Transition metal chalcogenides as emerging electrocatalysts for urea electrolysis

Urea electrolysis is an up-and-coming approach to realize sustainable energy-saving hydrogen fuel production and purification of urea-bearing wastes (e.g. urine, industrial wastewater). To attain a high urea electrolysis efficiency, high-performance electrocatalysts are highly required. Of late, transition metal (TM) chalcogenides-based materials are emerging as promising candidates for urea electrolysis. The catalytic performance of TM chalcogenides-based catalysts is optimized by tuning the internal/external characteristics, including nanostructure control, composition optimization, and heterostructuring. In this review, recent achievements in high-efficiency electrocatalysts based on TM chalcogenides for urea electrolysis are critically discussed. First, the electrochemistry of urea electrolysis is analyzed. Next, recent progress in TM chalcogenides-based electrocatalysts for urea electrolysis is detailed. The electrocatalyst design strategies are particularly elucidated, as well as the catalyst structure–performance correlation. Ultimately, perspectives on crucial scientific issues in this booming field are highlighted.     

Introduction of high valent Mo6+ in Prussian blue analog derived Co-layered double hydroxide nanosheets for improved water splitting

Herein, we report a facile method for synthesizing MoCo-layered double hydroxide (LDH) nanosheets employing Prussian blue analog (PBA) as the precursor. The introduction of Mo in Co-LDH modulates the electronic structure, increases the number of active sites and electrochemical surface area to improve the hydrogen evolution, oxygen evolution, and overall water splitting activity. As a result, PBA-derived Mo_0.25Co_0.75-LDH nanosheets demonstrated 10 mA cm^?2 current density at only 220 mV and 115 mV overpotentials for OER and HER, respectively. The overall water splitting was attained at 1.52 V cell voltage for 10 mA cm^?2 current density.     

Hydrothermal synthesis of nickel hydroxide nanostructures in mixed solvents of water and alcohol

Nickel hydroxide nanosheets and flowers have been hydrothermally synthesized using Ni(CH₃COO)₂·4H₂O in mixed solvents of ethylene glycol (EG) or ethanol and deionized water at 200 °C for different time. The phase and morphology of the obtained products can be controlled by adjusting the experimental parameters, including the hydrothermal time and the volume ratio of water to EG or ethanol. The possible reaction mechanism and growth of the nanosheets and nanoflowers are discussed based on the experimental results. Porous nickel oxide nanosheets are obtained by heating nickel hydroxide nanosheets in air at 400 °C. The products were characterized by using various methods including X-ray diffraction (XRD), fourier transform infrared (FTIR), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), field emission scanning electron microscopy (FESEM). The electrochemical property of β-Ni(OH)₂ nanosheets was investigated through the cyclic voltammogram (CV) measurement.     

Mathematical models of the nickel hydroxide active material

A review is presented of the mathematical models that have been developed to describe the phenomena that occur in the active material in the nickel electrode. The review includes models that describe the reaction thermodynamics, proton diffusion, electron conductivity, semiconductor effects, and the reactions in the solid phase. The appropriateness of these models and their usefulness in predicting phenomena observed in nickel-based batteries are discussed. Received: 17 October 1999 / Accepted: 26 December 1999     

酒石酸掩蔽铝-丁二酮肟重量法测定镍钴铝三元氢氧化物中镍

镍钴铝三元氢氧化物中Ni质量分数为45%~60%、Al为0.5%~1.5%,丁二酮肟沉淀镍的pH条件下,Al3+会水解沉淀而干扰测定。试验对丁二酮肟重量法进行改进,采用酒石酸作为Al的掩蔽剂,从而建立了酒石酸掩蔽铝-丁二酮肟重量法测定镍钴铝三元氢氧化物中Ni含量的方法。试验评价了Al对丁二酮肟重量法测Ni的干扰,并确定了酒石酸的最佳掩蔽用量,测定实际样品801505型镍钴锰三元氢氧化物（Ni0.8Co0.15Al0.05(OH)2）和851005型镍钴锰三元氢氧化物（Ni0.85Co0.1Al0.05(OH)2）的RSD（n=11）分别为0.24%、0.31%,加标回收率分别为100.20%、99.68%,且测定值与ICP-AES基本一致。     

基于可再生能源的水电解制氢技术（英文）

在全球变暖,污染日益严重的今天,发展可再生清洁能源成为了当务之急.然而可再生能源(风能、太阳能)本身具有间断特性,这就需要寻找一种合适的能量媒介储存能量来保证其能源的稳定输出.当前,我国各地不断出现弃风、弃光和弃水电事件,据国家能源局的公开数据,仅2016年,全国弃风电量497×10~8 kW·h,弃光率仅西部地区就已达20%,弃风弃光日臻凸显[1].从地域方面来看,我国光伏发电呈现东中西部共同发展格局,其中,西部地区主要发展集中式光伏发电,新疆、甘肃、青海、宁夏的累计装机容量均超过5×10~6 k W·h,而中东部地区除集中式光伏发电外,还重点建设分布式光伏发电,江苏、浙江、山东、安徽的分布式光伏装机规模已超过100万千瓦.我国光伏发电集中开发的西北地区也存在严重的弃光问题.根据中国光伏行业协会发布的报告,我国的弃光现象主要集中于西北的新疆、甘肃、青海、宁夏和陕西五省区.据统计,2016年,五省区光伏发电量287.17×10~8 k W·h,弃光电量70.42×10~8 k W·h,弃光率为19.81%,各省区光伏发电并网运行数据如表格所示.可以看出,新疆、甘肃光伏发电运行较为困难,弃光电量绝对值高,弃光率分别达到32.23%和30.45%[2].在新能源体系中,氢能是一种理想的二次能源,与其它能源相比,氢热值高,其能量密度(140 MJ/kg)是固体燃料(50MJ/kg)的两倍多.且燃烧产物为水,是最环保的能源,既能以气、液相的形式存储在高压罐中,也能以固相的形式储存在储氢材料中,如金属氢化物、配位氢化物、多孔材料等.对可再生和可持续能源系统,氢气是一种极好的能量存储介质.氢气作为能源载体的优势在于:(1)氢和电能之间通过电解水技术可实现高效相互转换;(2)压缩的氢气有很高的能量密度;(3)氢气具有成比例放大到电网规模应用的潜力.制氢的方式有很多,包括:化石燃料重整、分解、光解或水解等.全球每年总共需要约40亿吨氢气,95%以上的氢气是通过化石燃料重整来获得,生产过程必然排出CO_2,而电解水技术利用可再生能源获得的电能进行规模产氢,可实现CO_2的零排放,可将具有强烈波动特性的风能、太阳能转换为氢能,更利于储存与运输.所存储的氢气可用于燃料电池发电,或单独用作燃料气体,也可作为化工原料.通过水电解方式获得的氢气纯度较高,可达99.9%以上.     

Yolk-shell nanostructural Ni_2P/C composites as the high performance electrocatalysts toward urea oxidation

Highly active and low-cost catalytic electrodes for urea oxidation reaction(UOR) are always crucial for exploration of urea fuel cells.Herein,novel york-shell-structural Ni_2P/C na nosphere hybrids(Ni_2P/C-YS)are rationally constructed via a hydrothermal method and subsequent phosphidation treatment under different temperature ranging from 250℃ to 450℃ for UOR applications.In the in-situ constructed hollow york-shell structure,the coupling of conductive carbon materials and active Ni_2P allows numerous interfaces facilitating the electron transfer and thereby accelerating the catalytic kinetics.The results demonstrate that Ni_2P/C-YS-350 nanocomposite can boost the UOR process with a low potential of 1.366 V vs.RHE at a current density of 50 mA/cm~2 in alkaline electrolyte and afford the superior durability with negligible potential decay after 23 h.This study presents that the carbon coated Ni_2P hybrid with the optimized crystallinities and hollow york-shell configurations can be a promising candidate for application in urea fuel cells.     

A nonstoichiometric structural model to characterize changes in the nickel hydroxide electrode during cycling

Experimental capacities and mass changes are recorded using an electrochemical quartz crystal microbalance during the first nine charge and discharge cycles of nickel hydroxide thin films cycled in 3.0 weight percent (wt%) potassium hydroxide electrolyte. For the first time, the film capacities have been corrected for the oxygen evolution side reaction, and the data used as input into a point defect-containing structural model to track the changes that occur during short-term cycling. Variations in capacity and mass during formation and charge/discharge cycling are related to changes in the point defect parameters, thus providing a structural origin for the unique experimental variations observed here and often reported in the literature, but previously unexplained. Proton-, potassium-, and water-content vary in the active material during charge/discharge cycling. The observed capacity loss, or capacity fade, is explained by incomplete incorporation of potassium ions in (or near) the nickel vacancy during charge, as additional protons are then allowed to occupy the vacant lattice site. The increase in water content during reduction parallels the expansion of the electrode that is well known during cycling. This result confirms the origin of the swelling phenomenon as being caused by water incorporation. The model and methodology developed in this paper can be used to correlate electrochemical signatures with material chemical structure.

Chemical deposition and exfoliation from liquid crystal template: Nickel/nickel (II) hydroxide nanoflakes electrocatalyst for a non-enzymatic glucose oxidation reaction

This work reports the synthesis of nickel/nickel hydroxides nanoflakes (Ni/Ni(OH)₂-NFs) at room temperature via a novel chemical deposition and exfoliation from a liquid crystal template mixture. The nickel ions dissolved in the interstitial aqueous domain of the Brij®78 hexagonal liquid crystal template were deposited by a reducing agent of sodium borohydride that concurrently reduces the nickel ions and generates extreme hydrogen gas bubbles, that exfoliated the nickel/nickel hydroxide layers. The Ni/Ni(OH)₂-NFs crystal structure, morphology, and surface area characterizations revealed the formation of semi-crystalline α-Ni(OH)₂ nanoflakes with a thickness of approximately 10 nm and a specific surface area of about 135 m²/g. The electrochemical measurements of cyclic voltammetry, chronoamperometry, and impedance analysis showed that the Ni/Ni(OH)₂-NFs exhibited significant performance for the glucose non-enzymatic oxidation in an alkaline solution in comparison to the bare-nickel hydroxide (bare-Ni(OH)₂) deposited without surfactant. The Ni/Ni(OH)₂-NFs electrode showed superior glucose oxidation activity over the bare-Ni(OH)₂ catalyst with a sensitivity of 1.078 mA mM^?1 cm^?2 with a linear concentration dependency range from 0.2 to 60 mM and a detection limit of 0.2 mM (S/N = 3). The enhanced electrochemical active surface area and mesoporosity of the 2D nanoflakes make the Ni/Ni(OH)₂-NFs a promising catalyst in the application of glucose non-enzymatic sensing.     

A quartz crystal microbalance study on a metallic nickel electrode

Electrochemical processes taking place on a Ni electrode have been investigated with the electrochemical quartz crystal microbalance. At potentials negative of ca. –500 mV vs. SCE, a closed frequency loop is observed without irreversible changes in the mass of the electrode. The phase transition - -Ni(OH)₂, taking place at potentials positive to –500 mV vs. SCE, is accompanied by an irreversible increase in the mass of the electrode. When Ni(OH)₂ is further oxidized, the frequency increase is followed by a decrease, indicating the transport of various species in both directions, i.e. from and into the electrode. During the Ni(OH)₂ oxidation reaction the transport of species responsible for the mass increase is slower than the charge transfer process.Contribution to the 3rd Baltic Conference on Electrochemistry, GDASK-SOBIESZEWO, 23–26 April 2003. Dedicated to the memory of Harry B. Mark, Jr. (February 28, 1934–March 3rd, 2003)     

高性能球型氢氧化亚镍的ICP-OES分析方法

建立了镍氢电池正极材料氢氧化亚镍中主成分锌、钴及杂质钙、镁、锰、镉的ICP AES测定方法。选择了仪器最佳工作条件 ,研究了镍基体对被测元素的干扰。方法的回收率为 95 .9%～ 1 0 3% ,RSD为 0 .93%～ 1 8%。     

Decoupled electrolysis for water splitting

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利用均相沉淀剂和形貌导向剂水热一步合成层状镍钴氢氧化物

本文利用在反应过程中同时添加均相沉淀剂六次甲基四胺和形貌导向剂十六烷基三甲基溴化铵,结合水热反应的方法一步合成了镍钴氢氧化物. 随着六次甲基四胺的水解,层状镍钴氢氧化物可以被合成而且避免了额外碱源的使用;同时,由于反应过程中十六烷基三甲基溴化铵参与的孔径调节,合成出来的镍钴氢氧化物具有可控的介孔尺寸13.4 nm以及较大的比表面积93.6 m²•g^-1. X射线衍射图谱表明合成出来的镍钴氢氧化物构型是α-Ni(OH)₂-β-Co(OH)₂. 扫描电镜表明合成出来的镍钴氢氧化物具有层状的结构. 正是因为层状介孔结构的存在,合成出来的镍钴氢氧化物在1A•g^-1电流密度下,比电容可以高达1902 F•g^-1;即使电流密度提高到8 A•g^-1,镍钴氢氧化物的比电容仍然可以保持在1250F•g^-1.     

Current status of membraneless water electrolysis cells

Commercial water electrolysis cells require a resistive, ion-permeable, gas-impermeable separator membrane between the electrodes to stop the hydrogen bubbles from mixing with the oxygen bubbles and vice versa. This work reviews the current status of ‘membraneless’ water electrolysis cells that safely avoid need for such a separator membrane. Three different approaches have been used to realize such cells. In the first approach, laminar flow within a microfluidic reaction chamber has been used to entrain the hydrogen and oxygen gas bubbles in separate, parallel streams that do not mix. In the second approach, closely-spaced porous electrodes have had liquid electrolyte divergently pumped through them to sweep the produced hydrogen and oxygen bubbles to different locations. In the most recent, promising approach, gas diffusion electrodes have been used to directly extract gas as it is produced, thereby avoiding discernible bubble formation and eliminating the need for a separator membrane to keep the gases separate.     

Ball-milling processing of nanocrystalline nickel hydroxide and its effects in pasted nickel electrodes for rechargeable nickel batteries

Nanocrystalline Ni(OH)₂ powder synthesized by a chemical precipitation method was processed using the planetary ball milling (PBM), and the physical properties of both the ball-milled and unmilled Ni(OH)₂ were characterized by scanning electron microscopy (SEM), specific surface area, particle size distribution, and X-ray diffraction. It was found that the PBM processing could significantly break up the agglomeration, uniformize the particle size distribution, increase the surface area, decrease the crystallite size, and reduce the crystallinity of nanocrystalline β-Ni(OH)₂, which were advantageous to the improvement of the electrochemical activity of Ni(OH)₂. The ball-milled nanocrystalline (BMN) Ni(OH)₂ was then used to alter the microstructure of pasted nickel electrodes and improve the distribution of the active material in the porous electrode substrate. Electrochemical performances of pasted nickel electrodes with a mixture of BMN and spherical Ni(OH)₂ as the active material were investigated, and were compared with those of pure spherical Ni(OH)₂ electrodes. Charge/discharge tests showed that BMN Ni(OH)₂ addition could enhance the charging efficiency, specific discharge capacity, discharge voltage, and high-rate capability of pasted nickel electrodes. This performance improvement could be attributed to a more compact electrode microstructure, better reaction reversibility, and lower electrochemical impedance, as indicated by SEM, cyclic voltammetry, and electrochemical impedance spectroscopy. Thus, it was an effective method to modify the microstructure and improve the electrochemical properties of pasted nickel electrodes by adding an appropriate amount of BMN Ni(OH)₂ to spherical Ni(OH)₂ as the active material.     

聚邻苯二胺/镍氢氧化物修饰电极的研究

采用循环伏安法(CV)在聚邻苯二胺修饰玻碳电极表面络合Ni2+,然后将其置于NaOH溶液中CV扫描成功制备了镍氢氧化物/聚邻苯二胺/玻碳修饰电极(Ni(OH)2/PoPD/GC).通过CV探讨了聚合和负载机理,电化学交流阻抗谱(EIS)表征了电极修饰过程中界面阻抗变化,扫描电镜表征了PoPD膜负载Ni(OH)2后的形态...     

Controllable synthesis of nickel hydroxide and porous nickel oxide nanostructures with different morphologies

Alpha-Ni(OH)(2) nanobelts, nanowires, short nanowires, and beta-Ni(OH)(2) nanoplates have been successfully prepared in high yields and purities by a convenient hydrothermal method under mild conditions from very simple systems composed only of NaOH, NiSO(4), and water. It has been found that the ratio of NaOH to NiSO(4) not only affects the morphology of the Ni(OH)(2) nanostructures, but also determines whether the product is of the alpha- or beta-crystal phase. A notable finding is that porous NiO nanobelts were produced after exposure of the Ni(OH)(2) products to an electron beam for several minutes during transmission electron microscopy (TEM) observations. Another unusual feature is that rectangular nanoplates with many gaps were obtained. Furthermore, porous NiO nanobelts, nanowires, and nanoplates could also be obtained by annealing the as-prepared Ni(OH)(2) products. A sequence of dissolution, recrystallization, and oriented attachment-assisted self-assembly of nanowires into nanobelts is proposed as a plausible mechanistic interpretation for the formation of the observed structures. The method presented here possesses several advantages, including high yields, high purities, low cost, and environmental benignity. It might feasibly be scaled-up for industrial mass production.     

Characteristics of hydrogen nanobubbles in solutions obtained with water electrolysis

A solution supersaturated with hydrogen obtained by water electrolysis was studied using cyclic voltammetry. The cyclic voltammogram of the solution supersaturated with hydrogen gave a peak current at −0.1 V vs. AgAgCl. No peak current in a solution saturated with hydrogen was observed by bubbling hydrogen gas through the solution. The peak current was influenced by the temperature and ion type of the electrolyte. The peak current was found to be due to the presence of hydrogen nanobubbles. The peak current increased with increasing hydrogen nanobubble concentration and decreased to zero within 3 h after electrolysis.