可控表面磷原子修饰提升超细W2C纳米颗粒电解水析氢反应性能

研究高活性和稳定性的非贵金属基析氢催化剂对解决当前能源危机和环境污染问题具有重要意义.碳化钨具有与贵金属Pt类似的d带电子结构,因而成为一类新兴的非贵金属析氢催化剂,受到广泛关注.磷掺杂是提高催化剂析氢活性的有效方法之一,然而目前最常见的构筑磷掺杂方法是使用多金属氧酸盐(POMs,如H3PW12O40),其固定的W/P原子比导致W2C中的掺杂浓度难以调控,并且磷掺杂主要是进入碳载体而不是碳化物本身,从而导致无法明确杂原子对其电催化析氢活性的贡献.本文采用植酸(PA)为磷源设计合成了可控磷掺杂W2C纳米颗粒,并探讨了催化剂组分、杂原子掺杂位置与析氢性能之间的关系.深入研究了磷掺杂碳化钨(WCP)的化学结构和析氢活性.与原始的W2C催化剂相比,WCP具有更高的本征活性、更快的电子转移速率和更多的活性位数量,并且在酸性和碱性条件下均表现出较好的析氢性能.特别是过电位为-200 mV时,WCP催化剂的本征活性在酸性和碱性条件下分别为0.07和0.56 H2 s-1,高出纯W2C(0.01和0.05 H2 S-1)数倍.同时,在电流密度为-10 mA cm-2时,优化后的WCP催化剂在酸性和碱性条件下的析氢过电位分别降低了96和88 mV.XPS及EDS元素分析结果表明,随磷源添加量增加,磷掺杂从碳化钨表面逐渐向内部扩散,进一步说明磷取代位置与析氢活性之间的构效关系,高浓度的表面磷取代可以加速质子捕获过程,从而显著提高其析氢活性,而过量的内部磷取代会破坏W2C结构,降低电子转移速率,从而导致析氢性能下降.利用密度泛函理论计算深入研究了WCP具有较好析氢性能的原因,与内部磷取代相比,表面磷取代会使碳化钨表现出更合适的氢吸附自由能,并且更加有效地降低了氢释放势垒,从而优化了析氢反应动力学.综上,本文为元素掺杂工艺提供了新的思路,同时研究了表面异质原子对析氢活性的关键作用,为该类催化材料的构效关系研究提供了新思路.     

脲醛树脂衍生的含氮碳层包覆的磷掺杂碳化钨(P-W2C@NC)全pH析氢催化剂

碳化钨由于其具有独特的类Pt电子结构和催化性能,使得其在电催化析氢领域吸引广泛关注。杂原子掺杂以及构筑高比表面积的碳化钨纳米材料是进一步提升其性能的重要策略。本研究以表面含有丰富极性官能团的脲醛树脂作为基底,在其支链骨架上均匀固载多酸阴离子簇,通过可控碳化获得了具有高比表面积的杂原子掺杂的碳化钨(P-W2C@NC)全pH析氢催化剂。该材料的BET比表面积高达136 m2 g-1。XRD、XPS、SEM和TEM表征证明催化剂是由含有磷掺杂的碳化钨纳米颗粒和包覆在碳化钨颗粒表面的薄层氮掺杂碳层共同构成。P-W2C@NC在全pH值电解液都具有高效的析氢性能,在0.5 M硫酸、1 M氢氧化钾和0.1 M磷酸缓冲液中,分别仅仅需要过电位83 mV、63 mV和179 mV就可以达到电流密度10 mA cm-2,并且具有超过20 h的长期催化稳定性。     

单原子掺杂二硫化钼析氢催化的进展和展望

层状二硫化钼由于具有独特的物理化学特性, 在电化学制氢领域受到广泛关注. 二硫化钼的氢惰性表面导致其在酸性和碱性电解液中的析氢活性都比铂差. 将单原子锚定在二硫化钼中能够有效活化惰性的基面，促使其成为先进的析氢电催化剂. 本文从单原子掺杂的二硫化钼的结构出发, 探讨了单原子在提升活性方面的具体机制, 总结了关于单原子掺杂的二硫化钼的制备方法、 表征手段和最新的研究进展, 以及单原子掺杂所产生的缺陷对于活性提升的重要作用. 最后, 基于单原子掺杂二硫化钼在析氢反应中的最新进展, 总结了该领域中相关催化剂的设计思想和主要挑战.     

不同晶相碳化钨的肼分解性能及其CO微量吸附量热研究

以WO3为前驱体考察了CH4/H2混合气氛下程序升温反应制备碳化钨的晶相转变过程,比较了不同晶相碳化钨催化剂的肼分解活性,并以CO为探针分子采用微量吸附量热技术研究了碳化钨晶相转变过程中催化剂的表面活性位. 结果表明,随W2C晶相的生成,催化剂对CO的吸附活化能力逐渐增强,纯相W2C表现有最好的肼分解活性. 当制备温度高于750 ℃时,样品表面形成的积炭抑制了碳化钨的催化性能. 表面洁净的WC在肼分解反应中具有优于W2C的类贵金属催化特性.     

直接甲醇燃料电池新型阴极非贵金属催化剂的制备及表征

制约燃料电池产业化的一个因素是其成本问题,尤其是贵金属催化剂的使用.若采用非贵金属催化剂,燃料电池的成本将会大幅降低.本文探索了一种新型非贵金属氧还原催化剂.首次利用微波加热法制备了具有高比表面的纳米碳化钨.XRD结果证明形成了碳化钨晶体,可以得到单纯的W2C或W2C和WC的混合物.通过TEM研究了粉末中碳化钨的颗粒大小和分布状况.结果表明碳化钨在碳载体上分散均匀,颗粒在10 nm左右.电化学表征结果表明碳化钨在碱性环境中对氧还原反应有一定的催化性能.同时证明碳化钨催化的氧还原反应几乎不受甲醇的影响.因此,碳化钨由于其独特的优势而具有在燃料电池中取代贵金属作为催化剂的可能.     

多孔二元过渡金属纳米片阵列电极制备及电催化析氢研究

碱性电解液中,电解水析氢的H2O解离过程非常缓慢,造成析氢反应较高的过电位和Tafel效率。选择具有本征高析氢活性的合金催化剂与水解离中心-过渡金属氧化物复合,并进一步优化复合物形貌结构,被证明是解决这个科学问题的重要策略。本文报道一例新颖的二元过渡金属纳米片阵列自支撑电极（MoO3-x-MoNi4@NF）, 多孔MoO3-x纳米片阵列均匀生长在泡沫镍电极表面,纳米片表面镶嵌着MoNi4合金纳米颗粒,多孔的纳米片阵列使得催化剂具有高的比表面积（57 m2/g）和丰富的活性位点。在碱性电解液中（1 M KOH）,MoO3-x-MoNi4@NF仅需要过电位30mV就能达到10 mA cm-2电流密度,如此低的过电位超过了贵金属催化剂20% Pt/C (32 mV)。同时,MoO3-x-MoNi4@NF具有超低的Tafel斜率,仅为31 mV dec-1,如此低的Tafel斜率得益于Ni-Mo合金与MoO3-x之间的协同催化剂作用的发挥,MoO3-x可以有效促进H2O解离并释放Hads,MoNi4纳米颗粒作为Hads吸脱附位点可以促进H2生成,这使得该催化剂有望替代贵金属铂用作碱性电催化析氢领域。     

红毛丹状磷化钴@钼钴氧空心微米小球用于碱性电催化析氢（英文）

氢气因其能量密度高、零排放和可再生的特点被广泛认为是最有前景的能源.电解水是一种产生高纯氢气的有效途径.目前,高性能的促进水电解的催化剂主要是贵金属材料,例如贵金属铂.然而,高成本大大阻碍了贵金属材料在电催化水分解中的广泛应用.因此,我们致力于研究具有高活性的非贵金属催化剂.因为电催化水分解析氢反应更容易发生在质子浓度高的条件下,所以研究碱性条件下催化析氢比研究酸性条件下催化析氢更具挑战性.在工业应用中,酸性电解质溶液对仪器设备的腐蚀性比碱性溶液更大,因此研究应用在碱性溶液中的析氢催化剂更有发展前景.过渡金属磷化物被广泛地研究作为高性能析氢电催化剂,然而过渡金属磷化物作为析氢催化剂的稳定性通常不是很好.我们通过钼元素的引入,提高过渡金属磷化物作为析氢催化剂的稳定性.电化学催化效率同样受到材料形貌和导电性的影响.大的比表面积有利于暴露更多的活性位点,使活性位点与电解质溶液的接触更加充分,有利于催化剂和溶液之间的传质.据报道,金属磷化物具有良好的导电性是由于磷化物中存在金属-金属键.所以合成具有大比表面积形貌的过渡金属磷化物材料能够满足析氢电催化剂对比表面积和导电性的两个需求.界面效应是调节催化剂性能的一个有效方法.析氢催化剂常常存在吸附质子能力过强或过弱、稳定性不好等问题.这些问题可以通过界面效应来解决.本文通过形成磷化估和钼钴氧的界面来调节改善磷化钴表面原来的电子密度,以达到理想的氢吸附自由能;同时此界面效应还能起到稳定催化剂性能的作用.本文首先采用水热法合成了红毛丹状钼钴氧空心微米小球前驱体.在钼酸根离子的引导下,利用奥斯特瓦尔德熟化原理一步实现了红毛丹状空心结构.前驱体再以次亚磷酸钠为磷源进行气相磷化,得到产物红毛丹状磷化钴@钼钴氧空心微米小球.通过扫描电镜和透射电镜对其红毛丹状空心结构进行了表征.利用X射线衍射和X射线光电子能谱等手段表征了材料的物相组成和价态分布.电化学测试均使用电化学工作站完成.该材料在碱性电解质溶液中展现了极好的电化学催化析氢性能,在电流密度为10 mA cm^-2时对应的析氢过电位仅为62 mV.在1 MKOH溶液中10 mA cm^-2电流密度下测试55 h,过电位仅增大约17 mV,显示了非常强的碱性析氢稳定性.得益于磷化钴和钼钴氧之间的界面效应,以及特殊的三维空心结构,红毛丹状磷化钴@钼钴氧空心微米小球表现出优异的析氢催化性能和稳定性.     

单原子改性二硫化钼电催化析氢

氢能是21世纪最理想的清洁能源之一。相比于天然气和煤炭制氢,电解水制氢具有成本低、效率高、无污染、原料丰富的特点,可以有效缓解CO₂过量排放导致的温室效应。电催化析氢需要活性高、稳定性好、廉价易得的催化剂克服反应能垒并加速动力学过程,对实现分解水制氢的规模化应用具有重要的推动作用。铂基催化剂被公认为性能最优异的析氢电催化剂之一,但由于丰度低、成本高,不适用于大规模产氢。二硫化钼(MoS₂)作为典型的二维材料之一,因其高活性位点暴露和高比表面积在析氢领域展现出一定的应用潜能,并有望取代铂基催化剂。本文基于MoS₂电催化剂在析氢领域的研究现状,对单原子掺杂改性MoS₂以提高其催化活性的研究进行了综述,以析氢过电位(Overpotential)及塔菲尔(Tafel)曲线斜率为依据,总结了贵金属单原子、非贵金属单原子及非金属单原子改性MoS₂催化剂的结构与性能以及它们之间的构效关系,在此基础上,提出MoS₂析氢催化剂目前存在的科学问题并指出了未来的努力方向。     

氮掺杂碳材料负载碳化钼的合成及析氢性能研究

过渡金属碳化物被认为是一类可替代贵金属的高效电催化析~*氢反应催化剂,提升其催化性能和稳定性能获得了广泛关注和研究。本文以钼酸铵和二氰二胺为前驱体,均匀混合后利用一步高温退火法制备了氮掺杂碳材料负载碳化钼(Mo_2C-NC)的复合材料。通过透射电子显微镜,X射线粉末衍射以及X射线光电子能谱等测试对该催化剂形貌,组成及结构进行表征。电化学测试结果表明,Mo_2C-CN复合催化剂表现了优异的电催化析氢性能:当电流密度为10 mA cm~(-2)时,在酸性和碱性体系中,Mo_2C-CN催化剂的过电势分别为和130和257 mV s~(-1),并且均展示出了优异的稳定性能。     

氧空位和磷掺杂协同增强铁钴基材料电解水催化性能

为了研发高效、稳定的电解水催化剂,我们以氧空位和磷掺杂为基础,通过原位浸泡生长和两步热处理的方法,在泡沫铁上合成具有氧空位和磷掺杂的纳米花结构作为析氢反应(HER)和析氧反应(OER)双功能电催化剂。CoFe₂O₄已被报道为一种很有前途的OER和氧还原反应(ORR)电催化剂,然而CoFe₂O₄在HER中表现出电导率差、电催化反应慢的特性。CoFe₂O₄中氧空位(Ov)的形成可以有效调控催化剂表面的电子结构,有助于产生更多的缺陷和空位,从而提高OER的活性。随后,引入磷原子填充在空位中,制备的P-Ov-CoFe₂O₄/IF在碱性电催化测试中展现出优异的HER和OER性能,在10 mA·cm^-2电流密度下HER和OER过电位仅为54和191 mV,Tafel斜率分别为57和54 mV·dec^-1,并具有良好的循环稳定性。     

The Catalytic Oxidation of Hydrogen on Nickel Oxides

The catalytic oxidation of hydrogen on highly-dispersed and sintered nickel oxides has been studied by a static method and the existence of two different kinetic rcgions established. Between 0 and 100°C the initial catalytic activity was not ionary and a strong poisoning effect of the reaction product was observed at all temperatnres up to 250°C. The activation energy of the reaction based on the initial reaction rates on freshly- outgassed oxide surfaces had a low value of 1–2 kcal. mole^?1 with both preparations. Between 250 and 350°C stationary catalytic activity was observed and the activation energy of the reaction was significantly higher, 12–14 kcal . mole^?1. The change of the activation energy is discussed in terms of the participation in the reaction of oxygen species in the catalyst surface layer which have different reactivities in the two temperature regions. A close analogy is noted between the carbon monoxide and hydrogen oxidation reactions on nickel oxide and a compensation effect is illustrated for a series of oxidation reactions on the oxide.     

Breaking Surface Atomic Monogeneity of Rh2P Nanocatalysts by Defect-Derived Phosphorus Vacancies for Efficient Alkaline Hydrogen Oxidation

Breaking atomic monogeneity of catalyst surfaces is promising for constructing synergistic active centers to cope with complex multi-step catalytic reactions. Here, we report a defect-derived strategy for creating surface phosphorous vacancies (P-vacancies) on nanometric Rh₂P electrocatalysts toward drastically boosted electrocatalysis for alkaline hydrogen oxidation reaction (HOR). This strategy disrupts the monogeneity and atomic regularity of the thermodynamically stable P-terminated surfaces. Density functional theory calculations initially verify that the competitive adsorption behavior of H_ad and OH_ad on perfect P-terminated Rh₂P{200} facets (p-Rh₂P) can be bypassed on defective Rh₂P{200} surfaces (d-Rh₂P). The P-vacancies enable the exposure of sub-surface Rh atoms to act as exclusive H adsorption sites. Therein, the H_ad cooperates with the OH_ad on the peripheral P-sites to effectively accelerate the alkaline HOR. Defective Rh₂P nanowires (d-Rh₂P NWs) and perfect Rh₂P nanocubes (p-Rh₂P NCs) are then elaborately synthesized to experimentally represent the d-Rh₂P and p-Rh₂P catalytic surfaces. As expected, the P-vacancy-enriched d-Rh₂P NWs catalyst exhibits extremely high catalytic activity and outstanding CO tolerance for alkaline HOR electrocatalysis, attaining 5.7 and 14.3 times mass activity that of p-Rh₂P NCs and commercial Pt/C, respectively. This work sheds light on breaking the surface atomic monogeneity for the development of efficient heterogeneous catalysts.     

Effect of surface structure on the catalytic behavior of Ni：Cu/Al and Ni：Cu：K/Al catalysts for methane decomposition

Methane decomposition using nickel, copper, and aluminum （Ni：Cu/Al） and nickel, copper, potassium, and aluminum （Ni：Cu：K/Al） modified nano catalysts has been investigated for carbon fibers, hydrogen and hydrocarbon production. X-ray photoelectron spectroscopy （XPS）, static secondary ion mass spectrometry （SSIMS）, thermal gravimetric analysis （TGA）, Fourier transform infrared （FT-IR）, secondary electron microscopy/X-ray energy dispersive （SEM-EDX）, and temperature programmed desorption （TPD） were used to depict the chemistry of the catalytic results. These techniques revealed the changes in surface morphology and structure of Ni, Cu, Al, and K, and formation of bimetallic and trimetallic surface cationic sites with different cationic species, which resulted in the production of graphitic form of pure carbon on Ni：Cu/Al catalyst. The addition of K has a marked effect on the product selectivity and reactivity of the catalyst system. K addition restricts the formation of carbon on the surface and increases the production of hydrogen and C2, C3 hydrocarbons during the catalytic reaction whereas no hydrocarbons are produced on the sample without K. This study completely maps the modified surface structure and its relationship with the catalytic behavior of both systems. The process provides a flexible route for the production of carbon fibers and hydrogen on Ni：Cu/Al catalyst and hydrogen along with hydrocarbons on Ni：Cu：K/Al catalyst. The produced carbon fibers are imaged using a transmission electron microscope （TEM） for diameter size and wall structure determination. Hydrogen produced is COx free, which can be used directly in the fuel cell system. The effect of the addition of Cu and its transformation and interaction with Ni and K is responsible for the production of CO/CO2 free hydrogen, thus producing an environmental friendly clean energy.     

氢气存在下一氧化碳偶联反应的化学和性能

实验研究了在氢气存在下，一氧化碳与亚硝酸乙酯偶联合成草酸二乙酸反应体系在典型操作条件下的化学反应和反应性能，结果表明氢气只与反应体系中的亚硝酸乙酯反应生成乙醇。由于氢气与一氧化碳在催化剂表面竞争吸附，并且氢的存在打破了生成草酸二乙酯所必需的正常的氧化还原过程：Pd^0→Pd^2 →Pd^0，因此氢的引入使一氧化碳转化率及草酸二乙酯选择性下降。此外，化学吸附测试结果表明氢气和一氧化碳是在催化剂表面同一活性中心上吸附。     

Effects of pretreatment and reduction on the Co/Al2O3 catalyst for CO hydrogenation

The purpose of this study was to investigate the effect of preadsorbed CO at different temperatures, calcination temperatures, the combined influence of reduction temperature and time, and pretreatment using hydrogen or syngas as reduction agents on the F-T synthesis （FTS） activity and selectivity of Co/Al2O3 catalyst. The reactivity of the carbon species at higher preadsorption temperature with H2 in TPSR decreased, whereas the carbon-containing species showed higher reactivity over Co/Al2O3 catalyst with low calcination temperature. This agreed well with the order of catalytic activity for F-T synthesis on this catalyst. The catalytic activity of the catalyst varied with reduction temperature and time remarkably. CODEX optimization gave an optimum reduction temperature of 756 K and reduction time of 6.2 h and estimated C5＋ yield perfectly. The pretreatment of Co/Al2O3 catalyst with different reduction agents （hydrogen or syngas） showed important influences on the catalytic performance. A high CO conversion and C5＋ yield were obtained on the catalyst reduced by hydrogen, whereas methane selectivity on the catalyst reduced by syngas was much higher than that on the catalyst reduced by hydrogen.     

Highly efficient epoxidation of alkenes with hydrogen peroxide catalyzed by tungsten hexacarbonyl supported on multi-wall carbon nanotubes

The preparation, characterization, and catalytic activity of W(CO)₆ supported on multi-wall carbon nanotubes modified with 4-aminopyridine is reported. The catalyst, [W(CO)₅@Apy-MWCNT], was characterized by physico-chemical and spectroscopic methods and found to be an efficient heterogeneous catalyst for green epoxidation of alkenes with hydrogen peroxide in MeCN solvent. The catalyst showed good stability and reusability properties in the epoxidation reactions.     

Desulfurization reactions on Ni2P(001) and alpha-Mo2C(001) surfaces: complex role of P and C sites

X-ray photoelectron spectroscopy and first-principles density-functional calculations were used to study the interaction of thiophene, H(2)S, and S(2) with Ni(2)P(001), alpha-Mo(2)C(001), and polycrystalline MoC. In general, the reactivity of the surfaces increases following the sequence MoC < Ni(2)P(001) < alpha-Mo(2)C(001). At 300 K, thiophene does not adsorb on MoC. In contrast, Ni(2)P(001) and alpha-Mo(2)C(001) can dissociate the molecule easily. The key to establish a catalytic cycle for desulfurization is in the removal of the decomposition products of thiophene (C(x)H(y) fragments and S) from these surfaces. Our experimental and theoretical studies indicate that the rate-determining step in a hydrodesulfurization (HDS) process is the transformation of adsorbed sulfur into gaseous H(2)S. Ni(2)P is a better catalyst for HDS than Mo(2)C or MoC. The P sites in the phosphide play a complex and important role. First, the formation of Ni-P bonds produces a weak "ligand effect" (minor stabilization of the Ni 3d levels and a small Ni --> P charge transfer) that allows a high activity for the dissociation of thiophene and molecular hydrogen. Second, the number of active Ni sites present in the surface decreases due to an "ensemble effect" of P, which prevents the system from deactivation induced by high coverages of strongly bound S. Third, the P sites are not simple spectators and provide moderate bonding to the products of the decomposition of thiophene and the H adatoms necessary for hydrogenation.     

酸性质对磷钨酸改性CeO_2上NH_3选择性催化还原NO性能影响

分别制备了磷钨酸、磷酸、偏钨酸铵及磷酸+偏钨酸铵改性的CeO_2催化剂,用于NO的NH3选择性催化还原反应(NH3-SCR),对酸改性的作用进行了研究。结果表明,不同酸改性后的CeO_2催化剂均含有弱酸和中强酸位,但酸量差别明显,依次为:磷钨酸/CeO_2偏钨酸铵/CeO_2磷酸+偏钨酸铵/CeO_2磷酸/CeO_2。由于磷钨酸改性的CeO_2催化剂中P与W之间相互作用,导致磷钨酸/CeO_2催化剂表面弱酸及中强酸含量较多,Ce物种和O物种相对活跃,有利于NH3的吸附、活化和NH3-SCR反应的进行;因此,磷钨酸改性的CeO_2催化剂活性最佳,在225-450℃下NO转化率高于90%。