Integrated electrocatalysts derived from metal organic frameworks for gas-involved reactions

Integrated electrocatalysts(IECs)containing well-defined functional materials directly grown on the current collector have sparked increasing interest in the fields of electrocatalysis owing to efficient activity,high stability and the fact that they are easily assembled into devices.Recently,metal organic frameworks(MOFs)provide a promising platform for constructing advanced IECs because of their properties of low cost,large surface area and efficient structural tunability.In this review,the design principles of state-of-the-art IECs based on MOFs are presented,including by hydrothermal/solvothermal,template-directed,electrospinning,electrodeposition and other methods.The high performance of MOF-derived IECs has also been demonstrated in electrocatalytic gasinvolved reactions.This is promising for green energy storage and conversion.The structure-activity relationship and performance improvement mechanism of IECs are uncovered by discussing some in situ technologies for IECs.Finally,we provide an outlook on the challenges and prospects in this booming field.

Surface modification of Cu_(2)O with stabilized Cu^(+) for highly efficient and stable CO_(2) electroreduction to C_(2+) chemicals

Copper(Cu)-based materials are known as the most attractive catalysts for electrochemical carbon dioxide reduction reaction(CO_(2)RR),especially the Cu^(+) species(e.g.,Cu_(2)O),which show excellent capability for catalyzing CO_(2) to C_(2+) chemicals because of their unique electronic structure.However,the active Cu^(+) species are prone to be reduced to metallic Cu under an electroreduction environment,thus resulting in fast deactivation and poor selectivity.Here,we developed an advanced surface modification strategy to maintain the active Cu^(+) species via assembling a protective layer of metal-organic framework(copper benzenetricarboxylate,CuBTC) on the surface of Cu_(2)O octahedron(Cu_(2)O@CuBTC).It's encouraging to see that the Cu_(2)O@CuBTC heterostructure outperforms the bare Cu_(2)O octahedron in catalyzing CO_(2) to C_(2+) chemicals and dramatically enhances the ratio of C_(2)H_(4)/CH_(4) products.A systematic study reveals that the introduced CuBTC shell plays a critical role in maintaining the active Cu^(+) species in Cu_(2)O@CuBTC heterostructure under reductive conditions.This work offers a practical strategy for improving the catalytic performance of CO_(2)RR over copper oxides and also establishes a route to maintain the state of valence-sensitive catalysts.

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-CO_(2)RR)可在温和条件下将CO_(2)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-CO_(2)RR的最新进展,分析了结构和表界面调控对E-CO_(2)RR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-CO_(2)RR电极的发展进行了评述与展望。

Hierarchical Carbon Microtube@Nanotube Core-Shell Structure for High-Performance Oxygen Electrocatalysis and Zn-Air Battery

Zinc-air batteries(ZABs)hold tremendous promise for clean and efficient energy storage with the merits of high theoretical energy density and environmental friendliness.However,the performance of practical ZABs is still unsatisfactory because of the inevitably decreased activity of electrocatalysts when assembly into a thick electrode with high mass loading.Herein,we report a hierarchical electrocatalyst based on carbon microtube@nanotube core-shell nanostructure(CMT@CNT),which demonstrates superior electrocatalytic activity for oxygen reduction reaction and oxygen evolution reaction with a small potential gap of 0.678 V.Remarkably,when being employed as air-cathode in ZAB,the CMT@CNT presents an excellent performance with a high power density(160.6 mW cm^−2),specific capacity(781.7 mAhgZn^−1)as well as long cycle stability(117 h,351 cycles).Moreover,the ZAB performance of CMT@CNT is maintained well even under high mass loading(3 mg cm−2,three times as much as traditional usage),which could afford high power density and energy density for advanced electronic equipment.We believe that this work is promising for the rational design of hierarchical structured electrocatalysts for advanced metal-air batteries.

Active facet determination of layered double hydroxide for oxygen evolution reaction

Oxygen evolution reaction(OER) plays an indispensable role in developing renewable clean energy resources. One of the critical bottlenecks for the reaction is the development of highly efficient electrocatalyst to decrease the high overpotentials of four-electron transfer process of OER. Recently, layered double hydroxides(LDHs) have been widely investigated among the most promising electrocatalysts for OER due to their high intrinsic activity, excellent stability as well as low-cost. However, it remains unclear how the exposed facet of the LDHs affects their electrocatalytic activity. Here we elucidate the active edge facet of LDHs towards OER by combining the finely control of edge facet ratio coupled with molecular probe method and computational calculation. The LDHs with higher edge facet area ratio show superior activity with low onset potential as well as decreased Tafel slope. The active edge site is further proved by blocking the unsaturated edge sites with cyanate probe anion, of which the adsorption largely inhibits OER activity. Furthermore, based on density functional theory(DFT) calculation, twodimensional map of theoretical overpotentials as a function of Gibbs free energy reveals that the edge(100) facet exhibits a much higher OER activity than basal plane(001) facet.

Hierarchical CoNi-LDH nanosheet array with hydrogen vacancy for high-performance aqueous battery cathode

Aqueous rechargeable multiple metal-ion storage battery (ARSB) has a large potential in energy storage devices due to their safe usage, low cost and high rate capability. Nevertheless, the performance of practical ARSB is largely restricted by low capacity and limited cathode materials. Herein, we demonstrate an efficient cathode material based on Co Ni-layered double hydroxide (LDH) nanosheets arrays with abundant hydrogen vacancy induced by electrochemical activation process for high performance of cations storage. Consequently, the electrochemical activated Co Ni-LDH (ECA-Co Ni-LDH) nanosheets arrays exhibit high metal ion (Li^(+), Na^(+), Zn^(2+), Mg^(2+) and Ca^(2+)) storage capacities, which is 9 times and 3 times higher that of unactivated Co Ni-LDH arrays and ECA-Co Ni-LDH without hierarchical structure, respectively.Moreover, the ECA-Co Fe-LDH also shows the possibility for practical applications in actual batteries.By coupling with a Fe_(2)O_(3)/C anode, the assembled aqueous battery delivered a large energy density of 184.4 Wh kg^(-1)at power density of 4 Wh kg^(-1) in high voltage range of 0–2 V. To our best knowledge, such high energy density and large working window of our assembled aqueous battery is exceeded other LDH-based aqueous battery or supercapacitor, and the energy density almost comparable than that of commercial Li-ion batteries. Moreover, almost no measurable capacitance losses can be detected even after 10000 cycles. In addition, this work also provides a strategy to develop a high energy density cathode for multiple metal-ion storage batteries.

Electrosynthesis of hierarchical NiLa-layered double hydroxide electrode for efficient oxygen evolution reaction

Oxygen evolution reaction(OER) is a key process for electrochemical water splitting due to its intrinsic large overpotential. Recently, layered double hydroxides(LDHs), especially Ni Fe-LDH, have been regarded as highly performed electrocatalysts for OER in alkaline condition. Here we first present a new class of Ni La-LDH electrocatalyst synthesized by an electrochemical process for efficient water splitting. The as-prepared NiL a-LDH nanosheet arrays(NSAs) give remarkable electrochemical activity and durability under alkaline environments, with a low overpotential of 209 mV for OER to deliver a current density of 10 mA cm^-2, surpassing most of previous reported LDHs eletrocatalysts. The presence of NiLa-LDH in this work extends the studies about LDHs-based electrocatalysts, which will benefit the development of electrochemical energy storage and conversion systems.

Integrated Nanostructural Electrodes Based on Layered Double Hydroxides

Layered double hydroxides(LDHs), as a class of typical two-dimensional materials, have sparked increasing interest in the field of energy storage and conversion. In the last few years, the research about LDHs as electrode active materials has seen much progress in terms of structure designing, material synthesis, properties tailoring, and applications. In this review, we focus on the integrated nanostructural electrodes(INEs) construction using LDH materials, including pristine LDH-INEs, hybrid LDH-INEs, and LDH derivativeINEs, as well as the performance advantages and applications of LDH-INEs.Moreover, in the final section, the insights about challenges and prospective in this promising research field were concluded, especially in regulation of intrinsic activity and uncovering of structure–activity relationship, which would push forward the development of this fast-growing field.

Metal vacancy-enriched layered double hydroxide for biomass molecule electrooxidation coupled with hydrogen production

The electrochemical oxidation of biomass molecules coupling with hydrogen production is a promising strategy to obtain both green energy and value-added chemicals;however,this strategy is limited by the competing oxygen evolution reactions and high energy consumption.Herein,we report a hierarchical CoNi layered double hydroxides(LDHs)electrocatalyst with abundant Ni vacancies for the efficient anodic oxidation of 5-hydroxymethylfurfural(HMF)and cathodic hydrogen evolution.The unique hierarchical nanosheet structure and Ni vacancies provide outstanding activity and selectivity toward several biomass molecules because of the finely regulated electronic structure and highly-exposed active sites.In particular,a high faradaic efficiency(FE)at a high current density(99%at 100 mA cm^(-2))is achieved for HMF oxidation,and a two-electrode electrolyzer is assembled based on the Ni vacancies-enriched LDH,which realized a continuous synthesis of highly-pure 2,5-furandicarboxylic acid products with high yields(95%)and FE(90%).

Co-thermal in-situ reduction of inorganic carbonates to reduce carbon-dioxide emission

Thermal decomposition of inorganic metal carbonates is the main path to prepare metal oxides;nonetheless,it is always accompanied by the emission of large amounts of CO_(2) as one of the gas products.This study reports a concept of co-thermal insitu reduction of inorganic carbonates by using the energy released by carbonate decomposition under pure hydrogen atmosphere,which reduces the decarboxylation temperature and significantly inhibits the CO_(2) emissions.A combination of hydrogen–deuterium exchange,isotope experiment,and density functional theory calculations demonstrates that the CO results from the selective cleavage of Ca–O bonds at the surface of CaCO_(3) via the direct hydrogenation mechanism at relatively low temperature.However,it undergoes the reverse water–gas shift reaction path at high temperature,i.e.,CO being produced by the reduction of CO_(2) released by the decomposition of carbonates.This study sheds light on the potential of green hydrogen technology for inorganic carbonate valorization toward high value-added products,which can facilitate the large-scale industrial applications.

Layered double hydroxide-based core-shell nanoarrays for efficient electrochemical water splitting

Electrochemical water splitting is an efficient and clean strategy to produce sustainable energy produc- tions （especially hydrogen） from earth-abundant water. Recently, layered double hydroxide （LDH）-based materi- als have gained increasing attentions as promising electrocatalysts for water splitting. Designing LDHs into hierarchical architectures （e.g., core-shell nanoarrays） is one of the most promising strategies to improve their electrocatalytic performances, owing to the abundant exposure of active sites. This review mainly focuses on recent progress on the synthesis of hierarchical LDH-based core-shell nanoarrays as high performance electrocatalysts for electrochemical water splitting. By classifying different nanostructured materials combined with LDHs, a number of LDH-based core-shell nanoarrays have been developed and their synthesis strategies, structural characters and electrochemical performances are rationally described. Moreover, further developments and challenges in devel- oping promising electrocatalysts based on hierarchical nanostructured LDHs are covered from the viewpoint of fundamental research and practical applications.