Cobalt/copper-decorated carbon nanofibers as novel non-precious electrocatalyst for methanol electrooxidation

In this study, Co/Cu-decorated carbon nanofibers are introduced as novel electrocatalyst for methanol oxidation. The introduced nanofibers have been prepared based on graphitization of poly(vinyl alcohol) which has high carbon content compared to many polymer precursors for carbon nanofiber synthesis. Typically, calcination in argon atmosphere of electrospun nanofibers composed of cobalt acetate tetrahydrate, copper acetate monohydrate, and poly(vinyl alcohol) leads to form carbon nanofibers decorated by CoCu nanoparticles. The graphitization of the poly(vinyl alcohol) has been enhanced due to presence of cobalt which acts as effective catalyst. The physicochemical characterization affirmed that the metallic nanoparticles are sheathed by thin crystalline graphite layer. Investigation of the electrocatalytic activity of the introduced nanofibers toward methanol oxidation indicates good performance, as the corresponding onset potential was small compared to many reported materials; 310 mV (vs. Ag/AgCl electrode) and a current density of 12 mA/cm² was obtained. Moreover, due to the graphite shield, good stability was observed. Overall, the introduced study opens new avenue for cheap and stable transition metals-based nanostructures as non-precious catalysts for fuel cell applications.     

Hydrothermal Transformation of Dried Grass into Graphitic Carbon‐Based High Performance Electrocatalyst for Oxygen Reduction Reaction

In this work, we present a low cost and environmentally benign hydrothermal method using dried grass as the sole starting material without any synthetic chemicals to directly produce high quality nitrogen‐doped carbon nanodot/nanosheet aggregates (N‐CNAs), achieving a high yield of 25.2%. The fabricated N‐CNAs possess an N/C atomic ratio of 3.41%, consist of three typed of doped N at a ratio of 2.6 (pyridinic):1.7 (pyrrolic):1 (graphitic). The experimental results reveal that for oxygen reduction reaction (ORR), the performance of N‐CNAs, in terms of electrocatalytic activity, stability and resistance to crossover effects, is better or comparable to the commercial Pt/C electrocatalyst. The theoretical studies further indicate that the doped pyridinic‐N plays a key role for N‐CNAs' excellent four‐electron ORR electrocatalytic activity.     

钴氮共掺杂碳基电催化剂的制备及性能调控

贵金属基电催化剂是促进燃料电池及金属-空气电池技术发展的关键材料,然而,其单一的氧还原/氧析出催化功能及高昂的制备成本制约了其推广应用。为此,开发低成本、高效的非贵金属双功能电催化剂至关重要。以核壳金属有机框架（MOFs）为前驱体,通过高温煅烧法制备具有核壳结构、高催化活性、高导电性的钴/氮共掺杂碳基电催化剂（Co/Co₃O₄@NGC）。结果表明：煅烧温度是影响电催化剂微纳结构、物化组成和催化活性的关键因素,最佳烧结温度为900℃;制备的电催化剂（Co/Co₃O₄@NGC-900）具有清晰的核壳结构和3D十二面体形貌,微表面遍布Co/Co₃O₄纳米颗粒和Co-N_x位点。同时,Co/Co₃O₄@NGC-900有机地结合了多元活性成分（如活性Co/Co₃O₄纳米颗粒、Co-N_x及N掺杂）和高度石墨化碳基底的共同作用,具备高效的氧还...     

碱性介质中甲醇在PdMnO_2/C上的电氧化行为

通过X射线衍射光谱法(XRD)、X射线光电子光谱法(XPS)、循环伏安(CV)及Tafel曲线等方法对PdMnO2/C催化剂及其在碱性介质中的甲醇电氧化反应进行了研究。研究结果表明:添加MnO2增强了催化剂在碱性介质中甲醇电氧化反应的催化活性。催化剂中引入MnO2可以使Pd的晶粒尺寸减小;并使Pd的表面出现大量的零价态金属(Pd0)和低价态氧化物(PdO)。但是PdMnO2/C催化剂上甲醇电氧化反应存在一个最佳反应浓度。     

A robust electrocatalytic activity and stability of Pd electrocatalyst derived from carbon coating

Palladium (Pd) as an efficient anodic catalyst has been extensively investigated in direct formic acid fuel cells (DFAFCs); while, Pd catalyst is electrochemically unstable in acidic electrolyte resulting in low stability retarding the widespread application of DFAFCs. In this study, a new method is invented to prevent the Pd nanoparticles from rapid dissolution by carbon layer originated from the carbonization of glucose. Ascribing to the presence of carbon layer, Pd electrocatalyst demonstrates much higher stability in comparison with Pd electrocatalyst without carbon layer in the course of stability tests. Robust electrocatalytic activities toward formic acid and methanol/ethanol oxidation are observed for carbon-stabilized Pd electrocatalyst resulted from the higher content of metallic Pd atoms coming from the carbonization process, in which Pd (II) species are further reduced. Moreover, the fuel cell performance of carbon-stabilized Pd electrocatalyst reaches 90 mW cm_Pd⁻² measured with 1 M formic acid; while, power density of bare Pd electrocatalyst is only 74 mW cm_Pd⁻². This work highlights that carbon layer carbonized from glucose improves not only the stability of Pd electrocatalyst, but also the electrocatalytic activity.     

Construction of NiFeP/CoP nanosheets/nanowires hierarchical array as advanced electrocatalysts for water oxidation

Cost-effective hierarchical electrocatalysts with excellent performance and high stability for water splitting play an important role in promoting social sustainable development. Herein, we report a three-dimensional (3D) trimetallic nickel-iron-cobalt phosphide with a hierarchical nanoarray structure grown in situ on carbon cloth via a combined method of two-step hydrothermal reaction and following low-temperature phosphating using a carbon cloth as a conductive substrate. The synthesized NiFeP/CoP/CC exhibits excellent oxygen evolution reaction (OER) catalytic performance, giving small overpotentials of 250 mV, 270 mV and 320 mV at current densities of 20 mA cm⁻², 50 mA cm⁻² and 200 mA cm⁻² in alkaline electrolyte, respectively, with a small Tafel slope of 51 mV dec⁻¹. In addition, the catalytic activity of the material remains stable for at least 50 h, and the turnover frequency (TOF) is 0.466 mol O₂ s⁻¹ at an over potential of 300 mV. These properties of the material are comparable to those of the noble metal catalyst RuO₂/CC, which may be ascribed to the hierarchical microstructure, good conductivity and desirable synergistic effect among metal ions.     

Ni/NiO@rGO as an efficient bifunctional electrocatalyst for enhanced overall water splitting reactions

Herein, we fabricated bifunctional, noble metal-free, highly efficient nickel/nickel oxide on reduced graphene oxide (Ni/NiO@rGO) by chemical synthesis approach for electrochemical water splitting reaction. Its structural and morphological characterization using thermogravimetric analysis (TGA), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), energy dispersive analysis of X-ray (EDAX) and X-ray diffraction (XRD) represents, Ni/NiO@rGO is having Ni/NiO NPs ∼10 nm (±2 nm) on graphene oxide with face-centered cubic (FCC) crystal structure. Moreover, the presence of Ni/NiO (2.26%), O (6.56%), N (0.74%) and C (90.44%) from EDAX analysis further confirms the formation of Ni/NiO@rGO and it also supported by FTIR studies. This nanocatalyst is examined further for electrocatalytic water splitting reactions (HER and OER). It demonstrated low overpotential 582 mV to achieve current density at 10 mA cm⁻² and smaller Tafel slope of 63 mV dec⁻¹ obtained in 0.5 M H₂SO₄ towards HER. Also, at the other end at onset potential of 1.6 V vs. RHE towards OER. It demonstrated low overpotential 480 mV to achieve current density at 10 mA cm⁻² and smaller Tafel slope of 41 mV dec⁻¹ in 0.5 M KOH towards OER observed. Hydrogen fuel is eco-friendly to the environment and noteworthy performance of earth-saving reactions.     

锡量子点制备及其电催化还原二氧化碳产甲酸性能

锡基材料在自然界含量丰富、价格低廉, 在电催化还原CO₂制液体燃料反应中具有巨大潜力。但是较低的产物选择性和较差的稳定性限制了其应用。本工作制备的锡量子点电催化剂(Sn-QDs), 具有高效、高稳定性和高选择性的电催化还原CO₂产HCOOH活性。Sn-QDs的平均颗粒尺寸仅为2~3 nm, 结晶性良好。小的颗粒尺寸增大了电化学活性面积(ECSA), Sn-QDs的ECSA约为锡颗粒的4.4倍。ECSA增大以及CO₂还原反应动力学加速, 促进了CO₂电化学转化。在-1.0 V (vs RHE)下, Sn-QDs/CN催化剂的HCOOH法拉第效率(FE_HCOOH)达到95%, 并且在宽约0.5 V的电势范围内能够保持在83%以上。此外, Sn-QDs/CN可以在24 h内保持良好的电化学稳定性。