Yiyun Fang

MOF derived Co3O4 nanoparticles embedded in N-doped mesoporous carbon layer/MWCNT hybrids: extraordinary bi-functional electrocatalysts for OER and ORR

Highly efficient and non-precious metal electrocatalysts for oxygen evolution reactions (OERs) and oxygen reduction reactions (ORRs) are at the heart of key renewable-energy technologies. Nevertheless, developing highly active bi-functional catalysts at low cost for both OER and ORR still remains a huge challenge. In this paper, Co3O4 nanocrystals embedded in N-doped mesoporous graphitic carbon layer/multiwalled carbon nanotube (MWCNT) hybrids are prepared by a facile carbonization and subsequent oxidation process of MWCNT-based metal–organic frameworks (MOFs). As a result, in alkaline media, the hybrid material catalyzes OER with an onset potential of 1.50 V (vs. reversible hydrogen electrode) and an over-potential only of 320 mV to achieve a stable current density of 10 mA cm−2 for at least 25 h. The same hybrids also exhibit similar catalytic activity but superior stability to the commercial 20 wt% Pt/C catalyst for ORR, making it a high-performance cheap bi-catalyst for both OER and ORR. The design concept of nonmetal-doped and precious-metal-free electrocatalysts from MOFs can be extended to fabricate other novel, stable and easy to use catalyst systems for advanced applications.

Nitrogen-doped mesoporous carbon nanosheet/carbon nanotube hybrids as metal-free bi-functional electrocatalysts for water oxidation and oxygen reduction

The development of metal-free catalysts for efficient catalysis of both the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) is extremely desirable in energy technologies. Herein, nitrogen-doped mesoporous carbon nanosheet/carbon nanotube (CNT) hybrids have been synthesized by the pyrolysis of glucose, urea and CNTs. Impressively, in 0.1 M KOH, the resulting hybrids afford remarkable OER activities with a low onset potential (1.50 V vs. RHE) and an exceptional over-potential (only 320 mV at 10 mA cm−2). Moreover, the same hybrids show comparable catalytic performance but better durability compared to the benchmark Pt/C (20 wt%) catalyst for ORR. The achieved ultrahigh catalytic performance of the hybrids originates from their large specific surface area (594.1 m2 g−1), high content percentage of N doping (8.5 wt%), and mesoporous structure, which leads to fully exposed active sites, improved mass/electron transport capability, easy adsorption/release of oxygen gas bubbles, and high structural stability. This work also provides a novel concept for fabricating heteroatom doped porous carbonaceous materials with integrated and improved catalytic performance for advanced applications.

MoS2 quantum dot decorated RGO: a designed electrocatalyst with high active site density for the hydrogen evolution reaction

Active, stable and cost-effective electrocatalysts are the key to water splitting for hydrogen production through electrolysis. In this work, we report MoS2 quantum dots (MoS2 QDs) decorated on reduced graphene oxide (RGO) synthesized by a facile sonication method as highly effective electrocatalysts for the hydrogen evolution reaction (HER). Compared with MoS2 sheets, the zero-dimensional MoS2 QDs have a defect-rich structure rendering these quantum dots with plentiful active sites, which can further enhance the catalytic activity by a synergistic effect with RGO. Electrochemical experiments demonstrated that the catalyst exhibited large cathode currents (a small overpotential of 64 mV for 10 mA cm−2 current density) and a Tafel slope as small as 63 mV per decade, achieving high stability simultaneously. This work opens up possibilities for preparing non-noble metal electrocatalysts while achieving high HER performance similar to commercial Pt catalysts (Pt/C).

Precious-metal-free Co–Fe–Ox coupled nitrogen-enriched porous carbon nanosheets derived from Schiff-base porous polymers as superior electrocatalysts for the oxygen evolution reaction

Water splitting provides a potential path for producing clean, renewable H2 and O2. However, improving the overall efficiency of water splitting is a challenging issue. Here, we designed Co–Fe nanoparticle coupled nitrogen-enriched porous carbon (CoyFe10−yOx/NPC) nanosheets as highly efficient non-precious-metal electrocatalysts for the oxygen evolution reaction (OER). Nitrogen-enriched porous carbon (NPC) nanosheets were prepared using a Schiff-base network (SNW) as the precursor and the SNW was based on commercially available and inexpensive monomers which were terephthalaldehyde and melamine. The resulting SNW possessed a high nitrogen content, a high surface area and a high density of metal-coordination sites. In addition, when used as the catalyst for the OER, the Co–Fe nanoparticle catalyst containing 30% Co (Co3Fe7Ox/NPC) showed the highest activity, requiring 328 mV over-potential to achieve a stable current density of 10 mA cm−2 for at least 15 h and a small Tafel slope of 31.4 mV dec−1 in 1.0 M KOH solution, which were comparable even superior to those of many other non-noble metal catalysts. Consequently, the high efficiency and durability make these supported amorphous Co–Fe nanoparticles potentially applicable for improving the performance for electrolysis of water and energy storage applications. More importantly, the support of electrode materials comes from the pyrolysis of porous polymers and this idea offers a new possibility for exploring overall water splitting non-precious-metal catalysts.

Ultrafine Co2P nanoparticles encapsulated in nitrogen and phosphorus dual-doped porous carbon nanosheet/carbon nanotube hybrids: high-performance bifunctional electrocatalysts for overall water splitting

The development of active, robust, and nonprecious electrocatalysts for both the oxygen evolution reaction and hydrogen evolution reaction (OER and HER) is highly crucial and challenging. Herein, ultrafine Co2P nanoparticles (NPs) encapsulated in nitrogen and phosphorus dual-doped porous carbon nanosheet/carbon nanotube hybrids are prepared via a straightforward pyrolysis method. Impressively, the hybrids exhibit remarkable catalytic performance for both the OER and HER in 1.0 M KOH solution, with a current density of 10 mA cm−2 at low over-potentials of 280 mV for the OER and 154 mV for the HER, respectively. More importantly, when fabricated as an alkaline electrolyzer, the hybrids afford 10 mA cm−2 at a cell voltage of 1.64 V with strong stability, rivalling the integrated performance of a commercial IrO2 and Pt catalyst couple. The achieved ultrahigh catalytic performance can be attributed to the nitrogen and phosphorus dual-doped carbon nanosheets, carbon-encapsulated ultrafine Co2P NPs, high conductivity of incorporated carbon nanotubes, large surface area (199.94 m2 g−1), interpenetrated macro-/mesoporous structure, and the strong synergistic effect among these factors.

Programmed synthesis of magnetic mesoporous silica nanotubes with tiny Au nanoparticles: a highly novel catalyst system

Magnetic mesoporous silica nanotubes were produced from carbon nanotubes using a well-controlled programmed synthesis method and were characterized by TEM, XRD, XPS, N2 adsorption–desorption and VSM. The well-designed nanotubes had a large specific surface area (1017 m2 g−1), a highly open mesoporous structure (∼3.2 nm) and high magnetization (18.6 emu g−1). Ultrafine gold nanoparticles were successfully supported on the thiol-modified nanotubes by a co-precipitation method. These unique multicomponent nanotubes showed high performance in the catalytic reduction of 4-nitrophenol (with a conversion of 99% in 6 min), and styrene epoxidation with high conversion (65%) and selectivity (58%). Interestingly, the new catalysts could be recovered by magnetic separation from the reaction mixture and could be recycled several times without any significant loss in activity. The unique nanostructure of the nanotubes resulted in a novel, stable and easy to use catalyst system for application in various industrial processes.

Mesoporous titanium dioxide coating on gold modified silica nanotubes: a tube-in-tube titanium nanostructure for visible-light photocatalysts

A novel tube-in-tube structured titanium dioxide (TiO2) based visible-light photocatalyst with non-metal doping and plasmonic metal decoration was fabricated using a well-controlled programmed synthesis method and was characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), N2 adsorption/desorption, X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy. The as-obtained tube-in-tube structure is composed of inner mesoporous silica nanotubes with high specific surface area and an outer layer of anatase TiO2 nanocrystals with considerable visible-light activity. For the photocatalytic degradation of rhodamine B (RhB) in aqueous solution, the photocatalyst showed superior photocatalytic activities compared with commercial TiO2 and nanometer-sized photocatalyst Degussa P25. The strategy is simple, but efficient, and can be extended to the synthesis of other multifunctional composites. It has opened a new pathway for the construction of hetero-nanocomposites with high activity and durability, which would serve as excellent models in catalytic systems of both theoretical and practical interest.

Coaxial ultrathin Co1−yFeyOx nanosheet coating on carbon nanotubes for water oxidation with excellent activity

The rational design of high-performance and non-precious metal electrocatalysts is highly important for energy technologies. Herein, for the first time, a coaxial ultrathin Co1−yFeyOx nanosheet coating on carbon nanotubes (denoted as Co1−yFeyOx/CNTs) is prepared by a one-step pyrolysis method. The fabrication procedure is ultrafast and uncomplicated, furthermore, it does not need any reducing agent, alkali, or surfactant. In 1.0 M KOH, the obtained optimal hybrids Co0.8Fe0.2Ox/CNTs25 wt% catalyze oxygen evolution reactions (OER) with a very sharp onset potential (∼1.45 V) and an exceptional over-potential (0.28 V, at 10 mA cm−2) for more than 14 h, benefiting from the abundant active sites of ultrathin Co0.8Fe0.2Ox nanosheets, the hierarchical tubular architecture, and the strong cooperative effect among Co, Fe and CNTs. Remarkably, the excellent activity and durability of Co0.8Fe0.2Ox/CNTs25 wt% for the OER is superior to commercial RuO2 and many other highly active precious-metal/transition-metal catalysts reported to date. The design concept for tubular iron-group binary metal nanosheet hybrids creates new pathways for energy technologies.