Synergistic effect of V and Fe in Ni/Fe/V ternary layered double hydroxides for efficient and durable oxygen evolution reaction

High-performance and stable electrocatalysts are vital for the oxygen evolution reaction (OER). Herein, via a one-pot hydrothermal method, Ni/Fe/V ternary layered double hydroxides (NiFeV-LDH) derived from Ni foam are fabricated to work as highly active and durable electrocatalysts for OER. By changing the feeding ratio of Fe and V salts, the prepared ternary hydroxides were optimized. At an Fe:V ratio of 0.5:0.5, NiFeV-LDH exhibits outstanding OER activity superior to that of the binary hydroxides, requiring overpotentials of 269 and 274 mV at 50 mA·cm^–2 in the linear sweep voltammetry and sampled current voltammetry measurements, respectively. Importantly, NiFeV-LDH shows extraordinary long-term stability (≥ 75 h) at an extremely high current density of 200 mA·cm^–2. In contrast, the binary hydroxides present quick decay at 200 mA·cm^–2 or even reduced current densities (150 and 100 mA·cm^–2). The outstanding OER performance of NiFeV-LDH benefits from the synergistic effect of V and Fe while doping the third metal into bimetallic hydroxide layers: (a) Fe plays a crucial role as the active site; (b) electron-withdrawing V stabilizes the high valence state of Fe, thus accelerating the OER process; (c) V further offers great stabilization for the formed intermediate of FeOOH, thus achieving superior durability.     

Tuning the electronic structure of NiCoP arrays through V doping for pH-universal hydrogen evolution reaction electrocatalyst

The exploration of cost-effective, high-performance, and stable electrocatalysts for the hydrogen evolution reaction (HER) over wide pH range (0–14) is of paramount importance for future renewable energy conversion technologies. Regulation of electronic structure through doping vanadium atoms is a feasible construction strategy to enhance catalytic activities, electron transfer capability, and stability of the HER electrode. Herein, V-doped NiCoP nanosheets on carbon fiber paper (CFP) (denoted as V_x-NiCoP/CFP) were constructed by doping V modulation on NiCoP nanosheets on CFP and used for pH-universal HER. Benefiting from the abundant catalytic sites and optimized hydrogen binding thermodynamics, the resultant V₁₅-NiCoP/CFP demonstrates a significantly improved HER catalytic activity, requiring overpotentials of 46.5, 52.4, and 85.3 mV to reach a current density of 10 mA·cm^–2 in 1 mol·L^–1 KOH, 0.5 mol·L^–1 H₂SO₄, and 1 mol·L^–1 phosphate buffer solution (PBS) electrolytes, respectively. This proposed cation-doping strategy provides a new inspiration to rationally enhance or design new-type nonprecious metal-based, highly efficient, and pH-universal electrocatalysts for various energy conversion systems.     

3D Network nanostructured NiCoP nanosheets supported on N-doped carbon coated Ni foam as a highly active bifunctional electrocatalyst for hydrogen and oxygen evolution reactions

A highly active bi-functional electrocatalyst towards both hydrogen and oxygen evolution reactions is critical for the water splitting. Herein, a self-supported electrode composed of 3D network nanostructured NiCoP nanosheets grown on N-doped carbon coated Ni foam (NiCoP/NF@NC) has been synthesized by a hydrothermal route and a subsequent phosphorization process. As a bifunctional electrocatalyst, the NiCoP/NF@NC electrode needs overpotentials of 31.8 mV for hydrogen evolution reaction and 308.2 mV for oxygen evolution reaction to achieve the current density of 10 mA·cm⁻² in 1 mol·L⁻¹ KOH electrolyte. This is much better than the corresponding monometal catalysts of CoP/NF@NC and NiP/NF@NC owing to the synergistic effect. NiCoP/NF@NC also exhibits low Tafel slope, and excellent long-term stability, which are comparable to the commercial noble catalysts of Pt/C and RuO₂.     

Nickel-carbonate nanowire array: An efficient and durable electrocatalyst for water oxidation under nearly neutral conditions

It is highly attractive but still remains a great challenge to develop an efficient electrocatalyst for oxygen evolution reaction under nearly neutral conditions. In this work, we report the transformation of Ni₃S₂ nanowire array on nickel foam into the amorphous nickel carbonate nanowire array on nickel foam (NiCO₃/NF). The resulting NiCO₃/NF shows high electrocatalytic activity towards water oxidation and affords current density of 50 mA·cm⁻² at overpotential of 395 mV in 1.0 mol·L⁻¹ KHCO₃. Moreover, this NiCO₃/NF is also durable with a long-term electrochemical durability of 60 h. This catalyst electrode achieves a high turnover frequency of 0.21 mol O₂·s⁻¹ at the overpotential of 500 mV.     

Cobalt nanoparticle decorated N-doped carbons derived from a cobalt covalent organic framework for oxygen electrochemistry

The low cost and highly efficient construction of electrocatalysts has attracted significant attention owing to the use of clean and sustainable energy technologies. In this work, cobalt nanoparticle decorated N-doped carbons (Co@NC) are synthesized by the pyrolysis of a cobalt covalent organic framework under an inert atmosphere. The Co@NC demonstrates improved electrocatalytic capabilities compared to N-doped carbon without the addition of Co nanoparticles, indicating the important role of cobalt. The well-dispersed active sites (Co–N_x) and the synergistic effect between the carbon matrix and Co nanoparticles greatly enhance the electrocatalytic activity for the oxygen reduction reaction. In addition, the Co content has a significant effect on the catalytic activity. The resulting Co@NC-0.86 exhibits a superb electrocatalytic activity for the oxygen reduction reaction in an alkaline electrolyte in terms of the onset potential (0.90 V), half-wave potential (0.80 V) and the limiting current density (4.84 mA·cm^–2), and a high selectivity, as well as a strong methanol tolerance and superior durability, these results are comparable to those of the Pt/C catalyst. Furthermore, the superior bifunctional activity of Co@NC-0.86 was also confirmed in a home-built Zn-air battery, signifying the possibility for application in electrode materials and in current energy conversion and storage devices.     

Ultrafine Fe-modulated Ni nanoparticles embedded within nitrogen-doped carbon from Zr-MOFs-confined conversion for efficient oxygen evolution reaction

Improvement of the low-cost transition metal electrocatalyst used in sluggish oxygen evolution reaction is a significant but challenging problem. In this study, ultrafine Fe-modulated Ni nanoparticles embedded in a porous Ni-doped carbon matrix were produced by the pyrolysis of zirconium metal–organic–frameworks, in which 2,2′-bipyridine-5,5′-dicarboxylate operating as a ligand can coordinate with Ni²⁺ and Fe³⁺. This strategy allows formation of Fe-modulated Ni nanoparticles with a uniform dimension of about 2 nm which can be ascribed to the spatial blocking effect of ZrO₂. This unique catalyst displays an efficient oxygen evolution reaction electrocatalytic activity with a low overpotential of 372 mV at 10 mA·cm^–2 and a small Tafel slope of 84.4 mV·dec^–1 in alkaline media. More importantly, it shows superior durability and structural stability after 43 h in a chronoamperometry test. Meanwhile, it shows excellent cycling stability during 4000 cyclic voltammetry cycles. This research offers a new insight into the construction of uniform nanoscale transition metals and their alloys as highly efficient and durable electrocatalysts.     

Pd/Fe3O4 supported on bio-waste derived cellulosic-carbon as a nanocatalyst for C–C coupling and electrocatalytic application

The current work describes the synthesis of a new bio-waste derived cellulosic-carbon supported-palladium nanoparticles enriched magnetic nanocatalyst (Pd/Fe₃O₄@C) using a simple multi-step process under aerobic conditions. Under mild reaction conditions, the Pd/Fe₃O₄@C magnetic nanocatalyst demonstrated excellent catalytic activity in the Hiyama cross-coupling reaction for a variety of substrates. Also, the Pd/Fe₃O₄@C magnetic nanocatalyst exhibited excellent catalytic activity up to five recycles without significant catalytic activity loss in the Hiyama cross-coupling reaction. Also, we explored the use of Pd/Fe₃O₄@C magnetic nanocatalyst as an electrocatalyst for hydrogen evolution reaction. Interestingly, the Pd/Fe₃O₄@C magnetic nanocatalyst exhibited better electrochemical activity compared to bare carbon and magnetite (Fe₃O₄ nanoparticles) with an overpotential of 293 mV at a current density of 10 mA·cm^–2.     

Interface engineering for enhancing electrocatalytic oxygen evolution reaction of CoS/CeO2 heterostructures

To realize renewable energy conversion,it is important to develop low-cost and high-efficiency electrocatalyst for oxygen evolution reaction.In this communication,a novel bijunction CoS/CeO₂ electrocatalyst grown on carbon cloth is prepared by the interface engineering.The interface engineering of CoS and CeO₂ facilitates a rapid charge transfer from CeO₂ to CoS.Such an electrocatalyst exhibits outstanding electrocatalytic activity with a low overpotential of 311 mV at 10 mA·cm?2 and low Tafel slope of 76.2 mV·dec?1,and is superior to that of CoS(372 mV)and CeO₂(530 mV)counterparts.And it has long-term durability under alkaline media.     

Homogeneous Co3O4 film electrode with enhanced oxygen evolution electrocatalysis via surface reduction

Homogeneous NaBH_4-reduced Co_O_4 thin film electrodes with enhanced oxygen evolution electrocatalysis were obtained via a controlled-synthesis route.Firstly CoOx colloids were synthesized via ethylene glycol solvothermal method and cast on conductive glass substrates.The oxygen evolution reaction(OER) electrocatalysis of these asprepared Co_3O_4 thin films were then significantly enhanced via a simple surface reduction by NaBH_4 solution.The OER catalytic performance of the NaBH_4-reduced thin films was strongly dependent on the NaBH_4 concentration.The use of NaBH_4-reduced thin film electrodes for OER in alkaline solution supported higher current density and consequently negative shifts of the onset potential compared to that of the pristine.The optimal B_(12.5,20)-Co_3O_4 thin films exhibited excellent OER catalytic performances:At the current density of 10 mA·cm~(-2),a low overpotential of 365 mV and a small Tafel slope of 59.0 mV·dec~(-1) were observed.In addition,these B_(12.5,20)-Co_3O_4 thin film electrodes possessed good stability that can well recover its OER performance in a 24-h chronoamperometric stability test.     

Synthesis of Chl@Ti3C2 composites as an anode material for lithium storage

Two-dimensional (2D) titanium carbide MXene Ti₃C₂ has attracted significant research interest in energy storage applications. In this study, we prepared Chl@Ti₃C₂ composites by simply mixing a chlorophyll derivative (e.g., zinc methyl 3-devinyl-3-hydroxymethyl- pyropheophorbide a (Chl)) and Ti₃C₂ in tetrahydrofuran, where the Chl molecules were aggregated among the multi-layered Ti₃C₂ MXene or on its surface, increasing the interlayer space of Ti₃C₂. The as-prepared Chl@Ti₃C₂ was employed as the anode material in the lithium-ion battery (LIB) with lithium metal as the cathode. The resulting LIB exhibited a higher reversible capacity and longer cycle performance than those of LIB based on pure Ti₃C₂, and its specific discharge capacity continuously increased along with the increasing number of cycles, which can be attributed to the gradual activation of Chl@Ti₃C₂ accompanied by the electrochemical reactions. The discharge capacity of 1 wt-% Chl@Ti₃C₂ was recorded to be 325 mA·h·g^–1 at the current density of 50 mA·g^–1 with a Coulombic efficiency of 56% and a reversible discharge capacity of 173 mA·h·g^–1 at the current density of 500 mA·g^–1 after 800 cycles. This work provides a novel strategy for improving the energy storage performance of 2D MXene materials by expanding the layer distance with organic dye aggregates.     

Metal-organic framework-derived Ni doped Co3S4 hierarchical nanosheets as a monolithic electrocatalyst for highly efficient hydrogen evolution reaction in alkaline solution

Hierarchical nanostructure construction and electronic structure engineering are commonly employed to increase the electrocatalytic activity of HER electrocatalysts. Herein, Ni doped Co₃S₄ hierarchical nanosheets on Ti mesh (Ni doped Co₃S₄ HNS/TM) were successfully prepared by using metal organic framework (MOF) as precursor which was synthesized under ambient condition. Characterization results confirmed this structure and Ni incorporation into Co₃S₄ lattice as well as the modified electronic structure of Co₃S₄ by Ni doping. Alkaline HER performance showed that Ni doped Co₃S₄ HNS/TM presented outstanding HER activity with 173 mV overpotential at -10 mA·cm^-2, surpassing most of metal sulfide-based electrocatalysts. The hierarchical structure, superior electrical conductivity and electronic structure modulation contributed to the accelerated water dissociation and enhanced intrinsic activity. This work provides a new avenue for synthesizing hierarchical nanostructure and simultaneously tuning the electronic structure to promote HER performance, which has potential application in designing highly efficient and cost-effective HER nanostructured electrocatalyst.     

Pre-sodiation strategy for superior sodium storage batteries

The irreversible consumption of sodium in the initial several cycles greatly led to the attenuation of capacity, which caused the low initial coulombic efficiency (ICE) and obvious poor cycle stability. Pre-sodiation can effectively improve the electrochemical performance by compensating the capacity loss in the initial cycle. Here, carbon-coated sodium-pretreated iron disulfide (NaFeS₂@C) has been synthesized through conventional chemical method and used in sodium metal battery as a cathode material. The calculated density of states (DOS) of NaFeS₂@C is higher, which implies enhanced electron mobility and improved cycle reversibility. Because of the highly reversible conversion reaction and the compensation of irreversible capacity loss during the initial cycle, the Na/NaFeS₂@C battery achieves ultra-high initial coulombic efficiency (96.7%) and remarkable capacity (751 mA·h·g^-1 at 0.1 A·g^-1). In addition, highly reversible electrochemical reactions and ultra-thin NaF-rich solid electrolyte interphase (SEI) also benefit for the electrochemical performance, even at high current density of 100 A·g^-1, it still exhibits a reversible capacity of 136 mA·h·g^-1, and 343 mA·h·g^-1 after 2500 cycles at 5.0 A·g^-1. This work aims to bring up new insights to improve the ICE and stability of sodium metal batteries.     

低温共沉淀法合成多孔CoFe LDH纳米片电催化剂

通过低温共沉淀技术合成了多孔CoFe层状双金属氢氧化物（CoFe LDH）纳米片。运用X射线衍射（XRD）、X射线光电子能谱（XPS）、扫描电镜（SEM）、透射电镜（TEM）等手段对产物的物相、组成及微观形貌进行了表征,并探讨了铁离子（Fe³⁺）含量对CoFe LDH纳米结构生长行为的影响,考察了制备的产物作为电催化剂在电解水析氧反应中的性能。结果表明,Fe³⁺的加入可以有效调节产物的形貌、结晶度和孔道结构。在合适的Co与Fe比例条件下,制备的CoFe LDH可形成多孔纳米片,且增大了总孔体积,增加了表面活性位点。同时,结晶CoFe LDH纳米片可促进Co和Fe离子间的电荷转移行为,从而提高产物的电催化活性。对于电解水析氧反应,当电流密度为10 mA/cm²时,结晶Co_0.67Fe_0.33 LDH多孔纳米片所需的过电势仅为291 mV,Tafel斜率为33 mV/dec,并展现出良好的循环稳定性。     

泡沫镍基三维空心球CoFe2O4@NF复合材料的制备与析氧性能研究

为降低电解水阳极的析氧反应过电位,采用一步水热法制备了泡沫镍基钴铁混合氧化物（CoFe₂O₄@NF）复合材料。采用XRD、SEM、TEM和XPS等方法对复合材料进行表征,并利用三电极体系对其电解水析氧催化性能进行了测试。结果显示：CoFe₂O₄以颗粒的形式聚集成空心球结构生长于泡沫镍基底上,其中空心球的直径大约4 μm,而CoFe₂O₄的粒径约为40 nm左右。在1 mol·L^-1 KOH溶液中,CoFe₂O₄@NF复合材料仅需293 mV的过电位即可达到20 mA·cm^-2的电流密度,Tafel斜率为51 mV·dec^-1。经过1 000次循环伏安扫描和10 h电流时间曲线测试后,其析氧性能依旧保持高稳定性,在析氧催化材料领域有着广阔的研究前景。     

Ag nanoparticles anchored on MIL-100/nickel foam nanosheets as an electrocatalyst for efficient oxygen evolution reaction performance

Metal-organic frameworks (MOFs) exhibit excellent application potential in the field of electrocatalysis.In this study,we first prepare MIL-100 nanosheets on nickel foam (MIL-100/NF) and then successfully anchor Ag nanoparticles (NPs) on the nanosheets (Ag@MIL-100/NF) for oxygen evolution reaction(OER) catalysis.This strategy dramatically improves the conductivity of MIL-100 and the Ag NPs are uni-formly dispersed on the nanosheets.The Ag@MIL-100/NF catalyst has excellent electrocatalytic perfor-mance and long-term corrosion resistance,with a low overpotential of 207 mV and a long-term stability of at least 100 h at a current density of 50 mA·cm-2.The experimental results demonstrate that this high OER catalytic performance is due to the improved charge transfer after loading Ag NPs,the com-bination of nanosheets and highly dispersed Ag NPs that expose more active sites and the adjusted chem-ical valence states of Fe and Ni in MIL-100.This work provides a surface decoration approach for the preparation of excellent catalysts directly used in the OER.     

FeS2@TiO2 nanorods as high-performance anode for sodium ion battery

Sodium-ion battery (SIB) is an ideal device that could replace lithium-ion battery (LIB) in grid-scale energy storage system for power because of the low cost and rich reserve of raw material. The key challenge lies in developing electrode materials enabling reversible Na⁺ insertion/desertion and fast reaction kinetics. Herein, a core-shell structure, FeS₂ nanoparticles encapsulated in biphase TiO₂ shell (FeS₂@TiO₂), is developed towards the improvement of sodium storage. The diphase TiO₂ coating supplies abundant anatase/rutile interface and oxygen vacancies which will enhance the charge transfer, and avoid severe volume variation of FeS₂ caused by the Na⁺ insertion. The FeS₂ core will deliver high theoretical capacity through its conversion reaction mechanism. Consequently, the FeS₂@TiO₂ nanorods display notable performance as anode for SIBs including long-term cycling performance (637.8 mA·h·g^-1 at 0.2 A·g^-1 after 300 cycles, 374.9 mA·h·g^-1 at 5.0 A·g^-1 after 600 cycles) and outstanding rate capability (222.2 mA·h·g^-1 at 10 A·g^-1). Furthermore, the synthesized FeS₂@TiO₂ demonstrates significant pseudocapacitive behavior which accounts for 90.7% of the Na⁺ storage, and efficiently boosts the rate capability. This work provides a new pathway to fabricate anode material with an optimized structure and crystal phase for SIBs.     

Carbon-coated lithium titanate: effect of carbon precursor addition processes on the electrochemical performance

In this paper,two carbon-coated lithium titanate(LTO-C1 and LTO-C2)composites were synthesized using the ball-milling-assisted calcination method with different carbon precursor addition processes.The physical and electrochemical properties of the as-synthesized negative electrode materials were characterized to investigate the effects of two carbon-coated LTO synthesis processes on the electrochemical performance of LTO.The results show that the LTO-C2 synthesized by using Li2CO3 and TiO2 as the raw materials and sucrose as the carbon source in a one-pot method has less polarization during lithium insertion and extraction,minimal charge transfer impedance value and the best electrochemical performance among all samples.At the current density of 300 mA·h·g^-1,the LTO-C2 composite delivers a charge capacity of 126.9 mA·h·g^-1,and the reversible capacity after 300 cycles exceeds 121.3 mA·h·g^-1 in the voltage range of 1.0–3.0 V.Furthermore,the electrochemical impedance spectra show that LTO-C2 has higher electronic conductivity and lithium diffusion coefficient,which indicates the advantages in electrode kinetics over LTO and LTO-C1.The results clarify the best electrochemical properties of the carbon-coated LTO-C2 composite prepared by the one-pot method.     

碳纸负载钴氧化物的制备及电催化析氧性能研究

高效且廉价的电催化析氧反应（OER）电极材料的制备对其在电化学能源转化和储存系统中的应用具有重要的研究意义。通过溶剂热法和不同气氛焙烧,分别制得碳纤维纸（碳纸）负载的两种钴氧化物（一氧化钴和四氧化三钴）,并将其用作OER电极的催化剂。运用X射线衍射仪（XRD）、场发射扫描电镜（FESEM）和X射线光电子能谱（XPS）技术分别对两种材料的物相、形貌和表面价态进行了表征及分析。结果表明：在氮气气氛下焙烧得到一氧化钴纳米片,而在空气下焙烧得到四氧化三钴纳米片。通过线性扫描伏安法（LSV）、循环伏安曲线（CV）、电化学交流阻抗测试（EIS）和计时电位法对两种材料的电催化析氧性能进行了研究。结果表明：一氧化钴电极比四氧化三钴电极具有更优异的析氧反应催化活性和稳定性。在1 mol/L 氢氧化钾电解液中,一氧化钴和四氧化三钴电极在10 mA/cm ²电流密度下对应的电位分别为1.568 V和1.617 V。     

钼钴二元硫化物制备及其电解水性能研究

为提升硫化钼全解水的催化能力,采用一步电沉积的方法在镍钴氧化物（NCO）基底上成功制备了钼钴二元硫化物复合电极,研究了添加剂、钼钴物质的量比和沉积时间对电极电催化性能的影响。实验结果表明,采用氟化铵作为添加剂、钼钴物质的量比为5∶7且沉积时间为750 s时,制备的Mo₅Co₇S_x@NCO-750电极具有最佳电催化活性,其析氢反应（HER）过电位和Tafel斜率分别为115 mV和67 mV/dec,析氧反应（OER）过电位和Tafel斜率分别为259 mV和42 mV/dec,全解水时槽压为1.61 V。复合电极电催化性能的提升一方面得益于钴的引入,在硫化钼中形成了高导电性和高催化活性的异质界面,另一方面材料中还存在丰富的具有优异电催化活性的缺陷位点。     

双功能yolk-shell钴@钴氮碳掺杂氧电极催化剂

以ZIF-67为模板,通过表面原位聚合多巴胺,与金属Co²⁺发生强烈螯合,释放出有机配体,得到中空的金属-有机结构材料（Co-PDA）。通过900℃高温处理得到类似蛋黄（yolk-shell）结构的金属氮掺杂碳材料（Co@Co-N/C）。这种特殊结构的材料具有优异的氧还原（ORR）和析氧反应（OER）电催化活性,在0.1 mol/L KOH电解液中,其ORR的半波电位为0.81 V,Tafel斜率为60 mV/dec;在电流密度为10 mA/cm²时,其OER过电位为390 mV,Tafel斜率为71 mV/dec,总的氧电极催化活性为0.82 V,是一种优良的双功能氧电极催化剂。