Efficient overall water splitting over a Mo(IV)-doped Co3O4/NC electrocatalyst

To meet the demand of producing hydrogen at low cost, a molybdenum (Mo)-doped cobalt oxide (Co₃O₄) supported on nitrogen (N)-doped carbon (x%Mo–Co₃O₄/NC, where x% represents Mo/Co molar ratio) is developed as an efficient bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This defect engineering strategy is realized by a facile urea oxidation method in nitrogen atmosphere. Through X-ray diffraction (XRD) refinement and other detailed characterizations, molybdenum ion (Mo⁴⁺) is found to be doped into Co₃O₄ by substituting cobalt ion (Co²⁺) at tetrahedron site, while N is doped into carbon matrix simultaneously. 4%Mo–Co₃O₄/NC is the optimized sample to show the lowest overpotentials of 91 and 276 mV to deliver 10 mA cm^?2 for HER and OER in 1 M potassium hydroxide solution (KOH), respectively. The overall water splitting cell 4%Mo–Co₃O₄/NC||4%Mo–Co₃O₄/NC displays a voltage of 1.62 V to deliver 10 mA cm^?2 in 1 M KOH. The Mo⁴⁺ dopant modulates the electronic structure of active cobalt ion (Co³⁺) and boosts the water dissociation process during HER, while the increased amount of lattice oxygen and formation of pyridinic nitrogen due to Mo doping benefits the OER activity. Besides, the smaller grain size owing to Mo doping leads to higher electrochemically active surface area (ECSA) on 4%Mo–Co₃O₄/NC, resulting in its superior bifunctional catalytic activity.     

Highly dispersed MnO nanoparticles supported on N-doped rGO as an efficient oxygen reduction electrocatalyst via high-temperature pyrolysis

Transition metal-based compounds, due to their excellent ORR catalytic performance under alkaline condition, have recently emerged as one of the most promising alternatives to noble metal-based ORR catalysts. It is worth noting that manganese oxide can take an unique advantage for decomposition of intermediate adsorption products H₂O₂ and can effectively reduce O₂ to OH⁻. However, most research has focused on MnO₂, while attention has rarely been paid to MnO catalysts. In addition, under high-temperature pyrolysis condition, MnO is the most stable manganese oxide but MnO nanoparticles easily agglomerate. Hence, it is very difficult to obtain well-dispersed and small-sized MnO nanoparticles. Herein, on the basis of pre-synthesizing uniformly distributed manganese complexes on the reduced graphene oxide (rGO), we innovatively prepare highly dispersed and small-sized MnO nanoparticles (~3.94 nm) via high-temperature pyrolysis, which are uniformly anchored on N-doped reduced graphene oxide (NrGO) as an efficient oxygen reduction electrocatalyst. The as-obtained MnO/NrGO (1050 °C) electrocatalyst achieves satisfactory onset potential (0.942 V) and half-wave potential (0.820 V) under alkaline condition. And the limiting current density is 4.17 mA cm⁻², which is very close to that of Pt/C (20 wt%, JM). Meanwhile, MnO/NrGO (1050 °C) catalyst presents superior longstanding durability and methanol resistance than Pt/C (JM). This work indicates that high-temperature pyrolysis can improve the purity of manganese oxide, simultaneously the defects of NrGO can reduce particle size of MnO nanoparticles, which are greatly beneficial to improve ORR performance. This work provides a new idea for research of MnO catalysts for ORR in the future.     

ZnSe/CoSe/NCDPH composites as anode materials for lithium ion batteries with high capacity and long cycle

In this paper, dopamine hydrochloride (DPH) is introduced to synthesize ZIF-8@ZIF-67@DPH in the preparation of ZIF-8@ZIF-67. ZnSe/CoSe/NC_DPH (N-doped carbon) composites are calcined in a high-temperature inert atmosphere with ZIF-8@ZIF-67@DPH as the precursor, selenium powder as the selenium source. ZnSe/CoSe/NC_DPH has high discharge specific capacity, good cycle stability and outstanding rate performance. The first discharge capacity of ZnSe/CoSe/NC_DPH is 1616.6 mAh g⁻¹ at the current density of 0.1 A g⁻¹, and the reversible capacity remains at 1214.2 mAh g⁻¹ after 100 cycles, the reversible capacity is 416.7 mAh g⁻¹ after 1000 cycles at 1 A g⁻¹. Therefore, ZnSe/CoSe/NC_DPH composites provide a new step for the research and synthesis of new stable, high-capacity, and safe high-performance lithium ion batteries. The bimetallic selenide composites not only have bimetallic active sites, but also can form synergistic effect between different metal phases, which can effectively reduce the capacity attenuation caused by volume expansion and reactive stress enrichment during lithium storage of metal oxide anode materials. Meanwhile, N-doped carbon can improve the conductivity and provide more active sites to store lithium, thus improving its lithium storage capacity.     

Metal–organic framework-derived Co@NMPC as efficient electrocatalyst for hydrogen evolution reaction: Revealing the synergic effect of pyridinic N–Co

Developing hydrogen economy is one of the feasible routes to reduce carbon emission in response to the energy crisis and global warming. The hydrogen generation by electrochemical water splitting has received widespread attention, but it is still challenging to fabricate high-efficient electrocatalysts to decrease the kinetic energy barrier of hydrogen evolution reaction (HER). Loading transition metal (TM) nanoparticles (NPs) into heteroatom-doped carbon materials (HCM) has been reported as a capable scheme to increase the electrochemical activity and stability, but the synergic effect between TM surface and HCM is still worth exploring. Ascertaining that, we used metal-organic frameworks (MOFs) as the sacrificial precursor to synthesis a series of Co NPs encapsulated in N-doped microporous carbon (NMPC) nanocatalysts (denoted as Co@NMPC) with different N species (such as pyrrolic, pyridinic and graphitic N). The nanocatalyst prepared at an appropriate condition displayed an outstanding HER activity with an overpotential of 193 mV in 1 M KOH solution and 132 mV in 0.5 M H₂SO₄ solution to reach 10 mA cm^?2 current density. Furthermore, the results of in situ shielding tests indicate that the synergy of pyridinic N–Co site owing to the intimate contact between Co surface and NMPC play the pivotal role in boosting HER performance. Density functional theory (DFT) calculations were employed to obtain an in-depth mechanism of synergic effect between Co and NMPC.     

Well-dispersed Co–Co3O4 hybrid nanoparticles on N-doped carbon nanosheets as a bifunctional electrocatalyst for oxygen evolution and reduction reactions

Bifunctional catalysts are vital for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in metal-air batteries. In this work, Co–Co₃O₄/N-doped carbon nanosheets (NCNs) were developed as highly efficient bifunctional oxygen catalysts via the pyrolysis of a hybrid ZIF-67/CNs precursor. It is found that the introduced CNs play important roles. On one hand, the introduced CNs can tune the surface contents of Co, N and/or O species that are closely correlated with OER and ORR activity. On the other hand, they also facilitate to achieve high specific surface areas for the catalysts. In addition, the introduced CNs helps the formed Co–Co₃O₄ hybrid nanoparticles with uniform and small sizes to be well-distributed on the NCNs substrates. Despite such important roles, it should be noted that a moderate content of the introduced CNs is required to achieve optimal oxygen catalytic activity. As a result, the optimized ZIF-67/CNs(1)-600 exhibits a low value of η₁₀ (~350 mV) for OER and a high value of E_1/2 (~0.85 V) for ORR. Its overall bifunctional activity (ΔE) is as low as ~0.73 V, which is comparable to the recent reported Co-based catalysts.     

Application of carbon nanostructures toward SO2 and SO3 adsorption: a comparison between pristine graphene and N-doped graphene by DFT calculations

We studied the adsorption of SO_x (x?=?2,3) molecules on the surface of pristine graphene (PG) and N-doped graphene (NDG) by density functional theory (DFT) calculations at the B3LYP/6-31G(d) level. We used Mulliken and NBO charge analysis to calculate the net charge transfer of adsorbed SO_x on pristine and defected graphene systems. Our calculations reveal much higher adsorption energy and higher net charge transfer by using NDG instead of pristine graphene. Furthermore, the density of state (DOS) graphs point to major orbital hybridization between the SO_x and NDG, while there is no evidence of hybridization by using pristine graphene. Based on our results, it is found that SO₂ and SO₃ molecules can be adsorbed on the surface of NDG physically and chemically with adsorption energies (E_ads) of ?27.5 and 65.2?kJ?mol^?1 (19.6 and 51.4?kJ?mol^?1 BSSE), respectively, while low adsorption energies were calculated in the case of using pristine graphene. So we introduced NDG as a sensitive adsorbent/sensor for detection of SO₂ and SO₃.     

Robust three dimensional N-doped graphene supported Pd nanocomposite as efficient electrocatalyst for methanol oxidation in alkaline medium

Pd nanoparticles (PdNPs) with the diameter of ～3.2 nm were successfully confined within a robust three dimensional (3D) N-doped porous graphene (R3DNG) via a polyol-assisted reduction strategy. The as-obtained PdNPs/R3DNG composite was characterized by SEM, TEM, XRD and XPS, and was conducted as electrocatalyst for methanol oxidation in alkaline medium. The results showed that PdNPs/R3DNG featured the remarkable electrocatalytic activity (2.71 A mg^?1 Pd) and outstanding cyclic stability (66.5% forward peak current retention after 1000 cycles), which is even superior to the state-of-the-art Pt/C catalyst. The synergistic effect between the support of R3DNG and PdNPs is believed to be responsible for the outstanding electrocatalytic performance.     

火焰化学气相沉积法制备氮掺杂纳米TiO_2研究

用火焰化学气相沉积法,分别以氨气为氮源、TiCl4为TiO2前驱体,在丙烷-空气湍流火焰中氧化制备氮掺杂纳米TiO2颗粒,以及用TiCl4为TiO2前驱体,在丙烷-空气湍流火焰中氧化制备纳米TiO2颗粒,然后在管式炉中,在氨气的环境下高温煅烧制备氮掺杂纳米TiO2颗粒。利用X射线衍射仪、紫外可见光谱仪、透射电子显微镜、X射线光电子能谱等分析方法对两种方法所制备的样品进行表征。结果表明:在相同的氨气流量下,火焰化学气相沉积法直接制备的氮掺杂纳米TiO2颗粒在波长400～500 nm的可见光的吸收强度大,氮掺杂量多。     

高掺杂N对金红石型TiO2电子结构和红移影响的理论研究

采用密度泛函理论框架下的第一性原理平面波超软赝势方法,在相同环境条件下分别建立了未掺杂和取代O高掺杂N原子的金红石型TiO2超胞模型,优化了晶胞的几何结构,计算了能带分布、态密度分布和吸收光谱.结果表明,金红石型TiO2-xNx超胞取x=0.0625的条件下,N的2p态与O的2p态发生杂化耦合,使其价带上移、最小带隙变...     

纳米ZnO可见光催化活性的改善及其降解性能

由于半导体ZnO禁带宽度较宽,因而其可见光催化活性较差。本文分别采用N掺杂、碳包覆、贵金属修饰以及半导体复合等方式来改善纳米ZnO的可见光催化活性,并以罗丹明B为降解污染物,对比了不同材料可见光催化降解有机污染物的效率。研究结果显示以氨水为氮源,通过水热法制备的氮掺杂N-ZnO光催化剂,相比于纯ZnO,对可见光吸收增强。采用葡萄糖水热碳化法所制备的C@N-ZnO样品则对有机污染物具有强的吸附能力,贵金属沉积所获得的样品Au/C@N-ZnO与半导体复合所制备的复合结构CdS/Au/C@N-ZnO在可见光区域具有更强的吸收能力。稳态和瞬态荧光光谱显示氧缺陷、贵金属沉积以及半导体复合形成异质结可有效提高光生载流子的分离效率,从而提高催化剂的光降解效率,并对催化机理进行了初步探讨。可见光催化降解罗丹明B结果显示CdS/Au/C@N-ZnO样品的反应速率是纯ZnO的6.7倍。