Highly dispersed ultrafine Pt nanoparticles on nickel-cobalt layered double hydroxide nanoarray for enhanced electrocatalytic methanol oxidation

Highly dispersed ultrafine Pt nanoparticles (NPs) were loaded on a nickel-cobalt layered double hydroxide (NiCo-LDH) nanoarray that was grown on Ni foam (NF) via an in situ redox reaction without any external agent between Co²⁺ (Co(OH)₂) in NiCo-LDH and PtCl₆^2-. The obtained Pt/NiCoLDH/NF composite was used as a catalyst for methanol oxidation in alkaline media, showing much higher electrocatalytic activity and better anti-poisoning ability and stability for methanol oxidation than commercial Pt/C, mainly because of the uniform dispersion of ultrafine Pt NPs, the synergistic effect and stable support of NiCoLDH. The NiCoLDH nanoarray effectively increased the specific surface area and location sites for supporting Pt NPs and enhanced the catalytic performance and tolerance to intermediate species. This enhancement was probably due to the synergistic effect between Pt and the NiCo-LDH nanosheets, in which the LDH can provide adequate OH^?_ads species for accelerating the methanol oxidation reaction (MOR).     

Intercalation and elimination of carbonate ions of NiCo layered double hydroxide for enhanced oxygen evolution catalysis

The developments of inexpensive and efficient oxygen evolution reaction (OER) electrocatalysts without noble metals are very critical for energy conversion and storage systems. In this work, a series of NiCo-layered double hydroxide (NiCo-LDH) and NiCo oxides using co-precipitation and thermal treatment method have been successfully synthesized. Structural characterizations have been investigated by X-ray powder diffraction (XRD), Field emission scanning electron microscope (FE-SEM) equipped with energy-dispersive X-ray mapping technology (EDS), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy respectively (XPS). By intercalating and eliminating CO₃³⁻ anions in the layers of bulk NiCo-layered double hydroxide (NiCo-LDH), the as-present catalyst (NiCo–CH) exhibit remarkable advantages for OER performance, including porous nanostructures, high surface area, high content of Ni³⁺ and Co²⁺ on the surface and abundant active sites. With these favorable features, NiCo–CH shows a much better OER performance than that of other catalysts and commercial Pt/C, which has a low onset potential (1.51 V), a low overpotential (343 mV at 10mA/cm⁻²) and a small Tafel slope (66mV/dec⁻¹). Our work presents an effective strategy to controllably design and synthesize NiCo-LDH electrocatalysts with optimizable OER performances.     

Co-MOF Derived NiCo-LDH Three-Dimensional Nanostructure on Carbon Cloth for High-Performance Supercapacitors

Co-MOF衍生的NiCo-LDH碳布三维纳米结构的构筑及高性能超级电容器研究

王苹 , 丁宁¹, 王艺蓉¹, 党宇鹏¹, 韩丹丹¹, 危岩²

（1．吉林化工学院 生物与食品工程学院,吉林 132022;

2．清华大学化学系,前沿聚合物研究中心,北京 100084）

^# 作者对本文有同等贡献.

中文说明：

采用离子刻蚀/交换反应法制备了钴基金属有机骨架（Co-MOF）衍生的NiCo层状双氢氧化物（NiCo-LDH）三维多孔纳米结构。采用X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）和X射线光电子能谱（XPS）对合成的样品进行了形貌和结构表征。作为电容器正极,优化后的NiCo-LDH样品在1 A.g^-1时具有226.3 mAh.g^-1的高比容量。基于NiCo-LDH正极和活性炭（AC）负极的混合超级电容器（HSC）比能达到27.39 Wh.kg^-1,并且具有较好的循环稳定性（5000次循环后容量保留率为93.5%）。

关键词: 金属有机框架; 超级电容器; 能量密度; NiCo-LDH

     

Photoanode of LDH catalyst decorated semiconductor heterojunction of BiVO4/CdS to enhance PEC water splitting efficiency

BiVO₄ is an ideal photoanode material for solar-driven photoelectrochemical (PEC) water splitting but it easily suffers from the recombination of photogenerated electrons and holes due to its low carrier mobility thus cause low efficiency of PEC water splitting. Herein, the BiVO₄/CdS/NiCo-LDH photoanode was prepared by combining methods of metal organic decomposition, chemical and electrodeposition. The photoanode photocurrent density reaches 2.72 mA cm⁻² at 1.23 V (vs. RHE), which is 3.6 folds of pure BiVO₄ photoanode and onset potential shifts 450 mV toward cathodic. The incident photon-to-electron conversion efficiency (IPCE) value is 2.86 folds of BiVO₄, the calculated photon–to–current efficiency (ABPE) is 1.24% at 0.62 V (vs. RHE). The obtained results are higher than that of most BiVO₄ based photoanodes published so far. The enhancement benefits from increase of visible light absorption capacity, enhancement of separation efficiency of photoexcited electron-hole and fast transfer of holes accumulated on electrode/electrolyte surface for water oxidation, which has been confirmed by calculating carrier density and carrier transport rate.     

Oxygen vacancy-rich flower-like nickel cobalt layered double hydroxides for supercapacitors with ultrahigh capacity

One of the main difficulties for high-performance supercapacitors (SCs) is to design rational structures with excellent electrochemical properties. Herein, oxygen vacancy-rich nickel-cobalt layered double hydroxide, which has excellent supercapacitor performance, is prepared through an electrodeposition procedure and in situ oxidation process on nickel foam substrate. The conductivity and electrochemical properties are significantly improved by oxygen vacancies, which can be adjusted via hydrogen peroxide treatment. NiCo-LDH with oxygen vacancy (O_v-NiCo-LDH) attains a superior specific capacity of 1160 C g^?1 at the current density of 1 A g^?1 and shows a good capacity retention rate (61% of its original specific capacity is left at 20 A g^?1). Significantly, when the power density is 1.75 kW kg^?1, the energy density of the assembled symmetric supercapacitor (SSC) device is up to 216.19 Wh·kg^?1. This vacancy engineering strategy is helpful to the design of active materials for energy storage devices in the future.     

Hierarchical design of NiCo-LDH NFs@Co(OH)2 nanosheets supercapacitor electrode material with boosted electrochemical performance

Layered double hydroxides (LDHs) have been considered as excellent pseudocapacitive electrode materials for supercapacitors because of their controllable layered structures and high theoretical specific capacitances. However, poor conductivity and shortage of effective active sites hinder their applications. Herein, in order to boost the capacitance performance, an electrode material composed of NiCo-LDH nanofibers with cobalt hydroxide (Co(OH)₂) nanosheets firmly anchored to or uniformly immobilized onto NiCo-LDH nanofibers surface is constructed. The material architecture takes advantage of superior capacitive activity from Co(OH)₂ with good electronic conductivity and dispersibility over the surface of NiCo-LDH nanofibers. The merits based on the elegant synergy between NiCo-LDH nanofibers and Co(OH)₂ nanosheets induce an outstanding specific capacitance of 858.9 F/g at a current density of 0.5 A/g. With the current density increasing from 0.5 to 10 A/g, the specific capacitance retention is 67.3%, indicating a good rate capability. Furthermore, the electrode material exhibits a capacitance retention of 83.7% after 2000 cycles at 10 A/g. These excellent electrochemical properties are due to the hierarchically designed structure and the cooperative contributions of NiCo-LDH nanofibers and Co(OH)₂ nanosheets, which shows great potential for energy storage applications.     

Hierarchical Ni/Co-hydroxides on NiCo2O4 for boosting the electrocatalytic activity of the oxygen evolution reaction

Herein, hierarchical Ni/Co-layered double hydroxide decorated NiCo₂O₄ electrocatalyst (NiCo-LDH@NCO) on nickel foam (NF) was synthesized using a facile hydrothermal method with electrochemical reconstruction. By converting the already existing NCO surface to hierarchical NiCo-LDH, a larger surface area and high electrical conductivity are obtained. Both structure and morphology of fabricated electrocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM) techniques. The electrochemical reconstruction process is accompanied by changes in the morphology of the NCO that significantly increase accessibility to the electrolyte and active surface area. Therefore, the as-obtained electrocatalyst exhibits excellent oxygen evolution reaction (OER) activity and long-term stability for 35 h continuous reaction, superior-performing the reported other OER catalysts. In addition, this work opens a new path for the development of highly efficient and innovative low-cost OER electrocatalysts able to replace Pt-based metals for energy conversion devices.