Coupling Magnetic Single‐Crystal Co2Mo3O8 with Ultrathin Nitrogen‐Rich Carbon Layer for Oxygen Evolution Reaction

Transition‐metal oxides as electrocatalysts for the oxygen evolution reaction (OER) provide a promising route to face the energy and environmental crisis issues. Although palmeirite oxide A₂Mo₃O₈ as OER catalyst has been explored, the correlation between its active sites (tetrahedral or octahedral) and OER performance has been elusive. Now, magnetic Co₂Mo₃O₈@NC‐800 composed of highly crystallized Co₂Mo₃O₈ nanosheets and ultrathin N‐rich carbon layer is shown to be an efficient OER catalyst. The catalyst exhibits favorable performance with an overpotential of 331 mV@10 mA cm^?2 and 422 mV@40 mA cm^?2, and a full water‐splitting electrolyzer with it as anode catalyst shows a cell voltage of 1.67 V@10 mA cm^?2 in alkaline. Combined HAADFSTEM, magnetic, and computational results show that factors influencing the OER performance can be attributed to the tetrahedral Co sites (high spin, t₂³e⁴), which improve the OER kinetics of rate‐determining step to form *OOH.     

Plasma‐Engraved Co3O4 Nanosheets with Oxygen Vacancies and High Surface Area for the Oxygen Evolution Reaction

Co₃O₄, which is of mixed valences Co²⁺ and Co³⁺, has been extensively investigated as an efficient electrocatalyst for the oxygen evolution reaction (OER). The proper control of Co²⁺/Co³⁺ ratio in Co₃O₄ could lead to modifications on its electronic and thus catalytic properties. Herein, we designed an efficient Co₃O₄‐based OER electrocatalyst by a plasma‐engraving strategy, which not only produced higher surface area, but also generated oxygen vacancies on Co₃O₄ surface with more Co²⁺ formed. The increased surface area ensures the Co₃O₄ has more sites for OER, and generated oxygen vacancies on Co₃O₄ surface improve the electronic conductivity and create more active defects for OER. Compared to pristine Co₃O₄, the engraved Co₃O₄ exhibits a much higher current density and a lower onset potential. The specific activity of the plasma‐engraved Co₃O₄ nanosheets (0.055 mA cm^?2_BET at 1.6 V) is 10 times higher than that of pristine Co₃O₄, which is contributed by the surface oxygen vacancies.     

Synthesis of a Hierarchically Porous C/Co3O4 Nanostructure with Boron Doping for Oxygen Evolution Reaction

Fabricating a low‐cost and highly efficient electrocatalyst is of importance for the development of renewable energy devices. In this work, we have synthesized an ultrafine cobalt oxide nanocatalyst (5–10 nm) doped with boron (BC/Co₃O₄) by using a metal–organic framework as a precursor, which exhibits an excellent catalytic activity for oxygen evolution reaction (OER). Owing to the improvement of accessible active sites by boron doping, the synthesized catalyst can reach a current density of 10 mA cm^?2 at 1.54 V with a low overpotential of 310 mV, superior than those of commercial RuO₂ and N‐doped C/Co₃O₄. This work provides a facile way to develop highly efficient catalysts for electrochemical reactions.     

Active Electron Density Modulation of Co3O4‐Based Catalysts Enhances their Oxygen Evolution Performance

Despite the fact that many strategies have been developed to improve the efficiency of the oxygen evolution reaction (OER), the precise modulation of the surface electronic properties of catalysts to improve their catalytic activity is still challenging. Herein, we demonstrate that the surface active electron density of Co₃O₄ can be effectively regulated by an argon‐ion irradiation method. X‐ray photoelectron and synchrotron x‐ray absorption spectroscopy, UV photoelectron spectrometry, and DFT calculations show that the surface active electron density band center of Co₃O₄ has been upshifted, leading to a significantly enhanced absorption capability of the oxo group. The optimized Co₃O₄‐based catalysts exhibit an excellent overpotential of 260 mV at 10 mA cm^?2 and Tafel slope of 54 mV dec^?1, superior to the capability of the benchmark RuO₂, representing one of the best Co‐based OER catalysts. This approach could guide the future rational design and discovery of ideal electrocatalysts.     

放电温度对LiNi3/8Co2/8Mn3/8O2电化学性能的影响

采用X射线衍射（XRD）、X射线光电子能谱（XPS）、恒流充放电、循环伏安及交流阻抗法，研究了放电温度对LiNi3/8Co2/8Mn3/8O2的倍率特性、锂离子扩散及电荷传递的影响.结果表明， 提高放电温度可显著改善LiNi3/8Co2/8Mn3/8O2的放电容量与倍率放电性能.尽管温度升高使电荷传递活性与锂离子扩散速度都增加，但电荷传递活化能比锂离子扩散活化能大一倍多，表明电荷传递步骤是其电化学反应控制步骤.温度对其电荷传递的影响大于对锂离子扩散的影响.温度升高，电荷传递速率加快，电化学嵌入-迁出反应加速，是其放电容量与倍率放电特性显著改善的主要原因.     

Dual Role of Silver Moieties Coupled with Ordered Mesoporous Cobalt Oxide towards Electrocatalytic Oxygen Evolution Reaction

Herein, we show that the performance of mesostructured cobalt oxide electrocatalyst for oxygen evolution reaction (OER) can be significantly enhanced by coupling of silver species. Various analysis techniques including pair distribution function and Rietveld refinement, X‐ray absorption spectroscopy at synchrotron as well as advanced electron microscopy revealed that silver exists as metallic Ag particles and well‐dispersed Ag₂O nanoclusters within the mesostructure. The benefits of this synergy are twofold for OER: highly conductive metallic Ag improves the charge transfer ability of the electrocatalysts while ultra‐small Ag₂O clusters provide the centers that can uptake Fe impurities from KOH electrolyte and boost the catalytic efficiency of Co–Ag oxides. The current density of mesostructured Co₃O₄ at 1.7 V_RHE is increased from 102 to 211 mA cm^?2 with incorporation of silver spices. This work presents the dual role of silver moieties and demonstrates a simple method to increase the OER activity of Co₃O₄.     

Controllable Synthesis of Fe-Doped NiCo2O4 Nanobelts as Superior Catalysts for Oxygen Evolution Reaction

As one of the promising clean and renewable technologies, water splitting has been a hot topic, especially the half-reaction of oxygen evolution reaction (OER) due to its sluggish and complex kinetics. Hence, Fe-doped NiCo₂O₄ nanobelts were designed and prepared as catalysts toward OER. By increasing the Fe amount, the catalytic performances of the as-synthesized products went up and then decreased. Profiting from the synergistic effect between Fe atom and NiCo₂O₄, all the Fe-NiCo₂O₄ catalysts exhibited superior catalytic activities to the corresponding NiCo₂O₄. In addition, the characteristic nanobelt architecture facilitates the conduction of electrons and the exposure of active sites. With the optimal Fe content, the 9.1 % Fe-NiCo₂O₄ yielded the smallest overpotential and Tafel slope among the catalysts, distinctly lower than that of RuO₂.     

Oxygen Evolution in Overcharged LixNi1/3Co1/3Mn1/3O2 Electrode and Its Thermal Analysis Kinetics

The oxygen evolution behavior in overcharged LiNi_1/3Co_1/3Mn_1/3O₂‐based electrode was investigated by differential scanning calorimetry and thermal gravimetric (DSC/TG). Meantime, its thermal kinetic parameters were calculated by Kissinger's and Ozawa's method. As observed by DSC/TG, two exothermic peaks at 239 and 313°C in washed cathode (4.6 V), were attributed to two steps of oxygen evolution. More importantly, the temperature of its oxygen release processes decreased obviously compared with that charged to 2.8 V. Activation energy (E) for the first and second oxygen evolution, both of which were assumed closely to be the first order reaction, between 200 and 350°C in Li_0.204Ni_1/3Co_1/3Mn_1/3O₂‐based electrode were calculated as 113.63 and 158.13 kJ·mol⁻¹, respectively and the corresponding Arrhenius pre‐exponential factors (A) of 1.05×10¹¹ and 6.46×10¹³s⁻¹ were also obtained. The different energy barrier of such two steps of oxygen evolution should probably be ascribed to the different bond energy of M–O (M=Mn, Co, Ni).     

A Surface-Oxide-Rich Activation Layer (SOAL) on Ni2Mo3N for a Rapid and Durable Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is key to renewable energy technologies such as water electrolysis and metal–air batteries. However, the multiple steps associated with proton-coupled electron transfer result in sluggish OER kinetics and catalysts are required. Here we demonstrate that a novel nitride, Ni₂Mo₃N, is a highly active OER catalyst that outperforms the benchmark material RuO₂. Ni₂Mo₃N exhibits a current density of 10 mA cm⁻² at a nominal overpotential of 270 mV in 0.1 m KOH with outstanding catalytic cyclability and durability. Structural characterization and computational studies reveal that the excellent activity stems from the formation of a surface-oxide-rich activation layer (SOAL). Secondary Mo atoms on the surface act as electron pumps that stabilize oxygen-containing species and facilitate the continuity of the reactions. This discovery will stimulate the further development of ternary nitrides with oxide surface layers as efficient OER catalysts for electrochemical energy devices.     

Co9S8/MoS2异质结构的构筑及电催化析氢性能研究

利用前驱物形貌导向法,成功制备了Co₉S₈/MoS₂异质结构催化剂,该催化剂在碱性析氢反应（HER）中表现出优异的催化活性及稳定性,其在10 mA·cm^-2处的过电势仅为84 mV.通过X射线粉末衍射（XRD）、透射电子显微镜（TEM）、电子自旋共振（ESR）、拉曼光谱（Raman）、X射线光电子能谱（XPS）和同步辐射（XAFS）等表征,证明了CoS₂/MoS₂在H₂氛围下煅烧形成Co₉S₈/MoS₂的过程中,CoS₂中Co的配位模式从部分八面体向Co₉S₈中的四面体转变,这种转变可活化MoS₂的惰性平面,从而使其更有利于吸附H^*.除此之外,接触角数据表明：该催化剂具有良好的亲水性,有利于电解液渗透及气体分子的迅速扩散,从而促进HER反应速率.由于异质结构间具有强烈的相互作用,该催化剂可表现出良好的结构稳定性.本工作基于Co₉S₈/MoS₂异质结构的成功构筑及对其HER催化机理的充分探讨,为后续硫化物异质结及其在电催化中的应用提供了良好的思路和研究基础.     

CoBx/Co3O4电催化剂的制备及其氧析出性能

采用NaBH4溶液处理经水热、热处理步骤制得Co3O4纳米棒,得到表面富含氧空位以及无定型CoBx的Co3O4(CoBx/Co3O4)氧析出(OER)电催化剂。利用X射线衍射(XRD)、场发射扫描电镜(FESEM)、透射电镜(TEM)、X射线光电子能谱仪(XPS)等技术表征了催化剂的物相、微观形貌、元素组成以及表面化学键结构等。通过电化学工作站测试了电极材料的OER活性、稳定性、电化学阻抗等。结果表明,经NaBH4处理后,Co3O4表面高价态Co被还原至低价态Co,最终其表面有无定型CoBx的生成,并含有大量氧空位,有效提升了OER性能。在1.0 mol·L^-1 KOH电解质溶液中,达到10 mA·cm^-2的电流密度时,CoBx/Co3O4所需的过电位由Co3O4的346 mV降至298 mV。     

Magnetic Field-Enhanced Electrocatalytic Oxygen Evolution on a Mixed-Valent Cobalt-Modulated LaCoO3 Catalyst

Extensive efforts to enhance the oxygen evolution reaction (OER) catalytic performance of transition metal oxides mainly concentrate on the extrinsic morphology tailoring, lattice doping, and electrode interface optimizing. Nevertheless, little room is left for performance improvement using these methods and an obvious gap still exists compared to the precious metal catalysts. In this work, a novel “mixed-valent cobalt modulation” strategy is presented to enhance the electrocatalytic OER of perovskite LaCoO₃ (LCO) oxide. The valence transition of cobalt is realized by ethylenediamine post reduction procedure at room temperature, which further induces the variation of magnetic properties for LCO catalyst. The optimized LCO catalyst with Co²⁺/Co³⁺ of 1.98 % exhibits the best OER activity, and the overpotential at 10 mA cm⁻² current density is decreased by 170 mV compared pristine LCO. Impressively, the ferromagnetic LCO catalyst can perform magnetic OER enhancement. By application of an external magnetic field, the overpotential of LCO at 10 mA cm⁻² can be further decreased by 20 mV compared to that of under zero magnetic field, which arises from the enhanced energy states of electrons and accelerated electron transfer process driven by magnetic field. Our findings may provide a promising strategy to break the bottleneck for further enhancement of OER performance.     

Optimization of Active Sites via Crystal Phase,Composition, and Morphology for Efficient Low-Iridium Oxygen Evolution Catalysts

Reducing the amount of iridium in oxygen evolution electrocatalysts without compromising their catalytic performances is one of the major requirements in proton-exchange-membrane water electrolyzers. Herein, with the help of theoretical studies, we show that anatase-type TiO₂-IrO₂ solid solutions possess more active iridium catalytic sites for the oxygen evolution reaction (OER) than IrO₂, the benchmark OER catalyst. Note that the same is not observed for their rutile-type counterparts. However, owing to their thermodynamic metastability, anatase-type TiO₂-IrO₂ solid solutions are generally hard to synthesize. Our theoretical studies demonstrate that such catalytically active anatase-type solid-solution phases can be created in situ on the surfaces of readily available SrTiO₃-SrIrO₃ solid solutions during electrocatalysis in acidic solution as the solution can etch away Sr atoms. We experimentally show this with porous SrTiO₃-SrIrO₃ solid-solution nanotubes synthesized by a facile synthetic route that contain 56 % less iridium than IrO₂ yet show an order of magnitude higher apparent catalytic activity for OER in acidic solution.     

复合电沉积制备Ni/NiFe2O4电极及其电催化析氧性能

采用共沉淀法制备尖晶石型NiFe2O4粉体,然后将其加入瓦特镀镍液中,采用复合电沉积制备Ni/NiFe2O4复合电极。通过改变镀液的pH值、阴极电流密度jk等条件,探索最佳工艺条件。运用扫描电子显微镜(SEM)、能谱分析(EDS)和X射线衍射仪(XRD)表征粉体以及复合电极的组成和结构。结果表明,在镀液pH值为5.8～6.0、jk为40×10-3～60×10-3A/cm2条件下,所得复合电极中NiFe2O4的质量分数最高可达55.15%。采用循环伏安、稳态极化以及恒电势阶跃,研究了电极在5 mol/L KOH溶液中的电催化析氧性能。与Ni电极对比,Ni/NiFe2O4复合电极的电催化析氧性能更好,比表面积是镍电极的23.02倍,表观活化能降低了62.07 kJ/mol。恒电势长时间电解析氧实验表明,Ni/NiFe2O4复合电极在碱性介质中具有较高的析氧稳定性。     

Co/Al2O3催化剂上3-甲基-2-丁烯醛选择性加氢反应

3-甲基-2-丁烯醛(3-MeCal)是一种典型的α,β-不饱和醛,其C=O加氢产物3-甲基-2-丁烯醇(3-MeCol)作为重要的有机中间体,在医药、香料、农药等生产领域有着广泛的应用.我们采用沉积沉淀法制备了Co/Al2O3催化剂,将其应用于3-MeCal液相选择性加氢反应中,考察了反应温度、H2初始压力、催化剂焙烧温度和还原温度对3-MeCal选择性加氢反应的影响.发现反应温度为80℃,H2初始压力为1×106Pa下,加氢反应效果良好.通过H2-TPR与XRD表征了焙烧温度对催化剂的影响,发现适当焙烧温度能增强Co物种与载体Al2O3间作用力.焙烧温度为600℃,还原温度为550℃下制备的催化剂反应48 min后转化率为23.0%,3-MeCol选择性达到88.6%.制备的Co/Al2O3催化剂具有良好的磁性,在外磁场作用下可与液相反应体系实现高效分离,循环使用3次后,催化性能没有明显下降,表现出良好的循环使用性能.     

NiSe2-CoSe2 with a Hybrid Nanorods and Nanoparticles Structure for Efficient Oxygen Evolution Reaction

Hetero-structure induced high performance catalyst for oxygen evolution reaction(OER)in the water splitting reaction has received increased attention.Herein,we demonstrated a novel catalyst system of NiSe₂-CoSe₂ consisting of nanorods and nanoparticles for the efficient OER in the alkaline electrolyte.This catalyst system can be easily fabricated via a low-temperature selenization of the solvothermal synthesized NiCo(OH)x precursor and the unique morphology of hybrid nanorods and nanoparticles was found by the electron microscopy analysis.The high valence state of the metal species was indicated by X-ray photoelectron spectroscopy study and a strong electronic effect was found in the NiSe₂-CoSe₂ catalyst system compared to their counterparts.As a result,NiSe₂-CoSe₂ exhibited high catalytic performance with a low overpotential of 250 mV to reach 10 mA·cm^-2 for OER in the alkaline solution.Furthermore,high catalytic stability and catalytic kinetics were also observed.The superior performance can be attributed to the high valence states of Ni and Co and their strong synergetic coupling effect between the nanorods and nanoparticles,which could accelerate the charge transfer and offer abundant electrocatalytic active sites.The current work offers an efficient hetero-structure catalyst system for OER,and the results are helpful for the catalysis understanding.     

Accelerating H2 Evolution by Anodic Semi-dehydrogenation of Tetrahydroisoquinolines in Water over Co3O4 Nanoribbon Arrays Decorated Nickel Foam

Coupling the H₂ evolution reaction in water with thermodynamically favorable organic oxidation reactions is highly desirable, because it can enhance the energy conversion efficiency compared with electrocatalytic water splitting, and produce value-added chemicals instead of O₂ in the anodic reaction. Herein, Co₃O₄ nanoribbon arrays in situ grown on nickel foam (Co₃O₄@NF) was employed as an effective electrocatalyst for the selective oxidation of tetrahydroisoquinolines (THIQs). Various value-added semi-dehydrogenation products including dihydroisoquinolines with electro-deficient or -rich groups could be obtained with moderate yields and faradaic efficiencies. Benefitting from the rich surface active sites of Co₃O₄@NF, a two-electrode (Co₃O₄@NF||Pt) electrolytic system drove a benchmark current density of 10 mA cm⁻² at a cell voltage as low as 1.446 V in 1.0 M KOH aqueous solution containing 0.02 M THIQ, which was reduced by 174 mV in comparison with that of overall water splitting.