy in the past decades.However,the doping sites of different sublayers in CCO and their contributions to the TE performance remain unrevealed because of its strong correlated electronic system.In this work,Sr and Ti are chosen to realize doping at the[Ca_(2)CoO_(3)]and[CoO_(2)]sublayers in CCO.It was found that figure of merit(ZT)at 957 K of Ti-doped CCO was improved 30% than that of undoped CCO whereas 1 at% Sr doping brought about a 150% increase in ZT as compared to undoped CCO.The significant increase in electronic conductivity and the Seebeck coefficient are attributed to the enhanced carrier concentration and spin-entropy of Co^(4+) originating from the Sr doping effects in[Ca_(2)CoO_(3)]sublayer,which are evidenced by the scanning electron microscope(SEM),Raman,Hall,and X-ray photoelectron spectroscopy(XPS)analysis.Furthermore,the reduced thermal conductivity is attributed to the improved phonon scattering from heavier Sr doped Ca site in[Ca_(2)CoO_(3)]sublayer.Our findings demonstrate that doping at Ca sites of[Ca_(2)CoO_(3)]layer is a feasible pathway to boost TE performance of CCO material through promoting the electronic conductivity and the Seebeck coefficient,and reducing the thermal conductivity simultaneously.This work provides a deep understanding of the current limited ZT enhancement on CCO material and provides an approach to enhance the TE performance of other layered structure materials.

Band degeneracy enhanced thermoelectric performance in layered oxyselenides by first-principles calculations

Band degeneracy is effective in optimizing the power factors of thermoelectric(TE)materials by enhancing the Seebeck coefficients.In this study,we demonstrate this effect in model systems of layered oxyselenide family by the density functional theory(DFT)combined with semi-classical Boltzmann transport theory.TE transport performance of layered LaCuOSe and BiCuOSe are fully compared.The results show that due to the larger electrical conductivities caused by longer electron relaxation times,the n-type systems show better TE performance than p-type systems for both LaCuOSe and BiCuOSe.Besides,the conduction band degeneracy of LaCuOSe leads to a larger Seebeck coefficient and a higher optimal carrier concentration than n-type BiCuOSe,and thus a higher power factor.The optimal figure of merit(ZT)value of 1.46 for n-type LaCuOSe is 22%larger than that of 1.2 for n-type BiCuOSe.This study highlights the potential of wide band gap material LaCuOSe for highly efficient TE applications,and demonstrates that inducing band degeneracy by cations substitution is an effective way to enhance the TE performance of layered oxyselenides.

Insight into the growth behaviors of MoS_(2)nanograins influenced by step edges and atomic structure of the substrate

The step edges and intrinsic atomic structure of single-crystal substrate play a critical role in determining the growth pathways of transition metal dichalcogenide(TMD)grains,particularly whether the TMDs will grow into wafer-scale single-crystal or anisotropic nanoribbons.Hereby,we investigate the growth behaviours of the MoS_(2)nanograins on(0001)and()sapphire substrates.On one hand,the step edges formed on the(0001)surface after thermal treatment are found to promote the macroscopic aggregation of MoS_(2)nanograins and to form unidirectional large triangular islands along with the<>steps in the annealing process,while on the pristine(0001)surface,the MoS_(2)nanograins grow into a random network-like pattern.Moreover,oxygen treatment on the substrate can further enhance the growth of MoS_(2)nanograins.Transmission electron microscopy and fast Fourier transform patterns reveal that the substrate could modulate the orientation of MoS_(2)nanograins during their growing process.On the other hand,the MoS_(2)nanograins on the surface could self-assemble into one-dimensional nanoribbons due to the strong structural anisotropy of the substrate.In addition,the ratio of Raman intensities for peaks that correspond to the and A1g phonon modes shows a linear relationship with the grain size due to the change of the“phonon confinement”.Moreover,new peaks located at 226 and 280 cm−1 can be observed in the off-resonant and resonant Raman spectra for the MoS_(2)nanograin samples,respectively,which can be attributed to the scatterings from the edges of as-fabricated MoS_(2)nanostructures.